Engine Foxbody powered F100 issues...

randyr

Member
Jul 16, 2010
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Hey Fellas, technically my vehicle isn't a Mustang but most of what's under the hood is so I hope you don't mind me seeking your help. Seven years ago installed a 92 5.0HO/AOD into my 1966 Ford F100 using the Ford Racing plug n play harness. The engine, trans, computer, etc all came from the same donor 1992 GT convertible. The only mods I've made are Explorer intake/ 65mm throttlebody, 70mm MAF, JBA shorty headers. This truck is my daily and was running perfectly until a few days ago. I drove to a meeting fine. After the meeting it started running really rough, sporatic idle, etc. Thought it might be running out of gas but filled it up and no change. Installed new few filter, no change. Cleaned MAF, EGR IAC, replaced TPS, tried a new distributor and even a different A9P ecu but the problem continues. I continue to go thru your Surge Checklist but nothing I've tried changes the outcome.
The computer is throwing no codes beyond the soft codes that are expected with the Ford Racing harness. The EGR is still in tact and working but there is no smog pump, etc, thus codes 81, 82 & 85 are expected. Code 67 is also present but there is a button to push on the module that bypasses that code for KOER test.
Anyway, I could sure use some help if you have any ideas what my problem is. The truck starts, runs smooth at 1000 rpms for a few seconds then begins to fluctuate up to 1200 or so then down to 200 back & forth, then dies. It won't stay running when put in gear.
Any thoughts??? Thanks!!!
 
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randyr

Member
Jul 16, 2010
29
6
13
You have checked for vacuum leaks right?
is your alternator charging?
Yes, I removed the upper plenum and found the screw-in vacuum tree was a little loose and one of the small hoses had a slight crack. I installed a new gasket on the plenum, plus new gaskets on the throttle body and still no change in the trucks symptoms. The alternator is charging fine.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Charging fine and charging correctly, we need technical info. Minimum 13.5 at all times, more at higher rpms.
fuel pressure? Remember technical info, pressure at idle and at a steady rpm around 1500 or so for a minute or so. Look for fluctuation in pressure. 34 psi at idle and 42 psi with vacuum line disconnected. (Close 2-4 lbs difference ok)
If that checks out, look at ignition components, wires, cap and rotor. Be methodical, test don't just replace stuff. Test, like pulling spark plug wires one at a time, while engine is running poor and up to temp.
I'm unfamiliar with the aftermarket harness you have but efi stuff requires good grounds so check them.
How long has this combo been together?
This is what I would do if I had similar problem.
 

randyr

Member
Jul 16, 2010
29
6
13
Charging fine and charging correctly, we need technical info. Minimum 13.5 at all times, more at higher rpms.
fuel pressure? Remember technical info, pressure at idle and at a steady rpm around 1500 or so for a minute or so. Look for fluctuation in pressure. 34 psi at idle and 42 psi with vacuum line disconnected. (Close 2-4 lbs difference ok)
If that checks out, look at ignition components, wires, cap and rotor. Be methodical, test don't just replace stuff. Test, like pulling spark plug wires one at a time, while engine is running poor and up to temp.
I'm unfamiliar with the aftermarket harness you have but efi stuff requires good grounds so check them.
How long has this combo been together?
This is what I would do if I had similar problem.
Hey, thanks so much for the additional response! This setup has been up and running perfectly for 7yrs with routine maintenance. The alternator is charging at 14.2 at idle. I have cleaned and checked the cap, rotor but have not pulled each wire off individually. I did try a brand new distributor and it changed nothing so I put my old one back in. The fuel pressure is at 35psi with the key on. I need to check it with the vacuum disconnected while idling and check for fluctuations at higher rpms. As for the aftermarket harness, Ford Racing designed it to function quite like the factory except without the smog pump connections and evap. The EGR, O2 sensors, IAC, TPS etc is all still in tact. Thanks again for your thoughts! It's just kinda freaky because it was running great and then on the next startup it went to crap! No warning, no clues! Argh! LOL!
 

jrichker

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Hey Fellas, technically my vehicle isn't a Mustang but most of what's under the hood is so I hope you don't mind me seeking your help. Seven years ago installed a 92 5.0HO/AOD into my 1966 Ford F100 using the Ford Racing plug n play harness. The engine, trans, computer, etc all came from the same donor 1992 GT convertible. The only mods I've made are Explorer intake/ 65mm throttlebody, 70mm MAF, JBA shorty headers. This truck is my daily and was running perfectly until a few days ago. I drove to a meeting fine. After the meeting it started running really rough, sporatic idle, etc. Thought it might be running out of gas but filled it up and no change. Installed new few filter, no change. Cleaned MAF, EGR IAC, replaced TPS, tried a new distributor and even a different A9P ecu but the problem continues. I continue to go thru your Surge Checklist but nothing I've tried changes the outcome.
The computer is throwing no codes beyond the soft codes that are expected with the Ford Racing harness. The EGR is still in tact and working but there is no smog pump, etc, thus codes 81, 82 & 85 are expected. Code 67 is also present but there is a button to push on the module that bypasses that code for KOER test.
Anyway, I could sure use some help if you have any ideas what my problem is. The truck starts, runs smooth at 1000 rpms for a few seconds then begins to fluctuate up to 1200 or so then down to 200 back & forth, then dies. It won't stay running when put in gear.
Any thoughts??? Thanks!!!
You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 

randyr

Member
Jul 16, 2010
29
6
13
You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
Yes, I have been using your Surging Idle Checklist and it's awesome. Perhaps I have missed a couple of things on it but so far, I have not found my problem. For clarification of terminology, please define "dumping the codes". By that, do you mean "retrieve the codes" from the computer or "erase the codes" so you get a fresh batch of codes? Perhaps, it's semantics, but either way, I get the same codes every time, which are all related to the smog pump which doesn't exist on my engine. The only codes I "dump" or "retrieve" from the computer are 67,81.82.85. My harness module has a "push to test" button to work around code 67 for the KOER test. I will go through your checklist again and see what I missed. Again, thanks so much for providing the checklist!!! It's a great resource!!!
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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I believe 'dump the codes' means to retrieve the codes from the computer.
have you done a 'computer reset' ? That is when you disconnect the battery for thirty minutes or so to erase codes and allows the computer to start fresh with no operational parameters. Then you drive it around, bring the engine up to operating temp and put some miles in a variety of speeds giving the computer 'fresh info' to work with.
i am leaning towards a bad connection someplace.
you do not have a msd (or something similar) box on it right?
 

randyr

Member
Jul 16, 2010
29
6
13
I believe 'dump the codes' means to retrieve the codes from the computer.
have you done a 'computer reset' ? That is when you disconnect the battery for thirty minutes or so to erase codes and allows the computer to start fresh with no operational parameters. Then you drive it around, bring the engine up to operating temp and put some miles in a variety of speeds giving the computer 'fresh info' to work with.
i am leaning towards a bad connection someplace.
you do not have a msd (or something similar) box on it right?
Yes, I did a computer reset again today. I don't think it will run well enough to go for a drive but may give it a try when traffic dies down. I did start it after the reset and after a few seconds it started the rough idle again. It would periodically smooth out for a few seconds then back to rough. I do not have an msd box or the like on it. It's the stock Mustang setup with TFI module, etc. I wonder if it would be beneficial to spray some electrical contact cleaner in each of the connections as I check them?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Contact cleaner is good idea, also make sure the pins are not pushing out when you push the connectors together and they are tight.
have you looked for fuel pressure fluctuations?
 

randyr

Member
Jul 16, 2010
29
6
13
Ok, so I was messing with the truck today. When first started it, it acts like it wants to run for about 5 secs then starts to surge and sputter as usual since the start of this thread. I still have the fuel pressure gauge attached to the stader valve so this time I noticed when it started to smooth out the fuel pressure is around 35psi but as soon as it starts to bog down the fuel pressure bumps up to 40psi. Shortly thereafter the truck died and now it won't start at all. It cranks but won't go ahead and fire up....with the key on, the fuel pressure holds at 35psi.
 

Gs87GT

Active Member
Sep 25, 2019
81
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Penn's Woods
How old is the battery? If older pull it and have it load tested. I wonder if your fuel pump or regulator is going bad?

When it was running poorly did it smell rich? Or normal?

If it won't run now that's probably good luck for because the issue has finally fully failed and you should be able to diagnose it now.

Go back to your basics. Spark, fuel, compression, timing. Pull your plugs and read them. That may give you a direction to go. Good luck
 

randyr

Member
Jul 16, 2010
29
6
13
So my trouble-shooting time has been hit or miss for the last few days but here's what I have..
-I have fuel pressure
- I have power to the injectors,
-the coil has fire
-the pip sensor and tfi module are working
-new throttle position sensor set at .82
-I soldered new capacitors in the ecu (there were signs of corrosion)
-cleaned MAF

I still have a no start condition....I'm now officially clueless as to the problem...
 

randyr

Member
Jul 16, 2010
29
6
13
Lets recap.
does it start with starting fluid
what is your fuel pressure (not 'fuel squirts out the schrader valve)
Spark?
No it doesn't start with starting fluid. Fuel pressure is 34psi and 42psi with vacuum line off the regulator. Yes, I have spark at coil, distr and injectors, tested with noid light
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
14,156
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193
polk county florida
Ok, I went back over the thread because I was confused, what started as a ruff running, surging idle problem has turned into a 'no start' condition, not uncommon and the confusion is not your fault.
you do not have a msd box on this?
the no start with starting fluid says no spark. You have spark at the coil but not at the plugs.
Paragraph 5a, pull the spout, see if it starts.
Even though you have confirmed several things on this list as good, I would start at the beginning and check it step by step, read it over to get familiar and gather the proper stuff to test with and keep notes.
 

randyr

Member
Jul 16, 2010
29
6
13
Ok, I went back over the thread because I was confused, what started as a ruff running, surging idle problem has turned into a 'no start' condition, not uncommon and the confusion is not your fault.
you do not have a msd box on this?
the no start with starting fluid says no spark. You have spark at the coil but not at the plugs.
Paragraph 5a, pull the spout, see if it starts.
Even though you have confirmed several things on this list as good, I would start at the beginning and check it step by step, read it over to get familiar and gather the proper stuff to test with and keep notes.
Thanks for the response...I do not have the msd box on this. I will the check the spark to the plugs again but 2 days ago it started and ran roughly for about 5 secs then returning to the no-start condition. I have also pulled the spout several times over the last few days and it has never started that way. I will review the checklist again and see if I've missed something. Thanks again!