jerking at high speeds

[mike561]

Today my car started jerking at high speeds on the highway (above 50mph) feels kinda like a "jump" as well. it will do it randomly not at a steady pace. all the plugs and wires have recently been replaced, as well as the carb rebuilt, doesnt sound like any misfiring. Im thinking it could be something with the tires...

[silicon212]

You running the feedback carb?

[j cAT]

Originally Posted by mike561

Today my car started jerking at high speeds on the highway (above 50mph) feels kinda like a "jump" as well. it will do it randomly not at a steady pace. all the plugs and wires have recently been replaced, as well as the carb rebuilt, doesnt sound like any misfiring. Im thinking it could be something with the tires...

could be the fuel filter or the ignition module..

low fuel pressure is possible..

[mike561]

yeah its the stock electronic carb, does it at low speeds sometimes too, idk how to describe it best, feels like a jerk, jump, skip, but at random intervals. it cant be a tire because it only does this when throttle is applied, with or without the AC on.

[silicon212]

That's what I thought. If you have access to a dwell meter, you might consider checking the duty cycle (dwell) of the M/C solenoid. If this is improper, or the air bleed is not set right, this will cause this issue.

Ask me how I know this ... <grin>

[mike561]

from experience i assume lol. if it makes any difference, i put it in neutral and reved the rpms high, no shakes. seems to only do it in motion, right around when the tranny goes into lockup gear too.

[mike561]

also, today i went to take off from a cold start, i floored it and herd a loud "POP" then the engine stalled, but started right back up.

Edit: i just pulled out a few spark plugs and some were covered in ash deposits, which probably explains this problem i hope. i will be replacing all the plugs and see if that fixes it. i've been using that gas additive crap which i read can cause this to happen. i was told to start running at least 89 octaine too

[j cAT]

Originally Posted by mike561

also, today i went to take off from a cold start, i floored it and herd a loud "POP" then the engine stalled, but started right back up.

Edit: i just pulled out a few spark plugs and some were covered in ash deposits, which probably explains this problem i hope. i will be replacing all the plugs and see if that fixes it. i've been using that gas additive crap which i read can cause this to happen. i was told to start running at least 89 octaine too

ash deposits are from oil/blowby gases etc. what fuel additive are you using ? too much is not better..this can cause combustion chamber deposits causing the need for higher octane.

pop was a backfire thru the carb not good ! recheck the timing ..

if you use regular plugs replace every 15,ooomi...check plug wire resistance when you replace plugs pull the plug wire boots only / carefully, use the boot puller tool if there on too tight...

[mike561]

I was using that STP fuel treatment for a bit. the ash deposits were so thick it was almost bridging the spark plug gap. I've been getting some blow by gases comming through the vented oil cap, but i dont remember it causing ash deposits like this before.

[j cAT]

Originally Posted by mike561

I was using that STP fuel treatment for a bit. the ash deposits were so thick it was almost bridging the spark plug gap. I've been getting some blow by gases comming through the vented oil cap, but i dont remember it causing ash deposits like this before.

I use marvel mystery oil with the fuel at 1 oz. per 10 gallons of fuel . this keeps the corrosion down and protects the complete fuel system from damage..this amount is used also in the new vehicles and other engines I own ..this product will over time make your engine run better..more is not better ..sounds like you used way too much stp additive..or you are consuming an excessive amount of engine oil...

[mike561]

Well i put new plugs in and all seems well now, no more shaking. four of the plugs looked horrible i should have taken a picture. I do lose oil right now because im running 10w30, but when i used 20w50 it didnt leak bad at all. I also get blow by smoke that comes out of the vented oil cap every now and then

[j cAT]

Originally Posted by mike561

Well i put new plugs in and all seems well now, no more shaking. four of the plugs looked horrible i should have taken a picture. I do lose oil right now because im running 10w30, but when i used 20w50 it didnt leak bad at all. I also get blow by smoke that comes out of the vented oil cap every now and then

the engine is worn . this is where the ash deposits are coming from. use the marvel mystery oil in the fuel . this should lossen the piston rings /compression rings over time . It is possible this may reduce the blowby gasses..usually at high mileage and worn these rings can stick ,,

[NOVAZ27]

Hello. You might check the oxygen sensor. I had the same problem with my "84" Caprice. I did all the usual suspects parts replacement but to no avail. Found out later that a weak oxygen sensor was a fault. The problem cleared right up right after it was replaced. My caprice has 325K mi. on the original 305. The oxygen sensor that was replaced had 310k mi. on it. They are suppose to be changed out at 50-60 k mi.

You might check the EGR & valve and it's control systems while you are at it. It could be dumping excessive exhaust gas in to some of cylinders. On my Caprice I just put a homemade block off plate where the EGR valve is suppose to go. End of that problem.

HOPE THIS HELPS.