Conquered Initial Problem, Followed by New One

[emtrichel]

A lot of you guys helped me out with an overheating problem originating from a bad water pump seal and I thank those of who you helped me out. I now have a new problem.

My truck will at times, seemingly random, misfire. The carb misfires when it’s cold and I get on it - but this thing is different and happens all the time under all conditions.

It’s a thumping noise coming from the engine, and it seems to be in tune (accelerates/decelerates) with the RPM’s. It also makes a huge loss in power.

Does anyone have any ideas what it could be?

 

[Frankenchevy]

first thing I'd do is verify timing. you need to rule out pre-detonation before something catastrophic happens. once you've dialed in timing, you can tune everything else better.

 

[legopnuematic]

check the advance weights in the distributor and the wires coming off of the pickup. My 76's weights had seized and the wires had fatigued (the vacuum advance pulls that in and out and doing that for 40 years they get brittle) and it started to do what you were describing, except it was through the exhaust and not the carb. Put a new Distributor in and it ran better and harder than it ever had.

 

[emtrichel]

first thing I'd do is verify timing. you need to rule out pre-detonation before something catastrophic happens. once you've dialed in timing, you can tune everything else better.

Could that still be the case if it hadn’t been doing it before, and does sound normal at times?

 

[Frankenchevy]

many factors can cause a "misfire". diagnosing over the internet can be difficult. a digital timing light is a great tool to have and can help diagnose problems and improve your engine's state of tune.

what have you done/replaced besides the water pump issue? how long has this problem existed?

 

[emtrichel]

many factors can cause a "misfire". diagnosing over the internet can be difficult. a digital timing light is a great tool to have and can help diagnose problems and improve your engine's state of tune.

what have you done/replaced besides the water pump issue? how long has this problem existed?

Only other thing I’ve done is an oil change. I wondered if I added enough oil for it to deep into spark plug wells, but didn’t see any. Plugs seemed fine too. It only started shortly after oil change. I know it needs a head gasket job.

 

[Frankenchevy]

Should take 5 quarts of 10w30 or thicker oil.

Remind me again...what symptoms point to bad head gasket? White smoke? Loss of water in cooling system?

There was a recent roadkill where they used a head gasket in a bottle product. Might limp you along until you’re ready to change it.