car breaks up at high load low rpm when cold?

7

7 sek mark

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ya pretty much as the title says when the motor is cool and a romp on it it stumbles pretty bad untill it hits about 4k rpm. once the motor warms up a little it runs fine but for say the first 10 or mins after i run it after it has sat for a while to cool all the way down it stumbles. i have changed the maf, ECU (had a extra laying here so i changed it just to see), plugs are new, MSD plug wires and coil packs are pretty new. only thing i could think is maybe the o2's might be bad they are about a year or 2 old could they be causing this problem?
 
Your not gonna like the answer.. but in my experience with the MSD stuff and I used ALOT of it over the last 8ish years.

The msd plug wires would only last right AT 1 year.. then I would have to have them warrantied out due to just what you describe.

I didn't have any problems with them..until after the first plug change on new wires.
It seems they are OK until they go thru a lot of "heat cycles", then the core becomes brittle and breaks.
Again, I never had any problems with them.. until that first plug change when the wires would get moved from their positions, then.. 9 times out of 10 I would have a missfire AFTER changing the plugs.

I went with Ford Racing wires after replacing about 6 sets of MSD's on a 1 year interval.

hope this helps
 
the wire are over a year over and i have changed plug about 15 or so times on these wires. i run copper plugs and i change them about every 2-3 months at the most i like to keep a fresh set of plugs in the car as it runs better on fresh plugs. so i change them when ever i feel the power fall way off.
 
Misfires under load are usually caused one or more bad wires. It could also be a bad coil or even weak power (i.e. alternator/battery). I would figure out which cylinder is missing, and then swap wires around and check again. I'm with him....new wires should fix it.
 
it brakes up bad like it has a random misfiring on random clys and it only does it when the motor is cold and at low rpms. when warmed up it runs fine throughout the rpm range and then cold it still runs like it should at higher rpms. it seems to be getting better but it still does it and i have not changed anything on it.
 
What year? You cannot change the ECU unless you change the cordinating MAF sensor that goes with that ECU. I would recommend changing it back to your original one, not saying that is the problem though.

Ok, re-read the original post. O2 sensors will not cause this because they system is in "open loop" until the O2 sensors get hot enough. You would only notice it for MAYBE 1-2 minutes, by then the O2's should be warmed up and in "closed loop".

You could possibly have a stuck open EGR valve. Have you checked for codes? No CE light can still mean you have codes.
 
I agree, it could be the EGR valve. I had this happen on another car with an aftermarket tune in it and it drove me nuts. It turned out PCM was opening the EGR valve at too low of load, and caused the car to stumble at low rpm especially when cold. You might also check the MAF if it is a load-related issue.
 
oh ok i did not know the MAF was set to that ECU i have 3 different ECU's and about 4 Mafs. so i guess i need to find out witch one goes with what. there anyways to tell other than just keep swapping them until it runs better? i guess this could also fix my super rich condition then huh? the car is rich enough to leave black stains on the back bumper with in like 2 days.
 
LOL Jamies right!

Ya man, the ECU is programmed to each MAF, I ran into this problem when I converted my Stang from Speed Density to a MAF sensor. Look at the ECU numbers and coordinate them to the MAF numbers, the last two digits should go together if I remember correctly. Its been about 6 years though so I may be wrong. Let me find the link.

Doesn't apply but gives you an idea with numbers (two letters).
http://www.stangnet.com/tech/maf/massairconversion.html

That should take car of your super rich condition because its basically running a different MAF settings and reading different settings.
 
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