North American Turbocoupe Organization

Full Version: EEC glitch?? - weird (long) story
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Had to do a minor repair on the pass side PRC (story for another time), and had to remove the plastic PRC cover. My BPV is pretty tight next to the cover, so I had to muscle the BPV out of the way to get the cover off (too lazy to remove the BPV). After the PRC repair, went for a ride. After a 20 to 80+ mph WOT 24 psi run, I let off and slowed down to the speed limit. Motor was running fine, but A/F wasnt bouncing, it was sitting near or at rich, depending on throttle opening. Soon the CEL comes on. BTDT before... leaking hose. Got home, and a few minutes of looking, found I had nearly pulled the BPV hose off the fitting on the IC, and the 24 psi boost made it worse, causing a small leak. Fixed that, and went for a ride to verify the repair. Ran great, but at low load, idle A/F would go rich, and turn on the CEL. Under cruise, no CEL and it was running closed loop. Checked TPS voltage, VAF voltage, looked for other small leaks, checked for leaking FPR, etc, etc and found nothing. Then I remembered a very similar problem (leak) from a few years back, and the solution:

I run 44 psi base FP, and the long term fuel trim must have been wacked out enough from trying to correct for the now repaired leak, that it couldnt relearn LTFT at low load and idle. I turned the FP down to 39, went for a few mile drive to relearn LTFT. All was well. Went back home, and reset FP back to 44. Went for a ride, problem solved. No CELs, stayed in closed loop when it was supposed to.

Yes, I could have disconnected the batt for 10 min to reset the EEC LTFT to 0, but I hate doing that, as I have to reset the audio system parameters, clock, etc.

Apparently, when running higher than stock FP, if the LTFT is railed out (which turns on the CEL) due to a vac / pressure leak, it wont correctly relearn LTFT at idle and low load unless FP is real close to stock. Weird.
Weird, but very good to know. IMHO this one should go into the FAQ.
Copied to the FAQs.
Real interesting Jeff. Good info!
Somewhere there is an engineer/designer that is saying;

"How much boost ??!"

"It did what ?????"

"We never intended that, I'm amazed it works"
I had strange EEC issue on the daughters '88 TC a few years back. She said the CEL was on, was running badly and had a gas smell. First off I noticed #1 injector was leaking and the base "O" ring was leaking and sucking the gas into the intake(talk about luck). After replacing the injector and "O" rings it ran fine but continued to light the CEL when crusing at highway speeds(I had cleared the rich code stored in memory). So I rechecked codes and it was clean no problems, I thought WTF??? After disconnecting the battery the CEL didn't come back on... Maybe if I had just left it alone it would have stopped comming on, but you know how women folk are......
Ya know, for a Professor, you're pretty damn smart....... Big Grin

Good Write up Jeff!
Forgot to mention that after I fixed the leak, but before I lowered FP to get the EEC to correctly relearn fuel trim, I ran KOER twice, and it came up a pass each time (except for the ever present KS code 25 since I didnt bang on the intake)
Would that be bug #2? CEL during codes when tested?
Matt, I had a CM 42 stored each time I ran the KOEO test. While trying to figure the rich / open loop at idle / low load problem out, I would run the KOEO test each time I tried something different, and always had a CM 42 after returning from a drive. The weird thing was that I didnt have any KOER codes other than the 25. Since nearly all the KOER test is done with the EEC keeping the motor reved up, except for brief the base idle part of the test at the end, I am guessing that the conditions during the KOER test didnt correspond to the idle/low load conditions that set the CEL in the first place.