at a loss, could use some help

[88hosebeast]

Hey guys. So here's the deal, I ran out of gas the other day. No big deal just get some gas and good to go right? Well not so much. Truck fired back up after a few times of cycling the switch to prime the lines. It idled fine but when I put it in gear and let the clutch out it runs like its starving for fuel( it occasionally runs good for a few miles). Figured I had either sucked some trash up into the filters or burned one of the fuel pumps. Replaced the filters and checked the fuel pressure(42 psi, key on, engine off; 38-45 psi key on, engine running) but it still ran like it was fuel starved. So I went ahead and replaced the pumps anyway and checked all the fuel lines and the fuel rail for blockages( there were none) still no change. Next I tried the injectors, no luck. Fuel pressure regulator also didn't help. For giggles I checked the ignition timing(10 degrees btc with the spout connector plug removed and the engine at normal operating temp) and the mechanical timing, both good. Also checked the compression, 150 psi across the board. Next I tried the throttle position sensor and the map sensor, neither helped. From there I tried plugs, wires, distributor cap, rotor button, coil and ignition control module and again nothing helped. While doing all this I noticed a crack in the exhaust manifold so I welded it up, didn't really expect it to help and of course it didn't. I've checked and rechecked all the grounds, plug-in connectors and wiring harness. Aside from the engine control computer I'm at a loss for what to do next, any help would be appreciated. Thanks.

 

[rtg143]

What's the vacuum reading at idle and when you increase the RPMs to around 2000 and hold it there?

 

[88hosebeast]

I'll have to dig out my vacuum gauge and check.

 

[88hosebeast]

17-18 inches at idle, 18-20 inches at 2000rpm

 

[rtg143]

That shows good exhaust flow. Was the gas that you put in clean and fresh?

 

[88hosebeast]

Fresh and ethanol free. Actually on the 3rd tank of gas since it happened. Mileage is down but not by much, 20-30 miles per tank.

 

[GoodOld85BlueBalls]

Could the ECM be confused? Pull the + battery cable and leave it off for a few min to reset it.

Check the codes before you reset it with an OBD tool. there is a whole section in the Library about OBD codes.

 

[88hosebeast]

I've reset the computer multiple time now.

 

[88hosebeast]

Only code it has is one for egr valve position sensor which its had for years cause i deleted the egr valve and associated plumbing back in my "hot rodding" days.

 

[theturbokid83]

I know the vac. reading can indacate exhaust flow but you really need to check the back pressure test from the o2 bung or the dpfe ports if it has them. i say this cus i have relied on a vac. test, but was wrong, back pressure test had held 12lbs at 1500 rpms. changed cats ran like a dream.

 

[88hosebeast]

Has no converter( also removed in my "hot rodding" days) and a new flowmaster muffler.

 

[theturbokid83]

well shit the only thing i can think of out of what you said was the ecu went bad the injector drivers might be messed up, thats what normaly gives out but it would more then likely misfire. did you check fuel volume not just pressure? cycling the key off and on back to back like that can fry a circuit board.

 

[88hosebeast]

Yeah it passed volume test. Biggest issue I'm having is I can't replicate the problem while testing components. It runs great till I get it on the road then it's sputter, run fine, sputter, run fine, sputter. The intermittent-ness of it is driving me crazy. I'm leaning towards the computer but the data stream I'm seeing on the scan tool seems fine. Injector timing and pulse width is right where it should be.

 

[Andy D]

the fuel line sucking air from a bad connection? or a leaky hose?

 

[rtg143]

Or a connection problem.