Stalling Issue

Sep 14, 2015
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#1
Hey guys, my 88 gt has been doing a ton of weird stuff lately. Its been inconsistenly surging for a while but it never inhibited me from driving the car but recently it started this new thing where every now and then after its been running for a while it will stall compeltely after seeming to bog down. The idle will drop to about 500 and the thing will struggle to run and soon die. Also giving it gas kills it immediately and the problem will persist after restarting it as well. I found the car has to be off for around 10 minutes before able to start and drive again. Its an intermittent thing but now its starting to happen to me everyday. I brought my car to a shop and they said they could only recreate the problem once which is strange to me because it happens to me so frequently. They also said it seems as if it starts running out of fuel but were unable to test. They’re isn’t any codes out of the ordinary either. I thought maybe hot tfi module but I relocated my tfi to the fender a while back so it shouldnt be failing. Any input on where I should begin to start testing would be greatly appreciated.
 
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jrichker

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#2
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.
 
Sep 14, 2015
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#3
Im aware of the surging idle checklist, but I’m not chasing a surge I’m trying to figure out why my car stops running after a while and refuses to restart. I’ve gone through that surging idle checklist many times and I keep comming up empty handed
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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#5
The checklist covers pretty much everything your describing, go back through it and don't skip around, I had to read it over once before I could do the list, I will say that my guess would be fuel delivery problem and testing for that is covered in there.
I would have little faith in a shop that could not check fuel pressure unless you have non stock fuel lines. You don't say if your car has any modifications.
 

Blown88GT

Founding Member
Nov 13, 1999
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Palm Beach Gardens, FL
#6
Hey guys, my 88 gt has been doing a ton of weird stuff lately. Its been inconsistenly surging for a while but it never inhibited me from driving the car but recently it started this new thing where every now and then after its been running for a while it will stall compeltely after seeming to bog down. The idle will drop to about 500 and the thing will struggle to run and soon die. Also giving it gas kills it immediately and the problem will persist after restarting it as well. I found the car has to be off for around 10 minutes before able to start and drive again. Its an intermittent thing but now its starting to happen to me everyday. I brought my car to a shop and they said they could only recreate the problem once which is strange to me because it happens to me so frequently. They also said it seems as if it starts running out of fuel but were unable to test. They’re isn’t any codes out of the ordinary either. I thought maybe hot tfi module but I relocated my tfi to the fender a while back so it shouldnt be failing. Any input on where I should begin to start testing would be greatly appreciated.
All the symptoms of a bad fuel pump, especially this: "giving it gas kills it immediately"
 
Sep 14, 2015
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#7
The checklist covers pretty much everything your describing, go back through it and don't skip around, I had to read it over once before I could do the list, I will say that my guess would be fuel delivery problem and testing for that is covered in there.
I would have little faith in a shop that could not check fuel pressure unless you have non stock fuel lines. You don't say if your car has any modifications.
The shop tried to test the fuel pressure but the problem went away before they had the chance to, once they checked it fuel pressure was fine and then they said they couldn't get it to do it again. I will go over the checklist again and double check everything related fuel issues and get back to you. Also, the car is not stock its a built 306 and the fuel pumpis a walboro 190. However this fuel pump did come with the car and I've owned it for 4 years so I have no idea how old ithe thing is so you may be on to something. Thanks for the input.
 
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General karthief

wonder how much it would cost to ship you a pair
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Aug 25, 2016
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#9
Yes, well not intermittent, just low fuel pressure or fuel pressure regulator causes fluctuations, just check the fuel system and run the tests
 
Sep 14, 2015
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#10
Tomorrow I will rent a fuel pressure tester and do some more investigating but I would like to mention this, I found that my o2 sensor harness had been rubbing up against the header and burned at least one of the wires down to the conductor. Could this cause an issue like this? Like maybe the car only runs decent in open loop then once it hits closed loop it gets thrown for a curve becuase the o2 isnt functioning correctly? Just spitballing, thanks for the input.
 

jrichker

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#11
The O2 sensor is critical to closed loop engine performance. Replace it with the same transmission specific harness that is already in the car.

O2 Sensor harness interchange and modification

Originally Posted by 302EFI

Revised 16-Oct-2011 to add O2 sensor harness warnings
The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU


Fox 5.0 O2 sensor drawing.jpg

Not all wires are shown for clarity and simplicity

See http://forums.corral.net/forums/gen...manual-auto-differences-year-differences.html for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.




Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.



Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.
 
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jrichker

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#13
Could a fuel pump issue be this intermittent?
Loss of power to the fuel pump generally sets codes 95 or 96. If you didn't find them in the code dump, look elsewhere for your problem.

The O2 harness you mentioned is the prime suspect in this case ; either replace it or repair it. Keep in mind that the O2 sensor harness is transmission specific.
 
Sep 14, 2015
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#14
But if the harness failed and causes the o2 to send bunk readings wouldnt the ecu just set it back to open loop and keep the car driveable? Just curious, I honestly have no clue.
 
Sep 14, 2015
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#15
Also I would like to note I have an sct chip in this thing and I feel like it prevents the check engine from illuninating sometimes. i just unplugged my 02 harness completely and the car didnt run any different nor did the check engine come on
 
Sep 14, 2015
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#16
Okay, Just tested fuel pressure. It tested normal at 40lbs when the car was running properly then just like clock work after a few minutes of running the problem occurred. Tested the pressure again and it was at 45. So that would point to the o2 sensor harness am I wrong? Like once the car is in closed loop the computer tells the injectors to starve the motor because of the bunk readings causing the fuel pressure to spike. Am I heading in the right direction or am I talking crazy?
 

jrichker

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#17
Okay, Just tested fuel pressure. It tested normal at 40lbs when the car was running properly then just like clock work after a few minutes of running the problem occurred. Tested the pressure again and it was at 45. So that would point to the o2 sensor harness am I wrong? Like once the car is in closed loop the computer tells the injectors to starve the motor because of the bunk readings causing the fuel pressure to spike. Am I heading in the right direction or am I talking crazy?
It really doesn'tmatter what you think, fix the O2 sensor harness; it is a must do item.

If there are still problems after that, we can regroup and consider other possibilities
 
Sep 14, 2015
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#18
It really doesn'tmatter what you think, fix the O2 sensor harness; it is a must do item.

If there are still problems after that, we can regroup and consider other possibilities
Okay, I'll contact you once I replace the harness.
 
Sep 14, 2015
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#19
Okay, harness has been replaced with a brand new one and the problem persists. If you unplug the o2 sensor harness the car will be able to run just fine just with a very high idle. Does that mean it has to be the o2 sensors?
 

jrichker

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#20
Okay, harness has been replaced with a brand new one and the problem persists. If you unplug the o2 sensor harness the car will be able to run just fine just with a very high idle. Does that mean it has to be the o2 sensors?
There are 2 different flavors of O2 sensor harnesses: 5 speed transmission.and automatic transmission. The O2 sensor harness MUST match the transmission type that is in the car.
 

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