FCN4SC
New member
Hello all. I am new to the board even though I have been lurking awhile. I have searched for this but haven't found anything that has helped. I apologize ahead of time because this will be a long post to explain everything.
I have a 1990 Bronco with the 5.0L that I am working on to get on the road for my 15 year old daughter. She's an awesome kid and when I asked her what she wanted for her first car, hands-down it's what she wanted. She has even been helping me quite a bit with getting it roadworthy and the interior as restored as possible, so it's been great.
When I bought it, it had not been on the road for awhile. The person I bought it from got it in trade from someone else who told him that he thought it had a bad head gasket. I have checked compression and all is actually great with it there. I also did an exhaust gas test through the cooling system and the fluid did not change color at all, so I do not suspect a bad head gasket.
I have been working on this off and on for a year and before anyone says anything about throwing parts at something, let me say that with the cost of parts being lower than the BMWs and Mercedes I usually work on and knowing that my daughter will be driving it, I have replaced some parts that did not necessarily need to be replaced but did so to try to ensure it is more reliable for her.
The problem I am currently facing is that once it gets warmed up, it bogs down and has no power and is misfiring. It even backfires through the intake sometimes. You can't get it to go over 10mph. If I stop, shut it off, and restart it, it is fine for a few minutes and then it starts happening again. It also idles great when you start it but it does not want to idle back down after driving it and stays up around 1100-1200 rpm. It drops back down to about 700-800 eventually, but it takes 10 times longer than it should take.
Now, here is what I have replaced and other work performed. It would not start at all about 8 months ago so I put a TFI module on it. That corrected it but was short lived. When I pulled the distributor to go through it, it was in bad enough shape that I decided to order a new Accel distrbutor and installed it. I put in all new plugs, wires, and coil. Mice had made enough of a house under the intake manifold so I pulled the intake manifold to check gaskets and clean everything. While in there, I pulled the wiring harness and repaired anything I could find that would be a potential issue. I also replaced all injectors. I have also replaced all vacuum hoses with silicon hoses and performed a smoke test to find leaks. I found that the charcoal canister has smoke coming out of it (from the smoke test pushing smoke in through the intake) but found nothing wrong with it so I assumed it was supposed to leak when pushing smoke backwards through the system. Maybe I am wrong on that. I have since replaced the IAC, the EGR control solenoid (mice had done a number on chewing it up), cleaned the EGR valve, installed a new Motorcraft MAP sensor, and dropped the gas tank to clean it and put in a new fuel pump while I had it out and a new fuel filter. Again, not all parts NEEDED to be replaced, but I am trying to ensure more reliability for a 15-16 year old daughter to drive. I also pulled the ECM and checked for leaking capacitors. I found 2 that looked as though the electrolytic was leaking from them so I put in a reman Cardone ECM. I have repaired everything I can find with wiring too (not just the injector harness) and had to put a new IAC connector on due to it having wiring issues. With all electrical connections, I soldered and heat shrink-ed and did not use crimp connectors. I also used new wire loom and fabric wiring harness tape anywhere I made repairs (and some places I did not make repairs, but wanted to clean up the harness). I have a new O2 sensor and Coolant sensor that I will be installing soon.
So, now I am facing this new issue that I can't seem to track down the cause. When I perform the KOER test, I do receive a code 41 (always lean) but I am thinking that is due to a shoddy repair on the exhaust in the crossover pipe before the O2 sensor and cat. There are no codes stored or current when performing a KOEO test. I have used a thermometer to check pre, post, and cat temps when the engine is warm and there is no major temperature difference so I assume the cat is not clogged. I would like to replace the pre-cat exhaust but not sure what a good source for a good price for that is. I was thinking of pulling it and welding it up myself. What I have noted is that when the engine is acting up and bogging, if I stop and do not shut the engine down, my fuel pressure reads about 30psi and if I blip the throttle, it DROPS instead of rises. If I shut the engine down when warm and restart it, the fuel pressure at idle is about 30psi and it rises when I blip the throttle. I did disconnect the FPR and the fuel pressure rises, so I am not suspecting the FPR. With the engine not running and the key turned to on (so the fuel pump primes the system) fuel pressure is about 40psi.
I think it is running lean when it is warm and high idling, but I don't think it is due to a vacuum leak, so I am not sure why it is and it makes no sense that the fuel pressure drops when throttle is applied. There is another thing that I am thinking is a clue. I have checked the wiring that goes back to the fuel pump and while I have not pulled it from the loom, I don't see anything noticeable that would be causing an issue. That said, I did pull all wiring out of the tail gate and replace the regulator, window motor, and make wiring repairs but the tail gate window rolls up VERY slowly still and does not want to roll all the way up. I am wondering if I am missing an electrical issue and the fuel pump is not pulling enough amps when hot... but I am not sure if the tail gate window harness is bundled with the fuel pump harness so maybe they are not related issues. What also makes this theory less likely is that I can shut it off when it is bogging and idling high and immediately restart it and the problem is gone at least for a few minutes.
I am kinda running out of ideas so I am hoping someone has some input. If the FPR is functioning correctly, why would fuel pressure drop when it gets warm but immediately return to normal if I shut it off and restart it? Could it be the fuel pressure relay? What in the circuit would get "reset" enough to have it working immediately correctly again after a restart? I would think that if it was a wiring issue, it would not work again after an immediate restart. Is there something with the ignition switch that could cause this behavior and that shutting it off and restarting it would clear it up?
A side note is that the transmission wants to clunk a lot when down shifting. I have adjusted the TV cable and gotten upshifts to be very smooth and downshifts to be smoother. I am not sure if this is related or not. It's the AOD transmission and I have replaced the fluid and filter. I am thinking about dropping the valve body and going through it and putting in a shift improver kit, but I am not sure it is necessary. It just wants to hunt for gears sometimes and does clunk more than it should... but that may be due to the engine not running right and RPMs not being where they should with the given throttle input. I do know that with the AOD it is not electronically controlled like the E40D and a mismatch in throttle position and RPMs or just rough running could cause the AOD to not shift right... at least I think I am right about that.
While I am willing to replace any parts that will make it more reliable, I am also kinda getting to a point where I do not want to just replaced parts anymore because I also want to ensure I have the money to have it repainted and reupholstered. We did go through the whole interior and repaint all plastics, added sound deadening, and repaired any cracked/broken/split plastics in the process. It now only needs a headliner, new visors, one piece of missing interior trim that hides rear tops fasteners, and the seats reupholstered.
Thanks so much ahead of time for reading this far, but also for any input. While I am not a mechanic by trade, I'm also not a total amateur. I have any tools needed to do any work and I know my way around things like an oscilloscope which I have used to troubleshoot things like BMW valvetronic systems causing random misfires. This one is just kinda stumping me given the odd nature of what is happening.
I have a 1990 Bronco with the 5.0L that I am working on to get on the road for my 15 year old daughter. She's an awesome kid and when I asked her what she wanted for her first car, hands-down it's what she wanted. She has even been helping me quite a bit with getting it roadworthy and the interior as restored as possible, so it's been great.
When I bought it, it had not been on the road for awhile. The person I bought it from got it in trade from someone else who told him that he thought it had a bad head gasket. I have checked compression and all is actually great with it there. I also did an exhaust gas test through the cooling system and the fluid did not change color at all, so I do not suspect a bad head gasket.
I have been working on this off and on for a year and before anyone says anything about throwing parts at something, let me say that with the cost of parts being lower than the BMWs and Mercedes I usually work on and knowing that my daughter will be driving it, I have replaced some parts that did not necessarily need to be replaced but did so to try to ensure it is more reliable for her.
The problem I am currently facing is that once it gets warmed up, it bogs down and has no power and is misfiring. It even backfires through the intake sometimes. You can't get it to go over 10mph. If I stop, shut it off, and restart it, it is fine for a few minutes and then it starts happening again. It also idles great when you start it but it does not want to idle back down after driving it and stays up around 1100-1200 rpm. It drops back down to about 700-800 eventually, but it takes 10 times longer than it should take.
Now, here is what I have replaced and other work performed. It would not start at all about 8 months ago so I put a TFI module on it. That corrected it but was short lived. When I pulled the distributor to go through it, it was in bad enough shape that I decided to order a new Accel distrbutor and installed it. I put in all new plugs, wires, and coil. Mice had made enough of a house under the intake manifold so I pulled the intake manifold to check gaskets and clean everything. While in there, I pulled the wiring harness and repaired anything I could find that would be a potential issue. I also replaced all injectors. I have also replaced all vacuum hoses with silicon hoses and performed a smoke test to find leaks. I found that the charcoal canister has smoke coming out of it (from the smoke test pushing smoke in through the intake) but found nothing wrong with it so I assumed it was supposed to leak when pushing smoke backwards through the system. Maybe I am wrong on that. I have since replaced the IAC, the EGR control solenoid (mice had done a number on chewing it up), cleaned the EGR valve, installed a new Motorcraft MAP sensor, and dropped the gas tank to clean it and put in a new fuel pump while I had it out and a new fuel filter. Again, not all parts NEEDED to be replaced, but I am trying to ensure more reliability for a 15-16 year old daughter to drive. I also pulled the ECM and checked for leaking capacitors. I found 2 that looked as though the electrolytic was leaking from them so I put in a reman Cardone ECM. I have repaired everything I can find with wiring too (not just the injector harness) and had to put a new IAC connector on due to it having wiring issues. With all electrical connections, I soldered and heat shrink-ed and did not use crimp connectors. I also used new wire loom and fabric wiring harness tape anywhere I made repairs (and some places I did not make repairs, but wanted to clean up the harness). I have a new O2 sensor and Coolant sensor that I will be installing soon.
So, now I am facing this new issue that I can't seem to track down the cause. When I perform the KOER test, I do receive a code 41 (always lean) but I am thinking that is due to a shoddy repair on the exhaust in the crossover pipe before the O2 sensor and cat. There are no codes stored or current when performing a KOEO test. I have used a thermometer to check pre, post, and cat temps when the engine is warm and there is no major temperature difference so I assume the cat is not clogged. I would like to replace the pre-cat exhaust but not sure what a good source for a good price for that is. I was thinking of pulling it and welding it up myself. What I have noted is that when the engine is acting up and bogging, if I stop and do not shut the engine down, my fuel pressure reads about 30psi and if I blip the throttle, it DROPS instead of rises. If I shut the engine down when warm and restart it, the fuel pressure at idle is about 30psi and it rises when I blip the throttle. I did disconnect the FPR and the fuel pressure rises, so I am not suspecting the FPR. With the engine not running and the key turned to on (so the fuel pump primes the system) fuel pressure is about 40psi.
I think it is running lean when it is warm and high idling, but I don't think it is due to a vacuum leak, so I am not sure why it is and it makes no sense that the fuel pressure drops when throttle is applied. There is another thing that I am thinking is a clue. I have checked the wiring that goes back to the fuel pump and while I have not pulled it from the loom, I don't see anything noticeable that would be causing an issue. That said, I did pull all wiring out of the tail gate and replace the regulator, window motor, and make wiring repairs but the tail gate window rolls up VERY slowly still and does not want to roll all the way up. I am wondering if I am missing an electrical issue and the fuel pump is not pulling enough amps when hot... but I am not sure if the tail gate window harness is bundled with the fuel pump harness so maybe they are not related issues. What also makes this theory less likely is that I can shut it off when it is bogging and idling high and immediately restart it and the problem is gone at least for a few minutes.
I am kinda running out of ideas so I am hoping someone has some input. If the FPR is functioning correctly, why would fuel pressure drop when it gets warm but immediately return to normal if I shut it off and restart it? Could it be the fuel pressure relay? What in the circuit would get "reset" enough to have it working immediately correctly again after a restart? I would think that if it was a wiring issue, it would not work again after an immediate restart. Is there something with the ignition switch that could cause this behavior and that shutting it off and restarting it would clear it up?
A side note is that the transmission wants to clunk a lot when down shifting. I have adjusted the TV cable and gotten upshifts to be very smooth and downshifts to be smoother. I am not sure if this is related or not. It's the AOD transmission and I have replaced the fluid and filter. I am thinking about dropping the valve body and going through it and putting in a shift improver kit, but I am not sure it is necessary. It just wants to hunt for gears sometimes and does clunk more than it should... but that may be due to the engine not running right and RPMs not being where they should with the given throttle input. I do know that with the AOD it is not electronically controlled like the E40D and a mismatch in throttle position and RPMs or just rough running could cause the AOD to not shift right... at least I think I am right about that.
While I am willing to replace any parts that will make it more reliable, I am also kinda getting to a point where I do not want to just replaced parts anymore because I also want to ensure I have the money to have it repainted and reupholstered. We did go through the whole interior and repaint all plastics, added sound deadening, and repaired any cracked/broken/split plastics in the process. It now only needs a headliner, new visors, one piece of missing interior trim that hides rear tops fasteners, and the seats reupholstered.
Thanks so much ahead of time for reading this far, but also for any input. While I am not a mechanic by trade, I'm also not a total amateur. I have any tools needed to do any work and I know my way around things like an oscilloscope which I have used to troubleshoot things like BMW valvetronic systems causing random misfires. This one is just kinda stumping me given the odd nature of what is happening.
