legacycentral bbs

I still have that damn missing/hesitation.

I replaced hoses, clamps and what not today. And bingo bango bongo the problem comes back.

Now a big news flash, or at least information flash. When the wagon is running great, with no detonation and no hesitation, the multimeter hooked up the O2 sensor always reads .8 ish when cruising or WOT. When the problem is happening, or when I get detonation, the sensor reads .6 to .65.

Since I seemed to have replace, repaired or inspected everything else under the sun, I am now onto suspecting the TPS. And what I suspect is that the closed throttle switch is getting thrown, or unthrown so this give the ECU a reading of a closed throttle plate even though everthing else is WOT or near it. This would explain why the MAF reads normal when this happens, why the rpms obviously stay the same (I am still in gear) and why the O2 sensor reads suddenly lean (fuel cut).

So, since I have an extra or two tps , I guess I will be replacing them tommorow. I will also be reading the codes tonight I hope. I have never done this because I always assumed I was getting a CEL from boosting the NA ecu. silly me.

Threw about 8 codes. But none definative since alot of them could be from non-conductive plug wires and vacumn leaks. Need to clear the codes in the morning and try again.

I'm pretty sure you'd get a trouble code thrown if the idle switch came on while the TPS wiper showed a wide open throttle. But small breaks in the traces that the wiper goes over can cause weird enleanments or enrichments.

Keep in mind that dumping in excess fuel can make the oxygen sensor read "lean" -- if it's rich enough to cause a misfire, none of the oxygen gets burned, and the sensor then sees lots of free oxygen, just as it would if the mixture were lean. In fact, any misfire causes a "lean" reading, even if the problem has nothing to do with fueling. That's why OBD-II requires ECUs to go into open loop if they detect too much misfire.

Definitely clear the codes and pull them again. I highly recommend wiring a couple switches on your dash to the connectors so you can read and clear codes without getting under the dash.

So I cleared the codes this morning. Had a "new" maf and throttle body with TPS sitting ready to go on. Take it out for a spin to get the codes to pop back up.

Nary a hiccup, spit or vomit from the car. Drove like a dream. Not a CEL to be seen until the moment I pull up in front of the shop, and that goes out immediatly.

The O2 sensor readings were in great shape, always in the .8 range when needed.

Could clearing the codes have cleared a "safe" mode in the ecu?

If I have the problem again, I am going to immediatley clear the ECU and see if a bad code is causing my problems.

Arg.....

douglas vincent wrote:Could clearing the codes have cleared a "safe" mode in the ecu?

Yes, it's possible. Apparently sometimes when the ECU performs corrections to its behavior for some reason, it remembers and performs the same corrections again in other similar circumstances.

If I have the problem again, I am going to immediatley clear the ECU and see if a bad code is causing my problems.

You mean you're gonna read the codes, then clear the ECU, right?

OK, heres the codes I pulled.

14,15. injectors. ? but think this is secondary to the problem

23 MAF signal, I get this probably due to the combination of non stock filter AND the poteniometer. Suspect this is not the problem

31 Abnormal voltage input from TPS. AHA!. Safe mode sets throttle sensor output to a fixed value. This would explain running either too rich (and bogging) or lean.

35 Canister purge solenoid valve ? Dont know what this is?

49 MAF again, use of improper air flow sensor.

I didnt clear the ECU of the codes I think, I just cleared the ecu for the moment and got rid of the CEL.

If problems still exist then the code-clearing procedure won't work. How did you clear them?

If there's an active TPS trouble code, the only times you should notice problems are when you rapidly change throttle position. When you quickly press the pedal you get some misfire as it runs momentarily lean, and when you let up quickly you get some bogging as it momentarily runs rich.

The MAF and injector codes probably originated when you were messing with those respective parts. Unless they come back after clearing, I wouldn't worry about them.

The purge valve is the solenoid under the passenger side intake manifold runners. It lets the ECU control flow from the charcoal canister to the little fitting on the top of the throttle body.