I had a hesitation that happened at low rpms (~2K), but did not happen when:

-it is raining, or it just rained
-when I "blip" the throttle first and then step on it

I fixed this completely by replacing the opti. I also replaced the coil, but I did that a few days later and the hesitation was gone before that, the new coil did make the engine run a little smoother though.

My theory:
At low rpms, when you step on the gas, you momentarily get a very rich mixture in the engine, which makes it harder for the spark to jump the gap on the plug. When it is raining or the humidity is very high, the air is more conductive to a spark and therefore the spark jumps the gap both in the opti and on the spark plug more easily.

I replaced the opti because I was already replacing the WP which was leaking on the opti. During this time of leaking, although the weather was dry, it seemed like the engine was performing like it was in the rain. This is what confirms the theory in my mind.

The reason there's no hesitation if you "blip" the throttle first, is that you already allowed a lot more air in the engine to lean out the mixture when you step on it the second time.

What do you guys think of this? Anybody else have this experience with the rain? If you do and you have a hesitation and a lot of miles on your opti, I would highly recommend replacing the opti!

Sam

 

I'm not the ignition expert, but your theory sounds like it may be part of the problem.

 

theoretically- yes

but- i'm going to go with negatory
water in the opti would have caused a clutter*** of misfiring, not make it run smoother.

Also, pure water does not conduct electricity... and I dont think TN has a major acid rain problem.. I could be wrong about this but there is no way waterpump leaking in the opti is curing a misfire

 

I didn't mean actual liquid water in the opti, but just very humid air, like would occur during heavy rain. The leaking of the WP on the opti merely made it a little bit more humid in there is what I am thinking. If I had waited longer, it would have gotten too humid in there with the consequences you were describing, that's why I replaced the whole thing.

This theory is the only way I can explain why my car was behaving like that and how it dissappeared. It was very noticeable how it would have much improved throttle response at low rpms when it was raining, that was not my imagination. It wasn't running smoother, just better response.

Any other ideas/opinions?

Sam

 

doubtful
you just had an optispark on its way out

 

Let me chime in on this.

I have the same problem. I had ext warranty and they replaced the EGR valve to fix this. Well it didnt fix it but it is not as bad now.

Now I had a friend of mine scan it with datamaster this weekend, and of course it didnt act up. I think it did it once. But we did notice I had 1 to 2 degrees of knock retard everytime I took off.

We thought to add the LT4 knock module might help. Also he mentioned it could be opti related too. So that would fall in line with your theory of blipping the throttle first. As the only time I get this problem is low rpm and med to high load.

Anyone besides me ever scan their car when it was doing this and get something?

Jason

 

Yes, exactly, I am just trying to understand what that means: "an optispark on its way out." I am suggesting that it is the increased gap in the opti that causes this stumble/hesitation and that manifests itself by getting better under conditions of humidity.

Sam

 

I scanned and logged data from my car a lot and I was never able to find anything. I even posted it here and emailed a log file to Injuneer and he was not able to find anything out of the ordinary.

The reason I want to see if this makes sense is that it would make for a nice check to see if the problem is caused by the opti or something else.

Sam

 

Nobody else an opinion on this? I know this is a problem that gets discussed a lot!

Sam

 

I have a similar problem (low rpm stumble). But my problem is different because I get more knock retard when it is humid. I'm gonna try blipping the throttle first and seeing what happens.

 

I fixed mine with a 4.56 gear. hahahaha, it jumps up in a hurry now! 4.10's it bogged 4.56 no bogg. I dont guess it had a choice but to go.