90 Chevy rough running


Old 06-30-11, 08:02 PM
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90 Chevy rough running

1990 Chevy Truck C1500 1/2ton 2WD 5.0L 8cyl.

Has been running rough for over a year, not used much. Has over 250K miles..odom not working. Can smell gas big time, even after truck is parked. Very Rarely will run ok after a while, will run worse other times...will idle as if it has a big cam in it. Thought it was a carb problem. Always starts after spinning a bit.... thought it was the miles on the start.

Put in new plugs ... old plugs looked great... surprised at that cause of the gas smell, but maybe the low miles it is driven. Used a spark plug checker and the Fire looked fine, but noticed that there was no spark at times and it wasn't starting till spark showed.

Found corrosion on the coil and rust in the coil wire, just on that end... dist cap end was fine. Wires are in very good shape except for that one, dist cap & rotor looked ok... going to replace though. Odd part ... with cap and rotor off there was some rust powder under rotor cap ... no where else.

Did a temporary clean out of coil wire and end of coil... still running rough. Have gone from thinking gas problem to elect problem. Dont know how to test for coil or module or pickup coil. My son is better at elec than me, but our book is not much of a help.

Also showing a code 33 about map sensor.

One final part. Early this spring I had to replace the intake manifold and the old one had one of the chambers totally blocked.. coming from the EGR valve ... if memory is right... being disabled is not fun.

any help much appreciated.
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Old 07-01-11, 04:09 AM
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Did you just try to clean the dist cap or did you replace it? Cleaning sometimes doesn't work completely as you may still have carbon tracks or "tartar" build up on the electrodes which will cause misfires. As far as smelling fuel, it sounds like a carb loading up, or the float not working properly. Have you changed the fuel filter? Is there one in the carb inlet? I'd go for new wires while you are at it. Sounds as if sitting has taken its toll on components.
Old 07-01-11, 07:17 PM
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I've never seen a 1990 engine with a carb,, You have a MAP code.. Have you done any diag on the code 33 yet??? If it does have a carb, verify that & also verify the year of the truck,,,

Old 07-01-11, 10:58 PM
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Good catch hopkinsr2.---- It is a 1990 with throttle body Injection. ...very sorry ...Being disabled and rushed easy mistake for me........ especially since I am an old carb guy.... I call it a carb and my son gives me heck and I still do it

Nothing with the code 33 yet. To much to fast and 100 degrees out... garage burnt down a couple years back also.

chandler ----- did a quick clean on the dist cap and rotor. Going to replace both. Fuel filter is back by tank and was changed a couple years ago along with new pump. Might toss in new wires, but these are not that old...have to find receipt.. might get free ones.

I know there are some different things here, but I thought someone might know something to help. I have never seen a coil wire rusted like that one. I can get a new distributor with pickup coil, module, dist cap and rotor for $125, but then dont want to add coil and find out is a gas problem.

thanks for any help... tired again will find out what I messed up tomorrow
Old 07-09-11, 03:40 PM
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Fixed for Now.... update.

Since the wires, dist cap & rotor cap were all warranted I went ahead and exchanged them out. Knew that wouldn't be the problem, but its nice to rule out things 100%. Bought a new coil [$27] since it had the corroded tip and that wasnt it either.

My son wasnt able to test for the code 33, map sensor ... high volt, low vac, but he was able to test for the pick up coil and it was ok. Went to U Pull It and got a map sensor anyway and the ignition control module. [$10] Put the control module in and it fixed the problem. Never put the Map sensor in. Cleared the codes and nothing has come back yet.

Need to drive it some after clearing everything. It seems to be touchy with light pressure on the gas pedal (not while parked) ... harder pressure runs fine. Still getting a gas smell, but very light right now.. gonna wait and see how things work out. Over 250K rough miles.....

AT U Pull It I found three other coils that all had the tip corroded ... wires were torn out so I couldnt see if the coil wire/coil side was rusted, but my guess is yes they were all rusted also. Have no clue as to why?

Still curious if anyone has an idea on why the old intake manifold on this truck had one "chamber" blocked.... the one the EGR was on?

Thanks much for all help and any ideas!

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