DTMAce's Z26 project - DD usage for the time being - 6-8-12

[1988GTU]

Is the exhaust glowing red up near the CAT?

[DTMAce]

Well, I got my fuel pressure tester this evening. (had a new one picked up for me). Will check that in the morning, its pissing down rain right now. lol

And then we can finally put to bed the rumors and innuendo about my pump being weak all its life. LOL (sorry Jon)

[DTMAce]

Is the exhaust glowing red up near the CAT?

Honestly, I don't know. Why?

I do know the upper intake seems to get hotter than normal, if I let it idle for 2 minutes or more (once it has been already run awhile)

[99GaGT3X00]

if it's glowing the cat's clogged.

[Money pit Beretta]

That by far is true and something I did think about. ACE what about the coolant temp sensor in the head? Just for fun, could it be just a little bad and not keep the fan running and still make the engine run rich?

[DTMAce]

Well, I plan to check the cat anyway, but no I haven't noticed that.

As for the fan? Hell that never runs unless the temp gets hot enough. So not sure where that comes into play.... Besides, the sensor/relay for the fan is on the Tstat, the one in the rear head feeds the gauge, if I recall correctly.

[DTMAce]

WELL.

I now can officially put the "fuel-pressure-low-causing-me-my-good-mileage" to bed.

Ran a test on it this morning.

Key on, pump primed: 40lbs on the nose.

Engine running, vacuum disconnected: 44lbs.

Engine revving, vacuum disconnected: I think it dropped to a low of maybe 42 or 40lbs, but it was like a quick flutter, not steady and it would go right back to 44. This happened when I would hit the throttle. I think it was more of a delay in response time to my revving it. But that was something I forgot to mention. lol

Vacuum connected, engine at idle: ~34lbs. (it bounced)

Vacuum connected revving engine: Zips right up to 44lbs.

Leak down test with engine off (obviously): Held 40lbs for the whole 15 minutes I gave it.

Seems to me the fuel pressure is fine. lol

[DTMAce]

Going to pull and swap the computers tomorrow at some point.

Any other ideas out there? I guess I can try to find the time to do a cylinder pressure test, but not looking forward to that at all. Such a pain in the ass getting to the backside.

Down to it being one of 3 things I think:

Computer.
Wiring harness.
Valve problem on a cylinder, or a bad head gasket. Hell, it does have 241k on the original head gasket after all.
Could throw different plugs at it, but they all looked good, not that it means anything certain, though I can pull them and visually make sure they are sparking I suppose. May do that when/if I do the pressure test.

Let me know if you think of anything else. Be sure to read the previous posts, I have thrown a ton at it already.

[DTMAce]

And it has gotten worse.

Now my gauges are screwed up, the second I turn on either parking lights or full headlights, it causes the RPM and speedo to go wacko. Either they scroll all over or just freeze in place. The odometer stops working right as well. And its running rougher than ever.

Starting to think that my problem is mostly electrical at this point, either a harness issue, or bad connection... However where to start? Why would turning on the lights cause the dash to go screwy? Anyone have an idea on what connector full of wires go to what at the computer, so I can narrow down the search? I want to make sure I don't have a bad wiring issue before I go swapping computers, as I don't want to take a chance on damaging the replacement if it IS a bad or messed up wiring issue.

2 facts I know for sure:

1: Wiring on this car is completely stock. I have never had to replace or redo any of the original wiring harness. It used to have an alarm system, but it was easy to remove without making a mess of the harness, they only tapped a couple of wires.

2: I have augmented the wiring, in that I added a battery feed for the rear amp, and have installed the LED lighting/resistors. But that is all mostly external in nature.

Apparently, chasing this problem has not revealed that I have found a problem to date, so apparently there is a wiring issue causing the engine to run like crap and giving me nightmares. lol

So I need to know which plug (at the computer) houses the timing/spark control wiring and which one houses the dash wiring. Can anyone tell/describe that?

Edit:

Just to clarify, I have NOT swapped the computers yet. This just happened on its own.

[berettaboi]

test your battery real quick... they do funny things on their way out. if you have another (working good in another car) swap it for a few days, see if things persist.

[DTMAce]

If the battery was going out, I think that would affect the cranking/starter in a noticeable way though..... I'm not feeling its a battery here. But yes, I can always try that. Now it could be something as simple as a bad ground someplace though. Hmmmm.

Will check into it.

Edit:

More to question, where are ALL the grounds found for the electrical system? IE, as in where they are located? I think one was on the firewall, but as to where? I'm sure this thing has multiple redundant connections on it in places. Thinking it may be a problem as simple as that. Going to have to slap myself if that's the case.

[scd88ga]

I'm going to go ahead and say the voltage regulator in your alternator is going out.

[DTMAce]

But the voltage on the dash shows that its fine. That, the oil pressure, temp and fuel are NOT affected. Only the RPM and the Speed are being wacked.

And the lights don't change intensity at all. If the battery or the alternator were causing the issues, I would see that with everything. But not everything is being affected. Primarily it appears to be ignition and dash, with the exterior lighting causing symptoms with the dash part only when turning them on. If I turn the heater fan on to max, that doesn't do anything, nor does using the windows or the rear defrost. Those things draw lots of power.

So I suspect that the battery and the alt are not the sources of this problem, but then I'm not ruling them out completely either. With everything I have been testing above, its hard to say. I appreciate the ideas however.

[scd88ga]

Alright, so instead of skimming and skipping around this thread, I actually read all of it from when you problem began. I can only come up with 1 problem that could explain all your symptoms. That being a bad VSS (Vehicle Speed Sensor), this would explain your cluster issues (tach, speedo, odo) as well as the issues with the car running poorly (rich) because a bad VSS can throw the ECM into a "limp mode". The same thing that the ecm defaults too when the CTS (Coolant Temperature Sender) goes bad making the car run VERY rich thus causing an eventual misfire among other problems.

Aside from your actual ECM going bad (which I doubt with that design) I can think of no other single component that would cause these multiple problems.

Good luck!

[DTMAce]

VSS? lol

So that would cause he gauges to act up only when I turn the lights on? Interesting. Where is that sensor?