2000 Gmc Jimmy P0171 Code

[k_dewitt]

Well I finally got the car running better and after 20 miles of driving around the check engine light came on and it first threw a p0300 code mulitple missfire so I cleared that code and it hasnt returned yet but the light came back on and its a p0171 the car runs great while driving doen the road but when I stop or its idiling it rough to say the least, it hasnt stalled but it has a very rough idle. Ive replaced all the plugs wires distributor rotor button fuel pump and filter and replaced all the fuel lines from an other problem, so im not sure if i should check the maf sensor or check the o2 sensors, any ideas would be great

[MT-2500]

Code 171 is fuel trim lean on bank 1.
Always confirm good fuel pressure.
Drive and see what other codes come back?

Check egr valve for carbon and carbon balls or leaking and for vacumn leaks?

Is it missing on one or more cylinders?
WHAT IS THE VACUMN READING AT IDLE AND AT 2k rpm?


HAVE YOU CHECKED OR CLEANED maf SENSOR?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[k_dewitt]

The fuel pressures are all correct they were just checked at the dealership on friday should I take off the egr and check or whats the best way to check the egr, Im gonna pull off the maf and clean it and see what happens, would a leaky exhaust cause this problem?? I havent had any other codes come up other than mulitiple missfire yesterday and that hasnt returned yet

[danielsatur]

Do a smoke test to pin point unmetered air leaks.

[k_dewitt]

How would I do a smoke test??

[danielsatur]

See www.youtube.com/watch?v=FfiQ7qWiG-M