86 5.0 efi runs terrible

[86 5.0 short box]

The TFI (Thick Film Ignition) is the aluminum module attached to the distributor. You might want to read up here on the results of the class-action suit won against Ford.

Basically, the module gets hot and fails, but when it cools the vehicle will run again. That write-up mentions 257 degrees F, but it isn't that precise. And, as the modules age the temp can easily come down - to the point the engine may only run a few seconds and then stall.

The fix is either to install a new module and hope it doesn't fail, or move the module to a cooler spot, like on the fender liner, like Ford did later.

Can that tfi module cause the engine to run on only 6 cylinders?

[85lebaront2]

Can that tfi module cause the engine to run on only 6 cylinders?

I don't think so, however, back when vehicles still had breaker points, I have seen a worn advance cam or bad bushings cause cylinders to not fire.

Try using your timing light on #3 and #4 plug wires to see if they are firing, if not, closely examine the distributor cap for cracks or carbon tracks. You don't mention plug wires, how old are they? Old rule I used in my shop was anything over 3 years by the date code was suspect.

If all this checks, with the cap and rotor removed, take the shutter (cup shaped with 8 vanes) off and check the vanes for signs of damage. The narrow vane is for #1 cylinder, then go counterclockwise viewed from the top to #4 and #3 and see if there are any obvious differences in them.

[Gary Lewis]

Can that tfi module cause the engine to run on only 6 cylinders?

I doubt it. The TFI failure mode is usually "on" or "off", meaning that it either works or doesn't.

But I suppose that if the teeth of the reluctor wheel in the distributor for those two cylinders were shorter, meaning that they didn't come quite as close to the pickup as the others, it might not fire on those cylinders. In that case I think the pickup module in the distributor would be the culprit. That module provides the signal to the TFI module that tells it to fire, and the TFI doesn't know which cylinder it is firing. But the pickup module does because each cylinder has its on tooth on the reluctor wheel.

[Gary Lewis]

I don't think so, however, back when vehicles still had breaker points, I have seen a worn advance cam or bad bushings cause cylinders to not fire.

Try using your timing light on #3 and #4 plug wires to see if they are firing, if not, closely examine the distributor cap for cracks or carbon tracks. You don't mention plug wires, how old are they? Old rule I used in my shop was anything over 3 years by the date code was suspect.

If all this checks, with the cap and rotor removed, take the shutter (cup shaped with 8 vanes) off and check the vanes for signs of damage. The narrow vane is for #1 cylinder, then go counterclockwise viewed from the top to #4 and #3 and see if there are any obvious differences in them.

Bill beat me to it. But we are on the same page. His "shutter" is my "reluctor wheel". And his idea of placing your timing light on 3 & 4 is a good one.

[86 5.0 short box]

I don't think so, however, back when vehicles still had breaker points, I have seen a worn advance cam or bad bushings cause cylinders to not fire.

Try using your timing light on #3 and #4 plug wires to see if they are firing, if not, closely examine the distributor cap for cracks or carbon tracks. You don't mention plug wires, how old are they? Old rule I used in my shop was anything over 3 years by the date code was suspect.

If all this checks, with the cap and rotor removed, take the shutter (cup shaped with 8 vanes) off and check the vanes for signs of damage. The narrow vane is for #1 cylinder, then go counterclockwise viewed from the top to #4 and #3 and see if there are any obvious differences in them.

I have excellent spark on all plugs and that would tell me the plug wires are good correct?

[85lebaront2]

I have excellent spark on all plugs and that would tell me the plug wires are good correct?

Maybe, under load they may act differently. Quick question, what spark plugs are you running? I have seen some strange behavior from plugs, particularly Bosch Platinum in Fords. I personally stick with Motorcraft for my Fords and Champion in the Chrysler.

[Rusty_S85]

Can that tfi module cause the engine to run on only 6 cylinders?

not running on two cylinders can only be a few things. No fuel to those cylinders, no compression to those cylinders, no spark to those cylinders, or mechanical failure such as broken rocker arms, bent or broken push rods, or a distributor cap with those two terminals heavily damaged, or the reluctor in your distributor is damaged on those two cylinders and not providing a signal to fire.

The TFI module is basically the ignition module that controls the coil it either fires the coil or it doesnt it wouldnt pick and choose

[86 12 Brutus]

not running on two cylinders can only be a few things. No fuel to those cylinders, no compression to those cylinders, no spark to those cylinders, or mechanical failure such as broken rocker arms, bent or broken push rods, or a distributor cap with those two terminals heavily damaged, or the reluctor in your distributor is damaged on those two cylinders and not providing a signal to fire.

The TFI module is basically the ignition module that controls the coil it either fires the coil or it doesnt it wouldnt pick and choose

I've seen the TFI do some strange things in the past which is why i brought it up. They act different under load. Also check the reluctor wheel in the distributor, i'm not saying this is definatly your problem, but you do need to start somewhere. Things act differently under load. I know i can do this in Brutus, but he has an electronic carburetor and not efi. But you can at least in Brutus, disconnect the computer and the truck will go into limp mode, the truck will run enough to get you home, and this is also how you adjust the carburetor. The engine computer takes care of your timing and spark advance, but like i said, i dont know anything about efi, but may be worth a check. I have all the books on the 86, if you need any info, ill be glad to send it to you. In the meantime, here is brutus with the tfi on the fender

[old55pete]

I have excellent spark on all plugs and that would tell me the plug wires are good correct?

One of the things I have noticed with my 5.0 EFI Bronco over the years, 34 years, There are two different ignition rotors for that engine, One the parts stores call " The California rotor "( it was also used in New York, New Jersie and one other state). I remember doing a tune up while stationed at Ft Bragg went to the local NAPA and bought cap, rotor, wires, plugs and filters. After the tune up was finished, it ran worse and I want to say that it was missing on 3 & 4. Because I was in NC and nobody asked I ended up with the wrong rotor, the 46 state rotor. After some digging at the NAPA, the finnaly asked if it was from California. They gave me the correct rotor and the miss went away.

Are you sure you have the correct rotor? look up your engine calibration number and see if you have the right one. They will both fit, but the Cal. one has a long tail on it with a pin on the bottom of the tail that goes through a hole in the Hallefect sensor cover.

The NAPA part number for the" Ca rotor" is MPE FA152SB, the 46 state rotor is MPE FA144SB.

Just a thought and a blast from the past.

[86 12 Brutus]

One of the things I have noticed with my 5.0 EFI Bronco over the years, 34 years, There are two different ignition rotors for that engine, One the parts stores call " The California rotor "( it was also used in New York, New Jersie and one other state). I remember doing a tune up while stationed at Ft Bragg went to the local NAPA and bought cap, rotor, wires, plugs and filters. After the tune up was finished, it ran worse and I want to say that it was missing on 3 & 4. Because I was in NC and nobody asked I ended up with the wrong rotor, the 46 state rotor. After some digging at the NAPA, the finnaly asked if it was from California. They gave me the correct rotor and the miss went away.

Are you sure you have the correct rotor? look up your engine calibration number and see if you have the right one. They will both fit, but the Cal. one has a long tail on it with a pin on the bottom of the tail that goes through a hole in the Hallefect sensor cover.

The NAPA part number for the" Ca rotor" is MPE FA152SB, the 46 state rotor is MPE FA144SB.

Just a thought and a blast from the past.

Steve, i forgot about that one. Good thought