Performance Problems

[rkarl89203]

Since 70,000 miles I have had the oddest performance problems with this car...I love this car, but it's weird trying to clear up problems sometimes.

2001 Daewoo Lanos....timing belt has been changed, no probs there....changed air cleaner, fuel filter, spark plugs, wires, redid some vacuum hoses, put tons of injector cleaner in, and no change....

It hesitates and bogs at various speeds, and follows almost no pattern....No smoke, no leaks, idles OK, but when you apply accelerator, it seems like there is a dead spot and then it catches and runs fast....almost feels like a fuel feed problem...spark and timing are OK......


I am running out of ideas....NOTE: It seems to be worse after right turns, but not always.....

Weird...anyone?

[rkarl89203]

UPDATE:

I read on another post about the throttle body/intake being cleaned...is there a procedure to tell one how to do this?

Maybe that's my problem...

anyone?

[MMamdouh]

can this be a weak fuel pump??

try to get a pressure reading for fuel pressure at idle... it should be some 42 PSI

MMamdouh

[rkarl89203]

I'll try it...thanks!

[Trey05Woo]

A tired fuel pump can defintely be the culprit, especially with your mileage but your symptoms sound to me like a failing TPS (throttle position sensor). The tps provides the engine computer with throttle blade angle. The computer injects more fuel as the throttle blade reads more voltage because the more the throttle is open the more air entering the engine, and the more fuel needed to operate. A faulty tps will cause a stumble, hesitation, or stutter symptom something like fuel cut off because the ecm does not know the relative throttle position and not increase fuel injection accordingly.

This sets a DTC BUT WILL NOT LIGHT THE MIL. So try to get a scan tool hooked up and check for codes p1121/22 in history. For some reason, daewoo engine management decided this is not an essential fault and the check engine will not come on even with the fault current.

[benzino]

i have this problem too... i was just about to replace the fuel filter... i hope that helps... i hope it isnt the tps

[Trey05Woo]

well there is an easy way to check the tps using a volt meter. just hook up the multimeter and back probe pin b (blk ground) and pin c (drk blue tps signal) and measure the voltage. Should read .4 volts closed, and at or about 5.0v at wide open throttle.

but the trick is to slowy crack open the tb and slowly operate it from closed to about 25% open, making several pauses, paying attention to the voltage readings. This is because the sensor is constantly operating in this range under normal driving and will wear out in this range.

What you want to look for is a steady even reading from 0 to 25% to wot. The voltage should never drop never spike, and should read steady and hold whenever the throttle blade is not moving.

[benzino]

sweet i'll check it out... fingers crossed lol

[rkarl89203]

Hi, OP here....

tried the Idle relearn' procedure and the idle seems better now, but the performance is still spotty.

On acceleration it almost sometimes feels as if it is fuel-starved.

What is involved in the actual changing of the Throttle position sensor unit? I've located one locally for cheap here and may just swap it out....is there any linkage or anything like that internally to hook up?

Thanks for any help!

[Trey05Woo]

The TPS is bolted to the throttle body via two phillips screws. You do not need to replace the entire tb assembly, you dont even have to remove the tb. The sensor is easily accessed, and one you replace it you musr perform idle relearn again.

Did you check the sensor? Check for dtc's? I wouldnt replace it unless you have isolated the problem as it. You could very well have a tired fuel pump as the symptoms are similar...

[PrecisionBoost]

...spark and timing are OK......

How do you know that your spark and timing are ok?

Keep in mind that checking spark at idle does not necissarily mean that your going to get good spark under load.

At that mileage... if you haven't replaced the spark plug wires I would do so immediatly.

I'm not saying this is your problem.... but it's worth looking into and good preventative maintenence with that kind of age and mileage on the vehicle.

[rkarl89203]

Hi there....I have recently changed both the plugs AND wires.....

The odd thing is that it actually DID seem to help...for about a week.....then back to the odd half-time weird hesitation ...

It's intermittent, and the CEL (when its on, which is only occasionally) shows nothing but occasional EGR valve fault, NEVER a flashing CEL......

The reason I am moving towards TPS repacement is cost: TPS= $26, fuel pump = $288....

It never actually stalls but sometimes have to press accelerator pedal all the way to the floor to get it to respond.....

[Trey05Woo]

Well egr could be your problem! If the egr is flowing too much exhaust gas (waste) into the engine it can very well drown it out. The engine can do nothing with the exhaust content but dump it out. The only reason EGR exists it to control emissions output. They figured if you introduce some of the exhaust gas back into the engine a second time any unburned mixture will burn up... Well that and now a days combustion temperatures run so high, EGR helps control these temps a bit. But too much exhaust gas will suffocate the engine, and cause it to stall, hesitate, run rough etc.

Just cause the mil is not flashing does not mean the EGR is working correctly. Infact, until a thread a couple weeks back, I had never experienced a EGR cause a flashing mil. And I have been working these cars consistently since 05.

I would definitely have the egr checked out sometimes all it needs is a good cleaning because carbon build up will cause the pintle to stick in the open position.

[benzino]

i was trying to backprobe the tps but i wasnt getting a reading...
Just wanting to make sure i was doing the right thing...
on my TB there are two plugs... one with 3 wires and one with 4
i tried back probing the one with 3; is that correct?

[rkarl89203]

OK, Original poster here.....

Please folks, don't hijack the post, I'm just trying to solve this weird problem.....

Update: I got the codes printed out for the CEL (which actually flashed for a minute today)....

P1404 EGR signal error (?)
P0303 Cylinder 3 misfire detected
P0405 EGR position sensor circuit low....

This is looking more and more like a EGR problem, but the cylinder 3 misfire is puzzling...
I tuned this up less than a month ago, totally. Plugs, wires, etc....I DID get the original Daewoo wires from Autozone, tho...
Looking at the engine from the front of the car which cylinder is #3?

any help is appreciated...thanks!