Bad Miss
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New User
Joined: Feb 2008
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From: Rapid City, SD
Bad Miss
I've got a 78 351M in a f250. It's missing on the number 2 cylinder, and all of the ignition parts have been replaced. Timing and spark are good. Pulled off the valve cover and to the naked eye, it looked like everything was moving properly. We did notice that when I stopped tuning it over, it sounds like compression is leaking throught the valves. What do you think, bad lifter? Flat cam? I've thinking about replacement cylinder heads from Autozone and a summit cam and lifter set. I just bought the truck, but I think it's been missing like this for a good while. I'm not really trying to build a race car, just get it running the way it should without going broke. Any advice would be appreciated.
Jason
Jason
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Joined: Jul 2007
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a miss is almost always a vacuum leak, the engine is getting air elsewhere from the carb and if its comming from a cilinder its probably a bad seat or a hard lifter, many things could be stopping the valve from properly clossing on the pistons compression stroke, but it aint a flat lobe on your cam.. take your heads of and check them with out tearing the engine apart. Although the best performance addon and not really that expensive would be to turn your engine into a 400 but that would include a total rebuilt....
just my op
just my op
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Joined: Jan 2007
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Do a compression check (or leakdown test) to see if there is a mechanical deficiency before you continue with anything else. Chances are that cylinder will come up low since the ignition parts are sound. A burned valve is not un-common. If it comes up low, take your clean oil can and squirt a couple in the hole. Roll the motor around a couple times and re-check the compression in that cylinder. If it comes up, the problem is from the top down. If it doesn't, most likely a burned valve my friend. If so, have the heads overhauled. Also if so, if your friends with the local engine shop, pull that head and have your buddy pull a valve out of bucket in his shop and grind the valve and seat, throw it back together and run it. Short term fix. But if your low on dough, it will buy you maybe 10-20,000 miles. I know I'll get hammered for that one, but I've had to do it during tough times. Also, look for bubbles in the radiator for a potential head gasket failure as well as evidence of coolant at the tail pipe while it's running. (does your coolant seem to be getting low all the time?)
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New User
Joined: Feb 2008
Posts: 12
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From: Rapid City, SD
Thanks for the replies. I got my hands on a compression gauge, so I'll monkey with it over the weekend. My current goal is just to get the truck reliable enough to take over daily driver duties. That way I can sell my 04 Ram and divert it's payments to the old Ford fund. Thank you again for your help. I'll post what I find out.
The coolant is good. No evidence of a blown head gasket.
The coolant is good. No evidence of a blown head gasket.
Last edited by dozerpilot; Mar 13, 2008 at 10:37 PM. Reason: More Info
