1985 F-150 5.0 (EFI) running issues

I recently purchased a 1985 F-150 XLT Lariat from an estate sale. During the drive home and since I've had it in the driveway, I've experienced the following issues.

On the way home from Greenbrier (about an hour drive), the truck started sputtering about halfway through the drive. It would lose all power for a split second and then get underway again. This got more frequent and progressively worse until the truck died and would not restart about three miles from the house. I was eventually able to get the truck started and get it home in a few quick leaps by letting it sit with the hood open a while.

Since getting it home, the truck experiences the following issues.

When the truck is cold started, it will usually fast idle just fine. Once the idle comes down after initial warm up, it will (most of the time) begin to act like it wants to die. The RPMs will dip and it will recover. It can do this for a while, or sometimes it will die very quickly. Other times it will eventually smooth out and will idle fine for a while.

I was able to troubleshoot it shortly afterward and tried to pull codes. KOEO gave me nothing. KOER only gave me a code 31 (EGR-related). I highly doubt that is causing my issues.

I was able to check the timing and it was set at 20°. I tried setting it to 10°, but it didn't want to stay running. I set it at 12° and it's been there ever since.

What I've done so far:
1. Replaced fuel pressure regulator, no change
2. Tune up (Autolite copper plugs, Motorcraft wires/cap/rotor), no change
3. Replaced exhaust components (in case cats were clogged: https://www.youtube.com/watch?v=cW5iM14gGPY), no change
4. Swapped in a known good MAP sensor, no change

I'm also have an issue that may be transmission related.

When I drove this truck home from the estate sale, the transmission shifted fine. One thing I did notice and have confirmed a few times thereafter is that the truck sometimes does not creep in drive like it normally should. Sometimes I will start the truck up, put it in drive, and it will just sit there as if I have the parking brake applied. It will move (jerkily) if I tap the accelerator.

On occasion, throwing it into reverse and then back into drive will allow it to creep normally.

I've taken it on short drives in the neighborhood since getting it home. I've also noticed that there seems to be a lot of drag on the drivetrain, as if I'm riding the brakes the whole time. It doesn't really coast all that well. I have not checked the rear drums.

Has anyone ever had this issue on an AOD-equipped truck or Bronco? I know very little about automatics, but it seems like a torque converter issue more than anything.

Hope y'all can help. Other than the issues above, the truck seems to run very well. And it's in absolutely immaculate shape with the exception of the sun-dried door panels.

1985 F-150 XLT Lariat from an estate sale.
How long has the truck been sitting before you started driving it home?
Dave ----

Running issue: EGR issues *can* cause weird things to happen at idle (EGR system tries to do something and can't, throwing everything off). Other issues I'd look into would be a faulty/wrong TFI module (would explain the sudden roadside death only for it run after cooling down, should be a gray module, not a black one), A sticking/faulty IAC valve (I've had this cause major idle issues on multiple newer Fords, cleaning them made it worse!), and a faulty engine temp sensor (the multi-wire one for the ECU, info should be in the 1985 EVTM on the site).



Transmission: Never had that issue with my AOD, but I will tell you the AOD is a somewhat unique design; for example, the TC doesn't have a lockup clutch; instead, it has dual input shafts where the inner is direct drive to the face of the TC (used partially in 3rd gear and fully in 4th/OD). Here is a deeper dive into the AOD's workings if you're curious: https://ateupwithmotor.com/terms-technology-definitions/split-torque-lockup-converters/6/

What does your ATF look and smell like? Pink? Red? Orange? Brown/Black? Burnt and/or gritty?

FuzzFace2 wrote

1985 F-150 XLT Lariat from an estate sale.
How long has the truck been sitting before you started driving it home?
Dave ----

That's a good question. I have theorized about bad gas causing my issues. I forgot to mention that I changed the filter in the reservoir a few weeks ago. It was the original filter. That didn't really fix any issues, either.

I'm betting it sat for probably close to nine to twelve months based on the number of dirt dauber nests I found in the engine bay.

ratdude747 wrote

Running issue: EGR issues *can* cause weird things to happen at idle (EGR system tries to do something and can't, throwing everything off). Other issues I'd look into would be a faulty/wrong TFI module (would explain the sudden roadside death only for it run after cooling down, should be a gray module, not a black one), A sticking/faulty IAC valve (I've had this cause major idle issues on multiple newer Fords, cleaning them made it worse!), and a faulty engine temp sensor (the multi-wire one for the ECU, info should be in the 1985 EVTM on the site).



Transmission: Never had that issue with my AOD, but I will tell you the AOD is a somewhat unique design; for example, the TC doesn't have a lockup clutch; instead, it has dual input shafts where the inner is direct drive to the face of the TC (used partially in 3rd gear and fully in 4th/OD). Here is a deeper dive into the AOD's workings if you're curious: https://ateupwithmotor.com/terms-technology-definitions/split-torque-lockup-converters/6/

What does your ATF look and smell like? Pink? Red? Orange? Brown/Black? Burnt and/or gritty?

That's interesting about the EGR. I'll have to go ahead and replace the valve and sensor.

I actually did already change the TFI. I forgot to mention that. I had a newer Motorcraft unit that I had purchased for my 1990 Grand Marquis, but also is the correct one for this truck. It's the correct gray color.

Unfortunately, I haven't yet driven the truck any considerable distance to test whether or not the roadside death when hot issue has been solved. I'll probably test that whenever I fix the idling issue.

I have a new temp sensor (the newer style that includes the updated connector plug). I'll go ahead and install that as well. I'll look into the IAC valve.

As far as the transmission goes, I haven't troubleshot that issue at all as of yet. I'll check the state of the fluid next time I work on it.

It won't be until at least this weekend (probably later since I'm planning a junkyard run this weekend). I'll report back when I've addressed what y'all have brought up here.

Edit: I've also ordered some lengths of vacuum hose. I also suspect that there may be vacuum leaks contributing to the truck's woes.

Giraffe wrote

FuzzFace2 wrote

1985 F-150 XLT Lariat from an estate sale.
How long has the truck been sitting before you started driving it home?
Dave ----

That's a good question. I have theorized about bad gas causing my issues. I forgot to mention that I changed the filter in the reservoir a few weeks ago. It was the original filter. That didn't really fix any issues, either.

I'm betting it sat for probably close to nine to twelve months based on the number of dirt dauber nests I found in the engine bay.

Its good you replaced the filter but you were still pulling and running on old gas and today's gas dose not last long.
How much gas is in the tank right now?
It may not be the only thing causing your problem but something to think about.
Dave ----

Before doing anything else- Getting some good gas with good detergent should be top of your list.

Get some ethanol free and put some techron additive in. Run a full tank of gas through and monitor.

I topped off the tank one the first drive home because I wasn't sure if the fuel gauge was working (it was). Because of how little I've driven it since, it still has about ¾ of a tank left. I'll go ahead and throw some of that along with some fuel injector cleaner into it and see if I can blow any cobwebs out.

I’ve been tinkering with the truck off and on for a while. I believe I finally solved the issue.

I was working on the truck the other day when I decided to start it up. Though it had been running on a couple of hours earlier, it didn’t want to start; it sounded like the battery didn’t have enough charge. It would barely turn over the engine. I jumped it using the family car. It started and idled fine.

It started idling badly again as soon as I went to remove the cables. I did some more troubleshooting from there and decided to replace the alternator. One reman unit from O’Reilly later (that just happened to have begun its life as a Motorcraft unit), and it’s running fantastic. No more dying when it’s warmed up.

I’ve been driving it every day for the past week. The new TFI module also appears to have fixed the sputtering/dying when hot issue.

Excellent!  I love a story with a happy ending.  

There may be a second fuel filter in your system that needs to be changed. it is after the high pressure fuel pump between the pump and the engine, my EFI Bronco has two filters. I know you said it was running good now with changing the TFI, but you might want to change the other filter too.