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Help! Engine has a rough idle and has a shake

ptrparker

ptrparker

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After a long drive up the grapevine on a hot day, something happened to my truck. I lost power and burnt up a couple spark plugs. When I returned home, I replaced plugs, cap, and rotor then drove to Vegas. the truck still had a shake but thought I could make it, another hot day. Once I got to Vegas, the truck started bogging down and eventually stalled. I believe this was due to vapor lock with the ethanol fuel on a hot day, but can't figure out what the shake is. The truck had a very consistent shake on idle, something was unbalanced for sure. I had a shop rebuild the heads because compression was low in number 8. also found a collapsed lifter in 8. had the heads rebuilt, replaced all lifters, new plugs, wires, cap, rotor, and rebuilt the carb. I inspected the old lifters and did not see any sign of a warn cam. I went to pick up the truck and the idle is still off. If I rev the truck, there is a pop in the exhaust. they are going to try and figure it out and think it may be timing or stuck secondary on the carb. they swear its not the cam. the engine has about 60K miles on it with an RV cam. It ran perfect before going up the hill. I only run Valvoline VR1 with Zinc and premium fuel.
-What would cause the problems after a hot drive up a steep incline (not towing anything, just me in the truck). I believe the stall is from the engine getting hot and creating vapor lock, but the shake was worse when cold and a little less when hot. its still there.
-Truck is a 1986 California Air/Smog with carb. I did replace the Spark Control Module about 2 years ago because I wasn't getting spark to the rotor, also replaced the rotor with a D.U.I., but the module failed about a year later, so I replaced with a GM module.

Maybe its just time for a complete new engine?
 
A vacuum gauge connected to manifold vacuum will help determine if the engine is sound. Which two plugs ? O r wires? burnt.
Double check the firing order.
Stuck secondary is unlikely, they are mechanically opened, should be easy to tell. They can be miss adjusted and cause issues.
A vacuum leak can cause your miss fire, the q jet intakes can crack and allow unmetered air in. This could have been caused by a hot run.
All the top end work was done after Grapevine run, and before Vegas trip ?
 
All work was done after both trips. Been at the mechanic for 2 months. The vacuum is strong. I think it’s the cam or bad pistons? When they pulled the heads, there was a ton of carbon on pistons, but was dry.
 
Just spoke to shop, compression is good, distro is good. Still has a sporadic miss.
 
May very well be the cam. New lifters are crap. It's a crap shoot if they break in and survive.
So if your cam has gone flat, the vacuum gauge will show that.
On the piston side of the equation, a ring land can break after getting hot. Getting hot on a hard run is 1 thing not horrible, but overheating is another can be damaging
 
never overheated, temp was actually not too bad around 210 maybe a little higher when it hit 105 outside. I asked the shop to check firing order. they are going to have a different mechanic take a look. At this point the entire top of the engine is new, thinking to get a block with a roller cam and just build it to last. I do live in CA so I have to pass smog or move to an unincorporated county, or better, move to a different state.
 
Are there any unincorporated counties left? I thought state law ended that years ago.
 
How did you burn up spark plugs? Are you talking about detonation? Burning a plug wire could certainly cause a shake. Is this an electronic carb?
 
Headers? Plug wires can easily get to close to them especially with the heat you were experiencing on the drive. I've had that happen (if I remember correctly) and it caused a shake because of the miss.
 
Plug wires were good, but replaced anyway. Plugs were burned up and oiled. Shop said valve guides were shot and compression bad, so heads were rebuilt. New EGR as well.
 
Could be a couple of valves aren't adjusted correctly. Again vacuum reading will show this.
Can't have a rock steady vacuum reading and a shakey engine.
 
Spoke to shop, all problems point to bad cam. I currently have an RV cam. Recommendation is to replace with a 350 350HP flat Tappet cam. anyone have any recommendations. Since it's apart, I may add an intake manifold, any recommendations here? it has the computer controlled carb.
 
go roller, there aren't any good flat tappet lifters to be had. Maybe Howard's. I maybe soured on them to. I have a nice fresh 355 with nos Engle cam and no lifters I trust to use.
Talk to @folkenheath about your options
 
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