Engine Wot Woes, Please Help!

rhannigan

Active Member
Sep 13, 2016
36
37
28
Las Vegas
Hello All,

I'm the proud owner of a 1990 Mustang GT lightly modded. I purchased the car 2 months ago and have started the process of restoring and modding. Below is a list of what I have done so far.

Tune Up:
  • New Ford Perf 9mm spark plug wires
  • Accel TFI Supercoil
  • MSD distributor cap and rotor
  • Motorcraft spark plugs
  • SVE Cold Air Intake Kit

Mods:
  • Off Road X-pipe
  • 40 series Flowmasters to dumps
  • Eliminated smog pump be using shorter belt but it's still installed
  • Advanced the timing to 14 degrees TDC

The car idles smoothly and runs strong until WOT. If I ease into the pedal the car runs smoothly and strong into the upper rpm's. However, if I stomp on it, the car hesitates and loses power at around 3000 rpm's! I watch the rpm needle drop and climb, drop and climb!

I have tried to diagnose the problem and been on forums reading through threads. I have cleaned the MAF and IAC. I've changed the fuel filter. I've checked the TPS voltage. Nothing seems to help.

I'm calling on the experts! Please help. included some pics below, only thing not shown is the CAI.

IMG_4429.JPG
IMG_5026.JPG
IMG_5089.JPG
 
  • Sponsors (?)


I do not see a list of codes.

Sight unseen: Look at the ignition system (coil, wires, plugs (again), etc), and fuel pump and regulator.

For me: Your Ford wires are also suspect. Consider picking up a a set of Taylor wires. Until then, run that thing at night and look for spark jump.

Please pull and post all codes.
 
I do not see a list of codes.

Sight unseen: Look at the ignition system (coil, wires, plugs (again), etc), and fuel pump and regulator.

For me: Your Ford wires are also suspect. Consider picking up a a set of Taylor wires. Until then, run that thing at night and look for spark jump.

Please pull and post all codes.
Thank you for the quick reply! I'll pull codes and post. I'll also check for spark jump. If I see spark jump, what do I do to correct?
 
Thank you for the quick reply! I'll pull codes and post. I'll also check for spark jump. If I see spark jump, what do I do to correct?


Replace your brand new wires with a set of Taylor wires.

Over the last 20 or so years, I've gotten Ford wires that were bad out of the box. You can also just replace the ones you see jumping if you want to hold off on the expense.
 
Welcome and nice car.

my 2 cents.

Nothing wrong with Ford wires. They are made by MSD to Ford's specs. Years ago when they outsourced them to a Chinee vendor they had issues with QC but have since improved.. I've used them on many cars without a problem, and just installed another new set on my current car. I'd be more suspect of the Accel coil as Accel parts are sub par.

What did you gap your spark plugs at? .55 thousands is normal for a N/A motor
What heat range spark plugs did you use? 25 is stock
If you installed a fenderwell CAI, that can change the airflow to the stock MAF and cause issues. You may need to clock the MAF to adjust for the air turbulence. I would put the stock CAI airboc back on and install a k&N filter as aftermarket CAI's offer minimal if any HP improvement. They are for looks. I would remove the stock air silencer.

As others have recommended run the codes as well.
 
Mikestang63 thanks for the info. I used motorcraft copper spark plugs. As for the gap, I'll recheck tomorrow. The car was doing this before the CAI install. What coil do you recommend?

I checked for visible spark jumping and saw none. I'll pull codes this weekend and post them.


Sent from my iPhone using Tapatalk
 
Once again driving home today the car ran well as always. If I press the pedal steadily, I can climb to redline. However if I stomp on it, the hesitation/misfire starts and the Rpm's drop and climb continuously.


Sent from my iPhone using Tapatalk
 
Mikestang63 thanks for the info. I used motorcraft copper spark plugs. As for the gap, I'll recheck tomorrow. The car was doing this before the CAI install. What coil do you recommend?

I checked for visible spark jumping and saw none. I'll pull codes this weekend and post them.


Sent from my iPhone using Tapatalk

stock coil works fine up to 400+ hp. Check to make sure all your wires are on solid on the plugs and cap ( you should feel the wires snap or grab on and resist if you try and pull them off) , theplug gap is correct amd the plugs are not loose in the cylinders. You dont need to go crazy on them. Snug them up and then maybe a 1/4 turn. If . Did you put a dab of dielectric grease in each end of the wires? that helps conductivity. Run the codes as your problem appears elsewhere. Could be a lot of things.
 
There isn't anything it the codes that would cause a problem; 11 is system OK code, 10 is a spacer code, and 8 is how many cylinders the computer is built for.

The 44/94 codes are due to no smog pump, and since you have an off road H pipe, they can be ignored.


Does the problem only occur at high RPM and on a warm engine?
 
Last edited:
There isn't anything it the codes that would cause a problem; 11 is system OK code, 10 is a spacer code, and 8 is how many cylinders the computer is built for.

The 44/94 codes are due to no smog pump, and since you have an off road H pipe, they can be ignored.


Does the problem only occur at high RPM and on a warm engine?

Something interesting to report, I live in Las Vegas, the ambient temperature since I've bought the car has been 103+ . For the last two days we have had a dramatic drop in temperature. The ambient temp during the day is 90-95 and the evening is 75-85.

Last night I took the car for a drive and noticed a dramatic drop in the number of misfires at WOT!

I got home and pulled the plugs, checked the gaps and used dielectric grease when reinstalling the plug wires.

Took out for again and had only one small misfire (pop) at WOT on my way to redline.

What is your opinion on why the misfires dropped with ambient temps?


On another note, as I was reinstalling spark plug 4, I accidentally broke the vacuum line that runs from the tree to the EGR valve. I had some vacuum line caps that I put on the EGR valve and on the 2-inch piece left of the broken line from the tree.

Will this pose any issue? I was considering an EGR delete. The car still runs good after the break.
 
The TFI module or PIP sensor inside the distributor are the 2 prime suspects in these type of temperature related problems.

The TFI module mounted on the distributor is one of the culprits for a high speed miss on a warm engine. If the problem does not occur when the engine is cold, the TFI module is definitely suspect. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

396_large.jpg


See Automotive Tools Specialty | Auto Mechanic & Technician Diagnostic, Testing Equipment | Thexton
TFIModuletroubleshooting.jpg


diagram courtesy of Tmoss & Stang&2Birds
TFI_5.0_comparison.gif




Removing the pollution control equipment from a 5.0 Mustang is a bad idea. All you have accomplished is to make the computer mad and spit codes. The pollution control equipment all shuts off at wide open throttle, so the HP losses from it on the car are 2-5 HP. The catalytic converters may soak a few more HP than that. None of the pollution control equipment reduces the HP enough to cost you a race in anything but professional drag strip competition. I seriously doubt that you will be in the final runoff on “Pinks”, so leave the smog equipment in place and make sure it is working correctly.

Know what does what before removing it. Remove or disable the wrong thing and the computer sets the check engine light and runs in "limp mode". Limp mode means reduced power and fuel economy.

If you removed the smog pump and still have catalytic converters, they will ultimately clog and fail.

Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by James Probst :ISBN 0-8376-0301-3.

It's about $20-$45 from Borders.com see http://www.amazon.com/ . Select books and then select search. Use the ISBN number (without dashes or spaces) to do a search

Use the ISBN number and your local library can get you a loaner copy for free. Only thing is you are limited to keeping the book for two weeks. It is very good, and I found it to be very helpful.

Remove any of the equipment and you will not pass a full smog check, cannot title the car in an area that does smog checks and have broken several federal laws. Granted that the Feds are short on people to check cars, but it is still Federal law.

"Why should I leave the smog equipment on if I live in an area that doesn't do smog inspections?"
What's good sauce for the goose is good sauce for the gander. I lived in Florida and had two smog pumps fail on two different 89 5.0 Mustangs. I replaced both of them, even though there was no emissions inspection. Why?

1.) It a federal law that requires emissions equipment to be in place and functional. I have no intention of breaking a law designed to protect my general health and wellbeing, even if I don't like it. I have respect for the rights and wellbeing of other people, and am not one of those whose nature is rebellion.

2.) Whatever imaginary "improvements" someone may strive for, there is very little evidence that the results of removing emissions results in a better car. I can achieve excellent results in performance with all the smog equipment in place and working properly. Maybe you can't, but that is no excuse for removing the emissions equipment. Look at the new 5.0 Mustangs – 281 cubic inches and 400+ flywheel HP with full emissions equipment with no aftermarket parts. That tells me that it is possible on a mass production car. It also shows that the guys that designed the engine knew what they were doing to achieve that goal.

3.) I like to breathe clean air, and working emissions equipment helps me do my part to make that possible. Los Angeles has breathable air even with millions of cars: Beijing, the capitol of China has some of the worst air in the world. Why – no emissions requirements for cars.

I don’t want to live where the air looks like this…
360_chinapollution_0304.jpg

See http://www.taipeitimes.com/News/feat/archives/2014/01/15/2003581312
 
The TFI module or PIP sensor inside the distributor are the 2 prime suspects in these type of temperature related problems.

The TFI module mounted on the distributor is one of the culprits for a high speed miss on a warm engine. If the problem does not occur when the engine is cold, the TFI module is definitely suspect. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

396_large.jpg


See Automotive Tools Specialty | Auto Mechanic & Technician Diagnostic, Testing Equipment | Thexton
TFIModuletroubleshooting.jpg


diagram courtesy of Tmoss & Stang&2Birds
TFI_5.0_comparison.gif




Removing the pollution control equipment from a 5.0 Mustang is a bad idea. All you have accomplished is to make the computer mad and spit codes. The pollution control equipment all shuts off at wide open throttle, so the HP losses from it on the car are 2-5 HP. The catalytic converters may soak a few more HP than that. None of the pollution control equipment reduces the HP enough to cost you a race in anything but professional drag strip competition. I seriously doubt that you will be in the final runoff on “Pinks”, so leave the smog equipment in place and make sure it is working correctly.

Know what does what before removing it. Remove or disable the wrong thing and the computer sets the check engine light and runs in "limp mode". Limp mode means reduced power and fuel economy.

If you removed the smog pump and still have catalytic converters, they will ultimately clog and fail.

Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by James Probst :ISBN 0-8376-0301-3.

It's about $20-$45 from Borders.com see http://www.amazon.com/ . Select books and then select search. Use the ISBN number (without dashes or spaces) to do a search

Use the ISBN number and your local library can get you a loaner copy for free. Only thing is you are limited to keeping the book for two weeks. It is very good, and I found it to be very helpful.

Remove any of the equipment and you will not pass a full smog check, cannot title the car in an area that does smog checks and have broken several federal laws. Granted that the Feds are short on people to check cars, but it is still Federal law.

"Why should I leave the smog equipment on if I live in an area that doesn't do smog inspections?"
What's good sauce for the goose is good sauce for the gander. I lived in Florida and had two smog pumps fail on two different 89 5.0 Mustangs. I replaced both of them, even though there was no emissions inspection. Why?

1.) It a federal law that requires emissions equipment to be in place and functional. I have no intention of breaking a law designed to protect my general health and wellbeing, even if I don't like it. I have respect for the rights and wellbeing of other people, and am not one of those whose nature is rebellion.

2.) Whatever imaginary "improvements" someone may strive for, there is very little evidence that the results of removing emissions results in a better car. I can achieve excellent results in performance with all the smog equipment in place and working properly. Maybe you can't, but that is no excuse for removing the emissions equipment. Look at the new 5.0 Mustangs – 281 cubic inches and 400+ flywheel HP with full emissions equipment with no aftermarket parts. That tells me that it is possible on a mass production car. It also shows that the guys that designed the engine knew what they were doing to achieve that goal.

3.) I like to breathe clean air, and working emissions equipment helps me do my part to make that possible. Los Angeles has breathable air even with millions of cars: Beijing, the capitol of China has some of the worst air in the world. Why – no emissions requirements for cars.

I don’t want to live where the air looks like this…
360_chinapollution_0304.jpg

See http://www.taipeitimes.com/News/feat/archives/2014/01/15/2003581312


Is there a TFI Module you recommend?