North American Turbocoupe Organization

EEC glitch?? - weird (long) story
Jeff K Offline
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.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized

Joe F Offline
Posting Freak
Weird, but very good to know. IMHO this one should go into the FAQ.
JR's Place - My '87 Turbocoupe

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