Ok i have a misfire i'm trying to figure out. here is some info on my car and the things i've done so far,

1994 LT1 160k miles Auto

Replaced items
Fuel Injectors
Fuel pressure regulator
Spark plugs
Wires
Mas air flow *didn't change anything so i put old one back on*
new air filter

Checked vacuum hoses also.

It seems to have a misfire at idle. Was having gas smell in the oil *didn't drive during this time* I just got done doing the fuel injectors and changing the oil and the problem is still there after driving about 15 miles. It has a very small misfire at start up but once warm it seems to get worst. Take off seems fine and no misfires is felt. power seems to be there *only had car for a month so it seems normal to me*. it seems if i baby it during driving it gets worst also and if i floor it, seens to clear up for a little bit but comes back. Any suggestions? Opti spark? I've searched and searched on this forum to come to the conclusion of the things i've already replaced and i'm running out of ideas. Thank you for your help!

Oh and no smoke or anything out of exhaust.

 

I am NOT an expert at all, but a real "misfire" will set a code. Do you have codes showing? I believe an expert can even see what cylinder it is. When warmed up I believe the front two oxygen sensors controls the air- fuel ratio. Not an expensive job. Dan

 

http://www.corvettebuyers.com/c4vettes/ecm.htm

 

Those are the symptoms that my 94 had before getting a new Delphi optispark dis. Now all is well, but that was having it diagnosed by a Corvette shop that did the work.

 

When I first bought the car, I was driving the car back I did have a brief check engine light but it went out shortly after coming on. And hasn't come back on since. I know newer cars store codes but Does this ob1 store codes or does check engine have to be illuminated?

 

It does store codes. Some turn of the SES (or SYS, as the case may be) light. Some don't.

 

I'll be checking them shortly. thanks for the replies everyone. I'll post updates later today.

 

H64 is the only code i got. which from what i can tell is an 02 sensor (exhaust lean). anyway to test the 02? Which 02 sensor would that be since i don't see it saying one or the other. Thanks again everyone.

Only 36 dollar each so i'll just replace them both. unless someone else thinks it would be something else?

 

I was just reading this thread and was going to suggest your O2 sensors may be the culprit. I just recently went through this. With my OBD1 PCM in place, I got not CEL or codes at all, but when I put the proper OBD2 computer in place I got a code specific to the driver's side O2 sensor, pre-cat. So you may not be getting a CEL for this. And it runs worse after warming up because the car is in open-loop mode and intentionally runs rich during warm-up. Assuming your sensors are old, I'd replace them both anyway. Focus on the pre-cat sensors - those are what the PCM uses to adjust air:fuel. The after-cat sensors are just to assess the health of the cats.

A little research showed that there are some dim views of the Bosch sensors. If you can find them locally, go for Denso or NGK sensors. They are still inexpensive. I think I got my Densos for ~$35ea at Advanced Auto. I think Napa had the NGKs in stock. AC Delco are the gold standard, but you probably have to order them from Rockauto. They are cheap there, but you have to wait. When you go to change them, make friends with PB Blaster and be patient. If you can fit an O2 sensor socket on them, use that (I have long-tube headers, so I don't know about stock placement). Did I mention patience? An strength. And patience.

It's possible that one of the three parts of the ignition is the culprit: ignition control module, coil, or opti. But I'd expect those to be worse at WOT, not better. WOT is also open-loop running, so the fact that your miss is not as bad a WOT makes me think O2 sensors, as does the H64 code you got.

 

And take a look at the thread herein on changing the O2 sensors. Some have the sensor bung just enough pointed to the tranny so you can get an open end on them. Many don't and you have to come in from the top with a host of long extensions.

Not a huge deal either way but you should be prepared either way.

 

My friend showed me his gear wrench type head on a swivel type O2 wrench he had that thing gets into the tightest spots and works great

 

I have a set of Snap-On that have the swivel head but they stop at 19 mm and 3/4 inch and I recall the 02 sensor is 7/8ths on the C4s.

 

My friend said it was a made just for O2's but I didn't ask the brand, yes 7/8". I think all O2's are 7/8" , correct?

 

you didn't check for codes before throwing money at it?

 

Honestly it slipped my mind about the check engine light being on because it stayed on for less then one min during driving and never came back. live and learn.


But even after changing the 02 sensor..... Still having the same issue. but Oil is still smelling like gas *have changed the oil 4 times now*. I seem to still have full power and no missing/stumble other then at idle.

 

also cleared codes. drove for 20+plus miles driving home and back and rechecked for codes. and no codes or check engine at this time. but same issues.

 

So I went out for a drive tonight but before I headed out tonight I decided to just to see if I could see arching. Looks like 4 wires are arching pretty bad on the spark plugs side, even though they are new. So tomorrow I'll pull plugs to check and change the wires. Any recommendations on a good set of wires? The ones I had were ac Delco.

and is there anything else that could be causing this? A bad ground? Spark not gapped correctly? (They were pre-gapped)

 

Are your wires old, I just put new AC Delco wires on my 94 coupe from RA and they do not arch in the dark that I can see and have no misfires that I know of and they fit the stock wire looms. I see you said they are new. I also do check plug gap on single electrode plugs even if pregapped do to shipping could close the gap if roughly handled.

 

Yes the plugs and wires are new. I even reapplied (not overly) dielectric grease on the boots to see if that would change anything. Still arching. I'm going to my shop tomorrow and going to change the wires and re check the gap on the plugs and see what happens. When I reapplied it helped some. but still 3 wires are arching. I'll get it All fixed one day, even if it kills me!

 

move the wires so they dont arch