strangest thing happened to me twice now, last night while leaving a traffic light, 2nd gear--while accerlerating my car stumbled pretty bad---its like the braking system was hit--but I didn't do that with my foot, I'm pretty sure the lights all went out for a brief sec or 2--kinda scared me driving at night, then the check engine light came on---I was too nervous to drive it home so I pulled over in a well lit area and looked under the hood thinking perhaps a vacuum line fell off the brake booster--but nothing unordinary. Shut the car off then restarted--engine light did not come back on. Drove home just fine, then leaving to school today-it did the same thing--but no check engine light---it reminded me of the time when my alternator was about fried, but my voltage seems to look just fine, reads 14 constant--if the check engine comes on again I will definately try and hook up the aldl chord/program and see what codes I get...Any tips in the mean time ?

 

Ok---just ran a datalogg on the car, heres what I got....
Code 33-Map High, (manifold air pressure)
Code 43-Knock esc

Not sure what either of these are or where to start looking to fix this, but my car Barely made it home, wasn't responding well at all under throttle, lights would all go off on digicluster everytime the car stumbled and it felt like the car slowed down each time too.... Before this stuff started happening the car ran Excellent!! I've had a rebuild done recently, maybe 5 months ago with about 2k miles on the 85

 

is this something I should let Chevy take care of? I was just curious because of why 2 codes were set at the same time---If I post a list of my computer readings at idle, would that help ?

 

Sounds like it could be a bad ground.

 

boy, would that be music to my ears if its only a bad gx, are you referring to the battery gx going to engine block? I'm pretty sure I checked the gx, and it did not wiggle loosely---JUST checked the battery and the gx checks ok, tight at the grx and engine block, same for the power

 

It could be any of the grounds, engine, wire harness, ect... Sounds like it may be loosing contact when you accellerate, then lose power.

 

chad.

Just saw this post....sound DEFINATELY like a ground issue. If I am not mistaken the grounds for the dash are the ones that connect onto the trans mount bolt on the driver's side lower trans bolt mount. There are a whole MESS of them there...Going to be a little hard to get at it with everything in there, but I *THINK* that is where they are at.

There are many different grounds on the cars...some in the front, some where I just said, and some in the rear of the car. I would go around with a fine tooth comb and try to get as many as you car....as I said before, something does not sound quite right and it sounds like its getting worse or "looser" now with the dash cutting out...You might wanna run another one down off the battery to the motor while your at it.

Grounds are tough to locate, maybe you can get a good book or something that lists them all and their locations. I wouldn't mind having that myself...I would go around and triple check/clean them all, even though I am not having any problems I am aware of...

Let me/us know what you turn up.

 

so perhaps I should look at the ground wire on the fuelpump side of pin connector on the ecm ? If I'm correct--I believe I tapped into that exact grx wire for the transmission signal wire---When Wiring up a digital dokota calibrator---I would need to remove the passenger panel and double check on that wire, but are you referring to that type of gx? fyi, I had to wire in a dakota unit because of the keisler transmission, but I've never had this problem before...just started happening

Ok, just checked the grx side on the ecm and I DID tap into that for gx for the speedsensor signal wire going to speedsensor. But that shouldn't hurt anything should it?

 

the gx wire tapped into the grx side of ecm shouldn't mess anything up right?

 

I would not tie anything into the ECM itself.......what do you have tied into there?

 

I tapped the gx wire coming from speed calibrator (digi dakota) into the ground side of the ECM (passenger side, it is tapped into a grx wire, I have a schematic of the ecm wiring.

 

bump...ski dwn whatcha think?

 

Chillcat....again I would not tie anything into the ECM wiring....you never know when you might be getting feedback through a line that might be supplying voltage to that ground...even though you don't want it to be there...

My fathers car I just noticed the last time at the track, which is all wired up through a painless fuse block, with EVERYTHING on its own circuit - I noticed by chance that when he shuts off his fans...this fuel pressure when the car is off and key is off, the pressure jumps to 7psi! So somehow, unknown at this point when he kills the switch to the fan, it energizes the fuel pump for a split second...can't even hear the pump come on, but its definately making the mechanical gage read 7psi- so the pump has to be turning moving fuel....

again everything was wires independant, but I suspect something is backfeeding the fuse block for a split second and the fuel pump is getting the power...otherwise the car runs and performs awesome...

Get that ground off there...grounds are easy to come by....and its one less thing to worry about whether that might be causing the problem.

WIsh I could be of more assistance in resolving your problem....but these things require patients and lots of time to figure out...start with locating all the grounds and cleaning and ensuring they are secure and in good condition..

 

just curious if you've replaced the coil lately? if yes I'll explain later.

 

no, I think the coil is about 1.5 years old now. Thanks Ski Dwn, that was really helpful and I will relocate that gx to an actual gx location--I have a feeling that that won't be the the culprit. So if the code 33 and 43 are going on same time, would that be a loose gx issue or if for some reason the maf needs replaced--would the maf trigger the knock to act weird and throw a code too?

 

If I remember correctly a code 33 does not infer the MAF is bad..usually an open circuit or relay is the cause for a code 33 to be thrown..and I don't believe even if the MAF were bad it would trigger the knock sensor.

 

Wow, iam getting the same code but little diff 34 (map low) and 43 at the same time, sometimes i get SES ON while driving, it comes on only when i punched it really hard, otherwise if i drive slowly i mean normal driving (no hard acceleration) SES never came.

I have been driving this car without any code for 7000 miles, the only thing i changed recently is exhaust which is really loud, and i do have dakota digital speedometer box. Iam sure some loose ground somewhere, KS and ESC module replaced last year about 10k miles on them so i dont think its KS or ESC module. Infact i thought its MAF related so i cleaned MAF with Electronic parts cleaner and replaced MAF relay. I will keep continue my diagnose but if u solved ur problem pl let me know, and i will do same. sami.

 

It does sound like a possible ground problem with the lights on the dash going out. Why not use the FSM to troubleshoot the codes (starting with the lowest number)? They were thrown for a reason and I'm not sure they use the same ground, but I don't think so. Checking these might be a step to lead you in the right direction.

 

never bought the service manual yet

 

tap on the dash over by the headlight switch and see if the lights come back on mine did it at night, and i slammed the headlight switch in cause i was mad and the lights came back.
also, when I got the car, shortly after starting, and backing up, the numbers in the gauges all went funny, and in about 5 minutes, everything was normal. did it every time.
I changed the ECM, and it went away but when the gauges all came back, the mileage readout was always as if I hit the MPG reset button
I think that's why they sold me the car so cheap
now it's 9 years later and it's for sale again. but oh sooooo much better car than when I bought it