Help;1990 250 3/4 ton problems

Check heads. Pressure check them. Sounds like you lost a valve. Or worse yet, the head has cracked.

Checked fuel pressure at the regulator? Checked pressure in each cylinder?

Sounds like a fuel pump.

Forgive me, I forgot to mention what another poster mentioned. You need to check the pressure of your fuel rail/supply.

A valve will not cause this symptom, and I don't see a cracked head doing the same.

This can't be a bad valve, cracked head or anything major because the engine will start right up and run normally for

Spent much of the day (another one wasted) verifying the fuel pump was doing its thing. Here's how it works, if anyone cares; when the ignition is first turned on the fuel pump starts. After the engine starts the fuel pump only keeps running if the ignition is on AND the engine has oil pressure. Loose oil pressure, pump stops. Took a while to figure *that* out, but thats how it works....and it does work properly. I can actually hear the pump run for a second or two after its stalls.

Don't think its a fuel pressure issue because I can see fuel coming out of the injectors (two, in a throttle body setup, no fuel rail) as the engine looses power and stalls.

Still stumped and no idea what to do next. Thanks for all of the suggestions!!! Hoping for more. Steve

Hadn't thought about that. Hummmm..... Steve

I was going to suggest the same thing. Sounds like a the porcelain in the converter is cracked, and blocking the exhaust.

It could still be a fuel pressure issue. Just seeing fuel at the injectors doesn't say much about pressure, which should be no less than

Another possibility is the distributor cap.

Chris, No smiles so far. Just scraped nuckles, blood and a fair amount of cursing. Finally got the converter out this morning and it *looks* fine but I do hear stuff rattling around inside which does not come out either end. The screen which is visible from either end looks perfect but I have no clue as to how these are built.

What to do next? Maybe find a CAT bypass pipe somewhere. Could still be a fuel pressure issue. This is getting old, fast.... Steve

I don't think there should be any rattling in the converter.

Converters used in GM were not solid so if the substrate breaks on the inside it will rattle without showing damage. I worked for a place that did exhaust work only and have seen such scenarios many times. It's possible the outlet substrate 'cake' can get plugged from debris from the inlet 'cake'. I've seen converters with no substrate left in them. It all goes into the muffler and plugs it up. Bypass the CAT and take it for a drive.

There you go! Since the cat is off, drive loud and proud and see if there is a difference. Just remember to cap the pipe, afterwards.

LOL if you can stand the roar of the motor. A CAT provides about a 35% reduction in exhaust noise.

Neighbors have never shown much consideration where noise is concerned, so I let her rip yesterday in the driveway. Open headers!

Same symptoms....starts easily, idles a little rough then it gets worse and eventually dies in a minute or so. By feathering the throttle I can keep it running longer but not much.

Hot wired the fuel pump to verify it is running and yes, I can hear it running.

Steve

That sucks. I had an old Dodge Dakota with a TBI 3.9 V6 innit that acted similar. Turned out to be the SMEC. Before that i was having fuel pressure problems after warmup. Pressure gauge in the input of the TB verified it. Pulled the tank and the fuel pump. Pump sits in a cup at the bottom. Neoprene hose on the pump outlet had split allowing most of the fuel to spray back out into the tank :) Replaced the hose and all was fine. The reason it acted up when it was warm was the steel fuel line followed the engine block. Best I can figure when the pressure dropped the fuel bubbled in the steel line. You'll need to test your fuel pressure if you haven't.

Several have suggested the original poste check the fuel rail pruesure, but he says there is fuel in the Throttle Body. Not good enough. Measuring will be cheaper than guessing as to the wrong part.

Although, it could be the fuel inlet, or, could be a clogged fuel filter. Has this been checked? If pressure is low it could be the pump, or the filter. I'd be considering the filter.

Blazer, pump is $350-400 plus tank-drop-replace labor.

Is there another fuel filter underneath, along the frame?

One clogged injector on a two injector TBI can cause the OP's symptoms. Was talking with a friend the other day who ran into this on an older Pontiac V6 that was TBI.

One of the first things I did was replace the fuel filter located under the body. It was OK. Also drained about a gallon of fuel to see if it was contaminated.

At this point could be a collapsed hose, broken pipe in the fuel tank or fuel pump, although I can hear it running.