Truck Won't Start, But Turns Over- Ideas???

[Fraser Beatty]

My current truck (80 GMC C25) was running/driving great the day before yesterday. It sat all day yesterday. When I went to fire it up today, I can't get it to start. It'll turn over strongly and as it should, but will not start. About every 20 revolutions of the engine or so, it will pop and sound as if it is going to start, but then promptly dies. Any ideas on what could be causing this, or list of things I should check?

Thanks for any help!

[jimmy3fan]

Sounds like an ignition module or pick up coil.

[joe231]

Ignition coil or module

[55chevy]

Fuel or spark, pull a spark plug wire, put a plug in it, ground it to the engine, turn it over to see if you have spark. If you have spark, then a fuel problem. If no spark, then coil or module. Replace the coil, if that's not it then you can usually return the coil. I tracked down an engine to the module this way, got a cheap one from the junkyard and that took care of it.

[craazy22]

Sometimes when you try to start and it pops it can be the timing

[Fraser Beatty]

I checked just now, and the truck appears to have spark. Pulled 3 plug wires, and all produced spark when held against the engine block. Truck also seems to be getting fuel, and the choke is working ok.

When I first found the problem, the truck would fire for a couple revolutions about every 20 revolutions I turned it over, but it has since quit doing even that. Would the timing just go over night like that? It was running perfect one day, and the next, nothing. Any more advice would be greatly appreciated!

[Sillyoldman]

Splash a little gas down the carb and try. Maybe a fuel pump issue? Also pull the distributer cap. Sometimes the condensor wire will rub on the spindle and in time wear through and short out. Shot in the dark but easy to check.

[73chevyman]

sounds like theres trash in the carb or the feul filter cloged.... change feul filter

[tucsonjwt]

Two thoughts:
1) Choke valve. Press the accelerator all the way to the floor to set the choke when the engine is cold. Press the accelerator all the way to the floor again and turn the ignition to start. See if that makes any difference. Also, the choke may look completely closed but may not be. After pressing the accelerator all the way to the floor when the engine is cold -stop - pop the hood - remove the air cleaner-pull back on the throttle linkage all the way with your right hand and press down on the choke valve in the carburetor with the other hand. Release the throttle but keep your hand on the choke valve to make sure is closes all the way. Dirt, stuck linkage, worn choke valve, etc. can leave the choke open just a tiny bit and prevent starting.
2) Do you drive your truck daily on the highway? If not, carbon builds up and causes trouble. If you don't drive it but once a week or so - varnish will build up and kill your carburetor. Spray carb cleaner down the carburetor once you get it started and keep the RPMs high while you continue to spray. Use up a whole can - having an assistant rev the throttle under the hood while you spray cleaner down the carb and all around the linkage helps. If the problem is the choke - convert to a manual choke so you have control over it - not an unreliable thermo coil.

[Fraser Beatty]

Sillyoldman/73chevyman: Pouring gas down the carb appears to do nothing. I seem to be getting lots of spark though.

tucsonjwt: Whenever one of these trucks won't start, the first thing I do is put the accelerator all the way to the floor. I tried it again though since you mentioned it, no luck though. The choke valve is free and can close all the way. I don't drive the truck at all, just start it up and run it up and down the laneway every other day or so.

[Slofarmtruck]

This may sound dumb but check to make sure your distributor is not loose and spun on you.

[tucsonjwt]

If you don't drive the truck at all - I think you are closing in on the problem.
You must have a ton of varnish and carbon in that carburetor. These old carbureted vehicles need to be brought up to operating temperature regularly and run for a while or you will always have trouble with the carb. Do you have access to another known good carb you can temporarily swap out? It doesn't take long to do, and you would answer the carb question quickly.
On the square bodies I have owned, all of the no start when cold issues have been related to choke or carb. All of the performance issues (missing, no start when hot, etc.) have been electrical issues.
One other thing - try a shot of starting fluid (ether) to get the truck started. If it doesn't work you can always use it next month when winter starts in the great white north.

[Fraser Beatty]

I checked distributor, everything seemed to be ok there. Starting fluid didn't help at all. I think I have another carb kicking around somewhere, will try it out and let you know what happens.

[tucsonjwt]

OK - you got a can of "winter fuel" ready to go.
Of course, I did say "known good carb", not one that is carboned or varnished up. I would take a comparable one off of your running fleet or a buddy's truck (temporarily), so you know you have a good runner. Should be no harm to the loaner carb, and shouldn't put the loaner vehicle out of service for more than 1 hour max. I think that will address the fuel delivery issue - assuming fuel pressure after the fuel pump is good. Of course, I am talking comparable intake/linkage setup - like both spreadbore intakes, etc., otherwise the bottom of the carbs won't bolt up - throttle body gaskets, etc., and you won't start it anyway. Good luck.

[Fraser Beatty]

We had a few cans of ether/liquifire kicking around for use on the tractors in the winter, I checked and I have 2 known good carbs available, will try and swap one on tomorrow and let you know how that goes.

[tucsonjwt]

After you swap the carb out, you will probably have to drop a little gas down the top of the carb if it does not start up after a few crank attempts, so don't give up if it does not start right up.

[Fraser Beatty]

Finally got around to swapping a known to be good carb on. NO LUCK! Still has the same symptoms, even with gas down the carb. Turns over strong, but doesn't want to start.

[77 350 Shorty Wide]

The best thing I can recommend is to do the following.
Go to the engine section and check the sticky about finding and setting tdc and timing.
Check fuel level in the carburetor and whether you have adequate fuel coming from the accelerator pump nozzels. Check to see if the choke is setting properly and that the vacuum pulloff is working. Check fuel pump output and pressure. Check compression.
Make sure all the valves are moving ie check for flat cam lobes.
You might check to see if the distributor gear is loose, I'm not sure what the consequences of the cotter pin being sheared off would be?

God Bless, Terry :-)

[urone]

does you truck have a ESC my 1986 Blazer acted the same way and after changing module 5 times it turned out to be the ESC (electronic spark control) located behind the glove box. I don't if your truck has thai item