GM 4.3 misses bad after warm re-start up any ideas - The HuntingPA.com Outdoor Community
 
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post #1 of 9 (permalink) Old 08-11-2013, 11:09 PM Thread Starter
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GM 4.3 misses bad after warm re-start up any ideas

1988 chevy truck with a 4.3 runs bad after a <span style="text-decoration: underline">warm </span><span style="text-decoration: underline">restart</span> ,misses,,etc,say i drive 10 miles stop for 15 minutes to one hour it does this ,, after a several minutes it will run ok ,,seem like its running out of gas during this time ??
Cold start ups it runs PERFECT ,until you do a warm restart ?? any ideas
did replace the o2 sensor got a code of lean O 2 some say vacuum leak have checked ,but like i said when you start it cold in the morning it runs perfect
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post #2 of 9 (permalink) Old 08-11-2013, 11:30 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

Could be a coolant temperature sensor.
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post #3 of 9 (permalink) Old 08-12-2013, 12:47 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

I had a 1996 Chevy Blazer with the 4.3L in it for years. At about 200K I had the exact problem you are seeing. I went through and replaced the O2 sensors as it was throwing a code that insinuated this was the problem. After changing them out, it still ran the same.

The symptoms were - Cold start - Touched the key and it fired right up immediately. It ran very strong but as soon as it warmed up it would have a hesitation at low RPM's, it'd miss constantly when pulling out from a stopped position. Finally it became nearly undrivable. I did some more research and everything I could find pointed to a vacuum leak, but I couldn't find one. All signs then pointed to an Intake Manifold leak.

So, I tore the entire intake off, cleaned up the block and the intake, laid a new gasket and put all the pieces back together. Truck took a couple cranks and fired right up. It ran strong for about another 8K then showed the same symptoms. I then ended up getting rid of the truck. My best guess was that the intake was warped. I should have checked it to make sure it was flat, but it didn't cross my mind.

My guess is that as the engine heats up, the intake and block expand, the intake being aluminum, it expands more than the cast block. with the seal already bad, it just increased the problem void enough to cause a leak big enough to make the engine run poor.

Also note - a warm restart, i'd have to crank on it for 5-10 seconds to get it to start, it would crank and sputter until it finally took hold and kept running. Man I still miss that vehicle, great mountain runner.

Good luck
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post #4 of 9 (permalink) Old 08-12-2013, 03:55 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

That year would have the Throttle body injection and a single, unheated, O2 sensor. A simple system.

Check that the cat is not plugging. My 88 S-10 had two honeycimbs in the cat w/ a screen in between & there was grit in there that would heat up and weld onto the screen until you shut down and let it cool off until it fell off again; then it would start fine and run good for a few min until the screen started to clog again.

4.3L EGR valves will stick open but then they won't idle well w/ the exhaust gas flowing as you slow down to stop.

Those TBI tuucks had two relays to power the fuel pump. One on the dash that worked when you turned the key on and another on the oil pressure sending unit. Should the firewall mounted relay fail to make the pump buzz when you turn the key on; cranking the engine until the oil pressure came up would energise the fuel pump and start the engine. kinda a failsafe. Maybe your main relay is affected by heat but is still working when cooled off. Watch and see if it cranks only until the oil pressure warning goes out & then starts. The relays are cheap!

PS: don't buy it at GM, I did for my 93 Jimmy 4.3 and inside the GM Goodwrench box was another white box saying 'Made In China'. That goodwrench box made it cost around $4.00 more than one from Advanced Auto Crap.

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post #5 of 9 (permalink) Old 08-12-2013, 06:22 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

Dave before you try the complicated stuff mentioned above it could be a minor problem such as a spark plug or wire bad..Replace the minor stuff first to see if it solves the problem...Also the 4.3 liters are known to gum up and will make them run poorly...Use a can of motor flush or take it to a garage that can decarbonize the engine..My 96 blazer got to the point it would barely start because of running rough I had it decarbonized and it run like new for a while..These engines need to run hot because they do gum up being a vortec engine...
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post #6 of 9 (permalink) Old 08-12-2013, 06:55 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

Quote:
Originally Posted by burk313
Dave before you try the complicated stuff mentioned above it could be a minor problem such as a spark plug or wire bad..Replace the minor stuff first to see if it solves the problem...Also the 4.3 liters are known to gum up and will make them run poorly...Use a can of motor flush or take it to a garage that can decarbonize the engine..My 96 blazer got to the point it would barely start because of running rough I had it decarbonized and it run like new for a while..These engines need to run hot because they do gum up being a vortec engine...
Is this an issue with the Vortec 350`s as well? My Tahoe has that engine. Thanks.

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post #7 of 9 (permalink) Old 08-12-2013, 07:21 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

Yes,buddy,all the vortec engines gum up..ALWAYS be sure to run the correct temperature thermostat in the engine NEVER cooler...My 96 blazer would run worse and worse until I had trouble starting it...I had it decarbonized which is not very expensive and it runs much better..You have to have it done every year or so when it starts running rough again..
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post #8 of 9 (permalink) Old 08-12-2013, 09:54 PM Thread Starter
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Re: GM 4.3 misses bad after warm re-start up any ideas

was just reading a GM book i have ,, a code reading came up with code 44 and said lean O2 sensor ,,the book says code 44 is a shorted 02 sensor circut ?? i think it runs directy to the ecm??
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post #9 of 9 (permalink) Old 08-13-2013, 07:34 PM
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Re: GM 4.3 misses bad after warm re-start up any ideas

If you worry yourself with those codes you will go crazy..Look at the simple stuff first...Oxygen sensors do not make engine misses..
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