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08-20-2011
When mine went bad it caused random missfire code, very rough ideling and wouldn't stay running. I disconnected and ran good enough to drive to autozone to have the pcm read and replaced the sensor there. A day after it was replaced the map went bad and caused strange surging and bucking
08-20-2011
No codes and I don't use shops. For what I paid for the parts that I put on it the other day would only be a third of what a shop would charge me. Some ppl live by shops but I don't. Yes it would be nice to have gm shop manual but I don't have 100 bucks for a book. So that's why there are these forums so the ppl can help others out from beginners to even experienced guys.
08-20-2011
Originally Posted by taman86
Gpona has the GM service manual online.
08-20-2011
it's 3 books and they are becoming rarer now
the online one is still pretty cheap but you need windows xp professional to run it w/ almost nothing on the comp
Originally Posted by TLSheff
08-20-2011
O.k. I had problem like this drove me nuts for months finally sent it to a shop took them two weeks to find it and it pissed me off when I found what it was. Somehow the positive battery cable got wedged between the engine block and exhaust manifold it melted the insulation around it the fused the wires together hard to find the spot was 1/4 the size of a dime. The dealer had just had it in for a recall and a week later this happened dealer could not find the issue told me "its an old car with a lot of miles it does weird things when it gets old cars are like that." Took it to an independent shop and like said two weeks later he found it. I threw $1,000 worth of parts in it at dealers suggestions including a $300.00 fuel pump, MAF, pcv valve, idle valve, throttle body. Dealer wound up reapinting my hood and bumper as a deal for my not taking him to court. So anyway try replacing or at least inspection the positive battery cable.
08-20-2011
Ok so far I have crank sensor, inspect grounds, and inspect positive cable. Did you car run bad all the time or just after it is warmed up, cuz mine only runs like garbage after it is warmed up. Wouldn't hurt to take a look anyways.
08-20-2011
Maybe it's something with the PCM. Maybe after it gets warmed up and switches loops its scewin something up causing it to run like chit
08-21-2011
I was thinking about that too man.
08-21-2011
Scantool scantool scantool... Just so you can see if the maf is intermitently cutting out or log the rpm's to see if there are any odd movements like the crank sensor is going.
08-21-2011
I have autotap just need my computer working to install it...
08-23-2011
To jump into taman's thread here. I'm the one in the thread he linked with the same symptoms. As he mentioned, I gutted the cat and all was well, for almost 2k miles. And then on Sunday, boom, back to the same symptoms. The only thing I can add really is it seems to occur when the engine is very heat soaked. Mine has only happened on very hot days especially when I've slowed down for traffic or in stop & go, it will be running fine and then slowly start falling on it's face until it will barely run. Before I gutted the cat it would also do it on the open highway at 75mph, just slowly losing speed. Once I shut it down, open the hood to cool things down for 20min it restarts, runs a little rough until I hit the throttle a bit to clear it out (like it's flooded). Then all is well. It runs so rough while it's coughing & puking. Now with the cat gone it smells super rich to me when it's acting up. I'm wondering if one or more injectors are going static when it's really hot and just flooding the crap out of it. Then once the engine cools they go back to normal.
08-23-2011
Well the guy that I mentioned before who I pm'd and also the op of the thread I have a link to in my first post, pm'd me this morning and his car is acting up again with the same symptoms as before and the same as my car. I told him he is welcome to post here if he likes, but to take a look at my thread. So turns out it wasn't a clogged cat.......
08-23-2011
Precisely the same thing. Mine doesn't smell very rich though. I can shut mine off and immediately start it and it will idel fine but will not accelerate well at all where as before I shut it off it will idel rough, shake, and fluctuate till it dies or I shut it off.
08-23-2011
Yes, mine will always restart & idle (roughly). I just can't drive it because it won't take any throttle or it completely bogs. At that point I just let it sit to cool. Then all is well again.
I switched the ignition module on mine with a known good one. Same results.
08-23-2011
Ok, I had an epiphany today while I was working and thinking about how the car is acting and what my boost guage is doing while it is acting up. One of previous posts I mentioned that the needle will spike on the pressure side then go back to the vacuum side as the engine is pullung vacuum given the throttle position. As I was thinking about this it occured to me that it is pre detonating in the intake manifold causing the spike in pressure. I think that for some reasson the timing is being retarded so much that it is actually igniting while the cylinder is actually on the intake stroke pulling fuel and air into the cylinder and while the intake valve is open, igniting the air fuel mixture and causing it to ignite while the valve is open.
A couple months ago while my computer and scanner were working I did a log while the car was acting this. The one thing I do remember from the log was, it was in the low 100's outside, the iat temp sensor was reading 140's and while accelerating lightly, being forced to by the car, to 45 and struggeling all the way, the knock retard was reading anywhere from 8* all the way up to 18* and the higher the retard the more I pushed the throttle.
Any thoughts?
08-23-2011
If your not gonna scan it and want to throw parts at it, do the crank sensor for as cheap as it will be. But make sure to do a "case learn" once its installed to calibrate everything again.
08-23-2011
If my computer is working then I would scan it. My question though pertaining to my above post is what sensors control ignition timing?
08-23-2011
Pretty much the computer is controlling timing from the Crank sensor, cam sensor on startup, knock sensors and TPS, MAF & MAP to calculate load on the engine. That's how I understand it. I agree with what you said above that mine certainly feels like it's pulling out tons of timing when it's bogging and I see spikes on digital boost gauge on the DIC if I floor it while bogging. Looks like intake backfires but I don't hear them. I guess it might be possible for a knock sensor to fail and it be telling the computer to pull tons of timing in this case. Only way to know would be to watch KR when it's happening.
08-23-2011
Well like I said in my above post, when I was scanning a couple months ago, this has been going on for a long time now, it was showing 8* ok kr while just lightly accelerating from a stop to 45.
08-23-2011
Which is illogicial.
have someone raise your noise floor to 1 V.
Or disable KR from 2500- to 3500 or so.
97's apparently have odd KR issues.
Last edited by matt5112; 08-23-2011 at 07:45 PM.
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