3100 problems

[darkfox]

ok hopefully you guys can help me out on this, since i am pretty stumped.

my lumina began exhibiting some weird drivability problems. first, it would have this weird hesitation at part throttle, where the engine ran normally and didn't miss but it just didn't have the power it should of had. when you floored it, it was fine. also, shifting was harsh and kind of late.

plugs and wires are new. tested both the ignition module and coil packs, all are good. no codes were thrown.

first i thought tps, because the problem was at part throttle. replaced. problem didn't go away.

when i unplugged the o2 (forcing the ECM into open-loop) my drivability returned, leading me to think that it was a bad o2 sensor. i replaced it, the problem persisted.

i checked all the vacuum lines, replaced some of them. problem persisted.

i replaced the coolant temp sensor, MAP and MAF. problem persisted.

i reset the computer. problem went away, then came back. in addition, i have a new problem... a weird condition at idle where the idle speed flucuates, causing the engine to eventually stall. replaced the idle air control valve, problem is still there.

now the computer does set a code, P0171 fuel system too lean.

i checked the fuel pressure with the engine running, it is at about 38psi at idle, 45 psi when i yank the hose off the fpr. so the engine is definately getting fuel. i know the injectors are spraying because i removed the upper plenum and cranked the engine to see the spray pattern, looks like they all atomize fine with no dripping.

i checked the harness in case i have a short. i didn't find anything. also cleaned all the electrical connections.

problem is still there.

i am stumped. every fuel-related sensor is replaced, ignition components are all new or checked and found good... fuel system works perfect.

WTF...

[mallard]

Does the engine miss under throttle happen only under load (when driving the car) or does it also happen in park/neutral?

[darkfox]

it doesn't miss at all. it just lacks power under part throttle while driving.

[Nels996]

Check you EGR valve or EGR passage. There known to get carbon build up and the EGR sticks open slightly. If you have a scan tool monator your EGR operation. Also check your fuel trims.

Nels

[JohnTheMan]

+1 egr passage

[darkfox]

already cleaned the egr. no help.

[darkstarsinner]

I had the same thing with my Grand Am 3100. My problem was the head gasket. Check for all the usual signs. Oil in your anti-freeze and vise versa. 3100's are known for this problem.

[darkfox]

Originally Posted by darkstarsinner

I had the same thing with my Grand Am 3100. My problem was the head gasket. Check for all the usual signs. Oil in your anti-freeze and vise versa. 3100's are known for this problem.

Originally Posted by darkfox

when i unplugged the o2 (forcing the ECM into open-loop) my drivability returned, leading me to think that it was a bad o2 sensor.

if it was the head gasket, the problem wouldn't go away when i unplug the o2. that and my oil is devoid of any signs of antifreeze.

[JohnTheMan]

jeeze man, i hadnt read all of the post, you relaly have replaced just about everything fuel related, thats so weird.

and removing the 02 sensor wouldnt have anything to do with the coilpacks/plugs..... ignition is fine, fuel is fine and i bet air is fine =\

dude im stumped too...

[JohnTheMan]

any way to check if the engine is pulling timing for some reason part throttle???

[darkfox]

good idea. i need to get my hands on a scan tool..

[60hundredLE]

I had some of the same symptoms and I had to replace the whole ignition module...but you checked that?

[darkfox]

ah i got rid of the car a long time ago, lol.

i eventually just left the knock sensor unplugged and that pretty much solved the problem. i'm sure the car still pulled timing because of the disconnected sensor, so it was never as strong as when i got it, but it ran a lot better than it was.

i ended up giving it away. new owners are pretty happy with it, considering it is reliable and was a free car, lol.

[JohnTheMan]

Originally Posted by JohnTheMan

any way to check if the engine is pulling timing for some reason part throttle???

yeaaaaaaaaaah! 10 points for me