I get random misfire, sometimes light comes on.

[Beretta1234567]

1988 Beretta GT

2.8L v6 with 5 SPD.

I had moved it to a 3.1L MPFI v6 and used 3.1L 1990 Beretta parts. For the swap.

I have new CPS, and known good ICM with known good coils.
I have 2 sets I already tried swapping and no change.
New wires.
Used plugs, but only had like 10k miles on them and I regaped and cleaned them.

I used the 90 electric temp sensor that goes by the thermostat.

I used the 88 electric temp sensor that goes in the heads.
I removed the map and installed the intake temp sensor from a 90 Beretta with 90 intake.


New o2 sensor.

1990 ECM from a 5 SPD and 1990 box.

I also installed the 1990 EGR and wired it up according to the book.

Code reader is with the book, I wish I would have brought that with me. Fail.
I used the black/red and black/purple wires for the intake temp sensor.

It's not a bad miss, but it's enough to feel it with a stick shift.
It is fine under load but when cruzing it can sometimes miss and cause a rhythmic forward backward motion of the car. And that can be annoying.

EDIT:
It misses cold or warm.
And does not buckle under load.

[themixer]

"rhythmic forward backward motion of the car. And that can be annoying"

http://www.beretta.net/forum/viewtopic.php?f=8&t=5602

this is exactly the same symptoms of my epic journey with my 3.1 5 speed 1991. Pretty much what I have found is the injectors are screwballed. I would suggest moving those 2.8 injectors over to your 3.1 if you still have them as a first step.

Although it could be anything and i haven't seen it in person just a suggestion

[Beretta1234567]

Now you mention it, thats the last thing I have to try.
All the other sensors and electronics have been replaced or swapped out.

I'll post back if it helps when I eventually get to it.

I was really hoping it was something less costly and easy to fix. :/

[themixer]

good luck trying to find working injectors also, i even bought new ones that failed after 3 months. currently swapping to 3400 motor just to get some reliability back !

[3X00-Modified]

3100 and 3.1 injectors are very similar, they vary by about 1 or 1.5lb/hr... You can take any set of small port 3100 injectors and put them in a MPFI engine and it will run fine.

[themixer]

If you can find a running car to take them out of that's the best!

[3X00-Modified]

Ebay search nets a bunch... just send them to a cleaner if your that worried too and they will tell you if there are any issues.

http://www.ebay.com/sch/i.html?_trksid= ... &_from=R40

so does GM 3.1L injectors

http://www.ebay.com/sch/i.html?_odkw=31 ... s&_sacat=0

[Beretta1234567]

Yah, these injectors were aftermarket from an auto store. It has been about a year and a half.

I am going to go find a Monte Carlo with a 3100 SFI. Engine and use them injectors.

I would like to use a 3400 SFI injector set of 6. Don't they ohm out the same and the 3.1L MPFI ECM can still run them?
They just flow faster right?

This will get a supercharger in the future, and I rather not buy injectors a second time so soon. lol

[3X00-Modified]

Yes they flow more but you don't want to use them unless you can calibrate the ECU to recognize that it now has 19 or 22lb injectors on it... If you just slap them in there the ECU will be compensating the fuel/air mix, and to be in constant correction with the ECU is not a good thing. The difference between the 3.1MPFI and 3100 is so minimal that the correction is not enough to be concerned about, 3400 is a different story.

[Beretta1234567]

Yah I was considering it because of the increased flow rate.
I have an aftermarket EPROM that I am using, it has a tune for N/A, or boost.
Anyways, when I finally get the boost, I will probaly have to up the fuel.

If not I can always reflash the chip.

EDIT:
Now that I think about it, Is the stock 88 beretta fuel pump enough to power the 3400 injectors?

[Rettax3]

Now that I think about it, Is the stock 88 beretta fuel pump enough to power the 3400 injectors?

Yes. I ran the original stock F/P in my '89 GTU for a long time on my SC 3800 with no problems until the pump finally just wore out (...166k+ miles...). Look at the fuel-lines -they are the same size (5/16") between the two engines, and the PSI at the fuel-rail test-port is within the same range. In theory, the pumps are essentially the same, in practice, the 2.8 pump works fine. The L67 3800SC Series II uses bigger injectors than the 3400 too. The L36 N/A 3800 Series II uses the same injectors as the 3400.
I am also running the 3.4 turbo in my '90 'Retta with the stock pump and 3400 injectors, but I only have a couple of hundred miles on that, so not well tested yet.

Yes they flow more but you don't want to use them unless you can calibrate the ECU to recognize that it now has 19 or 22lb injectors on it... If you just slap them in there the ECU will be compensating the fuel/air mix, and to be in constant correction with the ECU is not a good thing. The difference between the 3.1MPFI and 3100 is so minimal that the correction is not enough to be concerned about, 3400 is a different story.

No offense Jon, but this is very surprising to me. I wouldn't think you would recommend using 3100 injectors on a 3.1 MPFI engine without tuning, you are usually pickier about that than I am, by far. Years ago, I tried running a N/A Series-I 3800 (TPI engine) with a 2.8 MPFI MAF ECU, a different setup than the Berettas use, but still a 2.8 ECU. It ran so horribly rich with the 3800 injectors that the car wouldn't idle and was completely undriveable. It continually after-fired, and actually dripped fuel out the exhaust-manifolds if it didn't catch after the first few cranks. It ran fairly well with two or three injectors DISCONNECTED, and it ran PERFECTLY once I put the 2.8 injectors back into it, despite the extra liter of displacement (but that shouldn't be too surprising considering the MAF configuration). I don't know what the S-I 3800 had for lb/hr injectors, but I can't see that they were much bigger than early 3100s... Have you actually tested and run 3100 injectors with an un-tuned 2.8 or 3.1 MPFI ECU? If so, I am curious if the plugs showed signs of fouling or heavy sooting, and how the MPG was effected? I realize that only a lb/hr or two doesn't sound like much, but that would be about 10% extra fuel being dumped in, and until the O2 sensor kicks in during closed-loop mode, the ECU has no way of knowing it is running that rich. Of course, I have gone the opposite direction, running a 15% bigger engine than the computer thinks it is running, and had no problems even with speed-density metering, but GM ECUs tend to run a little rich during open-loop mode...

[themixer]

I myself didn't have much success with running 3100 injectors in my 3.1 until i got a chip from WOT-TECH, But I don't claim to be any sort of expert. The chip was the only thing that leveled out my BLM to around 128.

[3X00-Modified]

Yes I've done a 3100 injector swap into a 3.1L for someone and the car ran fine.

VIN T - 1989-1993 3.1L 189cid V6 MFI
#17102747 {ACDELCO Part # 217267} {replaces 217-255} CODE 5235136
Max Flow: 15lbs(1.952gms/sec) OR 16.6lbs depending on source
Supply Pressure: 43.5PSI(300Kpa)
Multec1 TFP

And there is incorrect info on 60degreev6 stating this

VIN M - 1993-1998 3100 SFI V6 - 189cid
#17113572 {ACDELCO Part # 2171388}
Max Flow: 19lbs
Supply Pressure: 43.5PSI
Multec 1

This pressure rating is only true for the 3400 engines in 99... the 94-98 3100's were only 17lb/hr. GM tagged the rings on the injectors to show this too, 3100 was a black ring and the 3400 was a red ring, externally they were exactly the same so they had to have some way to show a difference.

So if you figure the stock injector is 15-16.6 and the 3100 is 17 max... it's so minuscule of a change you wont really need to fix the ecu.

If you HAVE the ability to calibrate and flash the computer and your doing other things then yes by all means I would suggest doing it but for a fix on a daily car it's not enough to concern yourself with.

themixer, I can almost guarantee that when factory your BLM was not at 128 and are you sure they were 3100 injectors? Stock calibrations on cars are never in the sweet spot.

[themixer]

when the motor was running properly it would float around 120-135 with the 3.1 injectors. When i could get all the 3100 injectors firing it i have to say it ran better with the WOT tech chip.

[ifixalot]

My 2 cents. I just had the same problem with my mini van.
Missing at cruise but seemingly fine under load.
I know you said you have new plug wires.
With mine the cause was two bad wires on the rear of the engine.
The wires are a pita to get off. I had changed the plugs 8k miles ago.
I guess the stress of pulling the wires off the plugs rips the conductor
inside the wire. One by one I removed and tested my wires. When I got
to the last two, the boot came off and the metal clip was left on the plug.
I could see the hole in the wire from the arcing that had been going on.
Unless those wires were newly installed right out of the box, you may have
damaged wires arcing inside causing the miss.