The Oldsmobile Connection

88delta88 · Joined: 09 Jun 2003 Posts: 2409 Location: Canada

Hey guys... Got a question, maybe you guys know just off the top of your head what this sounds like - I havent even checked into it myself yet.

I get the service engine soon light 10 seconds after I start the car, and it will only stay lit, when you've got yoy foot off the pedal. As soon as you start accelerating, it goes out. It'll come back on as soon as you get to the next light.

Maybe I'm crazy, but it seems like the idle revs are up a lot higher than normal, and the exhaust has a funny smell.

First thought into my head was O2 sensor... Any suggestions?? Otherwise, I'll fire up the old ALDL, and check it (need to find a mouse for my computer first).

88delta88 · Joined: 09 Jun 2003 Posts: 2409 Location: Canada

Ok, at lunch time, I was able to drag out a mouse to the car and do some diagnostic.

Amongst all the flags it shows, I picked out 4 flags that meant the most, and looked most suspicious.

At the top of my list, was the TPS LOW flag. I beleive this means that the throttle position sensor is screwed somehow, and that wouldnt surprise me. A guy at work says they get carboned up at idle and cruising positions, and that would explain why it goes off under acceleration.

The RICH flag was on steadily, the CLOSED LOOP MODE was on steadily, and one flag called "DRP OCCURED" flickers on and off... I dont know what a DRP is.

Nothing was wrong with the O2 sensor, or anything else.

The funny thing is, the only item that was an actual error code was the TPS LOW flag. Help!!!

86Delta · Joined: 06 Nov 2003 Posts: 281 Location: NJ, USA

well once it warms up it should be in closed loop. and with it staying rich, it could be because of your TPS. the computer might be thinking there is more air going in than there really is and it is richening up the mix. the TPS is a bitch to change, pretty sure the throttle body has to come off because you can't get to the bolts with it on the car. i don't see how the TPS could get carboned up considering it is on the side of the throttle body and not inside the TB in any way. pretty sure the TPS is adjustable, but considering this happened all of the sudden, i would replace it.

88delta88 · Joined: 09 Jun 2003 Posts: 2409 Location: Canada

I did some research on the internet last night. They said a typical GM TPS should register at idle 0.4 volts. And at wide open throttle it should register 4.85 volts. The computer goes into alarm mode when the voltage drops below 0.2 volts for more than 4 seconds, and automatically simulates a 2.6 volt signal (50% throttle) so that you can still drive the car.

This makes a hell of a lot of sense, and when we tested the sensor, sure enough, the low end was at 0.16 volts, and the top end was 2.25 volts - a BIG difference over what it should be. New TPS sensor is only 75 bux anyway, and beleive it or not 86delta, we got the damned thing off in like 2 minutes!!! I even thought to myself - its on the bottom of the throttle body, lets start ripping it off...

Anyways, going to buy one today, and we'll see what kind of other problems (rough idle, poor performance) it might fix.

DKnight · Joined: 10 Nov 2003 Posts: 63 Location: Huntington, WV

I didn't see this message sooner, or I would've responded. I looks like you've got it under control, heh. The opposite problem as I had...running rich. Sure wish I had that ALDL software and an in-car computer, haha. Oh well. Maybe someday.

DK

Brando · Joined: 06 Jun 2003 Posts: 3069 Location: Michigan, USA

Yea...I still never hooked that damn thing up...I got a cable waiting.... :shock:

TOC Admin
Brando

88delta88 · Joined: 09 Jun 2003 Posts: 2409 Location: Canada

Brando!!! I'm going to have to give you shit for that... You cant just have a cable and laptop ready to go and not try it!!! Its way to easy to hook up to let it sit!!! And way too cool to play with!

Anyways, I bought the TPS sensor for 75 bux!!! (glad I dont have a VIN C motor, they are 100bux!). I stuck it on, and positioned it so at idle it registered 0.38 (as close to 0.4 as possible), and tried it out. 0.38V at idle, and now completely floored, it registers 4.45V. This is great, all my rough idle, hesitation problems dissappeared! Its like driving a new car!!! I would recommend that if you dont think your car is outputting like it should to check this sensor for voltage at wide open throttle. My old sensor was only outputting 2.25V when it should be 4.5V - Computer only thought I was pressing the throttle 1/2 way!!!!

I'm happy, that one little sensor could make such a difference in my engine, and the ALDL computer basically told EXACTLY what was wrong (I just had to prove it wasnt lying!)

Now, without removing my battery cable from the + terminal, how do I reset the ECM memory so the flag will go away? Anyone know? I just dont want to lose the settings on my stereo :-)

86Delta · Joined: 06 Nov 2003 Posts: 281 Location: NJ, USA

On my SnapOn scanner there is way to clear codes on most cars, but some older cars the battery needs to be dissconnected.

strokercutlass · Joined: 09 Jun 2003 Posts: 379 Location: Wis

88, it may be possible to pull the ECM fuse in the fuse box, allowing the codes to clear, yet not losing power to all systems. There may be either 1 or 2 fuses for the ECM. Otherwise, some of the GM cars had a plugin in a smaller cable coming off the positive side of the battery, which allowed the ECM to be disconnected w/o unhooking the battery.

88delta88 · Joined: 09 Jun 2003 Posts: 2409 Location: Canada

Cool! Thanks, I'll look for the fuses... Although I dont think my car has a connection on the batter just for ecm... if it does, i'd have to take the whole side post off anyways...

Oh well, i think I read somewhere that the ecm clears error codes after so many successful starts without the code. The light doesnt come on anymore...