Lean condition when hot

[sgtpoliteness]

Hi there everyone. I've got a '77 Cherokee with a 360//th400/QT that I've converted a BJYL 16197427 $0D TBI into from a '94 Chev 1500 2wd. I've got a Masters E2000 fuel pump delivering 13psi, clean tank, new filters. Truck runs great until the ambient temp starts to climb (say above 70 or so) and only after almost getting home from work, say after like 20 minutes or so of driving in stop, mostly go traffic. I live in Arvada, Colorado - 5500 feet or so. Again, it runs great until that 20 minutes in or so. I never get above around 25% duty cycle on the injectors. I've confirmed watching the BLMs that high-MAP is getting really lean, really fast. I noticed watching it on the way home, real time, that I was getting into the 150's, which I've never noticed before.

I've thought about checking fuel volume as well as pressure. But, I figured, if there wasn't enough fuel wouldn't the injector duty cycle kick up? PE is coming on. I also though it was occurring when it hit 94* C, but it'll get to that not even half way home on a day like today. But, I'll try to pay more attention to that tomorrow on the way in.

Thank you!

OH! I also noticed while I had Tuner Pro RT connected that it read '4 Errors (?)' or malfunctions at the bottom of the screen. I checked the malfunction codes, but nothing. Ideas?

[steveo]

But, I figured, if there wasn't enough fuel wouldn't the injector duty cycle kick up?

nope; not in PE

but you'd see it in your trims as it was happening, and also an increase in inj. pw at that point..... which you are seeing

so either you have a bigass vac leak of some kind happening while hot, or... some kind of fuel supply issue.

well, you need to monitor fuel pressure when hot and under load to ensure it isnt dropping. can you mount a pressure gauge on a hose or something that'll reach the windshield?

remember a hot pump draws more power, perhaps your wiring isnt up to the task, or it's just plain failing for some reason. i recently had a walbro pump fail in exactly the same way. it wasnt staying cool due to not being submerged properly, and after about an hour of driving, it'd start making some funny noise, and pressure would drop under load. it was perfectly fine until that point

[sgtpoliteness]

Yeah, I should be able to get a fuel gauge mounted up and tape it to the windshield, or something like that. I'll get hot fuel pressure checked out and I'll also check pump resistance and for voltage drops between the fuel pump relay and the pump itself.

My pump is inline, just forward of the tank along the inside of the frame-rail. I'm wondering if cooling is an issue and it's just worn out. I've had the conversion on for over a year now and have put a couple thousand miles on it or so.

EDIT - Ran terrible on the way in the AM. Same conditions as at the tail end of the drive home in last night. Coolant never got above 90* C, ambient air temps are less than 60* F. I was able to check voltage at the pump when I got to work, 13.9. Resistance of the pump is 1 ohm. It's even running lean at idle now, 135. High MAP blocks are 150-160+. I'm going to check fuel pressure as soon as I can this AM.

EDIT 2 - Fuel pressure good at idle and revving the engine @ 13psi. I checked my filter before the pump and there was some sediment in it (I'm assuming from the little bit of crap I couldn't get out of my tank). I cleaned the filter and I'll drive it later. Perhaps this could be a volume and not a pressure issue. I'm also going to try to find the liter-per-minute flow specs for my pump and test that.

[sgtpoliteness]

I cleaned the pre-pump filter and fired the truck up. I'm now reading 25psi (!!), as opposed to the 13psi from before cleaning the filter. This seems to be way too high for TBI, right?

[lionelhutz]

Sounds like a fuel pressure regulator problem.

[sgtpoliteness]

Sounds like a fuel pressure regulator problem.

Yeah, I was wondering that. I'll do some searching on signs of TBI FPRs failing.

After running it for an hour to 90 minutes, the fuel pressure dropped from 25psi to 12psi. I found a bit of sediment again in my glass filter. It was stuck to the filter and when I tapped it, it fell to the glass. I picked up a couple of the plastic fuel filters to put in place of the glass one but it looks like I'll be replacing the tank with a plastic one sooner rather than later.

Edit - So, I installed a new, bigger, clear fuel filter pre-pump and ran the engine for another hour. Couple of things. My main idle BLM is 145 (!). Fuel pressure reads 20psi, but if I pinch the return for just a split second is shoots way up to 80psi! I thinking the FPR is bad and isn't allowing enough fuel to the injectors?

[jim_in_dorris]

Pinching the return line should cause the fuel pressure to shoot up. you may just need more fuel at idle, what are the BLMs at cruise? Is it going into closed loop? Are you still have temp issues?

[sgtpoliteness]

Pinching the return line should cause the fuel pressure to shoot up. you may just need more fuel at idle, what are the BLMs at cruise? Is it going into closed loop? Are you still have temp issues?

Should it shoot up that much? I ask because the TBI diagnosis stuff I've seen read that anything over 10psi meant a faulty FPR. Of course, I don't exactly have a stock fuel system. My concern with the 145 was that a week ago it was at 128. I wasn't able to drive it to check cruise BLMs after replacing the filter this afternoon, but on the way in this AM they were 150-160. Funny you should ask about open/closed loop because I noticed for the first time that it was dropping into open loop once in awhile, which it never did before (I installed a heater HO2 sensor when I did the conversion).

That last time I ran into this much weirdness my chip had come loose from the socket and the file was corrupted.

Edit - The end of last week I dropped the tank and replaced both the sending unit and pick-up seals. I also cleaned the tank out some more (someone did one of those terrible liners decades ago and I'm getting the last of it out).

[delcowizzid]

pre filters are a pain when they block regular.i have one car ive tuned 4 times start tuning and it would start running like shit after a while then fuel pressure at idle would start jumping up and down then it would slowly drop to 0psi blocked the pre filter every time you could even hear the pump cavitating trying to suck fuel through the filter.

[jim_in_dorris]

Should it shoot up that much?

When I was having troubles with my truck, the return line got plugged/pinched, and my fuel pressure was 45-48 psi (i needed 13). So yes if your pump will deliver it then you will see that much with the return line pinched. 150/160 is pretty lean, I would start thinking about a vacuum leak if your pressure looks normal.