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4.3l stumble

I have a 93 chev K1500 throttle body that has an anoyying stumble accelerating from a stop and seems to surge at partial pedal on the highway. It seems to work fine with the pedal mashed to the floor although acceleration is lack luster. It seems to idle a little low, but with increased idle it seems to have a miss. If you goose the throttle at idle it also seems to choke and sometimes backfires. I've had the base timing readjusted and checked, replaced the plugs, cap rotor button, and wires last year, replaced the fuel filter yesterday and changed the oil. A mechanic said it may be my fuel pump crapping out starving the engine of fuel. ANY IDEAS??? Thanks..

Reply to
tuck(r)
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plugged injectors?

Reply to
David Norris

Pickup Coil?

Reply to
Martin Riddle

Ten bucks says it's the EGR valve.

Doc

Reply to
"Doc"

If it was then it would stumble WORSE on full throttle.

Doc

Reply to
"Doc"

Nope. Problem would be present throughout the RPM range, not just at certain levels.

Doc

Reply to
"Doc"

I'll elaborate. From a DEAD stop, with engine at operating temperature, A/C OFF, give it very very light throttle, just to get her barely rolling. Does she bumble and pop when you do this?

That thing have an electric or vacuum actuated EGR? If vacuum, AND if it stumbles during the above test, unplug the EGR vacuum solenoid feed line from the throttle body and plug the port with a vacuum cap. Now see how she runs.

Doc

Reply to
"Doc"

Sure sounds like it to me Doc.

Pull it off and look for a chunk of carbon holding the pintle off the seat. Clean it and install a screened gasket and I'll bet the problem goes away.

Reply to
Steve W.

It does bumble at incease in throttle and smooths out when you back it off a bit, I'll give your Idea a try and let you know what happens....Thanks,

Reply to
tuck(r)

I had the egr valve removed and cleaned (took a lot of carbon out of it) but the truck is still missing at low rpm and burning rich. It almost seems like the timing is off but I've checked the base timing with the timing light with the advance unplugged and it seems fine. Vacuum at idle however is at 16 inch Hg, is that ok?

Reply to
tuck(r)

It's a tad low but still within range.

Doc

Reply to
"Doc"

Hey "Doc", thanks again. As usual you were right on target. I had taken the truck to the dealer to check out the problem and low and behold it was the egr valve as you suspected. It seemed to be operating ok to me visually but we found out that the spring inside the valve itself was weak. I got a new one (expensive) and put it on and now it seems to be idling better now but I'll have to wait for tomorrow to see how she runs first thing in the day and if its still burning rich.

That saves me the cost of a fuel pump and the labor to drop the tank and install it to find out the problem would not have been solved. Again I thank you and thanks to the group for your help.

Randy

Reply to
tuck(r)

You're very welcome. Glad to be of help.

Doc

Reply to
"Doc"

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