This car is slowly killing me with P0131 and P0171

[chadicenhour]

Have someone drive it while you monitor the sensors on the scanner unless you have software that allows you to review recorded data in graph form, otherwise isolate your O2 sensors on the scanner and observe the voltage change while the car is being driven, low voltage is lean, high voltage is rich. The voltage should change constantly over the full range. Constant voltage or sluggish to small changes in voltage suggests there is a problem in that area. I believe your fuel pressure should be higher than 40 psi on a 99 car. A lean condition should show up in your O2 sensor voltage. Some of the GM cars have a dual speed pump control, not sure if that is part of the problem you're having.

Check your TPS voltage also for a linear change with accelerator position.

TPS seems to be fine. I can't remember the exact specs, but it was .55v to 3.55 or 4.55 volts. I have a bad memory. I didn't see any drop in voltage throughout accelerating. About the o2 sensors, I don't quite understand them, but I remember seeing one of them, which I think it was the downstream sensor that was slowly switching or sometimes it was like it stopped completly. The fuel pressure I think was around 45 at idle and like I said, about 40 while driving it in any manner. I thought it was a little on the low side, but I'm not sure what the specs are suppose to be.

[geldartb]

does your transmission slam into every gear. for example with these cars when the maf is unplugged or bad it will revert to the max fluid pressure for the tranny which results in hard shifts.

i had my maf take a dump on me today. it was fine when i left the garage but 10 minutes down the road the car started acting funny so i stopped checked everything thinking i popped off a vac line but all was good so i sat there for a minute thinking and it wasnt until i was driving away that i knew what it was. it was shifting way harder than it normally does. also the car ran like shit and it didnt want to stay running.

[chadicenhour]

does your transmission slam into every gear. for example with these cars when the maf is unplugged or bad it will revert to the max fluid pressure for the tranny which results in hard shifts.

i had my maf take a dump on me today. it was fine when i left the garage but 10 minutes down the road the car started acting funny so i stopped checked everything thinking i popped off a vac line but all was good so i sat there for a minute thinking and it wasnt until i was driving away that i knew what it was. it was shifting way harder than it normally does. also the car ran like shit and it didnt want to stay running.

The trans feels great. I know exactly what you're talking about with it slamming into gear. I tried to drive the car with the MAF disconnected today and it resulted in very harsh shifts. For some reason I still don't want to rule out a bad maf. Thanks for the help.

[Joseph Upson]

TPS seems to be fine. I can't remember the exact specs, but it was .55v to 3.55 or 4.55 volts. I have a bad memory. I didn't see any drop in voltage throughout accelerating. About the o2 sensors, I don't quite understand them, but I remember seeing one of them, which I think it was the downstream sensor that was slowly switching or sometimes it was like it stopped completly. The fuel pressure I think was around 45 at idle and like I said, about 40 while driving it in any manner. I thought it was a little on the low side, but I'm not sure what the specs are suppose to be.

Keep your eye on the O2 sensor, they should be very close in operation especially since they are heated for near instant closed loop and reading exhaust that hasn't changed very much after passing threw the cat. My sensors parallel each other when both are working.

I would also research the fuel pressure, it should be lowest at idle and increase with throttle openning if there is a vacuum signal. I drove several hundred miles unknowingly on a bad fuel pump until it finally nearly left me broad side in the path of traffic after attempting to enter the median from a side road. 40 psi is good but if it is supposed to be 55 psi it isn't good enough.

[chadicenhour]

Keep your eye on the O2 sensor, they should be very close in operation especially since they are heated for near instant closed loop and reading exhaust that hasn't changed very much after passing threw the cat. My sensors parallel each other when both are working.

I would also research the fuel pressure, it should be lowest at idle and increase with throttle openning if there is a vacuum signal. I drove several hundred miles unknowingly on a bad fuel pump until it finally nearly left me broad side in the path of traffic after attempting to enter the median from a side road. 40 psi is good but if it is supposed to be 55 psi it isn't good enough.

I read somewhere (I think it was on the Solus) that B1S2 should have a steady reading and not fluctuate too much. Does this sound right? Mine doesn't fluctuate much at all while cruising, but if I get on the throttle it changes a little. Also, the fuel pressure seems to be within spec. I hate this car even though I get alot of compliments on it. If I don't figure this problem out soon, I'm gonna have to sell it or pay someone that knows what the hell they're doin to fix it.

Oh, on a side note, I pulled the MAF out to clean it and found that the idiot that owned it gutted the screen out and the piece on the other side had been cut out. I was hoping that the MAF was damaged so I bought one from a salvage yard and cleaned it and put it on with no change in how it runs other than smoothing the idle out some. I HATE THIS ENGINE! My 4 liter ranger ran better than this engine. Anyway, I was watching the TPS % and noted that the power kicks in at about 70% throttle. WHY? Voltage is .55 closed to 4.55 wot. I also noticed that it got to 99% at 4 volts and it still had throttle left that went to 4.55 volts and never getting to 100%. I can't see how there is .55 volts left after getting to 99% throttle. Does this seem right.

Ok, so another thing I was pondering was the muffler could be plugged. When I got the car, the kid had the exhaust cut off behind the resonator and turned out the side with no muff. I had a local shop run new pipe back to the original muff that came with the car. I'm wondering if there was a reason this idiot had the exhaust like this. Whats the chances the muffler could be clogged. I had an 89 Probe Gt that wasn't getting full boost after putting a manual boost controller on it. After driving it around for a few days, the muffler blew up and I had instant power. I HATE THIS CAR!

[86FieroSEv6]

Two things. The throttle percentage is a conditioned parameter, always use throttle sensor voltage. Just make sure that the throttle percentage is 0 at closed throttle. The only way to really see a potentiometer based sensor is to use a live oscilloscope, you will more readily detect glitches in the signal when sweeping the throttle. Next, fuel pressure is half the battle, you need to have adequate fuel volume as well. You will want to test for fuel pump dead-head pressure, that is by blocking the return momentarily. Also, you can use a milliamp lead for a digital volt/ohm meter and there is a formula for calculating the pump RPM. Take readings at idle and as you power-brake the engine to force fuel delivery. I have had pumps pass on pressure but mess up when the injectors get to flowing and it has to keep up.

[chadicenhour]

Two things. The throttle percentage is a conditioned parameter, always use throttle sensor voltage. Just make sure that the throttle percentage is 0 at closed throttle. The only way to really see a potentiometer based sensor is to use a live oscilloscope, you will more readily detect glitches in the signal when sweeping the throttle. Next, fuel pressure is half the battle, you need to have adequate fuel volume as well. You will want to test for fuel pump dead-head pressure, that is by blocking the return momentarily. Also, you can use a milliamp lead for a digital volt/ohm meter and there is a formula for calculating the pump RPM. Take readings at idle and as you power-brake the engine to force fuel delivery. I have had pumps pass on pressure but mess up when the injectors get to flowing and it has to keep up.

Can you explain dead-head presssure please? I'm assuming pressure should increase with the return pinched? How long is momentarily? Do this with the engine off or running? Thanks so much, I appreciate everyones help!!

[86FieroSEv6]

The technically correct way is to disconnect the return fitting and block the fuel rail outlet tube, the problem is that it is no walk in the park due to the design of the pressure regulator and outlet tube. If your beast has the rubber hose section instead of plastic (from the engine to the fender wall) you can use some smooth jawed pliers to momentarily (2-4 seconds, enough time for a stable pressure reading) clamp the hose. A simple series of key on, engine off cycles will spool up the pump, or you can use output actuator mode on an advanced scanner, or you can apply twelve volts to the fuel pump test connector or you can key on and bridge the fuel pump relay connections (pin 30 to pin 87). I do not recommend running the engine for this test. Compare the pressure value obtained against the pump manufacturers spec. for max pressure. I have had a few pumps that were brand new out of the box cause some mysterious symptoms due to cheap manufacturing and the only way found out was to check the pump under stress. Where I work I don't have a handy piece of highway to fly down with a pressure gauge taped to the windshield :-)

[chadicenhour]

I never found the problem with my car. I did replace the fuel pump with a new one and had no change in performance. It still feels sluggish. I'm tired of throwing parts at it. I guess I'm gonna save money and take it to a dealer.