1989 5.0 Will not go in to closed loop, bogs when accelerated, no codes

[L\Bronco]

Good luck!

 

[Dadpool]

Good luck!

We have it back. We also found a parts 89 xlt exactly like my sons and picked it up. It runs and drives but it's rough on the eyes and has no title. It was a salvage yard tow that never got claimed. To avoid confusion, we will callcthe one thats we need fixed "1" and the parts "2".We took 2s ecm and installed to 1 and the issue improved by about 25%, but it it still on the struggle bus on acceleration. Will test fuel pressure. We can compare to 2 for verification purposes. 2 ran buttery smooth. Put 2s map on 1 and it ran like . Put 1s back on and then it ran as it did before.
I am also going to verify TDC with piston 1 and intake valve with a snake cam just to make sure that is all good.

 

[Dadpool]

We have it back. We also found a parts 89 xlt exactly like my sons and picked it up. It runs and drives but it's rough on the eyes and has no title. It was a salvage yard tow that never got claimed. To avoid confusion, we will callcthe one thats we need fixed "1" and the parts "2".We took 2s ecm and installed to 1 and the issue improved by about 25%, but it it still on the struggle bus on acceleration. Will test fuel pressure. We can compare to 2 for verification purposes. 2 ran buttery smooth. Put 2s map on 1 and it ran like . Put 1s back on and then it ran as it did before.
I am also going to verify TDC with piston 1 and intake valve with a snake cam just to make sure that is all good.

It is looking like the problem is resolved! Swap of PCM did help, but not fully. Verified all timing components, then moved on to fuel system. Rail pressure was 30 psi, all the way around. No changes with out vacuum, when high RPM, just a flat 30. This has been replace 2x before. Did a warranty on the autozone part and now it is driving as expected. My feeling is any of the little quirks it still has will be resolved once we swap the wiring harness. there are many cuts, splices and ends that have exposed wire on it, that is why I am insistent on swapping out with the 2's.

 

[johnnyreb]

Greetings fellow Bronco owners.

I have a 1989 with the 5.0 AOD that my son and I have been fighting for about 3 years after putting in a new engine. I won't go through all the details but will list the most recent that we are running in to.I

I gave up after a couple of years and sent it to 2 different mechanics. The first one back burnered it because it was taking too much time to diagnose.
I took it to another recommend one and they found a bad ECT, replaced but it was still running rich. After checking seveal other item they replaced the ECM and it started running correctly and not rich. They sent it home with us and my son drove it for a month and it started running rich again. We took it back in december and they relooked over everything and came up with the injectors we got were wrong causing it to not go in to closed loop. They were a set of reman ones from AutoZone. I know they are not known for reliable parts but its what we could afford. After double, tripple checking their site, in store I wasn't convenced that the injectors were the issue, but I got the manager to warranty them and got another set of the same type for them to try. It still was running rich and not going in to closed loop. They back burnnered it. I suggested that they try a set of know good injectors I had out of an 88 302 from a Crown Vic that I put in my Falcon. They agreed, so I pulled them and gave them to the mechanic. A month later they still haven't tried them, so I brought it home and put them in.Other than a couple of broken O rings they went in with no issues, and I did replace the O rings.
It started and seemed to be doing ok, but still rich and not going in to closed loop.

I since replaced the ECT again ( I had a spare new one for my Falcon) still no change. I attempted to test the sensor but giving the location, it is difficult to get a reading once at temp. I tried with it running under hot water and it seems to be within specs, I don't remember the values off hand. I decided to run a new line to the ECM for the ECT, keeping the original wires in the loop since I seen it provides grounds to the TPS, MAP and several others.
Now as of this weekend with a cleared ECM it will start, it calibrates a bit after reaching temp then tries to go in to closed loop, but then jumps back in to closed loop, bumping the idle to 1000 rpm. When trying to drive it, it bogs down at low RPMs, but smooths out at around 2500 to 3000. Once it is shut off, it is hard to start again.

To the best I can tell by spraying some carb cleaner on it (before it warms up) there are no vacuum leaks in any vacuum lines, which have all been replaced from the plastic lines. No leaks on the TB and between the upper and lower intake.

Fuel pressure when KOEO is around 30ish and holds steady, so I don't believe the the injectors are leaking. Fuel pressure seems good when running, but there is no change in how it runs if the vacuum line is removed from the FPR. Research found maybe a weak or back fuel pump. The one on the frame is making noise, but with a auto stethoscope to the tank, I can not hear it buzz when key is turned on.

Timing is at 10 btdc with spout unplugged and advances to around 20 at idle.
Parts replaced that could be causing the issues, and slightly inconclusive test results
TPS, IAC, ECT Multiple times, MAP, ACT, FPR during the install of the engine. It does have a knock that was not replaced.

I have reverted back to the stock wiring for the ECT, verified all ground and pin outs from sensor connectors via continuity, and that they are all getting the 5v ref power.

This does have the emissions removed, so we get a TAD and TAB code, but that is expected. Otherwise, just 11, system pass.

I will be verifiying the in tank pump again and getting that replaced this weekend, if NAPA will order in the pump before I bring them the old one to warranty.

Plugs and plug wires, cap and rotor are new. Reman Dizzy, so TFI module or PIP could be suspect but not likely.

Any other ideas I can try on this thing?

ETHANOL GAS WILL EAT THE FUEL SENDING UNIT UP. I just dropped the fuel tank in my bronco today and my sending unit had the FLOAT EATEN AWAY. THIS IS THE 2ND SENDING EATEN BUY ETHANOL FUEL---IT IS MOST OF THE PROBLEM PEOPLE ARE HAVING. IT NEEDS TO BE OUTLAWED--ITS GARBAGE.

 

[Dadpool]

ETHANOL GAS WILL EAT THE FUEL SENDING UNIT UP. I just dropped the fuel tank in my bronco today and my sending unit had the FLOAT EATEN AWAY. THIS IS THE 2ND SENDING EATEN BUY ETHANOL FUEL---IT IS MOST OF THE PROBLEM PEOPLE ARE HAVING. IT NEEDS TO BE OUTLAWED--ITS GARBAGE.

I have my son running ethanol free fuel because of how horrible it is.

 

[L\Bronco]

It is looking like the problem is resolved! Swap of PCM did help, but not fully. Verified all timing components, then moved on to fuel system. Rail pressure was 30 psi, all the way around. No changes with out vacuum, when high RPM, just a flat 30. This has been replace 2x before. Did a warranty on the autozone part and now it is driving as expected. My feeling is any of the little quirks it still has will be resolved once we swap the wiring harness. there are many cuts, splices and ends that have exposed wire on it, that is why I am insistent on swapping out with the 2's.

Fantastic!
Way to go!
Cheers!

 

[Dadpool]

Fantastic!
Way to go!
Cheers!

The entire engine wiring harness has now been replaced. I think we still may have a weak link in the fuel system though. There is a slight bit of sluggishness when taking off if doing more than a casual acceleration, and if holding a steady speed, say 45 mph, after a few minutes if feels like it starts to chug a little. Put the tester back on the fuel rail and we seem to be flat 35ish on pressure again, with and without vacuum. The kiddo is going to put the FPR from the donor on to see if that makes a difference. If it doesn't I'll be starting to test pressures on the pumps to ensure we don't have one of those failing, again! Otherwise, it is driving running much, much better.

 

[L\Bronco]

Good call on the regulator.
Cheers

 

[ShadetreeSeattle]

The ethanol fuel thing, that cannot just be the problem here. yeah it can damage components over time, but this is a runability issue that has not been resolved yet imo. it's not about ethanol. these engines will run just fine with current fuel, in a stock format... we have to remember that these computers are dumb as a bag of hammers from this time period. it will in many cases not throw a code. I encourage people with OBD1 stuff to review the code chart, whether a 2 digit or 3 digit code set, it will make it pretty clear what things it can even set a code for in the first place, which is well, not much...mostly open or shorted circuit kind of things. I seldom have ever seen much valuable info. That being said, yeah, if you have codes, share them. Most pre OBD2 stuff is a lot about breaking out the multimeter, vaccume gauge, timing light, and lots of research. By far, finding literature on the EEC-IV computer, or getting a good copy of the Ford FSM, that helped me understand how and why it can behave poorly. The thing will almost never throw a code for a runability issue. It will poorly try to throw a code for anything that was barely required by EPA in that time period. and believe me, it will never throw a code worth much. Even post 1996 OBD2 requimerents barely met this standard.

If it bogs on acclleration, that can mean a few things. If it does great after heavy load, like after you wide open throttle it, if you punch the go pedal, if it is great after you are cruising at 65mph, it's likely not a fuel delivery problem it would struggle after a certain fuel load. when near wide open throttle, well, it's getting a lot of fuel, it's doing its thing. It mostly rules out fuel delivery... Those fuel pressure ratings are not great either, but the truck should run under those conditions. There's something else going on here. Intake or vaccume leaks show their face worse the slower the engine runs. Thats my 2c. Just off the top of my head.

 

[Dadpool]

Good call on the regulator.
Cheers

We tested directly from the tank. I did not have a way to T it off, so I just removed the output line and put on my gauge and got 5 psi. I had no method of clamping it off on the fuel pump on frame, or the filter, (which has been changed) so I don't have good reading directly from it other than from the fuel rail. I did see some changes depending on how I have the gauge placed. It's just a Harbor Freight vacuum and pressure gauge, so not a great one, but requires a adapter hose to fit the rail, so depending of if it laying down or hanging makes a difference on the reading. It is close to 40 when hanging without vacuum and backs down a few psi with.
The last shop that had it did a TPS sensor, which we had replaced a dozen times already, so I am wondering if its another crappy Auto zone one. It seems to have it's points of where it feels held back depending on where the pedal is at in acceleration. But here is the kicker. We cleared calibration, and it seems great for several drives, well beyond the point of re calibrating, then out of no where it starts running a little rough with a high idle, about 900 rpm in park.We can clear it again, and the problem goes away. Considering we have no history on the thing 2 (donor) ECM, I instructed my son to swap back the one we pulled out of thing 1 to get thing 2 going again (keeping the spare parts running so we can move it around as needed) and see what happens.

Most of the sensors and solenoids on thing 2 are still FORD, FOMOCO or Mortorcraft stamped parts, so we have been putting those on where needed. I should have swapped out the TPS while I had the TB off, but didn't.

 

[Dadpool]

The ethanol fuel thing, that cannot just be the problem here. yeah it can damage components over time, but this is a runability issue that has not been resolved yet imo. it's not about ethanol. these engines will run just fine with current fuel, in a stock format... we have to remember that these computers are dumb as a bag of hammers from this time period. it will in many cases not throw a code. I encourage people with OBD1 stuff to review the code chart, whether a 2 digit or 3 digit code set, it will make it pretty clear what things it can even set a code for in the first place, which is well, not much...mostly open or shorted circuit kind of things. I seldom have ever seen much valuable info. That being said, yeah, if you have codes, share them. Most pre OBD2 stuff is a lot about breaking out the multimeter, vaccume gauge, timing light, and lots of research. By far, finding literature on the EEC-IV computer, or getting a good copy of the Ford FSM, that helped me understand how and why it can behave poorly. The thing will almost never throw a code for a runability issue. It will poorly try to throw a code for anything that was barely required by EPA in that time period. and believe me, it will never throw a code worth much. Even post 1996 OBD2 requimerents barely met this standard.

If it bogs on acclleration, that can mean a few things. If it does great after heavy load, like after you wide open throttle it, if you punch the go pedal, if it is great after you are cruising at 65mph, it's likely not a fuel delivery problem it would struggle after a certain fuel load. when near wide open throttle, well, it's getting a lot of fuel, it's doing its thing. It mostly rules out fuel delivery... Those fuel pressure ratings are not great either, but the truck should run under those conditions. There's something else going on here. Intake or vaccume leaks show their face worse the slower the engine runs. Thats my 2c. Just off the top of my head.

I'm not saying the ethanol fuel is a problem, but I do take in to consideration that ethanol was not a thing in fuel when these engines were manufactured, so performance may vary. It is only .50 more a gallon for ethanol free, so I am having my son run it along with some Seafoam to clean out the system until we get all the kinks worked out. With it running so rich for so long, the top of the pistons are have some deposits on them already, and it's only 3 years old.

I lost count on how many cans of carb cleaner I have been through trying to find vacuum leaks on the intake, vacuum lines, tb, ect. Unless it is something more internal, I feel confident that there are no external vacuum leaks.

 

[L\Bronco]

We tested directly from the tank. I did not have a way to T it off, so I just removed the output line and put on my gauge and got 5 psi. I had no method of clamping it off on the fuel pump on frame, or the filter, (which has been changed) so I don't have good reading directly from it other than from the fuel rail. I did see some changes depending on how I have the gauge placed. It's just a Harbor Freight vacuum and pressure gauge, so not a great one, but requires a adapter hose to fit the rail, so depending of if it laying down or hanging makes a difference on the reading. It is close to 40 when hanging without vacuum and backs down a few psi with.
The last shop that had it did a TPS sensor, which we had replaced a dozen times already, so I am wondering if its another crappy Auto zone one. It seems to have it's points of where it feels held back depending on where the pedal is at in acceleration. But here is the kicker. We cleared calibration, and it seems great for several drives, well beyond the point of re calibrating, then out of no where it starts running a little rough with a high idle, about 900 rpm in park.We can clear it again, and the problem goes away. Considering we have no history on the thing 2 (donor) ECM, I instructed my son to swap back the one we pulled out of thing 1 to get thing 2 going again (keeping the spare parts running so we can move it around as needed) and see what happens.

Most of the sensors and solenoids on thing 2 are still FORD, FOMOCO or Mortorcraft stamped parts, so we have been putting those on where needed. I should have swapped out the TPS while I had the TB off, but didn't.

Im not a fan of throwing parts, but, that being said, I have less than zero faith in todays build quality.
Your TPS theory has some merit for sure.
The older system didnt use a closed throttle voltage spec, it just took the lowest value it saw as closed, a few tenths of a volt higher and it was considered part throttle. At part throttle the pcm stops learning and adjusting idle and goes to dashpot mode awaiting a decell (it assumes you are driving). A bad tps can momentarily drop below its normal CT range and reset the value to the lower number, then you are in dashpot mode at idle which equals 900-1200 rpm depending on hardstop setting.(base idle)
When you clear it, the pcm relearns closed at the normal number until the glitch happens again.
Plus, if it glitches while you are accelerating, it will miss the tps change rate and wont go into accel enrichment mode. (Simulates an accelerator pump in a carb.)
Hope that helps
Cheers

 

[Dadpool]

Im not a fan of throwing parts, but, that being said, I have less than zero faith in todays build quality.
Your TPS theory has some merit for sure.
The older system didnt use a closed throttle voltage spec, it just took the lowest value it saw as closed, a few tenths of a volt higher and it was considered part throttle. At part throttle the pcm stops learning and adjusting idle and goes to dashpot mode awaiting a decell (it assumes you are driving). A bad tps can momentarily drop below its normal CT range and reset the value to the lower number, then you are in dashpot mode at idle which equals 900-1200 rpm depending on hardstop setting.(base idle)
When you clear it, the pcm relearns closed at the normal number until the glitch happens again.
Plus, if it glitches while you are accelerating, it will miss the tps change rate and wont go into accel enrichment mode. (Simulates an accelerator pump in a carb.)
Hope that helps
Cheers

I feel we are on the final, final, final home stretch, for the engine that is. I do still believe we have a TPS issue, but the rest of the acceleration issues was.... upper intake gasket. The issue with that gasket wasn't on the outer part which is why I couldn't find a vacuum leak with carb cleaner. It was tore on the inside part between the intake ports. We must have done that when we replaced the injectors. The last lingering issue with the TPS is when starting up and letting it idle down, when you put it in gear it kicks the idle up to about 900 instead of the lower 5-600 it should be. If you do a quick step on the gas before shifting in to gear, RPMs are as they should be. This was shop #3's part replacement, so I am going to have them do it, or at least get me the part and test it before installation. I am going to have shop #2 verify this week using their lab scope that everything is good. They are my most trusted shop, as they have been doing top notch work on the stuff I can't do on my jeep, which both the bronco and the jeep are now pictured in my profile

Feel free to stay tuned to the many other topics I'm sure I'll post about such as..
Keeping auto locking hubs or replacing and with what kits? I already know that I should replace with Manual, but that's a 2026 problem, ha ha ha!
Push button 4x4 works, but will not go into low range. Motor clicks so it would seem to be getting power.
Leaky steering box. rebuild or replace?
Once the AOD dies, rebuild, use the parts one, or replace with a small block C6?
I want to thank you L\Bronco for your expertise, advice and willingness to keep up on this what seemed to be never ending problem child of a bronco!

 

[L\Bronco]

I feel we are on the final, final, final home stretch, for the engine that is. I do still believe we have a TPS issue, but the rest of the acceleration issues was.... upper intake gasket. The issue with that gasket wasn't on the outer part which is why I couldn't find a vacuum leak with carb cleaner. It was tore on the inside part between the intake ports. We must have done that when we replaced the injectors. The last lingering issue with the TPS is when starting up and letting it idle down, when you put it in gear it kicks the idle up to about 900 instead of the lower 5-600 it should be. If you do a quick step on the gas before shifting in to gear, RPMs are as they should be. This was shop #3's part replacement, so I am going to have them do it, or at least get me the part and test it before installation. I am going to have shop #2 verify this week using their lab scope that everything is good. They are my most trusted shop, as they have been doing top notch work on the stuff I can't do on my jeep, which both the bronco and the jeep are now pictured in my profile

Feel free to stay tuned to the many other topics I'm sure I'll post about such as..
Keeping auto locking hubs or replacing and with what kits? I already know that I should replace with Manual, but that's a 2026 problem, ha ha ha!
Push button 4x4 works, but will not go into low range. Motor clicks so it would seem to be getting power.
Leaky steering box. rebuild or replace?
Once the AOD dies, rebuild, use the parts one, or replace with a small block C6?
I want to thank you L\Bronco for your expertise, advice and willingness to keep up on this what seemed to be never ending problem child of a bronco!

Thanks Dadpool!
Old Broncos are like home reno’s, just when you think its over, your wife wants different cupboard door pulls, and it starts all over.
These things are hobbies, not transportation, so make sure you enjoy the process if you can. (Im starting round 3 on my Frankenbronco this winter.
Cheers

 

[91BroncoPickup]

I feel we are on the final, final, final home stretch, for the engine that is. I do still believe we have a TPS issue, but the rest of the acceleration issues was.... upper intake gasket. The issue with that gasket wasn't on the outer part which is why I couldn't find a vacuum leak with carb cleaner. It was tore on the inside part between the intake ports. We must have done that when we replaced the injectors. The last lingering issue with the TPS is when starting up and letting it idle down, when you put it in gear it kicks the idle up to about 900 instead of the lower 5-600 it should be. If you do a quick step on the gas before shifting in to gear, RPMs are as they should be. This was shop #3's part replacement, so I am going to have them do it, or at least get me the part and test it before installation. I am going to have shop #2 verify this week using their lab scope that everything is good. They are my most trusted shop, as they have been doing top notch work on the stuff I can't do on my jeep, which both the bronco and the jeep are now pictured in my profile

Feel free to stay tuned to the many other topics I'm sure I'll post about such as..
Keeping auto locking hubs or replacing and with what kits? I already know that I should replace with Manual, but that's a 2026 problem, ha ha ha!
Push button 4x4 works, but will not go into low range. Motor clicks so it would seem to be getting power.
Leaky steering box. rebuild or replace?
Once the AOD dies, rebuild, use the parts one, or replace with a small block C6?
I want to thank you L\Bronco for your expertise, advice and willingness to keep up on this what seemed to be never ending problem child of a bronco!

I cannot stress enough using a RedHead steering gear box and a Borgeson steering shaft. 1st mods I did and made night and day (like a 2022 F150 smooth) difference.

Great thread, BTW - helping me diagnose my '91.