Bad idle and sputtering when hot

[Stantheman]

I have a 92 mustang 5.0 with some mods done. when cold started it has a rough idle unless I unplug the iac the rpm’s drop the way they should. it’ll drive fine for about 10 mins and then it’ll bog completely on its face past half throttle and will eventually die if you don’t pull over and let it cool down. I’ve listed the mods done down below some that might not matter but i listed them anyway thanks.

World product 200cc heads forged DSS SX series Pistons Scat I beam rods
Scat 347 crank
Bored .40 over
30 or 36lb injectors
High flow oil pump
255 fuel pump
70mm mass air
70mm throttle body
(Edelbrock intake Port matched to the heads)

 

[AeroCoupe]

What ECU and is it tuned? Would think yes but you didn't say.

 

[Stantheman]

Stock ecu and no tune

 

[AeroCoupe]

There is your problem. You need a chip and a dyno tune to fix that mess. Stock ECU for a mass air car is programmed for a stock 302 with a 55mm MAF, 58mm TB, 19 lb/hr injectors, etc. You can change the heads, cam, and intake and properly tuned it will run fine. Once you change the amount of fuel going in (larger injectors) or the amount of air through the MAF (larger size) it cannot compensate unless you are using a MAF that is calibrated for those injectors. Then when you couple more cubic inches it just throws too much at it and it cannot compensate.

So your choice is to either grab something like an SCT chip and get to a dyno with a tuner that knows these older systems or go stand alone and dive into the deep end of the pool.

Also, do you have an adjustable fuel pressure regulator? Other thing I will say is that you may not have enough injector but that depends on the camshaft and rpm range you want to run. I have a 331 and run 42's as it needs a lot of fuel up past 5,000 rpm.

 

[Stantheman]

There is your problem. You need a chip and a dyno tune to fix that mess. Stock ECU for a mass air car is programmed for a stock 302 with a 55mm MAF, 58mm TB, 19 lb/hr injectors, etc. You can change the heads, cam, and intake and properly tuned it will run fine. Once you change the amount of fuel going in (larger injectors) or the amount of air through the MAF (larger size) it cannot compensate unless you are using a MAF that is calibrated for those injectors. Then when you couple more cubic inches it just throws too much at it and it cannot compensate.

So your choice is to either grab something like an SCT chip and get to a dyno with a tuner that knows these older systems or go stand alone and dive into the deep end of the pool.

Also, do you have an adjustable fuel pressure regulator? Other thing I will say is that you may not have enough injector but that depends on the camshaft and rpm range you want to run. I have a 331 and run 42's as it needs a lot of fuel up past 5,000 rpm.

But the thing is that it only does it after you’ve been driving for a little bit when it’s first started the things a rocket

 

[AeroCoupe]

Get a chip and a tune. The car is in open loop when started and after a set time it goes into closed loop. Open loop means it ignores the O2 sensors and closed loop it reads and adjusts off the O2 sensors.

 

[Stantheman]

Get a chip and a tune. The car is in open loop when started and after a set time it goes into closed loop. Open loop means it ignores the O2 sensors and closed loop it reads and adjusts off the O2 sensors.

Thanks I’ll try that and get back appreciate the help.

 

[Mstng93SSP]

Have you checked for codes? What you are describing sounds like you might have a bad sensor. I have a 331, AFR heads, Comp Cam, intake, 24 lb injectors and it runs and idles like stock on a stock computer with stock tune. Check for codes and see what that tells you.

 

[AeroCoupe]

@Mstng93SSP, have you checked your air fuel ratio as I would think it would be lean. Only say this as the old 306 in my Coupe ran out of fuel with the 24’s so I dropped 42’s in and got it retuned and gained hp and torque across the curve. My current 331 is running off the same 42’s with a different tune as it was horribly lean on the 306 tune.

 

[Stantheman]

Have you checked your air fuel ratio as I would think it would be lean. Only say this as the old 306 in my Coupe ran out of fuel with the 24’s so I dropped 42’s in and got it retuned and gained hp and torque across the curve. My current 331 is running off the same 42’s with a different tune as it was horribly lean on the 306 tune.

Have you checked your air fuel ratio as I would think it would be lean. Only say this as the old 306 in my Coupe ran out of fuel with the 24’s so I dropped 42’s in and got it retuned and gained hp and torque across the curve. My current 331 is running off the same 42’s with a different tune as it was horribly lean on the 306 tune.

Also the maf sensor’s top is missing but all the electronics inside look fine

 

[AeroCoupe]

Sorry man that was directed at Mstng93SSP so I fixed that.

With regards to your MAF. Do you know if it is calibrated for the injectors that are in the car currently? Take a picture and post it if you can.