p0174 454 vortec

[gbiddlec]

I get nearly the same issue intermittently in my '99 7.4L. I've been shotgunning parts at it without much luck. I get P0171 (bank 1 lean) and occasionally P0174. I also get the same O2 code. My issue came up after installing new injectors. Mine runs fine most of the time and I drive it daily. The only noticeable issue I see, other than the dash light, is that it will stumble bad when I start the engine when already warm. I.E. if I drive to town and then stop at the store, shut it off, and then restart a few minutes later. When I do this the engine will not rev up at all and sounds like it backfires if I floor the pedal. This lasts for around 20-30 seconds and then it kicks out of it. It runs fine on a cold start.

I tell you this as, you might try getting it up to temp, shutting it off and then restarting to see if you can recreate the issue.

 

[Schurkey]

Showing goofy coolant temp readings does not totally indicate the temp sensor is defective.

That could just as easily be a wire harness problem including a poor connection anywhere between sensor and ECM.

In fact, it could be a faulty ECM--although that's pretty unlikely.

Realistically, you'd shove in a different sensor after making a quick check of the harness and connector. Then re-test. If you still have goofy readings, sure, maybe you got a defective sensor...but the chances of it being harness or ECM increase. And that means spending more time 'n' effort to investigate the wires and connections.

 

[dirtautoguy]

I had a chance to work with it some more today. I checked around the wires and followed them the best that I could without totally taking loom apart. nothing looked broken or disturbed that I could see.

the real kicker we found is when I hooked up a fuel pressure tester. when I screwed the tester in it did spray any gas out. which I thought was odd I cycled the key a couple times and had 0 psi. I feared that maybe was dead and now blocking my garage. but it did start and at idle it was holding 50 psi very steady. when the truck was shut off pressure dropped to 0 immediatly and did not hold pressure at all. I tried cycling the key again while I could see the gauge and it would build about 5 psi and drop to 0

in my head I am thinking the fuel pressure regulator is shot. the pump and filter have less than 5000 miles on them and I believe they are in good working order. I would think that a injector issue would present more drivability issues though I have not had much experience with injector issues.

I talked to a local trusted mechanic and he quoted about $340 labor plus parts. his only concern was once he gets in there and does the regulator if there will be any problems with the injectors. the parts store said the regulator is about $100.

I am certain that I could handle the job its just a matter of when I can get to it and getting the weather to cooperate at the same time.

but before we pull the trigger on this of course I am still open to thoughts

 

[stutaeng]

50 psi does sound a bit low. I don't know what the specification is for the 7.4 Vortec. That will explain the lean running. For some reason one bank is bit higher than the other, but not by much. I thought 10% was the threshold for throwing the CEL.

Is the bank that's lower fuel trim also the bank with the fuel rail connection to the lines?

I'd still do some more testing before condemning the FPR, but it's starting to point to that being the issue.

 

[Schurkey]

I hooked up a fuel pressure tester. when I screwed the tester in it did spray any gas out. which I thought was odd I cycled the key a couple times and had 0 psi. I feared that maybe was dead and now blocking my garage. but it did start and at idle it was holding 50 psi very steady.

Extended cranking time? Sounds like there's no fuel pump prime. Could you hear the pump running when the key was turned from "Off" to "Run"?

I'm wondering if the fuel pump relay or related wiring has failed; the fuel pump doesn't run until the engine has cranked long enough to build oil pressure.

Did you verify that the fuel pressure gauge is accurate? Just because the gauge reads "50" doesn't mean you have 50 psi. The gauge could be damaged in various different ways. I'd want to at least compare it to another gauge or three; and preferably at or above the expected fuel pressure to assure that the needle can swing that far. If you expect 60 psi on the engine, test the gauge at 60, but also test at...75 or 100 or whatever max pressure the gauge is intended for. (But not above max pressure.)

when the truck was shut off pressure dropped to 0 immediatly and did not hold pressure at all. I tried cycling the key again while I could see the gauge and it would build about 5 psi and drop to 0

Curious. Low battery voltage? Pump runs, but not very well until the alternator kicks the voltage to 14+?

Not holding pressure seems to be a SECOND problem, perhaps totally unrelated to the lack of pressure when turning the key.

 

[dirtautoguy]

atleast part of the problem has been fixed.

after doing some more thinking and research on what some of you have said I put the gauge back on the truck and then pinched off lines. the return line had no change the pressure bled right off. so I pressured it up and pinched both lines off and the pressure held fine. (although it was still low.)

from another forum I had found this test indicated that the pressure issue was on the pump side and not the regulator side. searching for more confirmation I noticed that his pump was a lot quieter than the pump in my 96. so I did a amp draw test at the relay and found that his pump was only drawing about 3 amps while mine drew about 6.8 amps.

satisfied we had found at-least one culprit we opted not to lay in the snow bank and have a shop replace the pump for us. we also opted and decided that doing the whole hanger and doing the filter at the same time couldn't hurt.

we went and got it today and immediately noticed some things. the truck idles much happier neither of us realized it was as bad as it was. and of course it also accelerates much much better and even sounds better.

just to further satisfy my curiosity I did some of the same tests we did before and found that this pump drew between 5-6 amps, could be heard without sticking your head in the wheel well, and the fuel pressure is also about 55 psi and when reved goes up over 60 psi. where the old one would drop below 40 if revved ( its a wonder it even ran) My dad said that it starts much faster and smoother too

the mechanic that did it said he tested the resistance and found that the new pump had less than half the resistance than the old pump ( he did not give numbers). he also said that one of the connections at the hanger had been leaking. he did not believe that it was a big enough leak the make the pressure immediately drop off but it was more of a seap.

I asked if I could have the old pump back because I am weird like that and looked at the O ring in question. it looked as though the O ring had been eaten away. it nearly disintegrated when I took it off to get a better look at it.

so atleast most of the problem appears to be fixed. it still has a very small miss at idle. which obviously could be a number of things. I am still suspect of whatever is going on with the temp sensor but I could not find anything more to condemn it or find any bad wires to say thats whats wrong with it.