Ok so the p10 has been down the last couple weeks and had replace the starter. Ok...couple f bombs later it was replaced and started fine. Kinda always had a sputtering problem but it has grown increasing worse in the weeks past. Car gets to 3500K or so and hits a sputter wall and then a couple seconds of sputter, boost hits and it rockets up the RPM(mmmm boost...anyway). I read all over g20.net and here and every says the same things:

Check MAF- Done and cleaned no problems to be seen.

Cap/rotor, plugs and wires- Done/done, new and gapped, not that old

Check ECU and reset: done; codes 33, 34 (O2 and Knock Sensor)
Bought new O2, stripped it. Bought new bung and replaced it o2 went in no problem. Checked ECU now and it says code 55(no problem). But it still sputters...

No noticeable leaks, WTF is going on????

Any tips welcome.

CJ

Play with the TH point in the SAFC the higher i set mine the better it got, same sputtering as you. Also how do you have the safc wired, and what kinda maf you got? Also do a pressure test, you propably have a hole somewhere you dont know about.

Thanks I'll play with that, maybe that is related to this more detailed problem:

Ok little up date: Car runs fine with every throttle postion except at about 1/4 throttle.

Could it be the TPS sensor?

yeah could be the tps or your low throttle settings if you have the safcII set for 0% for low throttle.

If you are having starting trouble also i would check for a leaking injector o-ring. I had an issue where my car was hard to start and would miss off of boost. On boost it ran great. Stumped the hell out of me checked my tps, timing, idle all the typicals but no go. Then i pulled the fuel rail turned key to on and fuel was coming out of the lower o-ring. Replaced the o-rings and car has run perfect since. Just my 2 cents.

Thanks I'll play with that, maybe that is related to this more detailed problem:

Ok little up date: Car runs fine with every throttle postion except at about 1/4 throttle.

Could it be the TPS sensor?


Yes, the TPS can create the problem you just stated..
I sometimes have trouble explaining things, cause im more of a visual kinda guy, but.. here it goes.. lol

When a TPS (aka potentiometer) wears out, a "dead spot" can form.. So, at a very common throttle position, (such as cruise speeds) like 1/4 throttle.. The contacts in the TPS will wear out on that exact spot because of inconsistant foot pressure on the pedal.. (creates a worn spot where electricity cannot complete its path).. Hopefully everyone understands that.. lol..

Now, this is what the ECU is seeing when you want to accelerate...
When you depress the pedal slowly to the floor, your TPS voltage increases accordingly.. Obviously the ECU sees the increase in voltage so it sends output signals to the actuators to add fuel etc.. Once you get to your "dead spot" on your TPS, (if that is the case).. the ECU is seeing the increase in voltage then suddenly the dead spot is hit and the voltage drops to zero or close to zero... The ECU just saw that voltage drop and thought you let off the gas pedal ubruptly.. Then, once the dead spot is passes (still depressing the gas pedal to the floor).. The ECU gets the according voltage for that throttle position and thinks u just smashed the gas pedal down again... This will cause the bucking or assumed sputter effect....

I hope all the made sense.. I tend to write a lot, but whatever.. As long as the point gets across. :biggthump

You can test your TPS for dead spots by hooking up an oscilloscope to a ground and to the signal wire of the TPS. Set the time and voltage divisions accordingly (probably best, 0-6 volts and the time in milliseconds) .. Then Slowly!! depress the pedal until it touches the floor... The scope should show a gradual smooth slope on the graph from just under 1V to about 5V.. (whatever the factory spec should be)
If there is a dead spot, the nice happy slope will fall to about zero once the dead spot is touched... <-- Obviously that isn't good when you see that on the graph, thus giving away the fact that your TPS is bad.

And that concludes how to test your TPS the precise and accurate way! :)

I hope that helps you find the problem! If not, keep pokin around and let us know what you discover!

-Neil

You looked at the maf and it looked OK? You need to be checking the voltage under driving conditions.

No noticable leaks, did you actually pressure test the system to check that? That is the best method for finding them!

Lastly what is the fuel pressure set too? Do you have a means of checking it?

I gotta make sure the SAFC is tuned right, is was a pretty reputable shop and has been on the same settings for over a year, may be its a little off.



Going to have to look at the o-rings, I did switch them from the DET to the DE+T so maybe their torn.



Neil- I don't excatly have access to an ocillascope, is there a way to clean that dead spot? or is it just gone? I do get what you are explaining, nice job by the way! I found on everythingg20.com that a TPS sensor is like $90 OEM, know any cheaper ones?


Wes- Haven't checked the voltage under load, will check that soon. My buddy has a pressure tester I 'll have to double check, any where that there are usually commons leaks to test?

If your TPS has a dead spot, you'll have to replace it.. It's contacts are worn down.. But, 90 bucks is about as good as it gets from what I've searched for a TPS..

Thanks homie.