Hey everyone, I have a 1986 F-150 that has been running great up until the day before yesterday. I was driving home at freeway speeds and all of a sudden the engine just cuts out. I pulled over to the side of the road and tried starting it for a couple of minutes and then it finally started back up as if nothing had ever been wrong. It did it again yesterday morning on the way to work. Again, after about a minute, it started back up. At lunch yesterday, I went to go to the store and had to stop at a stoplight. As I went to drive forward, the truck died and wouldn't start back up. The electrical system inside the cab didn't hiccup, dim or anything and I had plenty of fuel. So I had it towed home and after some initial diagnostics, I found that there was no spark to the spark plugs.
Since the rotor and cap were pretty well worn anyway, I replaced those with new, and same problem. I then put a volt-meter on the input side of the coil and saw 6.something volts there. On the output side, I saw 12+ volts. I then ran through a test in the Haynes book and hooked up a test light to the tach input of the primary coil and saw the light flash as it was supposed to when the engine was turned over. However, the light didn't light up, what-so-ever when I put it on the output side of the coil. Would you guys say bad coil at that point or is there something else I should check?
Mike
P.S. I forgot to mention, that when it was running "fine", when I hit the breaks hard it would die as well.
Well, it is a 302 5.0L EFI with Auto transmission. I replaced the coil last night and the truck started and I thought everything was fine until I drove it to work this morning and it died going into the parking lot. It then idled really erratically, trying to die and then coming back up to speed over and over again. MAP sensor?
ok. I went out and started the truck and unplugged the MAP sensor and it ran worse without it than with it. I also am now noticing black smoke coming out of the exhaust. So now I am not sure what it could be.
86 efi 302 has the tfi module on the distributor right? when it cuts off put a test light on the ground side of the coil plug and crank it and see if it flashes. if no flash then its more than likely the tfi module.
Yeah, the TFI is on the distributer and last night it was getting flashes, but no spark. Replacing the coil helped that and I am still getting flashes. I replaced the MAP sensor and it is still ideling really bad. I am leaning toward the TPS now, but dreading having to replace it since the position it is in means having to remove the throttle body and I hate messing with that.
ok so its running rich as hell right now or only while the map was disconnected? do you have a vacuum pump? and/or a voltmeter? this way you can test the tps and the map.
MAP is good. It is brand new. Just replaced it during lunch. It is running rich with or without the MAP plugged in. I am not sure about the vacuum pump, I know it has a smog pump on it. And I am at work right now, so don't have a volt meter handy. I did end up buying a Code reader during lunch as well, so will hook it up after work in the parking lot and see what it gives me. The TFI and the TPS are relatively cheap parts, they are just in akward areas, so doing a 'quick' swap of these parts isn't easy, which is why I want to narrow it down first.
edit: Duh, now I know what you meant by a vacuum pump. Yes I have both a vacuum pump and a voltmeter, but both at home.
Last edited by tazzmann; 11-05-2009 at 06:09 PM.
Reason: Duh moment
when i asked about the vacuum pump i meant one that you can hook to the map and pull a vacuum on it and see how it reacts. and your tps should be the same as mine. it should have a little harness that plugs into the engine wiring harness (i think its like 6-8"?) which allows for easier testing. just need to back probe the signal wire in the tps harness and see what the voltages are.
ok. I won't be able to do any of that until tonight when I get home and have the proper equipment on hand. Hopefully, I will make it the 19 miles back to my house.
One question though, just to make sure. Is the TPS under the throttle body on the left side as looking at it from the front of the truck? or is that something else?
Ok. I took a break and went out and ran the KOEO diagnostic and it returned an error code of 83. The continuous memory shows codes 18 and 22.
Now, according to the book, a code of 83 is: EVP/EGRC/EGRV
Code 18 is: Loss of Tachometer input/IDM Circuit Failure/SPOUT circuit grounded
Code 22 is: MAP or BARO Sensor out of range.
Code 22 could be due to the fact that I had the MAP sensor unplugged while driving it. Code 83 has something to do with the EGR Valve position sensor (Whatever that is) and 18 has to do with the TFI. So still not sure what to look at first.
Mike
Last edited by tazzmann; 11-05-2009 at 06:52 PM.
Reason: misspelling
i once had a pontiac where my EGR sensor went out. it caused similar issues but not quite as dramatic. more like spuddering like it was ganna die. i changed it and it fixed everything. dunno if this is relevant at all.... i dunno if this is right but what i took away from it was it seemed like to much exhaust gas was being recirculated and choking the engine especially if i floored it.... i could be totally wrong tho
Last edited by andrew_516; 11-05-2009 at 07:18 PM.
Yeah, that is what it is doing currently. I had heard that unplugging the vacuum line to the egr valve should make the engine run better if the egr valve is faulty. Don't know if this is true or not, but i might give it a try after work today.
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