My 1994 Chevrolet C1500 with a 4.3L V6 is really loping and getting bad gas mileage. Not the EGR valve.?

Question

Starting Saturday, my truck has been idling very roughly and making about 8mpg (compared to 16 earlier that day). It doesn't vibrate when you give it throttle though. I cleaned the throttle body, changed the oil (to Royal Purple), replaced the spark plugs with Bosch Platinum 4, checked the plug wires, distributor car and rotor, replaced the coolant temperature sensor, put cleaner in the gas, checked and cleaned the EGR valve, checked vaccuum lines, and everything else I can think of. It's still making plenty of power like it used to but it's getting about half the gas mileage and idling very rough (shaking the whole truck like a 454). It sounds like it's running on about 4 cylinders at idle. I'm thinking it might be an exhaust valve or two because the tailpipe sucks in air about every stroke (if you hold a dollar or piece of paper at the end, it sucks it in) If you have any ideas I would really appreciate it.
P.S. I recently replaced the fuel filter too.
-Evan

Answer 1

i own a repair shop and you need to run a compression check on it and see what the compression is,it may have burnt a valve on It,or its possible it might have jumped a tooth or two on timing,all you can do is check it and see but i have found with the 4.3 engines that they usually will jump a notch on the timing chain and gears and this causes it to run rough and idle poorly but check it real good it may have slipped a notch out,,good luck,i hope this help,s.

Answer 2

the first thing to do is check for codes. If the check engine light is on, this is a clear indication that the computer can't make sense of the data it is seeing.
If there are no codes present, check for a loose or broken vacuum line at the MAP sensor.
Check also for a dribbling fuel injector. You can't see the flow/spray pattern at idle or running, but you can remove the air cleaner housing, and with a timing light pointed at the injector tip(s) look to see if ther is an inordinate amount of fuel being metered. If so, check the fuel pressure (possible regulator failure) or a pintle not seating in one of the injectors.

Good Luck

Answer 3

You need to eliminate posibilities, and narrow it down a little.

With the engine warm, and idleing, remove one spark plug wire from the Dist. cap and determine by idle sound and speed if it changes.

If when you remove a wire, and NOTHING changes, pull the spark plug and inspect the plug, it may be fouled or not gapped right.

If the engine is cold, start it and spray glass cleaner on the exhaust manifold while it's running and see which exhaust port is NOT getting hot. Pull that spark plug.

If you don't have a compression tester, stick your finger in the spark plug hole and have someone crank it over. If you can't keep your finger in the hole, you have other issues.

Answer 4

Seems impossible that it's even running... That went beyond me... If it's sucking in at the exhaust stroke than it would be letting out on the intake stroke, but then it wouldn't get fuel so....Stuck valves or bad cam..... Clogged cataltic converter.... Damn I can't understand this one... Sorry....

Answer 5

recheck your wires make sure you did not put one in the roung spot when you changed your plugs

Answer 6

verify the distributor base lock nut and bolt, the distributor base might desire to be unfastened in its mounting , which might placed the timing out.hassle-free because it sounds, might desire to be the project.

Answer 7

check the trouble codes, it's probably in limp mode :(