As an aside my long term trim went from negative 8.6 to 4.5 last night so could just be coincidence but perhaps swapping the MAF had some effect.

 

P1179 is "Long term fuel trim too rich, banks 1&2 (AMFR)", "AMFR = Air Mass Flow Rate". The ECU is reporting too much fuel, not enough air, or maxed out on air trying to lean out the fuel mixture. Usually it means dirty air filter or dirty MAF. If you had a leaking injector it would report which cylinder or all cylinders as a misfire and that aint happening. Try the FPR if you have one handy, see what that does.

 

I'd think it's more than a coincidence it changed with the MAF.

 

Right. The code indicates the ECU thinks it is having to put in more fuel than it should.

A leaky injector would not necessarily cause a misfire if it wasn't a major leak (which it isn't). An ounce or two of leak an hour should still allow satisfactory combustion it's only when it sits that it accumulates. That would explain slow pressure drop while not running and occasionally need to crank a couple times after sitting overnigjt. On the other hand if it's only leaking an ounce an hour and the cylinders are otherwise running fine I likely would not get a code and more importantly it probably wouldn't result in a noticeable low pressure while running (30psi). That makes fuel injectors slightly inconsistent with the symptoms.

A FPR would explain everything as would something with the pump. But pulling the fuel rail and checking and maybe replacing injectors if they are leaking or not spraying is free as is replacing FPR since I have both lying around from my other engine. If the results of changing these are nothing I will move attention to the pump.

On an unrelated note this morning I heard a whistling from my MAF. Removed the air filter box from the MAF and it was obviously coming from upstream of the MAF and not the filter. Went for a drive. Came home and the noise was gone....

Not sure what to make of that.

 

Said that backwards ecu thinks it is having to put in too much less fuel than it thinks it should... I may be confusing myself.

 

Today as usual had to give it to attempts at cranking to get started. Noted that when I came out the truck had no fuel pressure as usual. AFter turning key but not cranking, pressure went to 20psi. Did this 3 or 4 more times without starting and still didn't got past 20 PSI. Started truck after two attemps and then pressure went to more or less 30 on the dot.

With truck running I rev it and the pressure drops. I understand this to be normal but again I think I am about 6-8PSI low w/ 30 @ idle. Then today, something new I tried - took the vacuum line off the regulator. From feeling the suction there is a clear vacuum. Once the line was off the fuel pressure quickly flutters between 28-30. Not sure if this is normal. Could not find anything indicating one way or another.

Still waiting to get my other intake manifold to try swapping FPR and injectors if FPR doesn't change anything.

Given there is a regulator in the system a "weak fuel pump" doesn't seem like it would cause these issues. Either the pump pumps enough fuel or it doesn't. If it couldn't pump enough fuel to get full pressure at idle, then it surely would have issues at WOT on the freeway which it doesn't. A leaky injector could explain the hard start after sitting but doesn't explain my periodic pending code (1179). Have got it again since the MAF swap so thinking both MAFs work fine.

Added an o-ring to the upstream side of the MAF which was missing. Did this as I heard it whistling the other day. Only way I could see this being of impact though was if warm air was getting sucked in right at the air which was hotter than the air from the air box. This could explain some variance in air volumes compared to expectation due to temperature but I think that's overall unlikely. And as this leak would be upstream of the MAF then it wouldn't be unmetered air anyway which seems like a bigger issue. Either way haven't had enough drive cycles to tell if this accomplished anything.

Still not much better off but think the code is either related to a vacuum leak (haven't found any though but maybe this is the cause of the whistling from the MAF when the air filter box is removed), a faulty FPR (but from reading these NEVER fail), or something else that I haven't even thought of....?

 

For anyone reading this thread in the future, I am 99% sure I found my problem. The short vacuum hose going from the driver side valve cover to the plenum I checked over previously and I couldn't find any issue but after checking and re-checking a few time I ended up with a large enough hole in it where it bent off the valve cover that it started whistling. I am guessing there was a very small hole previously and my taking it on and off made it worse. Replaced this hose and within 4-5 drive cycles my LT fuel trim went from the original -8 or so it was at to -0.78 and no codes in a dozen or so drive cycles. Idle was never bad but has smoothed out a bit too.

From monitoring the fan clutch and listening carefully I think it needs replacement but haven't got around to it yet. Also, my two tries needed for a cold start has not gone away but I think that's probably a leaky injector which I will also look into when I have time as well as replacing the fuel regulator with my backup to see if pressure increases but I think at 30 psi it is not low enough to have substantial consequences (other than perhaps fuel economy will improve).