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-   -   About to run my '87 Carrera off a cliff - still surging and backfiring (http://forums.pelicanparts.com/porsche-911-technical-forum/624098-about-run-my-87-carrera-off-cliff-still-surging-backfiring.html)

ischmitz 08-22-2011 06:31 AM

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 08-22-2011 06:40 AM

Ok, thanks Ingo

Tippy 08-22-2011 07:27 PM

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 08-29-2011 07:30 PM

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!!!!!:eek:):

- 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 08-30-2011 10:25 PM

Power issues or speed sensor issues.

Tippy 08-31-2011 06:09 AM

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 08-31-2011 06:29 AM

Quote:

Originally Posted by Tippy (Post 6190252)
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 08-31-2011 07:15 AM

Misunderstanding. No CDI box.

stlrj 08-31-2011 07:36 AM

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

Tippy 08-31-2011 11:09 AM

Quote:

Originally Posted by stlrj (Post 6227969)
Nobody will help you run it off the cliff unless you post some pictures.

http://forums.pelicanparts.com/uploa...1314817776.jpg

Tippy 08-31-2011 11:16 AM

UPDATE:

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


Where's that cliff at??? :D

Tippy 08-31-2011 02:18 PM

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 09-02-2011 09:48 AM

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 09-02-2011 07:12 PM

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 09-02-2011 07:54 PM

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 09-03-2011 02:15 AM

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

Rey

BoxsterGT 09-03-2011 07:46 AM

:)

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 09-03-2011 12:28 PM

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 09-04-2011 07:15 PM

Quote:

Originally Posted by techman1 (Post 6233445)
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.

Quote:

Originally Posted by jorian (Post 6233489)
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.

Quote:

Originally Posted by speednme1 (Post 6233716)
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.

Quote:

Originally Posted by BoxsterGT (Post 6233991)
:)

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.

Quote:

Originally Posted by ant7 (Post 6234393)
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 09-05-2011 01:01 AM

Quote:

Originally Posted by Tippy (Post 6236424)
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.


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