CEL at WOT

[ob1murry]

Hey guys,

I just got my 89 Supra (Auto) up and running again recently. Everything had been working fine on it until Sunday when it threw a CEL about 30 miles from home. I was able to find a bobby pin and check the code, which was 21. I ordered a new O2, and replaced it this evening, then took the car out for a drive to make sure everything was good. Everything is fine with the car, except when I got on the highway and hammered it, it would throw a CEL at WOT, right when the transmission kicks down. If I back out of it for a second or two, the CEL goes away, but if I get back on it again, it comes back. I got home, checked the codes again, I only see 12 and 13, no codes for knock or lean conditions, which is what I would have expected. While I certainly understand these are issues that need to be fixed, at least on the surface, they don't seem to me like they are related to the CEL at WOT, because I would expect these codes to keep the CEL at all times.

The car does have a few mods, but nothing super extensive that I would think would cause an issue:

NGK Plugs (.032 gap) and Wires
LIPP Intake Adapter and Pod Filter
LIPP O2 Housing
3" Downpipe
HKS Catback
FMIC
No EBC or MBC, car runs pretty solid at ~10 psi.

I've gone over the car pretty thoroughly recently, and don't have any boost or vacuum leaks that I found, and even when the CEL is thrown, the car runs pretty hard, it's certainly not hitting fuel cut or anything like that.

Can anyone help steer me in the right direction here? Am I totally off base, and the CPS is absolutely the cause of that CEL at WOT at highway speed? What else should I be looking for as a potential cause?

Any help is much appreciated.

 

[Nick M]

12, 13, and 14 are low numbers and come first because your car will stop running if you don't deal with them. Forget about the symptom of the MIL and when it turns on at this time. Those are order of importance.

 

[ob1murry]

Yeah, I understand that. Perhaps I worded this poorly, but my concern was more or less is it possible that those were the codes being throw when the CEL came on? Perhaps the sensor or wiring was loose and at WOT, it shorted out? These seems like codes that would cause a constant CEL, so why was the indicator not constantly lit? Had I not checked for stored codes, I would had no idea there was an issue. Do codes 12 and 13 not throw a constant CEL, just store the codes?

 

[jetjock]

One of us is cornfuzed. Maybe this will help:

1) Codes are stored regardless of whether the MIL stays lit.

2) Only "hard" faults will keep the MIL on. If the problem fixes itself the light will go off.

3) This doesn't apply to code 51

3) 52 is the only code that will keep the MIL lit until the next key cycle.

 

[3p141592654]

12 or 13 would suggest a wiring problem or other issue with the CPS. It may be that the harness is damaged and engine movement is causing it to be intermittent. I would jiggle the wiring near the CPS at idle and see if you can get the engine to stall.

 

[ob1murry]

Sorry, if I what I said was originally uncear guys, it was like 1:30 in the morning, and I was running on fumes.

3p141592654 seems to have gotten the gist of what I was asking though, which was basically, since I had just cleared all of the codes, and let the car idle for about 10 or 15 minutes, then checking the codes again (there were none), before going for a drive, is it possible that codes 12 and 13 are the ones that were causing the CEL at WOT, or were they unrelated. I assumed they would have been unrelated, because before jetjock's post, I just assumed that the only codes that would trigger the light and allow it to turn off, would be something like knock.

I've been busy so far this weekend, but I'm going to go and try to check out the CPS connection and wiring later today if I get a chance, or over one of the next few days. I'll be sure to report back when and if I find any issues with it.

 

[jetjock]

If you had cleared codes then the CPS ones were likely what triggered the light. After all faulty CPS wiring is a common issue on these cars.

A few more points:

1) Many codes will not be set from just idling. The same applies for the MIL. Several parameters be met (rpm, temp, speed, etc) first. And remember, setting codes in memory and illuminating the MIL are two different things. Codes are always set while the MIL isn't always lit.

2) A fault that lights the MIL will extinguish it if the fault disappears. The code remains set in memory however. The only code that will keep the MIL on (until the next key cycle) even if the fault clears itself is 52.

3) Detonation (knock) does not set that code or light the MIL. It's set by a loss of feedback in the knock control system.

All this is one reason to check codes on a routine basis. During an oil change for example. And never try to set ignition timing without first checking for codes become some will not allow it.