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Old 10-20-2008, 08:50 PM   #1
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Engine runs rough after warm up

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
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Old 10-21-2008, 09:57 AM   #2
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I just changed the ECT sensor......still runs like azz.
Maybe the TFI module on the dizzy?
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Old 10-21-2008, 12:15 PM   #3
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Maybe the dizzy itself. loads of guys have reported problems with the MSD unit. Since I don't have one I haven't paid attention to the exact problems, but "search" is your friend.
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Old 10-21-2008, 12:23 PM   #4
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Look at the TFI module. Pull codes if you can.
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Old 10-21-2008, 04:55 PM   #5
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I just replaced the TFI and the coil....still running rough. I will try to pull the codes tomorrow.
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Old 10-22-2008, 01:08 AM   #6
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Quote:
Originally Posted by DVLDOG458 View Post
I just changed the ECT sensor......still runs like azz.
Maybe the TFI module on the dizzy?

dont cahnge anything until you pull codes, thats why the ECM is there it will tell you whats not working correctly, and give you a starting point on things to check and go from there.

but if you think logically about the problem alot of people are misleading you heres why.

when the car is cold and you start it it is running "open loop" which means it does not take any sensors reading into account in running the car, it runs off its internal table, well it does read the temp sensor when it is warmed up it is running "closed loop" whcih means it is now running the engine based on what info the sensors are giving it, no longer using the cold start table to run the engine.

with that being said it is more then likely just a sensor given bad/false/no reading to the ecm.

just becasue it missfiring and sputtering doesnt mean it is the distributor, especially since it doesnt happen unitl the car warms up, which means you can pretty much elimintate the distributor from the source of the problem.

do a KOEO and KOER test make sure teh car is warmed up when you do the KOER test

LUK
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Old 10-22-2008, 09:40 AM   #7
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Quote:
Originally Posted by red89notch View Post
dont cahnge anything until you pull codes, thats why the ECM is there it will tell you whats not working correctly, and give you a starting point on things to check and go from there.

but if you think logically about the problem alot of people are misleading you heres why.

when the car is cold and you start it it is running "open loop" which means it does not take any sensors reading into account in running the car, it runs off its internal table, well it does read the temp sensor when it is warmed up it is running "closed loop" whcih means it is now running the engine based on what info the sensors are giving it, no longer using the cold start table to run the engine.

with that being said it is more then likely just a sensor given bad/false/no reading to the ecm.

just becasue it missfiring and sputtering doesnt mean it is the distributor, especially since it doesnt happen unitl the car warms up, which means you can pretty much elimintate the distributor from the source of the problem.

do a KOEO and KOER test make sure teh car is warmed up when you do the KOER test

LUK
Your posts make me roll my eyes every time.

Nobody is correct because they are not a god like you.

First off, when the disty warms up the PIP and TIF are known to fail and cause erratic RPM readings. More so the TFI, which if you know a thing about mustangs is one of the most common reason for rough run when warm, or stalling. Once they cool down it runs fine.

Please tell me how I'm 'misleading' him here.
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Old 10-22-2008, 09:45 AM   #8
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Quote:
Originally Posted by DVLDOG458 View Post
I just replaced the TFI and the coil....still running rough. I will try to pull the codes tomorrow.
Let us know what you find.

Have you tried to bypass the BTM? I know some MSD systems start to run crappy when heated up, I would also check you timing with the SPOUT in when it starts running like poo. If it's jumping all around that would give you a decent place to start.

If I could find them I would give you acceptable ohms resistance for the varible temps for your air temp sensor and ECT. I will see what I can dig up.
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Old 10-22-2008, 09:59 AM   #9
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Quote:
Originally Posted by red89notch View Post
but if you think logically about the problem alot of people are misleading you heres why.

...when it is warmed up it is running "closed loop" whcih means ...
just becasue it missfiring and sputtering doesnt mean it is the distributor, especially since it doesnt happen unitl the car warms up, which means you can pretty much elimintate the distributor from the source of the problem.

do a KOEO and KOER test make sure teh car is warmed up when you do the KOER test

LUK
Red, I don't think anyone here is trying to mislead him, I know I'm not. If you re-read his post you'll see he said it starts running like poo after 1/2 hour of driving. That's a LONG warm up... closed loop shouldn't take more than 5 to 10 minutes unless he lives on the south pole. Something is warming up then overheating.
Still great advice for him to pull codes though.
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Old 10-22-2008, 09:26 PM   #10
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Good info guys!
Today I only had a few minutes to work on the truck, so I bypassed the new BTM and it seemed to run worse. So I hooked it back up.
I also noticed that I was getting some detonation under mid load. ( it was cold here so the windows were up) Even when I cranked the BTM up to 3.
Do the Mustang ECM's have a pin for a knock sensor? The reason I ask is because my stock wiring harness that is on the truck has an electrical connection for a sensor that I never had hooked up. The Ford Racing massair conversion kit that I am running is a n overlay harness w/ a A3M1 ECM.
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Old 10-23-2008, 09:55 AM   #11
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No they don't, obviously depending on year. But if you have a 87-93 computer it won't.

I couldn't tell you that 100% but I'm almost positive. How old is the tank of gas that's in it? Have you tried to just run it with the SPOUT out and 18-22* of total timing?

Just trying to take the computer out of the timing equation.
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Old 10-23-2008, 10:13 AM   #12
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you can put a scope on the O2 sensor to see if it's a lean miss. Also are you sure you don't have an egr problem? How about a vacuum leak between the upper and lower mani?
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Old 10-23-2008, 04:44 PM   #13
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I just filled up on 93 octane.....bad gas maybe?
I also put a EGR delete kit on when I put the new engine in.
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Old 03-31-2009, 09:41 AM   #14
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*UPDATE*


It was a bad mass air meter. I installed a PMAS 95mm from JD's and it workd great.
Thanks guys!
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Old 03-31-2009, 03:21 PM   #15
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Sweet!

Now go tear some #### up with that beast!
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