Question: Idling & Running Rough

[Cruise]

Recently my 1994 LT1 4 speed automatic has been idling very rough and will lose power under acceleration. If I drop down a gear ( keeping the RPM's higher ) it will run okay - but not 100%. It feels like bad gas or low octane, but I have changed fuel with 94 octane a few times ( and octane booster ) and it is still happening. There are no service engine codes showing. I am looking for some help to see if it sounds like a fuel filter issue or an ignition issue?

 

[mlm0]

how about fuel filter?

 

[LT4man]

How many miles?

When were the spark plugs and/or ignition wires replaced?

 

[96gs917]

Need more info... Mileage, service history? Could be bad fuel, clogged fuel filter, ingnition wires, plugs,
clogged cat. Did you do anything to the car recently? Clean the engine? If you aren't getting any codes, it could be
time for a new optispark.

 

[toptechx6]

Instead of asking for OPINIONS why not do some simple testing to help isolate the problem? If you have or can borrow a fuel pressure gauge use it and compare the reading with specifications (should be approximately 42 PSI) Many ignition problems can be traced to deteriorated secondary ignition wires on our old cars, with the engine running look carefully for arcing from the spark plug and coil wires at night or in a dark garage. If done inside a building make sure of course that the door is open or otherwise properly ventilated to avoid carbon monoxide (CO) poisoning. Good luck!

 

[Cruise]

Thanks for the responses back so far. The car is basically stock with 75K miles. I have already replaced the plugs and wires about 25K ago and I did the dark test recently to see if there was any arcing - only a small amount after I sprayed bit of water on the wires. I replaced the fuel filter on the weekend, but unfortunately it seems to be running worse. I have had to change two oxygen sensors over the last couple of years. No codes visible. If I do have to replace the opti spark, GM wants $450 for a cap and rotor, are there any aftermarket versions that are good quality?

 

[LT4man]

When you spray water on the ignition wires, there should be absolutely NO arcing or sparking occurring.

If there is, then wherever the arcing is occurring, is suspect.

Yes, ignition wires can fail in 25,000 miles. Or a substandard set of wires can deteriorate.

Read this: MAGNECOR Race Wires: WELCOME TO MAGNECOR!

All you ever wanted to know about ignition wires, but were afraid to ask!

What you are describing (lack of power at low RPMs, bit more power at high RPMs but not as smooth as an LT1 should be) is a misfiring engine.