I have been working on my 1985 F150 302 EFI on and off again for the past couple months. I am about 2k deep and running out of things that I should check to try and fix the problem I am currently facing.
The list of things I have checked and replaced, then it will be followed with the codes I pulled from my OBD1 Reader (OTC 4000 HD)
Distributor (Put in correctly)
Spark Plug wires
Fuel Pumps (All 3 were bad so I replaced 1 high pressure and 1 low pressure to try and get the car running I will add the other when I get it running right)
ECM capacitors (the 3 main capacitors had blew and were leaking on the board so I cleaned it and I soldered some more efficient ones on the board.)
Most of the other sensors but I am willing to check them again and get voltage readings but using the haynes guide, the sensors fell within the spec in the book.
Checked for a vacuum leak and I couldn't find any.
These are the codes I pulled before I disconnected the battery for half an hour and tried to drive it around.
KOEO with I think a C code mixed (Forgot to separate)
18 (idm circuit failure or spout circuit grounded wasn't sure)
31 (pfe below minimum voltage of .24 volts)
54 (Act Vat -40)(ACT sensor signal is greater than the self test maximum of 4.6 volts)
63 (has intermittently failed below minimum .6)
12 (Can't Control rpm during er self test high rpm check)
25 (Knock sensor during dynamic test)
34 (pfe or evp circuit above the closed limit of .67)
44 (thermactor air injection system inoperative)
EGR had a block plate in because I wasn't sure it was the problem and it still runs terribly.
The main issue: When giving 1/2 to 3/4 throttle it will backfire and stumble over itself. When idling it will idle well for a moment then almost stall out. You can also visibly see the lights flicker when that occurs. I am pretty much stuck atm. Any help would be appreciated I am pretty much willing to test whatever is needed. Only things I don't have currently is a timing light and a way to tap into the fuel lines. I have a pretty much every other tool that I should need.
Wow! With those codes and the way it is running it could be a whole lot of things. But the main one I'd worry about is the ECU. You don't know that it is good, especially given the problems it had. And a problem with the ECU could cause it to spit out all sorts of codes - and run poorly.
So I'd be looking for another ECU to at least test with. Perhaps someone on here has one you can at least borrow if not buy.
Another worry is the timing chain. The backfire/stumble is typical when the chain has jumped time as that messes up both cam and ignition timing. Have you checked to see how much slop you have in the chain? If your engine has a fuel pump blockoff plate you can pull it and see how loose the chain is, and the factory spec is 1/2" of slop, max. If you don't have a plate then use a 15/16" socket on a breaker bar and see how much you can turn the crank back and forth before the rotor in the distributor turns.
And then there's ignition timing itself. Not knowing what others have done to this truck I'd get a timing light and check. You have to pull the SPOUT connector to test. But if the initial timing is way off then your timing chain may have jumped.
Thanks for the reply!
I’ll probably start with the cheaper stuff and work up from there. I’ll add more to the thread later this week when I’m able to work on it again. Hopefully I’ll be heading a bit more in the right direction so I can stop throwing parts at it LOL.
proper plan. now is the time for testing and measuring. as frustrating as it may be, diagnosing is NOT deciding. all too often we decide "it must be" and so on.
how many miles are on this engine?
can you see any tell-tale signs of the timing chain having been replaced like visible gaskets or glops of silicone etc. ?
anything out of expected range will mess with the ecu as all of its actions are based on "known standards". get two of more out of range and the old garbage in, garbage out shows up.
back to basics. and you cannot adjust valve timing with the distributor. ignition timing only! one is tuning and one is foundational as a known standard to the ecu.
The truck itself has 171000 miles and the engine itself is pretty clean. I pretty much have been assuming that they really didn't do much maintenance on this vehicle. Everything that I have replaced on the vehicle was original and when I was in it I didn't seem any silicone or anything around the timing chain. I'll be busy with work until the 21st so thats when I'll really dig into it. I'll probably ordering the timing light and verify if the timing is off.
With an old vehicle you shouldn't assume that the harmonic balancer is good. Over the years the rubber on them shrinks and the outer ring can move relative to the inner ring, which means the timing marks will be off.
So before you set the timing you should at least look at the balancer closely to see if the outer ring appears to have slipped. Obvious clues are that the ring is cocked on the inner ring, or isn't flush the whole way around.
But it is even better to find TDC on #1 by pulling a spark plug and either using a piston stop or something like a straw against the piston. Then, with #1 at TDC, see if the TDC mark on the balancer aligns with the pointer.
If the caps on your ecu were bad, start by changing the ecu. Given the milage and the conditions in an engine compartment ( with all my years of electronic experience, i'm surprised some of this stuff in particular, the tfi module lasts 5 minutes down the road) Electronics do not like heat at all, and if those caps were buldging, you can rest assured the transistors in the ecu are not operating to spec regardless if you changed the caps or not. Definatly start there.
Nick and George
1986 1/2 F150 XLT Lariat 4X2 300 Six - C6 - 3:08 in a 8.8 - Fully Loaded - 8 Foot Box
Owned since new
I am back with some more news.
Checked the timing chain and it was nice and tight and the timing was set at 10 degrees (looks like it was replaced at one point since it was newer). I was still having problems with the car retarding itself so and after testing a few more things I am going to shoot for the ecm and getting a replacement for it. I have tested most of the mechanical things that could cause these problems and updated older parts that were worn and this is what I am left with. The car is getting ample fuel, all the sparkplugs are firing correctly, the cylinders are good so this seems to be the last bit. Another note is that this truck has been sitting for at least 3-4 years at a MINIMUM because the dash is completely baked and I would be surprised if the years out in the sunlight not moving could have caused some problems. I have the ecm number so I will be getting that as soon as possible. (also turns out I had a timing light so didn't need to buy one so yay I guess)
At least if the ecm is fully functional I should be able to get some decent codes from my tests at a minimum.
Thanks for the help guys