GlockLT4

Ok, so I have a slight miss at idle all the sudden. I haven't changed a thing. (tried different octane gas and didn't help). On the way home to dallas over the weekend i did some datamaster logging and i just got through looking at it and I was pretty much stochiometric in norman, but when i got to dallas i was rich. very odd i thought.. until I talked with a buddy that said humidity will cause you to run more rich :eek: . I looked back at the log and i noticed i got richer and richer on the way home, and it was more humid in dallas than in norman. It is still missing now that I'm back in norman, but the humidity has spread up to here.

This make sense? I've never heard this before, but it seems to make sense to me. I guess I need to reconfigure my injector constant to make it run closer to 128. It's running at 120 right now. Hopefully that is the reason for my miss. It does fine above idle .. new plugs, wires, and opti.


[Modified by Glock'94, 9:01 PM 4/29/2002]

Red94Vette

I've had that idle miss for months now. I am just about ready to try out a new opti. I ordered MSD wires today and bought some new plugs. My water pump is going out so I'm pricing one tomorrow. Maybe some water got in the old opti-spark?

If you fix it please tell me what you did.

Thanks

Steve85

On a modern engine humidity should reduce power but shouldn't cause a misfire at idle.

On an older engine, fuel delivery was controlled by the volume of air flowing through a venturi. With high humidity, that given volume of air has a lower concentration of oxygen. Leaving extra fuel with no oxygen to mix with.

On a computer controlled engine you have a back up, the O2 sensor provides feedback and should be letting the PCM know that it's delivering too much fuel. Here the PCM should back off the amount of fuel to maintain stoichy. Less power but greenpeace thanks you :rolleyes:

Your injector constant may work, if your programmed for max HP, the PCM may not make all the necessary adjustments. Given GM's history of programming, they err on the side of rich to protect the engine, I would guess that you've had to lean out the fuel to achieve max HP. There are so many other variables in the equation (e.g. there may be a minimum injector pulse width number to prevent it from going too lean, no matter what else it may see)

Just wanted to shed some light on the humidity issue for ya.

GlockLT4

Alright thanks ski .. the guy i talked to is a carb guy.. so that makes sense why he said that. I guess I'll try the injector constant thing and hope it helps. I the car was running perfectly when i left :(.

cesar

corvettes are suppose to have a small jump at idle due to the cam. in the video that came in my 92 the miss or jump is mention related to the LT1 :seeya

GlockLT4

Well, first off I don't have a stock engine :). And second, it is not normal because I'm noticing it. I never noticed it before.

John Row

I've been noticing an occasional miss at idle.

I don't know if any of this is related. Last week I got a check engine light, engine died and was hard starting. I pulled codes and got a 16 & 36 and 25 & 48.

16 - Low res spark - Opti:eek:
36 - Hi res spark - Opti :eek: :eek:

25 - IAT
48 - MAF

I had recently put a vented (old base, new cap) opti, but had not finished connecting the vacuum. The Service Manual said if the vacuum lines were plugged it could throw a 16 & 36. I blew out the opti and connected the vacuum and have NOT had a repeat of the above activity since. I still need to repull codes and see what remains.

Every miss at idle makes my stomach jump for now. :cuss



[Modified by John Row, 5:55 PM 4/30/2002]

GlockLT4

I know EXACTLY what ya mean!

I always worry that if my car dies on me .. and won't start back up, it'll be the THE worst spot :nonod: So far she's never left me stranded :flag

John Row

Even with my above problems, if I let the car cool for 30-60 minutes it would start and run for quite a while.

I had it towed home once because my wife was freaking out and I wanted her to see what was necessary to tow the Vette in case she ever had to have it done.

Lone Ranger

Is this true? The video that came with my '95 says nothing about it. Anyone else heard this? I mean... I guess it would make sense if the LT1 stock cam is a little more aggressive than previous and other small block cams. But this is the first time I've heard that Chevrolet says a slight roughness in the idle is normal.


[Modified by Lone Ranger, 7:49 PM 5/1/2002]

R23HTC

I've noticed a slight roughness at idle depending on what spark plugs I've used and how old they were. (new or old)

GlockLT4

Brand new NGK's at .04"