What we have is a 355 sbc. Went to the carshow this past saturday night and on the way home it started skipping. Replaced the plugs, swapped the wires, swapped the mallory distributor with another mallory distributor. Has a blaster coil which we swapped out, new resistor, drained the gas tank and put fresh fuel in it. Set the timing several times and still hasn't changed a thing. Any ideas??
Engine skipping can't figure it out
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Compression test is in order, you may have burnt a valve.
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saitek5678
valves are not the problem. What Kind of SPARK advance? check the wiring if any in the disributer
valves are not the problem. What Kind of SPARK advance? check the wiring if any in the disributer
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improper adjustment, crappy fuel. All it takes is a little carbon on the seat and it will burn pretty quick. I have also seen a loose plug alowing cold air to be sucked into the cylinder and it burnt the valve.Tubbed71 said:
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saitek5678
Oh you replaced the dist. Or did you? check all the wiring , EVERYTHING for the ignition. I think your loosing spark somewhere
Oh you replaced the dist. Or did you? check all the wiring , EVERYTHING for the ignition. I think your loosing spark somewhere
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saitek5678
I would guess skipping is a missfire. Burnt exhaust valves were common in Buicks about a million years ago, they would missfire on that cylinder or cylinders at a idle. this is the only valve problem I have heard of after doing this eight hours a day for the last 27 years. Chevy, Around 75 had cam issues, also pontiac the cams would round off and make the engine backfire through the intake. I don't know just expeirence I have enjoyed.
I would guess skipping is a missfire. Burnt exhaust valves were common in Buicks about a million years ago, they would missfire on that cylinder or cylinders at a idle. this is the only valve problem I have heard of after doing this eight hours a day for the last 27 years. Chevy, Around 75 had cam issues, also pontiac the cams would round off and make the engine backfire through the intake. I don't know just expeirence I have enjoyed.
If you have headers check to see if one has burned a spark plug wire. I found out the hard way it can happen easily.The main one i had trouble with was either #1 or #3 cylinder i cant remember which. Could be any wire tho. I've had brand new spark plugs fail in a matter of days. Ive had spark plugs get so much combustion junk on them that they bridged the gap on the plug and cause it to not fire. There are tons and tons of things that could be making this happen but i would say it is likely an ignition problem rather that something more serious.
I've checked all the wiring and its ok. The plug wires are fine and not touching the headers and plus I put another set on just to make sure they were not breaking down. It started out with a point's Dist and then we put a mallory electronic dist in there and then tried another mallory we had laying around and all three done the same thing.
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Start by determining what cylinder has the problem. An easy way to do this is (w/the engine idling) by removing the plug wires and grounding them, one by one, until the cylinder that does not change the idle speed or sound is found.Tubbed71 said:
Once the cylinder has been isolated, test it for compression and check the rockers to see if they are loose at all.
If you didn't change the dist. cap while you were doing the dist. and wires, plugs, etc.- check it closely for carbon tracking inside it, or just replace it w/another known to be good.
You could possibly be another victim of the oil formula change that has affected so many flat tappet cam users.
I have a spark tester that is pretty simple to use, just hold it on the plug wires while the engine is running and it lights up. All of the wires checked out ok. Also had three different caps as well. I'm about to do a compression check in a few so maybe we can find something out.
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The point isn't whether or not the plug is sparking- it is whether or not the cylinders are doing any work- one obviously (by your description) isn't doing any work. By removing one plug wire at a time, you will isolate which cylinder is faulty.Tubbed71 said:
Then you can concentrate on that particular cylinder- not on all 8. But some folks just like to spend time in the shop. I prefer cruising. :mwink:
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It sounds like he already changed everything electrical. I was trying to give him a different avenue of troubleshooting. A compression test. Burnt valves are not as common as they used to be due to different valve and seat metals that are used. However we do not know the year of this engine so anything is possible. If it is from the leaded gas era, the valves and seats will go away fast with unleaded fuel. Also it was the 305 Chevys that were wiping out cams not 350s. Usually the number 2 exhaust valve cam lobe. I changed many of them.saitek5678 said:
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