Any ideas?

[BobT]

Not really an outdoors question but here goes.

1992 GMC 2500. 350 V8. New starter, new battery, turns over like the breeze, can hear the fuel pump when key turned, can smell fuel, but won't fire when cold or damp when it has been sitting for a while (overnight or longer). By cold I mean as warm as about 40 degrees or perhaps higher. Plug it in for an hour and it fires right up.

I'm thinking something in the electronic ignition or on-board computer if there is one, like a cold solder joint that loses contact when cold or damp.

Would it be best to put it on a scope and check it out? Would they be able to make a determination without it failing when they check?

Bob

[Jeremy airjer W]

How do the plugs look? Worn out plugs and cool damp weather = flooded engine. Our deflood season started with the cold rainy weather we had a couple of weeks ago. There where getting towed in left and right.

Are you getting spark? If you smell fuel I would have to guess that injectors and pump are working. Check for spark directly at the coil if thats o.k. then work you way to the plugs.

What if you cycled the key (on off on off) a couple of times then try to start?

Have you tried holding the throttle pedal all the way to the floor then cranking? This should activate deflood mode and shut off the injectors to help clear out excessive fuel in the intake and combustion chamber.

Experience rather than a scope will likely solve this problem. Unless something obvious is seen by the person working on it than it will likely need to act up while its in the shop in order for an accurate diagnosis.

[folke2000]

Had a similar problem with a '96 Ford Pick up. I would suggest trying the coil wire first, and then if that doesn't work new plug wires. If it's not firing at all, I would bet the coil wire.

Hope this works.

[Sutty]

You could do the spray test for your plug wires, get a spray bottle and spray some mist around your wires when its running and see if your engine bogs down.

[BobT]

Sounds like you guys are in agreement that a first place to start would be with the coil and/or spark plugs and wires.

When it turns over there is no indication of any attmept to fire at all but then if I plug it in for a little while it starts right up normally. That leads me away from sparkplug wires but the coil wire?....hmmmm. Didn't even give that a thought. Goes to show that I haven't worked on a vehicle for a long time. I know if it was an old vehicle with points and condensor I would be thinking points. My old M International has done this from time to time and usually just cleaning up the points and dist. cap does the trick but with electronic ignition, well...

Thanks, I'll give your ideas a try. If you think of anything else...

Bob

[Scott K]

I have seen a few ignition modules and pick ups in the dist go bad, with this exact concern.

[Jeremy airjer W]

I think we may have missed something here. When you say plug it in do you mean plug in the block heater or plug in a battery charger?

If you plugging into a block heater than I would suggest scanning the computer to see what the coolant temp sensor is reading before you plug it in. If its wiggin out it could read far below 0 degrees wich would cause the engine to flood quickly or it could be reading above 200 degrees which would cause to engine to go way lean. Before I did that I think I would definetly pull a plug and see what the gap is.

[BobT]

I am talking about plugging in the block heater. Battery is fine, starter is fine, engine turns over just fine. Just no ignition at all, not even a hickup. If I was working with an old carburator system, I'd be inclined to suspect it was flooded and press the pedal to the floor. Since I know this can be effective with some electronic systems I tried this with this vehicle as well but it didn't help. This problem has been around for some time. The truck belongs to me mother-in-law in Hibbing and so it's a couple hundred miles away. I look at it when I get the chance. She has taken it in and received diagnosis ranging from starter to alternator to intake manifold gasket. None of which I believe would cause this kind of problem and so I'm of the impression the places she's taken it to don't have a clue. It would expect it to at least give something to indicate it is trying to start but nothing.

My wife had a Nissan once that would do this if the outside temperature was below 0 degrees. Wait for the temperature to get above 0 and it would start normally. The only difference was that plugging it in didn't help.

I'm heading up there this weekend to bring the truck home and leave her one of our vehicles to use. Maybe I can finally get to the bottom of it.

I think you have given me some good starting directions.

Bob

[BobT]

Follow-up:

I went to Hibbing this weekend to see if I could get that GMC started and bring it home to work on it. It wouldn’t start. Turned over like nobody’s business but would not fire at all. This time I noticed that I couldn’t hear the fuel pump run when I turned the key on so on a whim I dropped a little gasoline down the intake throat and guess what? It started and ran until it consumed what I poured in. I repeated it a few times and came to the conclusion that the fuel pump is the likely source of the problem.

My wife decided to stay up there and try to bring it to a mechanic today to verify and make repairs. When she called to make the appointment he suggested that she try giving the fuel tank a bump. So she did and the truck started.

At first I couldn’t imagine why this would have been such an intermittent problem and how it appeared to work after plugging in the truck. I’m now convinced it was a coincidence. I assume that when we were trying to start it, opening and closing the truck door was possibly sending a vibration through the truck and this was enough to get the pump to work for a while; similar to my wife banging on the fuel tank.

Bob

[Jeremy airjer W]

Who would have thought! Apparently not any of us!!

Its the thought that counts. Glad to hear that at least some progress has been made. I hope that does the trick for ya!!