4K breakup?

[Kooldino]

So for some reason, on occasion, when I boost hard, the power breaks up at around 4000rpm.

My AFR is ~12:1, and my spark gap is around .028, last I checked. I'm also only running 11psi right now, so I don't think I'm blowing out the spark. I run 94 octane gas.

When the car hasn't been running for long, it will break up at certain rpms whether I'm in boost, nuetral, or anthing. When it warms up, it does fine.

Any ideas?

 

[Bigg Tim]

too much gas. When it's in "cold mode" the ECU dumps more fuel so when you get on it, you are adding to it and thus the stutter. You really can't tell the A/F number's yet becaue things aren't up to temp yet. This is only if the coolant temp is under 180, is it? I have that now with the O2 tuning, but not before with the other setup. I notice once it get's to 180, it gets out of that mode and you're all set. Is yours similar?

 

[funktownp5]

I know my car does the same thing. When i datalogged the fuel on a cold start it was

dumping twice as much fuel compared to being warm.

 

[Kooldino]

too much gas.

But my WBO2 said I was running 12:1 or so...doesn't seem like too much to me.

When it's in "cold mode" the ECU dumps more fuel so when you get on it, you are adding to it and thus the stutter. You really can't tell the A/F number's yet becaue things aren't up to temp yet.

I was driving it for 10+ minutes.

This is only if the coolant temp is under 180, is it?

Not sure, but I'll certainly check next time.

 

[Bigg Tim]

I noticed that my WBO2 doesn't read accurate until about the same time the car is up to operating temps. So you may be getting an incorrect reading. Dunno

 

[Kooldino]

Checked it last night, it was 190*F

 

[Bigg Tim]

so it still did the same thing? Maybe the temp I have is incorrect, anyone know more about this?

 

[Kooldino]

It still does it until the car has been run for 20 mins. It breaks up between 4 and 5K. It's fine before 4K, and fine after 5K. Once the car has been run for 20 mins, it's smooth inbetween 4 and 5k as well.

 

[Bigg Tim]

It still does it until the car has been run for 20 mins. It breaks up between 4 and 5K. It's fine before 4K, and fine after 5K. Once the car has been run for 20 mins, it's smooth inbetween 4 and 5k as well.

Don't know man, that doesn't sound like the cold mode thing. Maybe the injectors are dirty? I'm just guessing here.

 

[SBD]

It still does it until the car has been run for 20 mins. It breaks up between 4 and 5K. It's fine before 4K, and fine after 5K. Once the car has been run for 20 mins, it's smooth inbetween 4 and 5k as well.

A volume of air requires more petroleum to combust at colder temp's than it does at warmer temp's. There is a lot of wasted fuel while cold. All ECU's have a "warm-up" routine that usually bumps idle up, adds fuel, and triggers various emissions systems (to deal with the waste fuel).

I've never messed with MPI, nor could I find a real good list of info about it, but I don't think they have provisions to adjust start-up fueling. Most all stand-alones have a "Coolant Temp Correction Map" which essentially allows you to apply a [positive] correction percentage based on coolant temperature. You're cars ECU could be correcting too much (rich), or it could be not correcting enough (lean), but it's hard to tell with your description. Remember, the correction is a percentage above normal operating temps pulse width.

If you can adjust coolant temp correction, try richening it up first (safe direction). If you get worse results, try leaning out the correction. However, even if you have it running right or not, I don't suggest running the engine hard until everything is up to temp.

 

[Bigg Tim]

The MPI is a piggyback and does nothing to the stock ECU unitl you say you want to. So during the cold starting, the ECU is back to factory until you want to change things. No need to change and correction factors, the ECU is already doing it.

So Kool, maybe you have it giving too much fuel in that area and it's causing that problem. It has to be something with the "cold Mode" but I can't see the ECU still in that mode if the temps are above 180 degrees.

 

[MPNick]

I don't think they have provisions to adjust start-up fueling.

.

Yes the MPI does have a cold start provision. It is used for helping out cold start with larger injectors. With stock injectors you do not need to use it.

We all need to remember that all this means nothing if something is wrong with the car. I do not know if the car has anything wrong with it, but things like air leaks, plugs, bad grounds can all cause prblems like this.

 

[Focus]

May be spark related as welll. Failing coils? Spark Blowing out. I know you use 93 but I blew out my spark with 103 octane.

 

[Kooldino]

May be spark related as welll. Failing coils? Spark Blowing out. I know you use 93 but I blew out my spark with 103 octane.

This has been my prime suspiscion for some time.

I remember over a year ago I had a similar problem during the winter. The plugs I was running were two stages colder than stock. Nick gave me some plugs that were one stage colder than stock (6 series NGKs??) and it helped out big time. Perhaps the MPI spark amp will solve my problem? Funny thing is, I only have this issue in the cold weather.

Also to note: last night I ran into the breaking up problem between 4K and 5Krpm in NEUTRAL. probably 30% on the throttle, neutral, and in an area where I did not have the MPI set to pull timing at all. Also, I was not adding any extra fuel. So as far as I know, the MPI was not modifying anything, unless I have some kind of hardware/wiring problem.

Time to go check my plugs...

 

[Kooldino]

Ok, checked the plugs...they were all gapped between .028 and .030, which was fine. I regapped them to .028.

One of them, however (closest to the battery) looked a tad green on the tip of the wire...which means detonation, IIRC...