Bad miss at WOT, Need Help!!!!!

kilby91 · January 18th, 2008, 12:45 AM

I have been tracking this problem down for a long time on this car and have yet to fix it. When the car is cold and i go for a cruise everything seems to be good and it climbs to redline. But once it heats up it will not climb past 5,000 under a load. And also while it is hot in neutral it will rev to 6,000 at part throttle, but at full throttle it starts to miss around 5000 and will not climb any higher. I have replaced every sensor, new fuel pump and filter, adjustable regulator, new distributor, new coil, new valve springs, and just about every other part that i thought would fix it. It sucks having to shift at 5,000 rpm when my combo should produce alot more. I am starting to wonder if it isn't a computer problem????

e3sean · January 18th, 2008, 01:08 AM

i am not sure what it is.. raise your fuel pressure a lil??

TheUNZippee! · January 18th, 2008, 01:08 AM

Welcome to the forums. A detailed list of your mods would help.

Speedstang302 · January 18th, 2008, 01:11 AM

^^^ dont listen to him he just wants to see you naked...

btw welcome...

TheUNZippee! · January 18th, 2008, 01:11 AM

Speedstang302 · January 18th, 2008, 01:26 AM

Originally Posted by TheUNZippee!

kilby91 · January 18th, 2008, 01:47 AM

It is a 91 gt 5 speed with Typhoon upper and lower intake, 70 mm TB and EGR, 351 heads (D0OE), E-303 cam with new trick flow valve springs, MSD wires and coil, new distributor/cap/rotor, 190 lph fuel pump, BBK adj. regulator (pressure @ 46psi), new ignition module, and a couple of others. Also the spark plugs have about 1,000 miles on them and they look like they just came out of the box, no color at all! I just put the regulator on today hoping i could crank up the pressure and fix it, but just like every other time i think i am about to have it fixed the problem returns!!! When it is cold it runs alot better and will rev to the rev limiter in neutral, but once it gets hot even in neutral it will not rev past 5,000??

problemCOBRA94 · January 18th, 2008, 01:52 AM

check the tps? just an idea

problemCOBRA94 · January 18th, 2008, 01:57 AM

upon cold start up the computer doesn't use the tps to determine fuel air ratio. It creates a rich/lean condition on purpose to keep the motor running while it is still cold. After it heats up it starts reading from temp sensors, IAC, TPS, MAF, etc. to determine air fuel mixture. This explains why that would cause it function properly at start up but not when warm. Thats what I would put my money on.

kilby91 · January 18th, 2008, 02:13 AM

TPS voltage is set to .98v at idle and 4.60v at WOT.

nolife · January 18th, 2008, 11:02 AM

I'm sure there are many things that can cause this but I went through something similar in the past and swapped out just about everything you mentioned, mine was a little more random and I don't think it was heat related. I changed the plugs wires and rerouted them so they would not cross over each other and I have not had the problem since. The wires I had that seemed to causing the problem were new Accels. I swapped them with my older cheap 8mm Bosch gray ones that were in my other stang. I don't know if the wires were the solution but the problem has not returned and the Accell wires work fine in the other stang.

I think your problem is spark related and not fuel. The TFI module could be bad as well.

kilby91 · January 18th, 2008, 02:02 PM

Yeah i am starting to think it is spark related also, because i have replaced all fuel parts that i can and problem is still there. I actually have a new TFI along with a new distributor that i put on the car and didn't really make a difference. I have the 8.5 mm msd super conductor wires, could they be arcing to each other? Also why would the spark plug not even look like it has ever been used? If is was loosing spark wouldn't the plug be soaked in gas?

mustangboy8909 · January 19th, 2008, 12:02 AM

i had this porblem on my car also i thought that maybe it was not making enough vacum at wot that was why, but in fact the problem was that the connector to my distributor was corroded so when it had to emit more sparks faster it would miss went to the local parts dealer got a new plug in for it and runs fine now

kilby91 · January 19th, 2008, 07:46 PM

Was your problem the same as mine and only did it when it got warmed up? Could you look at your harness and tell that it looked corroded?

January 18th, 2008, 12:45 AM	#1
kilby91 Regular 1991 Mustang GT Join Date: Dec 2007 Location: Jackson, MS Posts: 130	Bad miss at WOT, Need Help!!!!! I have been tracking this problem down for a long time on this car and have yet to fix it. When the car is cold and i go for a cruise everything seems to be good and it climbs to redline. But once it heats up it will not climb past 5,000 under a load. And also while it is hot in neutral it will rev to 6,000 at part throttle, but at full throttle it starts to miss around 5000 and will not climb any higher. I have replaced every sensor, new fuel pump and filter, adjustable regulator, new distributor, new coil, new valve springs, and just about every other part that i thought would fix it. It sucks having to shift at 5,000 rpm when my combo should produce alot more. I am starting to wonder if it isn't a computer problem????

January 18th, 2008, 01:11 AM	#4
Speedstang302 MM Fanatic 1989 Mustang 5.0 dunno yet Join Date: Apr 2007 Location: Massachusetss Posts: 4,755	^^^ dont listen to him he just wants to see you naked... btw welcome... __________________ new project..89 5.0 full restoration beginning..

January 18th, 2008, 11:02 AM	#11
nolife Hardcore Enthusiast 91GT, 88GT, 02GT Join Date: Dec 2006 Posts: 1,723	I'm sure there are many things that can cause this but I went through something similar in the past and swapped out just about everything you mentioned, mine was a little more random and I don't think it was heat related. I changed the plugs wires and rerouted them so they would not cross over each other and I have not had the problem since. The wires I had that seemed to causing the problem were new Accels. I swapped them with my older cheap 8mm Bosch gray ones that were in my other stang. I don't know if the wires were the solution but the problem has not returned and the Accell wires work fine in the other stang. I think your problem is spark related and not fuel. The TFI module could be bad as well. __________________ Looking for a decent 90-92 Titanium hatch pull cover and retaining clips Last edited by nolife : January 18th, 2008 at 11:04 AM.

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January 18th, 2008, 01:08 AM	#2
e3sean MM Fanatic 1988 lx 5.7 10.53@127 125shot Join Date: Nov 2007 Location: arizona Posts: 4,634	i am not sure what it is.. raise your fuel pressure a lil??

January 18th, 2008, 01:47 AM	#7
kilby91 Regular 1991 Mustang GT Join Date: Dec 2007 Location: Jackson, MS Posts: 130	It is a 91 gt 5 speed with Typhoon upper and lower intake, 70 mm TB and EGR, 351 heads (D0OE), E-303 cam with new trick flow valve springs, MSD wires and coil, new distributor/cap/rotor, 190 lph fuel pump, BBK adj. regulator (pressure @ 46psi), new ignition module, and a couple of others. Also the spark plugs have about 1,000 miles on them and they look like they just came out of the box, no color at all! I just put the regulator on today hoping i could crank up the pressure and fix it, but just like every other time i think i am about to have it fixed the problem returns!!! When it is cold it runs alot better and will rev to the rev limiter in neutral, but once it gets hot even in neutral it will not rev past 5,000??

January 18th, 2008, 01:52 AM	#8
problemCOBRA94 Regular 1994 Mustang Cobra it runs now. Kinda... Join Date: Mar 2007 Location: Rocklin, ca Posts: 72	check the tps? just an idea

January 18th, 2008, 01:57 AM	#9
problemCOBRA94 Regular 1994 Mustang Cobra it runs now. Kinda... Join Date: Mar 2007 Location: Rocklin, ca Posts: 72	upon cold start up the computer doesn't use the tps to determine fuel air ratio. It creates a rich/lean condition on purpose to keep the motor running while it is still cold. After it heats up it starts reading from temp sensors, IAC, TPS, MAF, etc. to determine air fuel mixture. This explains why that would cause it function properly at start up but not when warm. Thats what I would put my money on.

January 18th, 2008, 02:13 AM	#10
kilby91 Regular 1991 Mustang GT Join Date: Dec 2007 Location: Jackson, MS Posts: 130	TPS voltage is set to .98v at idle and 4.60v at WOT.

January 18th, 2008, 02:02 PM	#12
kilby91 Regular 1991 Mustang GT Join Date: Dec 2007 Location: Jackson, MS Posts: 130	Yeah i am starting to think it is spark related also, because i have replaced all fuel parts that i can and problem is still there. I actually have a new TFI along with a new distributor that i put on the car and didn't really make a difference. I have the 8.5 mm msd super conductor wires, could they be arcing to each other? Also why would the spark plug not even look like it has ever been used? If is was loosing spark wouldn't the plug be soaked in gas?

January 19th, 2008, 12:02 AM	#13
mustangboy8909 Regular Join Date: Feb 2007 Posts: 107	i had this porblem on my car also i thought that maybe it was not making enough vacum at wot that was why, but in fact the problem was that the connector to my distributor was corroded so when it had to emit more sparks faster it would miss went to the local parts dealer got a new plug in for it and runs fine now

January 19th, 2008, 07:46 PM	#14
kilby91 Regular 1991 Mustang GT Join Date: Dec 2007 Location: Jackson, MS Posts: 130	Was your problem the same as mine and only did it when it got warmed up? Could you look at your harness and tell that it looked corroded?

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