Hello All! I'm trying revive a 1987 F150 that my dad traded a bottle of Johnnie Walker for. It's coming along pretty well, except that I can't make it run properly. It starts up just fine, and idles smooth, until I try to give it gas. If I floor it, nothing happens for a moment, except the RPM drops a little. Then the ECU realizes something's up and the engine revs. After I release the pedal, it sort of forgets how to idle. It drops down too far, and if it's cold, it'll stall; other times it surges back, drops down again, surges back. Sometimes it'll stabilize. When it stalls, it'll start right back up like nothing happened. I tried to hold it at 2k to warm it up for the KOER test and had a hard time controlling engine speed. It's like the engine has no idea where my foot is. If I try to drive the thing, it surges. No backfiring. No misfiring, at least not since I replaced the EGR solenoid that was stuck open. New gas.

My dad wants to rip out the EFI and put a carb on it, but that sounds too much like admitting defeat.

I'm active on another car forum and know how frustrating it is when someone posts "plz halp it dn't run right" with no background. With that in mind, here's way too much information.

1987 F150. 4.9l. EFI. 4x4, four-speed manual. Was dual tank, converted to single tank with the proper fuel reservoir.

What I've tested/tried, and other things that might be related:
TPS tests good. 1.03-4.49v on the green wire, smooth rise, no breaks. Given the symptoms, this is a source of great confusion to me. Part of me wants to chuck a new TPS at it and see if anything changes, but again, the old one tests good, and I'd rather not shotgun parts at this thing.
MAP tests good. 152 Hz on the green wire KOEO, and the number rises and falls if I blow or suck on the vac line.
New EGR control solenoid. EGR valve closes properly.
Fuel pressure sits around 50 psi at idle, 59 if I floor it or pull the vac line off. No gas leakage from the regulator. New low-pressure pump, filter, and fuel.
Temp sensors tested, coolant temp sensor replaced. Both sensors appear to be in range (from what I could find) and all sensors are getting power.
New spark plug wires, cap, rotor, valve cover gasket, PCV valve, and upper intake manifold gasket. Replaced vac lines while I was in there. Checked the vacuum valves for the air injection system, no faults found.
This truck was infested by mice when we got it, and cleaning out that mess required tearing out nearly all of the interior, including the dash. They left the wiring alone, strangely; I'm more worried that I may have screwed something up, either while cleaning or during reassembly.
A/C deleted due to rodent damage. Looks like the evaporator rotted through from the mice and tried to fumigate them. Sadly, it didn't work.
Replaced the battery ground to the frame (was cut for some reason) and re-spliced a couple smaller wires going to the negative terminal.
Charcoal can is not connected. Purge solenoid is missing. There's a mystery harness on the driver's side of the motor with a two-pin plug and a big rubber diode hanging off that I hope goes to the purge. I plugged the vacuum ports on the throttle body for now.
Exhaust doesn't smoke or smell like gas or coolant. (Muffler was full of chicken feed and mice and smelled terrible, so I cut it off.)

Codes:
KOEO: 67. Neutral park switch. I bypassed the clutch interlock, so this does not surprise or worry me.
Continuous Memory: 11.
KOER: 12, idle control. Given that the truck doesn't run properly off-idle, either, I suspect this is a symptom rather than a cause. Nothing changed when I swapped it for a spare idle motor I had on the shelf. 25, Knock sensor not tested. The code table I referred to suggested ignoring this code unless the engine is pinging, which mine doesn't seem to be doing.

Any ideas? I've read that the capacitors tend to leak in the ECU; if fixing this truck is as easy as replacing a few caps, I'd be fine with that. Of course, if there's some other simple cause that wouldn't involve tearing into the dashboard again, I'd like that even better. Either way, I'd like to get this thing back on the road! Thank you for reading through all this and TIA for any advice you may have.

 

Did you check timing?

Could also take the cover off of the computer and see if it's damaged.

 

I opened up the computer tonight and everything inside looks fine, irritatingly. I might replace the caps anyway just to see if it changes anything.

I hadn't thought to check the timing! Should've done that after the KOER test, when it was warmed up. I'll give it a go the next time I can get it out of the shop (got a blown-up Nissan penning it in at the moment).

 

Red or Black?

(I know, I'm not helping.....)

 

Not sure what you're asking--the Ford's two-tone red, if that's what you're after. Well, it was two-tone red; the side stripes were peeling so we're painting those white. Looks pretty sharp! If only it ran.

A friend and I ran a timing test on it tonight. Near as I can tell, it's running something like the suggested 12 degrees at idle (a little to the left of the big notch on the timing indicator). If we increase revs slowly, the mark moves left; if we punch it, the timing dives towards the right. I'm fairly sure this is correct.

Capacitors are en route and I'm really hoping that particular Hail Mary pays off.

 

It was a reference to:

 

Oh! Black.

 

You may have been gyped!

J/K

Even at high school age I knew JW Black was the good sippin' whiskey. I saw a kid mixing it w Dr Pepper (or something similarly disdainful) at a HS party and realized I was in with a bad crowd. He had no doubt stolen it from Dad's liquor cabinet and it was, no doubt, noticed when it came up missing. I hope he got a good a**-whoopin' for that.

Sorry for the derail. I can't help... you already know waaay more about these trucks than I do. I've just got boozy HS party stories.

 

Capacitors definitely need replaced if 30 years old, that's not a hail mary. If they last 10 you're doin' good.

People always talk about how "they look good."
Unless you've got X-Ray Specs, there's nothing to be gained by looking at them.

 

I agree, except when they are leaky, burnt, or broken and obviously bad.

 

Well no that's the point, they don't usually leak. And even then, not until long after they've failed.

 

I totally agree with you, except for the point that you made that it's *pointless* to visually inspect them.

 

LOL even I know you don't mix the good stuff with Dr. Pepper!

Good to hear the straws I'm grasping at are good ones. The new caps get here Tuesday.

 

The capacitors finally came today! I installed them, put the computer back in, blipped the throttle... and it had the exact same hesitation as before. Then it idled down and nearly stalled. Looks like the computer wasn't the problem.

I messed around with the TPS some more, couldn't find a fault, and decided to pull the throttle body to see if there was a big chunk of carbon clogging a passage or something. To my surprise, the gasket was all scrunched up and puckered! I've never seen one do that before. On closer inspection, I found that the manifold's mating surface had a ridge at the bottom of the machined area that stuck out where it shouldn't. I have no idea how it got there, but there it was. The gasket had a little piece torn out to clear it, like whoever installed it knew the bump was there and didn't think it would matter. The bump was thicker than the gasket, though, as evidenced by the scar it left on the throttle body, so that gasket was never properly clamped! It was at this point that I remembered the previous owner saying that the truck never really ran right.

I filed off the ridge, cleaned out the carbon, made a gasket, slapped it back together, and went for a test drive down the driveway and back. The surging and stalling is gone! It didn't even complain when I let out the clutch without touching the gas, it just went! That's the good news. The bad news is that it still hesitates when I hit the gas.

I need to check the timing again now that I've changed how the engine is running (and now that I've looked up how to do it properly). I'm also wondering if the throttle stop is adjustable. I noticed the butterflies don't close completely, and I'm wondering if they're supposed to. Maybe someone adjusted this to try and mask the air leak, and the volume of air passing through that isn't what the computer expects? Maybe I'm overthinking this? Any ideas you have, I'd love to hear.

 

Thanks for the update & info, sounds like progress.