Resolved 1989 Mustang bogs down after 3-5 minutes of driving.

Alabama · Feb 11, 2025

I've been at this for a bit. While driving, the initial time i take off and go through the gears, I have no issues. After coming to a stop, accelerating and then when accelerating through third, fourth and fifth, between 2500-3000 RPM's my car does not accelerate and tries to die. Here is what I have done so far since owning the car (I am ok with the parts so far as I am trying to restore the car). I have replaced the fuel tank, fuel sending unit, fuel pump with CJ Pony's kit at 225 lph, fuel filter (pre tank change so may be an issue), new distributor cap, distributor rotor, new plug wires, coil pack, fuel pressure regulator, TPS sensor, 02 sensors (had EEC codes for these), IAC control motor, coolant temp sensor (came with kit). I don't have a smog pump nor an EGR, there is a delete kit on. When I replaced my tank, I didn't order the sound deadening material so I can hear my fuel pump in my car when operating. While driving, and I get into the above condition, it sounds like my pump is muffled or struggling/binding as the frequency of the pump changes. I put a fuel pressure tester on the fuel rail, during initial start I get 35 psi at idle, increases as I "gun" the engine then drops to 35 psi. After driving and I get into the above condition, the fuel pressure drops to approx 10 psi and remains. Once this is observed, I can turn the car off for about 5 seconds, restart the car and it'll run normally for another trip through the gears until I come to another stop. Kind of like there is something in the fuel tank that eventually gets sucked up to the fuel pump inlet, but is very repeatable which is why I don't suspect something floating in the tank. Current KOER codes are as follows: 21R, 94R, 44R, 33R, 13R and 8. Any help would be greatly appreciated. Thanks in advance.

General karthief · Feb 11, 2025

Change the fuel filter again, then see if it clears up.
Important notes:
Just because it's a 'new' part does not equal 'working' part. Many sensors today are defective right outta da box.
There is a diagnostic procedure to test each one. Go here and fallow directions.

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

Welcome to

gkomo · Feb 11, 2025

Dumb question maybe but are you sure the fuel filter was installed in the correct flow direction?

AeroCoupe · Feb 11, 2025

First thing I am going to ask is did you perform the KOER test with the engine up to operating temperature?

C = Continuous memory code
O = Key on engine off (KOEO) code
R = Key on engine running (KOER) code

Code 8 - If you got this at the end of the KOER test then it is telling you it doesn't like something with Cylinder #8. See post #5 in the linked thread below.
Code 13 - RPM Not Within Self-Test Upper Limit [R], Idle Speed Control motor or Air Bypass Not Controlling Idle Properly - Generally Idle too High
Code 21 - Engine Coolant Temperature [ECT] Sensor Out Of Self-Test Range. 0.3 to 3.7 volts [O,R] (this could be due to the engine not being up to operating temperature)
Code 33 - EGR Valve Opening Not Detected [CM,R] (most likely due to the EGR delete so you can ignore)
Code 44 - Secondary Air System Inoperative. Bank One, Passenger Side [R] (most likely due to the EGR delete so you can ignore)
Code 94 - Secondary Air Injection Inoperative. Bank Two, Driver Side [R], Torque Converter Clutch Solenoid Circuit Failure [O] (most likely due to the EGR delete so you can ignore)

J

Thread 'Cylinder Balance Test'

Apr 9, 2007

How do you do a cylinder balance test? Please be specific on what to do as I am totally clueless on how to do this!

My guess with regards to the fuel pressure falling off is a weak fuel pump. You should be getting 39 psi +/- 2 psi at WOT or at idle with the vacuum disconnected from the fuel pressure regulator (FPR). Weak fuel pump could be debris on the sock filter or the pump just not being good anymore.

Alabama · Feb 12, 2025

gkomo said:
Dumb question maybe but are you sure the fuel filter was installed in the correct flow direction?

No dumb questions, but I replaced it with a new one today, arrow follows flow from tank to front. Thanks though.

Alabama · Feb 12, 2025

General karthief said:
Change the fuel filter again, then see if it clears up.
Important notes:
Just because it's a 'new' part does not equal 'working' part. Many sensors today are defective right outta da box.
There is a diagnostic procedure to test each one. Go here and fallow directions.

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

Welcome to

Long day today after work. Here is what I have done. I replaced the fuel filter, test drove, same indications. Followed the diagnostic procedure you linked, found no new faults. KOEO codes went from 11 to 10. KOER codes came up with a 95, which was new. Did some research and found that I do, in fact, have 12 V into and out of the inertia switch, 12 V at the relay, so that system is good. Pulled my steering column panels off near the steering wheel, found my ignition switch zip tied together. Broke the zip tie and it fell apart. Replaced my ignition switch and problem seemed to get better, took longer for the condition to reappear, but it happened again. KOER codes are as follows: 21, 94, 44, 33, 13, 8 all with an R, 33 and 95 with a C. Haven't checked it since my most recent test drive after replacing the ignition switch. I really appreciate your help and look forward to getting this problem resolved, even if it is replacing the fuel pump again. I have sent my A9L off for bench repair in Georgia last year, but that is not to say the fuel control portion hasn't gone bad. Gotta be a way of telling. When I go back out there I will get any new codes off the car and update. Thanks again.

Alabama · Feb 12, 2025

AeroCoupe said:
First thing I am going to ask is did you perform the KOER test with the engine up to operating temperature?

C = Continuous memory code
O = Key on engine off (KOEO) code
R = Key on engine running (KOER) code

Code 8 - If you got this at the end of the KOER test then it is telling you it doesn't like something with Cylinder #8. See post #5 in the linked thread below.
Code 13 - RPM Not Within Self-Test Upper Limit [R], Idle Speed Control motor or Air Bypass Not Controlling Idle Properly - Generally Idle too High
Code 21 - Engine Coolant Temperature [ECT] Sensor Out Of Self-Test Range. 0.3 to 3.7 volts [O,R] (this could be due to the engine not being up to operating temperature)
Code 33 - EGR Valve Opening Not Detected [CM,R] (most likely due to the EGR delete so you can ignore)
Code 44 - Secondary Air System Inoperative. Bank One, Passenger Side [R] (most likely due to the EGR delete so you can ignore)
Code 94 - Secondary Air Injection Inoperative. Bank Two, Driver Side [R], Torque Converter Clutch Solenoid Circuit Failure [O] (most likely due to the EGR delete so you can ignore)

J

Thread 'Cylinder Balance Test'

Apr 9, 2007

How do you do a cylinder balance test? Please be specific on what to do as I am totally clueless on how to do this!

JBeenken

Replies: 15

Forum: Fox 5.0 Mustang Tech

My guess with regards to the fuel pressure falling off is a weak fuel pump. You should be getting 39 psi +/- 2 psi at WOT or at idle with the vacuum disconnected from the fuel pressure regulator (FPR). Weak fuel pump could be debris on the sock filter or the pump just not being good anymore.

Thank you for the information. I have recently replaced the fuel pump, along with the sending unit and tank itself, with a kit from CJ Pony, not saying the fuel pump they sent me is good. I also replaced the fuel pressure regulator recently. I will reinstall the fuel pressure test set, remove the vacuum from the fuel pressure regulator and check it. The engine was up to temp when I ran the test, did replace the ECT sensor as well (part of a kit for the engine that included 02 sensors, IAC motor, TPS sensor among others that have been replaced). My idle is high, I understand I need to do a base idle reset as it sits between 900 and 1000 warm now but want to fix the current issue first.

AeroCoupe · Feb 13, 2025

We need some history on the car. What year is it? Was the car originally a 4 cylinder? What transmission did it have originally and what does it have now? Basically anything that has changed on the car from the factory to now. Also, what brand of pump and sensors did you put on the car? What brand of cap, rotor, and plug wires?

There are a lot of parts out there that are just junk which is why I am asking all these questions. If the car was a 4 cylinder and got swapped then you will most likely need to wire up the secondary fuel pump circuit because swap cars typically do not have this.

Alabama · Feb 13, 2025

AeroCoupe said:
We need some history on the car. What year is it? Was the car originally a 4 cylinder? What transmission did it have originally and what does it have now? Basically anything that has changed on the car from the factory to now. Also, what brand of pump and sensors did you put on the car? What brand of cap, rotor, and plug wires?

There are a lot of parts out there that are just junk which is why I am asking all these questions. If the car was a 4 cylinder and got swapped then you will most likely need to wire up the secondary fuel pump circuit because swap cars typically do not have this.

Perfect. I have a 1989 Mustang GT 5.0. It is maroon over titanium or grey. Originally a 302 and from what I can tell, still has original motor installed, not willing to pull off plenum yet to verify number on engine. Originally a 5 speed, still a 5 speed. I am not the original owner but do know that the 130 Amp alternator upgrade was completed prior to me buying the car. Doesn't have the original radio. Has an aluminum drive shaft. Still drums in the back, four lug all around. I am not tracking any other modifications from stock. As far as what I have completed pertaining to this issue, I replaced the fuel tank, pump and sending unit with a kit from CJ Pony (PN FTK18). The old tank was horrible on the inside with corrosion amongst other things. The kit came with a 255 LPH high flow fuel pump (Walbro Fuel Pump according to their website). I have also replaced other components. I replaced the distributor cap and rotor and plug wires with a D.U.I. Performance Distributors Firepower Ignition Kit which included a 5.0 Dyna Module TFI, Screamin' Demon Coil, 5.0 Cap and Rotor, and Livewire plug wires. I also replaced the engine sensors from LMR's 1987-1993 Mustang Engine Sensor Kit - 5.0 which is the LMR PN LRS-1207A-K, contained 2 new NTK 02 sensors, 1 Idle Air Control Motor, 1 Throttle Position Sensor, 1 Coolant Temperature Sensor, 1 Air Charge Temperature sensor, all changed out. I recently replaced the fuel pressure regulator with a new one from Autozone and a Duralast fuel filter yesterday. I did get a 95 code yesterday, shot power into and out of the inertia switch, 12V both sides, and 12 V at the fuel pump relay under the drivers seat. I am trying to be as specific as possible in order to allow the best advice to come my way. If I can provide any other information, please let me know and I will do what I can. I really do appreciate all the help.

Alabama · Feb 13, 2025

Alabama said:
Long day today after work. Here is what I have done. I replaced the fuel filter, test drove, same indications. Followed the diagnostic procedure you linked, found no new faults. KOEO codes went from 11 to 10. KOER codes came up with a 95, which was new. Did some research and found that I do, in fact, have 12 V into and out of the inertia switch, 12 V at the relay, so that system is good. Pulled my steering column panels off near the steering wheel, found my ignition switch zip tied together. Broke the zip tie and it fell apart. Replaced my ignition switch and problem seemed to get better, took longer for the condition to reappear, but it happened again. KOER codes are as follows: 21, 94, 44, 33, 13, 8 all with an R, 33 and 95 with a C. Haven't checked it since my most recent test drive after replacing the ignition switch. I really appreciate your help and look forward to getting this problem resolved, even if it is replacing the fuel pump again. I have sent my A9L off for bench repair in Georgia last year, but that is not to say the fuel control portion hasn't gone bad. Gotta be a way of telling. When I go back out there I will get any new codes off the car and update. Thanks again.

Latest update. My fuel pressure at the rail is 34 psi with everything connected. It does jump when I gun the engine. The rise is dependent on how much I gun the engine. When I disconnect the fuel pressure regulator, the fuel pressure is 42 psi. Warmed up the engine for new codes, KOEO codes were 11 then 10, nothing in Continuous Memory. KOER codes are as follows: 94, 44, 33, 13, 8. No Continuous Memory codes. Thank you again.

Alabama · Feb 13, 2025

Alabama said:
Perfect. I have a 1989 Mustang GT 5.0. It is maroon over titanium or grey. Originally a 302 and from what I can tell, still has original motor installed, not willing to pull off plenum yet to verify number on engine. Originally a 5 speed, still a 5 speed. I am not the original owner but do know that the 130 Amp alternator upgrade was completed prior to me buying the car. Doesn't have the original radio. Has an aluminum drive shaft. Still drums in the back, four lug all around. I am not tracking any other modifications from stock. As far as what I have completed pertaining to this issue, I replaced the fuel tank, pump and sending unit with a kit from CJ Pony (PN FTK18). The old tank was horrible on the inside with corrosion amongst other things. The kit came with a 255 LPH high flow fuel pump (Walbro Fuel Pump according to their website). I have also replaced other components. I replaced the distributor cap and rotor and plug wires with a D.U.I. Performance Distributors Firepower Ignition Kit which included a 5.0 Dyna Module TFI, Screamin' Demon Coil, 5.0 Cap and Rotor, and Livewire plug wires. I also replaced the engine sensors from LMR's 1987-1993 Mustang Engine Sensor Kit - 5.0 which is the LMR PN LRS-1207A-K, contained 2 new NTK 02 sensors, 1 Idle Air Control Motor, 1 Throttle Position Sensor, 1 Coolant Temperature Sensor, 1 Air Charge Temperature sensor, all changed out. I recently replaced the fuel pressure regulator with a new one from Autozone and a Duralast fuel filter yesterday. I did get a 95 code yesterday, shot power into and out of the inertia switch, 12V both sides, and 12 V at the fuel pump relay under the drivers seat. I am trying to be as specific as possible in order to allow the best advice to come my way. If I can provide any other information, please let me know and I will do what I can. I really do appreciate all the help.

I forgot to mention that someone completed the EGR delete, the connector has the correct plug installed. Thanks again.

AeroCoupe · Feb 13, 2025

Verify the plugs and wires like Mustang5L5 laid out above. If this does not fix it then I have a couple suggestions.

So two things immediately jump out at me which are the 5.0 Dyna Module TFI and Screamin' Demon Coil. I would not run them on my car if you paid me. Get a stock TFI module (search on here as there are several threads on which ones to get) and I would suggest a Standard Ignition Blue Streak coil.

Other thing is the ECU is over 30 years old and we are seeing all kinds of weird issues with them due to their age. If you intend on keeping the car spend the money and send it here to have it rebuilt.

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECU Repair Service

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECUEngine Computer Repair ServicePlease fill out the R&R form here once you've placed your order.A Trusted Product with LIFETIME WARRANTY QUICK TURN AROUND TIMEDomestic and International Shipping available! Our Team is Available Monday - Friday 9am to 5pm...

www.theecuexchange.com

Alabama · Feb 13, 2025

AeroCoupe said:
Verify the plugs and wires like Mustang5L5 laid out above. If this does not fix it then I have a couple suggestions.

So two things immediately jump out at me which are the 5.0 Dyna Module TFI and Screamin' Demon Coil. I would not run them on my car if you paid me. Get a stock TFI module (search on here as there are several threads on which ones to get) and I would suggest a Standard Ignition Blue Streak coil.

Other thing is the ECU is over 30 years old and we are seeing all kinds of weird issues with them due to their age. If you intend on keeping the car spend the money and send it here to have it rebuilt.

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECU Repair Service

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECUEngine Computer Repair ServicePlease fill out the R&R form here once you've placed your order.A Trusted Product with LIFETIME WARRANTY QUICK TURN AROUND TIMEDomestic and International Shipping available! Our Team is Available Monday - Friday 9am to 5pm...

www.theecuexchange.com

Thank you for the suggestions. I did send my ECU to these guys about two years ago and had them repair and test it. I had a different issue with the car just dying on me, they found the normal two or three solder'd pieces coming apart. Not saying my 30 year old ECU is not bad in another portion now though. Thank you again.

FastDriver · Feb 13, 2025

Do you trust your fuel pressure readings? I skimmed and could've missed it, but if your car is dropping to 10 psi when warm, you have address that and stop worrying about any extraneous electronics. It's probably the new pump, voltage to the pump, or regulator.

Alabama · Feb 14, 2025

FastDriver said:
Do you trust your fuel pressure readings? I skimmed and could've missed it, but if your car is dropping to 10 psi when warm, you have address that and stop worrying about any extraneous electronics. It's probably the new pump, voltage to the pump, or regulator.

I do trust the fuel pressure readings. It doesn't drop to 10 psi until I drive it for a bit, cycle through the gears once. When I slow down and then accelerate, that is when the fuel pressure drops to 10 psi.

FastDriver · Feb 14, 2025

Yeah... That absolutely should not happen. Do you measure pressure at the rail? Could be pump, voltage to tge pump, the filter, the regulator, crimped line, making more power than pump can support (would be extremely lean). Can't think of much else.

Alabama · Feb 24, 2025

I ended up replacing the fuel pump again, like General karthief stated above "Just because it's a 'new' part does not equal 'working' part". Not certain how to get it to link his name. I appreciate all the help and insight. I have come across another issue but that is for another thread. Thanks again.

AeroCoupe · Feb 24, 2025

the "@" symbol immediately (i.e. no spaces) followed by "General karthief" without the quotes.

General karthief · Feb 24, 2025

Keep this thread going, you have members that will get an alert when a post is made.
You can change the title by editing, the three little dots at the bottom of the post box (?), to alert a member hit the @ then their screen name like @Alabama and they get a annoying alert.

limp · Feb 24, 2025

Alabama said:
like General karthief stated above "Just because it's a 'new' part does not equal 'working' part".

Even a blind squirrel finds a nut sometimes....

Resolved 1989 Mustang bogs down after 3-5 minutes of driving.

Member

wonder how much it would cost to ship you a pair

now i can hopefully expect to receive the shaft

lube between the nut and the face. I know my lubes

Member

Member

Member

lube between the nut and the face. I know my lubes

Member

Member

Member

lube between the nut and the face. I know my lubes

Member

I was uncomfortably high & wearing a helmet

Member

I was uncomfortably high & wearing a helmet

Member

lube between the nut and the face. I know my lubes

wonder how much it would cost to ship you a pair

wrap a little cheese around it and its a done

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