Any ideas why my truck could be running rough after warm up? It runs perfect at cold start up but after about 1/2 hour or so during normal driving conditions the truck will start to miss,spit,and stall. And when it cools down it runs great again........WTF!
My truck is a 1991 Ford F-250 with 408W and a 9psi Powerdyne. The truck was converted to massair and I'm running 42# injectors w/ a Pro-M 75mm cald for 42# injectors MSD BTM and MSD dizzy.
Any suggestions would be great. It's gotta be something small.

Thanks,
JD

 

Engine Coolant Temperature sensor (ECT)?
OR
Air Charge Temperature sensor (ACT)?

 

I just changed the ECT sensor.
I was thinking maybe the TFI module on the dizzy?

 

Did the problem start before or after you changed the ECT?

 

It ran rough before I changed the ECT sensor.
I just replaced the TFI and the coil....still running rough. I will try to pull the codes tomorrow.

 

W/o the luxury of scan error codes I'd start with the the MAF sensor and they get contaminated more than they go bad. Remove MAF sensor & see if the 2 small coils are intact, if ok use the Electronic contact cleaner or MAF cleaner. I do As long as the can's handy, remove & give the O2 sensors a douching through the openings of the probe shields improve their accuracy. Looks like you can just lean the ladder right against the exhaust pipe! Could you give me a quick run down on the MAF conversion? Like how input gets introduced to the PCM kinda stuff & $$. Also the fact that it is entering closed loop function implies that ECT sens. function is in it's ball park as to accuracy.

 

Before I installed the 408w I sent out the maf to Pro-M to be recald for 42#injectors. So that is like brand new.
I also changed the O2 sensor,TFI module,ignition coil, and the ECT.
As far as the mass air conversion kit, Its a Ford Racing kit I bought a few years ago.
Heres a link:
http://www.fordracingparts.com/parts...tKeyField=1179

 

Update!

It ran good for awhile with a new O2 sen.....but after about a 1/2 hour it started running like poop again.
Its almost like its fouling out the O2 sensor.....Is that possible?

 

There may be more than one O2 before cat and after cat.

 

The whole exhaust is aftermarket from the header flange to the exhaust tip.
On my year truck it only had 1 O2 sen. I placed an 02 bung in the header collector on the passenger side.

 

did this start recently with everything from your combo working fine before?


I'd look at fuel pressure, and another thing is my `89 5.0 with 10psi ran like **** when I just had 42lb injectors and a calibrated MAF for 42's on it. It was fine on throttle, but after playing around on the highway, pulling off and coming to a red light for example, it would try to stall because it was getting too much fuel at idle when warmed up.

went away with an SCT chip and a good dyno tune, fwiw.

 

I run a Kirban FPR at approx. 41 psi.
I did have most of these parts on before I installed the 408w. And it ran great...almost regret doing it.The parts that are new are:
MSD BTM
MSD dizzy
9 Psi supercharger pulley...was a 6 psi
Ford racing 42# injectors
Recal Pro M Bullet 75mm mass air meter...was calibrated for 24#

I did bring my truck to a dyno shop and they told me that my PCM was too primative to add a chip. And in the past when a vehicle (similar to mine IE early Mustang )that had a chip on it ran slower with it installed.?????? Got me! Maybe they are just lazy.

I'm real tight on cash right now so I'm trying to get a game plan going before I dump a poop load of cash at it ....again.

 

sounds like that shop can't tune ford EEC-IV, try to ask around for a shop that is an SCT dealer and knows how to tune 5.0 mustangs / EEC-IV ford ECU's.

But the best way IMO would be to learn yourself, you'll need a TwEECer R/T and a Wideband A/F monitor.

IMO the problems you're having are from the 42# "calibrated" MAF

you could probably get it to run quite well with a stock MAF sensor, smaller injectors and a vortech FMU if you don't want to tune it.

 

After your latest hardware upgrades did you wipe the KAM? Ford recommends it after engine hdwr. mods, sensor replacement or components related to ECU. This causes the adaptive learn table entries to purge and they rebuild with entries that reflect proper integration. The KAM is protected by a 20 min. capacitor to protect it from accidental loss. It helps w/ its discharge if the headlights are on when battery is disconnected for at least 20 mins. check out this link (when you get there, scroll to top of page): http://www.mazdas247.com/forum/showthread.php?p=3863560

 

Doesn't take much to contaminate the MAF. a half decent size dirt particle or contact w/ a fingertip! Electronic contact cleaner wont hurt it.