About to run my '87 Carrera off a cliff - still surging and backfiring

[ischmitz]

I have seen worse. In modern OpAmp circuits it can cause offsets and leakage but the Motronic is pretty robust and won't be affected.

[Tippy]

Ok, thanks Ingo

[Tippy]

UPDATE again.......

- Cleaned all of the solder joints with alcohol, swabs, and cotton balls on the DME
- Inspected for cracked solder joints - found none by the naked eye - saw a bunch that were repaired before
- Disconnected CHT plug at intake and the car immediately died
- Did a compression test (cylinders warmed and WOT) and the lowest cylinder was 120 PSI and the highest was probably 130 PSI (mind you this a 7.5:1 CR motor)
- Played with 8-position selector switch on DME and no better results from position 0, position 1 (1.5% enrichment), to position 2 (2.8% enrichment) <- data given by "ischmitz"
- Tuner who burned my chip said he can't really tell if the chip is bad, that all he could do is look at the maps and what he has stored on his computer

When doing the compression test and reading the plugs, all of the center electrodes and porcelains were nicely clean with just a hint on whitish/ashy color on the edges while a slight blackness around the threaded area of the plug.

The plugs look almost brand new indicating to me that this is still a lean condition - even though my fuel pressure is reading higher than what the tuner states he tries to set them at.

The statement above baffles me because I am running higher fuel pressure than stock (FPR is not adjustable), while having way bigger injectors, along with way lower compression over stock.

Not a hint of black smoke comes out of the tailpipe that would indicate a rich condition.

I am stumped.

I need a stock chip if anyone has one.........

[Tippy]

ANOTHER UPDATE:

I am getting closer but discovered I have 2 problems - both fuel and ignition. I finally got the engine to run smoother, rev easier, and build boost sooner. The 8-position switch on the back of the DME did the trick.

I put it on position #2 (2 clicks clockwise) which is 2.8% enrichment according to "ischmitz". Wow, what a difference! It was lean after all as I suspected......fuel side fixed.

But, the surging and cutting out is still there! It has the classic signs of a coil dying; runs good cold, acts up as it gets warmer, and then acts really erratic once it is hot.

Replaced the coil this evening and no change.......

Did a new search using "cutting out" and found some interesting ideas of what may cause a Carrera to exhibit these symptoms (I am shocked at how many cars have had this problem!!!!!):

- CHT (mine checks out good but who's to say it doesn't short-out intermittently? I disconnected it once while it was running and the engine immediately died out)
- DME relay (don't have one hand....I know.......a death sentence)
- Loose trans ground (easy check, just need to do it but I am pretty sure it is good)
- Failing ignition switch (this one has piqued my interest as it gives power directly to DME and fuel pumps)

Regarding the ignition switch; my tach drops but my fuel pressure seems to remain the same when I get a cut out of power. I am assuming the fuel damper keeps the pressure up during the drops in power?

What would cause my tach to drop when the engine cuts out???

[ischmitz]

Power issues or speed sensor issues.

[Tippy]

Today I'm getting a new DME relay and distributor cap.

I'll just keep throwing parts at it until I resolve I guess....

[stlrj]

Originally Posted by Tippy

The ignition box (CDI?) and coil are original from what I can tell.

If this helps......

The distributor came from Craig Garrett "cgarr" and worked just fine after I rebuilt the engine.

What's a DME doing with a CDI ignition? Never heard of it.


That might be your problem.


Pictures might be helpful.




Cheers,

Joe

[Tippy]

Misunderstanding. No CDI box.

[stlrj]

Nobody will help you run it off the cliff unless you post some pictures.

[Tippy]

Originally Posted by stlrj

Nobody will help you run it off the cliff unless you post some pictures.

[Tippy]

UPDATE:

New distributor cap and DME relay - no change.......

Where's that cliff at???

[Tippy]

Welp, so much for the 8-position switch fixing the fueling problem. It runs like it did before and now, it doesn't even want to rev off idle when under no load. It is nearly undriveable (I didn't even take it for a spin) but hopefully whatever the hell is giving me this headache will just go KAPUT!

I yanked on the fuel pump wires (they are not factory ran due to having the 2 -044 pumps) and the DME wires trying to get it to make hiccup and nothing when idling. I even disconnected one fuel pump and it idled pretty much the same.

The only thing I can thing of is the DME at this point.

[Tippy]

Checked power to DME at the main harness and relay - seems to be good and steady.

Sanded DME/sensor grounds on intake #1 and still no change.

Right off idle, it runs really terrible.

1. Going to try and source a DME for testing.
2. I want to oscilloscope what I can too if I can get one.

Where do I find the parameters? Do you just look for variances I assume when keeping constant RPM?

[techman1]

Idle position switch going bad can cause a lot of the problems you are having, and possible the CHT like you spoke of. I believe there is a test procedure in the bentley book, and other places.

[jorian]

Did you end up finding/trying a stock chip? I may be able to locate my stock one (87' 3.2 NA) with some searching around.

[speednme1]

I have a stock chip from my previous 85 3.2. Let me know if you needed.

Rey

[BoxsterGT]

Just find a Pelican who will try your ECU in his car. That will answer any questions on the chip.

Don't put his in your car for fear you may have some fault that broke your ECU.

Len

[ant7]

hi,
try disconecting the rev counter, i had a similar fault on a car many years ago, and it turned out to be this.
hope this helps, if only to eliminate it.
Anthony.

[Tippy]

Originally Posted by techman1

Idle position switch going bad can cause a lot of the problems you are having, and possible the CHT like you spoke of. I believe there is a test procedure in the bentley book, and other places.

I replaced the idle microswitch already. I've tested the CHT at different temps and it seems to be in spec. Now, if it is acting erratic, that could be a possibility.

Originally Posted by jorian

Did you end up finding/trying a stock chip? I may be able to locate my stock one (87' 3.2 NA) with some searching around.

No I didn't but it would not matter anyways. I have 3.4L P&C's and 55lb/hr injectors. Thanks.

Originally Posted by speednme1

I have a stock chip from my previous 85 3.2. Let me know if you needed.

Rey

Thanks for offer but I realized since I have 55lb/hr injectors, it wouldn't work anyways.

Originally Posted by BoxsterGT

Just find a Pelican who will try your ECU in his car. That will answer any questions on the chip.

Don't put his in your car for fear you may have some fault that broke your ECU.

Len

Good idea, just have to find someone who has a car like mine. That has been quite a challenge.

Originally Posted by ant7

hi,
try disconecting the rev counter, i had a similar fault on a car many years ago, and it turned out to be this.
hope this helps, if only to eliminate it.
Anthony.

Do you mean the tachometer?

[ant7]

Originally Posted by Tippy

I replaced the idle microswitch already. I've tested the CHT at different temps and it seems to be in spec. Now, if it is acting erratic, that could be a possibility.



No I didn't but it would not matter anyways. I have 3.4L P&C's and 55lb/hr injectors. Thanks.



Thanks for offer but I realized since I have 55lb/hr injectors, it wouldn't work anyways.



Good idea, just have to find someone who has a car like mine. That has been quite a challenge.



Do you mean the tachometer?

hi,
yes, if its faulty it could be affecting the low tension circuit causing weak or no spark.
worth a try i guess, seen as you seem to have tried most everything else.
hope this helps.
Anthony.