Yet another P0171/74
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Yet another P0171/74 Well, it's back at it again. Codes P0171/P0174 (lean condition) popped up AGAIN. Thought I had the problem solved by converting to 'Vette filter/regulator and it worked for a while. Pressure at the fuel rail is 56lbs (my gauge?) and long term fuel trims bounce from 10 to 25. Voltage is at least 13.6 with fans and A/C on. Used starter fluid and can't find any vacuum leaks. Strange thing is, starting a cold engine the trims go to about max but after warming they drop to about 12. I've changed the intake gaskets and even got an inch/pound torque wrench to properly tighten. Had one collector flange leak but solved that. Any ideas? Oh, engine is a 2003 LM4, stock.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Codes P0171/74 Well, the more I work on solving the problem, the worse the problem gets. Used a new fuel pressure gauge and it read 52 lbs. Changed my in-tank pump and the pressure was the same. Changed the filter/regulator and the pressure slowly went down to 36 lbs. Just can't believe a new filter/regulator could be that bad. Of course fuel trims are maxed out lean. The problem seems to be getting worse and I can't figure out how to stop it. Any ideas?
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Code p0171/74 Had a Wix 33737 in and swapped it for a Car Quest unit just to rule out the filter/regulator as the problem. For the pump I had a Bosch unit for an '03 Trailblazer which fit my Poly tank fine. Swapped that out for an AirTex unit just to rule out pump problems. Strange part is, last night I tried to prime the system and the pressure went to 5 lbs. System is taking a fast nosedive with no problem spotted...yet! Going to break the fuel line at the rail and see what comes out today. Then swap the pumps out again to see if I can get back pressure. I've inspected the fuel line running to the front with no damage noted. More to follow when I find something.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Well, found out the Car Quest filter/regulator would only go to 36 LBS and the AirTex pump didn't do much better. Back to the Bosch pump and Wix filter/regulator and about 55LBs. Don't know if the lower pressure is because of the regulator or pump. I'll use the AirTex housing for a Walbro pump or an '88 Camaro TPI pump. Where is a good sspot to buy a non-knockoff Walbro pump? As I understand it the TPI pump is for a system that only requires 47 LBS but will easily go to 58 LBS. Is this correct?
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Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Code p0171/74 Took the AirTex unit apart and compared the pump to an '88 TPI unit and they are about the same except for the size of the pump discharge. I need a 3/8" nipple on the pump and it's 5/16". Did research on the Walbro 255 and can't seem to find the answer as to size of discharge nipple. Even e-mailed several sellers of "genuine" Walbro pumps but they DIDN'T KNOW! Can't they pick up a pump (that they are selling) and MEASURE the nipple size? Anyone have a Walbro pump laying around please measure the discharge nipple for me.
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Verdad Gallardo Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Trying to bring closure to this thread so that others who may have the same problem can find a solution. Called PSI today, and discovered that the ECU had been programmed for 30 lb injectors and I have 22 lb. I've sent the ECU back to them (PSI) for correction. I should not have to post anything else to this thread if, after getting the ECU back, the LTFTs are correct. Only problem I see in the future is that I used an E-cigarette to test for vacuum leaks and the engine my have a nicotine fit.