Z-26 3.4 DOHC Turbo

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Rettax3
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Z-26 3.4 DOHC Turbo

Postby Rettax3 » Sat Nov 17, 2018 10:44 pm

Note: Okay, this will be the 'final' resting place for the info on this car, as it goes along. Most of the 'build' as it happened is in the 'General' section under 'Finally', but as this is now a 'ride' and not a 'build' or 'discussion', I felt it should come here.

So, here it is:
The car: 1995 Z-26, bought with 105k miles for $400 with the all-too-common 3100 rod-knock, courtesy of GM's typically failed LIMGs.
MidnZ3b.jpg
This was how I bought the car. From the outside, it still looks the same. Nice start for $400...


Black Rose Metallic (BRM) with grey interior, and typically equipped for a '95 Z; A/C, Cruise, Power Windows and Doors, Cassette Radio, FE3 Suspension and the 16" Saw-Blade Z Wheels.

This was a well-liked, cared-for Z before the LIMG failure. Nice tires, the paint was kept clean and probably waxed, I would guess it was garaged for most of its' life. There are definitely flaws, but they are fewer than expected for a 23-year-old car. Even the engine-bay was kept clean (at least on the top). Virtually zero rust, except for minor surface corrosion underneath the battery.


The Engine: 1995 LQ1 3.4L DOHC V-6, also known as the 'VIN X' 24-Valve H.O. Twin Dual Cam engine. This is a full SFI engine, MAF operated fuel management.
3.4 Rgt2b.jpg
Sitting around for ten years will collect dirt, even in a garage. I've replaced what is necessary, but will refrain from rebuilding a 60k-mile engine, unless it needs it. This was complete, for $150. Really good bang for the buck, if you can make it fit.


These engines were de-tuned by GM, rumors persist that it lost ~33% of its' initially design power, supposedly to keep the then-new 4T60E alive for the duration of its' warranty, and in '95 it was rated at 210 H.P. (add five more for the manual transmission models) and 215 foot-pounds of torque. The most interesting note being that the red-line was set about 1,000 RPM higher than the engine's push-rod siblings had. This was a High-Output RPM engine from the start. '95 was the last year with a lower CR (Compression Ratio) and supposedly the last year this timing-belt engine remained non-interference.

I pulled this particular example around a decade ago, intending on swapping it into a Fiero GT, but never got back to that car. The donor was a Chevy Lumina Z-34, wrecked at only ~64k miles. The engine cost me $150 at the local yard, complete from intake to oil-pan, accessories to flex-plate, even included the PCM (the W-Body Luminas placed the PCMs under the hood in '95) and wiring harness.

The Transmission: 1988 Muncie/Getrag 282, sourced from a Beretta GT.
282Transx1b.jpg
I prefer the external-slave five-speeds. Although fitment near the Turbo would have been easier with an internal concentric slave-type, this is my style of choice -and what I usually find at the yards anyway. $120 bought this whole package, including a near-new stock clutch and flywheel.

This is the oldest style of 282 -external slave-cylinder mounted on a steel bracket, and a fully housed jack-shaft. With it, I installed an LUK pressure-plate and the six-puck Stage-3 ceramic clutch disc from my GTU, replaced in that car when it got the 6-speed upgrade several years ago.
3.4Clutch2b.jpg
This LUK pressure-plate hides a six-puck ceramic Stage-3 friction disc. Unfortunately, it just isn't up to an LQ1 under boost, unless fully engaged before applying throttle.
This was the first clutch-disc in my GTU that didn't slip with the modified L367 3800 SC. Unfortunately, I've found that the LUK does not have sufficient clamping force for the LQ1 under boost...

Boost? Yep: The Turbocharger is a Garrett T-04,
T-04 & Wrapped DP1a.jpg
T-04 installed. The waste-gate and the bypass valve (MAF prevents me from running a super-cool BOV, too bad, with 9-pounds of boost and that size intake, it certainly would be heard unloading!) match. Eventually, the AFPR will too, they are available with the same color anodizing.
turbo 'kit'1a.jpg
Here is my basic 'kit' I put together for the Turbo and exhaust. This was a good chunk of money, even though I already had the Turbo. I've done enough turbo projects to know about what I need though, so this was about 95% of the whole thing.

externally waste-gated unit, sourced from my '90 Turbo 'Retta -the pushrod 3.4 in that car had some troubles spooling that big turbo, so I moved it here. Before that, the turbo was brand new. The intercooler is another Blackstone unit, a very compact one that fits under the hood, where the battery usually sits. A full 3-inch mandrel-bent exhaust system runs back to a dual-out Flowmaster muffler, which then terminates in Twin Dual (see what I did there?) Z-26 exhaust-tips. A high-flowing short cone-filter keeps it fed on the 3-inch inlet side, again, still kept inside the engine-bay. A silver-faced backlit Vacuum/Boost gauge installed at an angle to the side of the instrument cluster clearly displays the 9-pounds of boost the wastegate is currently dialed in for. It will look more at home once I swap in the silver-faced electroluminescent gauge face from my other '95 Z-26...

Extras: The five-speed is rowed with an early-'90s Grand Am shifter -this uses a threaded shaft instead of the Berettas' stamped-steel arm for the shift-knob to attach to. I found a heavy Stainless Steel shift-ball I liked for a good price -it feels great and looks great with a 'Neo Chrome' finish.

While installing the clutch-pedal assemble, I swapped on a Fourth-Gen Camaro pedal pad, and matching 'ABS' brake pedal pad, both with honeycomb design.

The LQ1 is usually topped by a plastic plate that fills the spot between the intake manifold's long runners and the huge front-bank valve-cover. I have replaced this with a trimmed-down IDI top-cover from a 2.4 Twin Cam LD9. This cover also keeps the ignition cables tucked out of the way on my engine, until they head to the coil-pack placed near the right strut-tower instead of mounted to the front of the engine, as they are also on older 2.8 and 3.1 MPFI engines.

What was needed: This swap has been talked about since this engine was actually hot news, that was a long time ago! There have only been a few serious attempts made that I am aware of, and nothing ever brought close to completion. This is a tough engine to fit in a Beretta, especially keeping in mind that it will need to be maintained, and possibly repaired someday. The LQ1 does use a timing-belt, but the belt is a unique design that is driven by an intermediate shaft -it does not run all the way to the crankshaft, nor does it drive the water-pump or anything else besides the four overhead cams. Therefore, the whole job can be done on it from the top, no wheel-removal necessary!

Custom engine mounts were required to position this engine in the Beretta's diminutive bay, and while harder to fab than the mounts in my GTU's 3800, they were very cheap to make.
A Big Block Mopar mount (cost was ~$3.60) and reclaimed steel plate made up the front lower mount, a stock GM bracket comprised the right rear, and a variation of the under-side transmission mount I designed for both my '90 Turbo 'Retta and my 5-speed Northstar Indy holds the transaxle in place. The stock Z-34 upper torsion mount bolts to a steel brace bolted across the entire length of the upper radiator tie-bar which in turn uses W-Body braces to bolt it to the strut-towers/strut brace (sourced from an H-Body) to keep the entire engine-bay supported and reduce body flex. The stock Z-26 torsion-brace ('Dogbone') bracket bolts right to the LQ1, but it now sits slightly rearward and lower than the stock 3100 did, so a custom Dogbone will be needed -I haven't decided if that is necessary yet. So far, the engine sits pretty solidly within the bay.

Radiator hoses were also a custom deal -I purchased a silicone hose kit for a Honda Civic, chopped one of the hoses into three pieces and installed a Toyota filler-neck/cap assembly from a 1NZ. One Civic hose is cheaper than two Beretta hoses, and will probably be easier to obtain in the future, sadly. The cooling fan is stock Beretta, but the '95 V-6 version is too thick, and would have to be installed prior to engine installation. I was able to wedge in a thinner unit, I believe it is from a '92 Quad...

Heater hoses were going to be as hacked-in as GM's original design (I am spoiled by how well the 3800's heater-hose fittings fit our cars), so I ended up with aluminum tube and a flare fitting on the engine's outlet, and a pipe and hose setup on the return. No leaks thusfar, heater works fine too. The throttle-body heater port has been plugged -I do not live in Alaska!

Wiring was what I made out of it: The LQ1 is a 60-degree V-6 at heart, and is run by the same ECM used on a 3100 SFI, so long as the 3100 came from a W-Body... It is a totally different ECM than the L-Body uses, and even retains a PROM chip in '95. But some of the sensors and accessories (especially the alternator -more on that later) are in different spots. Reflashing the Beretta's PCM and splicing in longer wires would likely work just fine, but I don't like splices. So, I totally integrated the LQ1's wiring harness with the Beretta's, keeping everything stock in the Beretta except for the tape and loom, and avoided splices everywhere except for the one-wire temperature sensor for the gauge.

The exhaust cross-over pipe had to be modified for the Turbo -but that was an optional add-on. Stock, the LQ1 is designed to exhale through 2.25-inch outlets, per bank! That is over twice the outflow given to the 3100, and matches the single 3-inch pipe I used after the turbo almost exactly. Oil supply and return lines were also made necessary for the Turbo, and I opted for a large oil-cooler to help prolong the big Garrett's lifespan.

The Clutch Line had to be altered due to the size and location of the Turbocharger. Plastic generally does not belong in an engine-bay, in my opinion, and the clutch-line is no exception. Mine is now steel, with AN (37-degree) flared fittings and adapters in place.

The Big Chill-Less, also known as the Compromise: The alternator on the LQ1 is mounted low, and to the rear of the engine. The Berettas have a frame-rail that arcs inward there, and unless I wanted the engine propped up high, the alternator wouldn't fit. So, I relocated it to the A/C compressor's spot, and deleted the A/C system. I can live with that -I also don't live in Arizona! The engine now uses a shorter belt, and while I've had concerns over the belt's contact to the water-pump which has changed due to the alternator's smaller diameter pulley, the car runs cool and consistent (according to my scan-tool, reading through the ECM).

Overall, this was one of the harder swaps I've done, but that was partially because I wanted it to be one of the cleanest too, regarding the general condition of the car. It took a long time to complete (months!) and I felt like the progress was constantly being stalled -but I also performed a five-speed conversion, and a Turbo installation too, which was not initially planned on being done right away.
Finished Bay4a.jpg
Almost there! A few odds-and-ends still to do, but the car runs and drives well. There is always something left to do...
Finishedish1b.jpg
For now, it is time to get to know the car.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby heavywoody » Mon Nov 19, 2018 2:54 pm

I really like this car and the uniqueness factor. Kudos!


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95 Z26 Turbo 3400 5spd - R&D Project
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Re: Z-26 3.4 DOHC Turbo

Postby themixer » Sat Nov 24, 2018 12:34 pm

This is rather neato you will have to take Pauly for a ride as it’s the big quad 4



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Re: Z-26 3.4 DOHC Turbo

Postby woody90gtz » Sat Nov 24, 2018 6:47 pm

I like all of his mad-scientist builds. Unique is cool.


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Re: Z-26 3.4 DOHC Turbo

Postby nocutt » Wed Jan 02, 2019 8:10 pm

DANG!!!!! :Rose: beleza
well done my man, its so bad you did not start all your mad science back in the heyday day (woody and I will be jocking); this right here would have been all over the place. I recommend you talk to Chris West from WCF (West Coast Fiero) he can provide some good guidance on the clutch.

I know you mentioned this way back on another thread, I think you should really isolate that ic, you also did not mention fuel and spark management. Forgive me if you mentioned this already...



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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Thu Jan 03, 2019 5:26 am

nocutt wrote:DANG!!!!! :Rose: beleza
well done my man, its so bad you did not start all your mad science back in the heyday day (woody and I will be jocking); this right here would have been all over the place. I recommend you talk to Chris West from WCF (West Coast Fiero) he can provide some good guidance on the clutch.

I know you mentioned this way back on another thread, I think you should really isolate that ic, you also did not mention fuel and spark management. Forgive me if you mentioned this already...

Thank you, this build was enough of a PITA even for me that I've paused at the 98.9% mark, and taken a little time to enjoy and get to know the car a little. I still have a small(ish) punch-list of things to do, but she is driveable, so I've been driving her (a little). I cannot bring myself to chop a hole in that perfect hood, so at some point soon I'll swap-over the really good hood I have (also in BRM from a '95 base) and set this one in storage. I may wait until nicer weather though. Once the intercooler is properly fed (and yes, isolated, I started the stainless steel separation plate, but installing it is on that punch-list), I'll feel more comfortable running the car a little harder.

I am running stock tune right now, I've thought about using my DHP on a Venture PCM and going sideways on the tuning part, but I would rather keep the current ECM (which is purely MAF-operated), and burn a chip for it -I still have to pick up an APU-1 (thank you Woody for pointing me to that direction) to do it right. Trying to tune the Venture PCM for the LQ1's VE and RPM range is not something I am comfortable with tackling at this time, especially since I ended up bolting in the T-04 ahead of schedule. Mostly, I am running the car out of boost, which isn't too hard to do as the LQ1 is a bit of a beast on it's own, and the car is plenty quick for the winding roads with occasional dog-walkers who think they should stay between the two yellow lines on the road %) . I have seen 12 psi on the gauge (briefly, I was looking for the wastegate setting and found it), though I would like to drop that down to 9 psi for regular duty. I also have it in Park/Neutral mode still, so it should be staying at a lower rev-limiter (my GTU's S/C 3800 bounces at 4200 or so when I set that mode, the LQ1 still spins well past 5k though, surprisingly). Until I have everything else done on it and see 1000 of my own miles on this engine, I'm not pushing it hard. :wink:

I'm still hearing a little compressor-surge during shifts, so either my bypass valve isn't working greatly, or it is too small. It is identical (exept for color) to the one I put in the '90 Turbo 'Retta with this same turbo on a pushrod 3.4, and that car seemed fine (although it wasn't spooling the turbo nearly as well) so I doubt it is too small to work. I may have to replace it. :o

The last drive I took it on was relatively long, maybe 1.5 hours mixed driving, with a few stops along the way running errands. I started getting an intermittent misfire, no codes but this ECM surprisingly has a 'Weak Cylinder' PID on my old scan-tool, which it reported as #3. Same as any 60-degree V-6, this is middle cylinder, rear bank. I still have concerns over these old injectors, that sat for so long, but I'm also thinking it could be a bad spark plug -I've now seen several new plugs bad out of the box over the last few years- or possibly a coil going out, so I'll likely swap them around and see if the weak cylinder moves when the car is acting up. Aside from this, the engine has a little vibration at around 2800 RPM, and the exhaust-note (which still disturbs me, as it sounds NOTHING like a 60-degree V-6 usually does) gets a little drony at anything between 2300 and 3000. Beyond that, she is actually nice to drive. The idle is a little erratic -likely the old IAC still waking up- and I intend to bump the minimum idle set-screw out a tad to help compensate for the lack of an auto-trans -again, my GTU had a similar issue with stalling after a long in-gear deceleration as the IAC isn't quick enough to respond when the clutch is pushed in and adjusting the minimum idle-set helped tremendously.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby nocutt » Thu Jan 03, 2019 9:31 pm

Rettax3 wrote:
nocutt wrote:DANG!!!!! :Rose: beleza
well done my man, its so bad you did not start all your mad science back in the heyday day (woody and I will be jocking); this right here would have been all over the place. I recommend you talk to Chris West from WCF (West Coast Fiero) he can provide some good guidance on the clutch.

I know you mentioned this way back on another thread, I think you should really isolate that ic, you also did not mention fuel and spark management. Forgive me if you mentioned this already...

Thank you, this build was enough of a PITA even for me that I've paused at the 98.9% mark, and taken a little time to enjoy and get to know the car a little. I still have a small(ish) punch-list of things to do, but she is driveable, so I've been driving her (a little). I cannot bring myself to chop a hole in that perfect hood, so at some point soon I'll swap-over the really good hood I have (also in BRM from a '95 base) and set this one in storage. I may wait until nicer weather though. Once the intercooler is properly fed (and yes, isolated, I started the stainless steel separation plate, but installing it is on that punch-list), I'll feel more comfortable running the car a little harder.

I am running stock tune right now, I've thought about using my DHP on a Venture PCM and going sideways on the tuning part, but I would rather keep the current ECM (which is purely MAF-operated), and burn a chip for it -I still have to pick up an APU-1 (thank you Woody for pointing me to that direction) to do it right. Trying to tune the Venture PCM for the LQ1's VE and RPM range is not something I am comfortable with tackling at this time, especially since I ended up bolting in the T-04 ahead of schedule. Mostly, I am running the car out of boost, which isn't too hard to do as the LQ1 is a bit of a beast on it's own, and the car is plenty quick for the winding roads with occasional dog-walkers who think they should stay between the two yellow lines on the road %) . I have seen 12 psi on the gauge (briefly, I was looking for the wastegate setting and found it), though I would like to drop that down to 9 psi for regular duty. I also have it in Park/Neutral mode still, so it should be staying at a lower rev-limiter (my GTU's S/C 3800 bounces at 4200 or so when I set that mode, the LQ1 still spins well past 5k though, surprisingly). Until I have everything else done on it and see 1000 of my own miles on this engine, I'm not pushing it hard. :wink:

I'm still hearing a little compressor-surge during shifts, so either my bypass valve isn't working greatly, or it is too small. It is identical (exept for color) to the one I put in the '90 Turbo 'Retta with this same turbo on a pushrod 3.4, and that car seemed fine (although it wasn't spooling the turbo nearly as well) so I doubt it is too small to work. I may have to replace it. :o

The last drive I took it on was relatively long, maybe 1.5 hours mixed driving, with a few stops along the way running errands. I started getting an intermittent misfire, no codes but this ECM surprisingly has a 'Weak Cylinder' PID on my old scan-tool, which it reported as #3. Same as any 60-degree V-6, this is middle cylinder, rear bank. I still have concerns over these old injectors, that sat for so long, but I'm also thinking it could be a bad spark plug -I've now seen several new plugs bad out of the box over the last few years- or possibly a coil going out, so I'll likely swap them around and see if the weak cylinder moves when the car is acting up. Aside from this, the engine has a little vibration at around 2800 RPM, and the exhaust-note (which still disturbs me, as it sounds NOTHING like a 60-degree V-6 usually does) gets a little drony at anything between 2300 and 3000. Beyond that, she is actually nice to drive. The idle is a little erratic -likely the old IAC still waking up- and I intend to bump the minimum idle set-screw out a tad to help compensate for the lack of an auto-trans -again, my GTU had a similar issue with stalling after a long in-gear deceleration as the IAC isn't quick enough to respond when the clutch is pushed in and adjusting the minimum idle-set helped tremendously.


Cool, sounds like you have errything under control :Bravo: The BOV might need a larger vacuum line, I guess it depends on where you are also sourcing the vacuum from.



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Re: Z-26 3.4 DOHC Turbo

Postby woody90gtz » Thu Jan 03, 2019 10:51 pm

Rettax3 wrote: The idle is a little erratic -likely the old IAC still waking up- and I intend to bump the minimum idle set-screw out a tad to help compensate for the lack of an auto-trans -again, my GTU had a similar issue with stalling after a long in-gear deceleration as the IAC isn't quick enough to respond when the clutch is pushed in and adjusting the minimum idle-set helped tremendously.


I can see where that would help your GTU in that specific situation, but adjusting that screw will only adjust your IAC steps at idle. As you adjust the blade open the IAC will adjust down and keep adjusting to reach the commanded idle in the tune. The better way to fix that is with the commanded idle speed. I realize you can't do this yet without the hardware, but it's gonna be the only way to get it to act right hot and cold.


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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Fri Jan 04, 2019 1:52 am

Nocutt, that is actually one of the thoughts I had then quickly dismissed -but if you think that could be part of the issue, I will try upgrading the vacuum tube size for sure. I have stock-type rigid vacuum-line on this, and I can't recall using lines this small before on one of my turbo cars (the BOV on my '97 Turbo Z-24 MIGHT use this type vacuum line...). The GTU's boost-control valve uses the same size vacuum tubing, but the vacuum solenoid is smaller on the GTU's Supercharger too... On this one, the upper-deck pressure is ported off of the IC at the top inboard corner -there was a bolt installed possibly for drain purposes, and although it wasn't perfect, I was able to thread an NPT fitting into it. The manifold-side is off the stock vacuum-tree at the rear of the upper plenum, behind the throttle-body.
woody90gtz wrote:
Rettax3 wrote: The idle is a little erratic -likely the old IAC still waking up- and I intend to bump the minimum idle set-screw out a tad to help compensate for the lack of an auto-trans -again, my GTU had a similar issue with stalling after a long in-gear deceleration as the IAC isn't quick enough to respond when the clutch is pushed in and adjusting the minimum idle-set helped tremendously.


I can see where that would help your GTU in that specific situation, but adjusting that screw will only adjust your IAC steps at idle. As you adjust the blade open the IAC will adjust down and keep adjusting to reach the commanded idle in the tune. The better way to fix that is with the commanded idle speed. I realize you can't do this yet without the hardware, but it's gonna be the only way to get it to act right hot and cold.


Here is my logic: The issue I had with the GTU, and now this car, is that both ECMs are confused as to why the RPMs are held so high with the TPS (and VSS) reading zero, and so shut down the IAC completely trying to attain the desired idle RPMs. When the clutch is depressed, nothing is holding the RPMs up any more, and by the time engine-speed settles below desired idle-set, the IAC cannot open back up fast enough to prevent a stall (sometimes, even frequently). Carefully balancing the IAC's need to reduce RPMs at all encountered temperatures and atmospheric conditions with the minimum idle set-screw's position holding the blade open just enough, I can get a far more driveable adjustment than what GM left for me. I'm sure the modded intakes and exhaust systems I build change the operating parameters enough that some adjustment should be expected anyway, so GM did fine for the stock configuration on the engines, I think.

Now, if I understand what you are saying, adjusting the desired idle speed up in the ECM's tune will give the IAC more time to recover the engine before stall, but won't that also cause a higher idle RPM all the time? With my slight adjustment up, I am cutting-out some of the 'basement' the engine can drop to, and reducing or (possibly) eliminating the stall-point that otherwise might be encountered. The minimum idle may be set a little higher than preferred under SOME conditions, but at least on the GTU, I've been able to get a pretty good adjustment on it for a more-than-happy medium.

Obviously, the manual-transmission cars have ECU programming that compensates, but I think some of that has to do with a VSS signal incorporated into that (you probably know for sure), and neither of these particular cars (nor the Venture PCM running the engine in my '90 Turbo 'Retta either) receive a VSS signal. So, unless I correct that feature of my designs, I am still going to be stuck with an idle problem if I try to handle it strictly by tune, right? In the case of my GTU, I need the VSS to signal the car's original ECU for the digital dash (my Northstar Indy has the same issue too, for that matter). On the other cars, it is just an easy way to side-step around cluster differences (if any) and the stock speed governor :twisted: . Not that ANY of my cars have EVER exceeded that speed. :pardon: I think you are correct, adjustments need to be made in the tune to have it all working 'right', but so far I've had good luck with a careful turn of the screw. :good:


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby woody90gtz » Fri Jan 04, 2019 7:30 am

There is a "throttle follower" in the the tune that opens the IAC while the throttle opens and you're driving. That keeps the IAC from having to make sudden adjustments. I'd have to double check to be sure, but I think that works in conjunction with the VSS...that could be why. Why can't you splice the VSS to run the signal to both computers? I did that in my 91 when I added cruise control and it all works correctly.


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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Fri Jan 04, 2019 2:13 pm

woody90gtz wrote:There is a "throttle follower" in the the tune that opens the IAC while the throttle opens and you're driving. That keeps the IAC from having to make sudden adjustments. I'd have to double check to be sure, but I think that works in conjunction with the VSS...that could be why. Why can't you splice the VSS to run the signal to both computers? I did that in my 91 when I added cruise control and it all works correctly.

Yes, I am certain that the 'throttle follower' is tied to the VSS (though you know far more about tuning than I do, in diagnostics and driveability testing, certain effects can be noted). As for splitting the VSS signal, I've never tried. I wasn't sure if splitting the signal would cause interference between the ECMs. I didn't find it necessary either, because of the positive results from adjusting the minimum idle set. But, if you've done it with success, then I will have to consider that as an option. If the LQ1 doesn't take to a set screw adjustment, then that will be near the top of my list on tune adjustments once I get an APU-1. Thank you for the input and advice Woody.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Thu Jan 10, 2019 2:40 pm

Rettax3 wrote:The last drive I took it on was relatively long, maybe 1.5 hours mixed driving, with a few stops along the way running errands. I started getting an intermittent misfire, no codes but this ECM surprisingly has a 'Weak Cylinder' PID on my old scan-tool, which it reported as #3. Same as any 60-degree V-6, this is middle cylinder, rear bank.

Found it. Because I don't like the idea of stuffing the IM and coil-pack under a hot exhaust manifold and behind a radiator, I had located them in front of the right shock-tower, behind the relocated battery. Unfortunately, the power steering pump sits in the same spot on an LQ1 as it does on an L82, and the pulley is very close to all six ignition cables as they run from the coils. The holder I put on the wires to the rear bank slipped down and #3 managed to touch the pulley and get abraded. Grrr, new wires too...


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Tue Feb 26, 2019 5:12 pm

Well, I finally broke something. The tranny-mount I made uses an aluminum 'saddle' that wraps over a steel square-tube and bolts to the top of the left subframe. The square-tube then houses the bolt that heads inboard to the plate I fabbed to mount to the bottom of the transmission. Well, the aluminum 'saddle' has cracked. This was actually part of an engine-mount, so it SHOULD have been strong enough, but not a big deal on its' own -I'll grab another broken mount and make another saddle. Then, I'll fab a plate to hold the outboard end of the bolt, and attach that to the outer side of the subframe -this was part of my original design, I just didn't finish it, then decided not to for vibration-isolation reasons. Better some vibes than a broken mount though... The bigger problem was caused when the mount broke, it allowed the drivetrain to shift down slightly, and the TPS hit the brake master-cylinder and broke. So, a minor fab-and-repair job awaits the DOHC-Z... Putting it #438 on the list.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Z-26 3.4 DOHC Turbo

Postby woody90gtz » Thu Feb 28, 2019 8:49 pm

It's always a domino effect...


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91 "SS" WOT 3400/5spd - 13.97@100.7 GEARHEAD dezign

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Re: Z-26 3.4 DOHC Turbo

Postby Rettax3 » Fri Mar 01, 2019 4:59 am

I feel it is more of replacing the weak-links in a chain until I practically have an all-new chain. I am not often surprised at which links fail, but I am some times surprised at which links hold strong. Now, on the installation and build-end of this beast, yes, it was definitely a Domino scenario. When solving one problem only creates one more though, I feel like I will eventually win -it is when two or three problems crop-up with each solution that I have an issue. =@


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26


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