check engine light dilemma
 

ok, so my fairly new to me truck has been great. needed a tranny when i bought it, had one installed. but noticed i was getting a check engine light (sometimes flashing). i scanned it & saw it had some misfire codes stored & some pending. i figured that since i didn't really know the history on the truck, i might as well change the plugs, wires, cap & rotor. it never had a drive-ability problem with it (other than the slipping tranny). on my way home from work (had the tune up related stuff done at a shop near work) i noticed that when i kinda stomp on it, i get a flashing check engine light (but everything drives & feels fine).

i throw my scanner on at a stop light & fine pending multiple misfire codes. not really sure what else it could be. it rides great, but that light flashes (seems to be when i stomp on the gas).

any ideas?

what year truck?
if you've already done plugs, wires, cap, and rotor - the next routine maintenance that can affect how it runs is the front O2 sensor.

do you feel the misfires, or is the CEL your only hint.
if you clear the codes, do you get only 1 or 2 cylinders misfiring, like 301 or 308, or are they scattered?

an an experiment, you could unplug the front O2 and run it disconnected. you'll get an new CEL related to O2 problem, but if it runs better it confirms the O2 is causing the problem.

it's a 99 ram 2500 5.9 gas.

no thing is, i have no problems other than the multiple misfire codes. ran good prior to tune up & runs good after. i just don't know why i would get this multiple misfire (flashing check engine light) under hard acceleration.

the computer uses the crank position sensor to detect tiny differences in how each cylinder contributes to rotation. it is measuring that at least one is outputting less horsepower than the others.

if you can get a single code like P0301, that's the computer telling you that cylinder 1 has a problem.

if the computer won't give you a code, consider a compression check.
did any one spark plug look worse than the others?
have you fixed your plenum yet? (they all have that problem).
does it ping? (spark knock).

Sounds to me like a classic case of the plenum flu....multiple cylinder misfiring is likely due to a vacuum leak caused by the plenum plate separating from the intake manifold. time to address it or you can say goodbye to your catalytic converter too.

A flashing/blinking CEL usually indicates a plugged catalytic converter. The OP should take his truck to a muffler shop and have the exhaust system pressure checked.

Also make sure the distributor cap isn't loose/misaligned/ rotor button bent. Trust me, it happens.

cap & rotor are good. the flashing CEL was happening even before i had the "tune up" done. i did it for maintenance & figured if it helped my situation it would be a win/win for me. i did get a solid check engine light prior to tune up for a misfire from cylinder 2. but it has not come back on since the tune up.


reading the plenum thread,
Symptoms of a blown plenum:
1. Excessive oil consumption
2. Heavy spark knock under load (sounds like a can of marbles when you have your foot in it)
3. Truck feels like it was castrated (loss of power)
4. Trouble getting up hills

i don't really have any of the symptoms other than the flashing CEL (multiple misfire). truck runs great, no oil consumption that i can see (from when i checked the oil level). i'll have to check the plenum as stated procedure in the plenum thread.

Does the engine shake when the converter locks up in third gear? Could be either fuel pressure or a fuel injector sticking. Also a crossed plug wire.

that's the weird thing. there are no symptoms other than the flashing light. absolutely no drive-ability problems. even under hard acceleration, CEL is flashing, but everything feels good, power is strong, & keeps accelerating.