isaac338

I feel like I've read a billion threads on this issue but I can't seem to fix it.

Truck didn't start last night when I was out, got it towed home. This morning it started and idled but died as soon as I hit the gas pedal. Now it'll start but only for about half a second before it dies.

The EFI fuse was blown and the fuel pump wasn't turning on, and I've replaced it. I've changed the fuel filter and verified there's gas spraying out of the fuel rail banjo bolts when you move the vane in the AFM. I don't have a fuel pressure gauge but I'm going to try and get one tomorrow.

If you unplug the AFM, the truck will start and idle for about 5 seconds before slowly dying. I tested the AFM as per the manual and all the resistances are within spec. Can the AFM be faulty but still test good with the standard test procedure?

The TPS tests to within spec (at least for closed and WFO throttle).

The fuel pump strainer is clean, blown out with compressed air (although it didn't need it, it was completely free of debris).

Anyone have any other ideas?

I guess I'm going to check the ground for the ECM next, and try to get a spark tester and some noid lights.

Thanks

abecedarian

if the intake duct between the throttle body and the AFM has a leak, either at the boots or in the tube itself, the engine may not be able to suck enough air through the AFM for it to keep the fuel pump on. matter of fact, any significant vacuum leak could cause the problem you're experiencing.

isaac338

I thought about that, but even wedging the flap in the AFM open with a screwdriver or something results in the exact same performance.

I haven't looked too hard for vac leaks - probably a nightmare without a running engine, but I'll look for obvious ones. Thanks.

abecedarian

Another thing may be plugged exhaust.

isaac338

Thought about that, too, but when it runs you can see the exhaust billowing so I doubt there's a potato up there or anything..

abecedarian

Hook everything up and have someone crank the engine while you selectively spray starting fluid around. If you have a vacuum leak, the engine will suck the fluid in and should run off it.

isaac338

Update: with the fuel pump test connector jumpered (ie fuel pump on all the time), and the AFM unplugged, the truck will run all day, albeit probably super rich (stumbling and crap). With the AFM plugged in, it dies straight up, fuel pump jumpered or not.

I don't get how this works.. obviously the fuel pump is shutting off after startup when the AFM is plugged in, but with the fuel pump connector jumpered the AFM should have no influence on the fuel pump.

My circuit opening relay tests fine.

isaac338

I don't know if anyone is following this or cares, but I replaced the AFM and no change. It runs now, but really, really rich (belches dark smoke and the plugs are covered in soot and it backfires like crazy if you gun it). I'm now thinking something in the vacuum circuit which controls the pressure regulator. The FSM says if you jump F and +B in the diagnostic connector and turn the ignition on you should hear fuel noises from the regulator, but I don't hear anything unless I suck on the vacuum line going to the regulator. Is this normal?

dark_fairytales

check all your grounds to your engine. i had that same problem and it was because i was missing some grounds by the PO. my mechanic had my truck for a month trying to figure this out and i worked on it for two month my self. we both could not believe it was a simple grounding issue

91-mexi-yota

im with dark fairy tells, if it wont run, but it.ll strt and idle all day, check over all ur wires, iv had it happen too my last 2 vehicles and it was simply a bare wire. my pick-up did the same thing and it was because the wires to the o2 sensore had literly molded to the exhaust. took it off the exhaust and runs perfectly now. so... check ur wires

isaac338

I was beeping out wiring for a good few hours yesterday. I dunno what the hell I did, but the truck runs perfectly after unplugging the coolant temp switch (next to the CSI timer) and plugging it back in.

Who knows?

edit: Also, there's a broken wire under the intake manifold. It's green with a black stripe, goes to the "HAC" input on the ECU. The problem is, the truck is EFI and doesn't have a HAC, and I can't find where the hell it's supposed to go. It has 7.5-8V on it with the ignition on. Anyone know what this wire is supposed to connect to?

91-mexi-yota

motor? 2.4 or 3.0? i got boh, and i like inkering. haha. i.ll find it for ya.

isaac338

22re.

91-mexi-yota

uhh uuhhh uuuhhhh... theres a plug under the intake manifold that has it and a red one myb.. its either ed or orange. haha. but theres a probly male plug that is right underneath the radiator hose by the efi manifold... not sure what it goes too but i did find it. haha

4Crawler

iTrader: (3)

Well, the AFM may test fine at it's plug, but you need to see if the ECU is seeing that same thing, that is are all the wires and connections between the two intact. Check the AFM connections at the ECU:
- http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml
- http://www.4crawler.com/4x4/CheapTri...roubleshooting

The FP test jumper basically bypasses the AFM fuel pump contact.

thook

That could be the wire to your auxiliary air valve. Seems I remember that wire being green.......definitely single. Don't remember the exact voltage it's suppose to get, but it runs off the COR for voltage. Doubt that would be the problem with keeping the motor running, but might make for choppy cold idling........which would exacerbate whatever problem you were having.

I was going to say check the ground terminal on the AFM harness connector as those can back out and give intermittent problems, but golly........maybe your wiring and/or connector on the ECT switch is going south. Then again, maybe it was just loose. Got the clip on there?

isaac338

Yep, the switch connector has the clip intact. It might have just been dirty, because the truck runs better than it did before it broke down. Who knows? I'm not going to look a gift horse in the mouth

I'll check the AAV and see if it's got a broken wire sticking out.

Roger, I've read your site a billion times, it's a great help. As I read the wiring diagram, the AFM has no bearing on the CO relay when the fuel jumper is in place. That's why I was confused.

91-mexi-yota

well glad it wasnt a bad fix, and like mine is, i hope ur keeps strong after somthin small like that. haha. goodluck and hope i helped a lil. C=

isaac338

Well, the truck died again. Same situation, piss pouring rain storm. I noticed some dampness in the carpet by the passenger kick panel. There's clear signs of wet on the ECU PCB near the top, and rust on the casing. Looks like I've got a leak somewhere that's going straight into the ECU.

Off to buy a new computer... thanks guys.

isaac338

New ECU plugged in and truck runs with a CEL. More troubleshooting tomorrow. Gotta fix that leak.