My Dad has a 1986 Ford F-150 Lariat with an inline 6. (I like my '71 F-100 much better! ) There is an electrical gremlin somewhere in the ignition. It runs REALLY rough and dumps a lot of unburned gas out the exhaust. To the point of irritating your eyes if you are around the truck at all. Once in a while it will run great and then go right back to crap. Hooking up a timing light to the ignition wires shows huge caps in when it fires. This happens with all the wires but mainly numbers 1,5, and 6.

This is what has been replaced:

Catalytic converter
Distributor (Yes, it points to #1 at TDC)
Plugs/Wires
Cap/Rotor
Coil
ICM (The one that fits on the side of the distributor)
(It has an electronic advance, not vacuum.)

Any ideas as to what could cause this? What are we missing here?

Thanks!

 

Hmm, well. If it is carbed, i would suspect a float needle that isnt seating, flooding out the carb. Thats all i can really think of. If it's EFI on the other hand, well, might be bad o2 sensor telling the truck to enrichen the mixture too much. Not really sure. Good luck with your problem.

 

I'm having the same problem on my 86 F150 302 with EFI. Done the same tests as you, and burned through 3/4 tank of gas trying to find something...to say she is running rich is an understatement. Also have unreliable spark on #1. I've replaced the coil and ignition module (mine is on the distributor also). I was considering replacing the EEC microprocessor. Any luck on fixing yours yet? Did you try the O2 sensor? Your input is greatly appreciated. If I figure anything out, I'll let you know.

 

If it has a O2 sensor, and it's been a while since it's been changed, you should change it out. I would recommend changing it every time you replace your spark plugs.

You could try unpluging the O2 sensor and see if the computer will go into open loop mode. If it runs better with it unplugged then replace etc...

If you have a feedback carb, check the air/fuel solonoid on the left side of the carb. If it's malfunctioning it could also be culprit.

Check the computer for codes, do a no start and run test to the computer, and see if you get any codes...

Hope this helps, good luck.

 

Just a suggestion if you've tried everything else, try to clean out the throttle body, its not enough to also have it shiny clean, but take a good look at those two small slits near the throttle plates inside the throttle body, the two fitting that are the vaccum fitting on the outside go to these two slits and can become clogged with carbon buildup...this would increase the air flow inside the throttle body...by pulling air through them tiny slits...if they are clogged, no air can go through them, thus, rough idle, poor gas mileage would be part of the problem too. This is only for the EFI engine...

 

If it has over 60,000 miles try replacing oxygen sensors. I've had better performance with factory Ford units, some are cheaper than aftermarket.

*check fuel presure regulator

*temp. sending unit (not switch, the one that goes to temp. gauge) one that tells ECM the engine temp.

*throttle position sensor

 

Its a 300 six. No sensors are going to make it run that bad. If the oxy sensor failed, the cpu would go into open loop, meaning it would run and use a little more gas, but even close to the point that raw gas would be dumping out of the exhaust.

also, 80-86s 300-6s have no Fuel pressure regular.

Its carburated. So, check your choke. Every ford 300-6 I've ever owned had the electric choke go bad, causing missing, bad running, etc. I almost guarantee that is your problem.. Warm the truck up and pull the air cleaner to see if the choke butterfly is open.

If that isn't it, alcan suggestion with the needle not seating is a good one, or the float could have a hole in it, and flooding it. However, I doubt either one because you can still start the truck.. If that was happening, it probably wouldn't start.

the ignition trouble is probably caused from the excess gas. The plugs are probably all fouled beyond belief..

when you figure out the problem, change the oil and plugs.. The oil will have a lot of gas in it (gas in oil = bad for bearings). The plugs will be fouled as well.

As for the person will the EFI302, check the fuel pressure regulator.. That would be the first place I'd start. Other than that, I can't help you with the EFI. I'd check the FPR b4 I changed the cpu

 

I tried the O2 sensor...no luck. I wasn't getting bad mileage before...in fact she was purring like a kitten. Shut her off, came back three days later and she would barely run, dumping raw fuel out the exhaust and running as if she was severly out of time. She will not even run with less than 1/3 throttle. I was wondering about the FPR myself but didn't think that would affect why I'm not getting consistent spark on #1. Or could it?

 

Could your gas have water in it? My brother has one just like yours, had the same problem, and just like mentioned above, it was the choke...stuck of coarse.

 

the FPR could do that.. If your cylinders are filled with double or triple the gas, your ignition will be fouled, and won't be able to fire as well.

pull the vacuum line on the FPR and see if there is any gas in it.. If there is, that could be your culprit.

On your truck, the other thing could be that you jumped a tooth on your timing chain. That would do it too.

BTW, the guy with the 300 could also have jumped a tooth in timing, but it is less likely with a 300 since it has a gear drive. It could have the plastic gears though, they can loose a tooth and cause problems.

 

YES, sensors can make one run bad, specifically Temp. sensors, could be fooling cpu to thinking engine is cold (as a choke on a carb.) and feeding to much fuel. TPS, also could be sending signal to cpu to add more fuel. (This recently happend on a friend's truck).

My uncle owns an 85 300-6. I have seen many 85 & 86 300-6 EFI.
According to Ford publications, about 85% of 85 & 86 300-6 were fuel injected,15% were carb.

 

Yes, it can make it run "bad" but not as bad as having the choke shut.

The TPS sensor on my 'carbed' '85 is unhooked completely. Didn't have a problem running. The temperature sensor for the computer is also disconnected b/c the harness plug was ripped off. The richest the feedback carb is in open loop mode, and it is rich, but not rich enough to cause those kinda of troubles. If you don't believe me, you can come and take my '85 for a ride. it runs decent considering how many parts are not hooked up or working.

I don't know which Ford publications you are referring to, but I think you will find that 85% of 85 & 86 302s were fuel injected, not 300s. I own an '85 300, and I've seen many, _many_ 300-6s in the junkyard, and none of them except '87 or newer have ever had fuel injection.

 

The TPS sensor I'm refering to is for EFI!!!!! Without it it won't operate. Carbs don't have TPS. Maybe you have central fuel injection??? The venturi position sensor is often refered to as TPS, this sensor tells the CPU where the throttle bores are at, but it does'nt regulate how much or how little fuel to send to engine like EFI, that is determined by venturi opening and vaccum much like a carb. I don't know of any carb equipped to have a cpu????? All 85 & 86 302's supposidly had EFI and starting in 86 351 & 460's were EFI. 85 351 & 460's were carb. There are exceptions, (as with anything in life),I have worked as Auto Technician for Ford for 21 years, and have seen a few combinations of supposidly not built. Ford claims most 300 EFI were shipped to West Coast of U.S.A. & most carbed to East Coast. I did'nt say I did'nt believe you, Cause there are allways variances & exceptions to every thing.

Do you have 300 6 in your truck???
THANK YOU FOR YOUR INPUT!!!