1986 Gt 5.0 Miss Fire At High Rpm Help!

Donovan Daly

New Member
Jul 25, 2012
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Hello, i have a 1986 mustang gt. 5.0 manuel transmission. I had a problem with the coil in the ignition module overheating and the car would shut down so i replased it but it turns out i needed a new distributor as well. As soon as i replased that (All motorcraft parts, as i got recommended to me) the car doesnt overheat anymore, but at High rpms (3'k and higher) it seemed to miss fire. I replaced the ignition switch because i was told that may be the problem, but it turns out that didnt work. I also cleaned and checked the battery terminals also that didnt work. Im sort of running out of options and i dont want to bring it to a shop (dont have alot of money to spend). It is very inconsistant. It seems on colder days it misses worse than on warmer days. Other times it runs almost perfect and other times you can barley touch the gas after realsing the clutch and it wont accelerate worth a :poo:. Once the car warms up it seems to run fine but after driving about 30 miles and i shut it off it seems like the battery is almost dead when you try to start it but it always starts up anyway. Im kind of at a loss here so ANY help would be awesome. If you need more details i have alot more so please help me out!
 
Did you put the white heat sink compound on the TFI module where it bolts to the distributor? If, not, the TFI will overheat and cause problems.
 
Did you put the white heat sink compound on the TFI module where it bolts to the distributor? If, not, the TFI will overheat and cause problems.
Well i had a problem with the TFI module were it would over heat and the car would shut of and it would take a while to start back up. i replased the TFI module and i still did that but the i replased the distributor and it stopped. Im not sure if i put in a White heat sink or not. If that were the problem would a cause miss fires like that? Because the car doesnt overheat and shut off like it did before so i know that isnt the problem. im wondering if it is a faulty distributor?
 
Well i had a problem with the TFI module were it would over heat and the car would shut of and it would take a while to start back up. i replased the TFI module and i still did that but the i replased the distributor and it stopped. Im not sure if i put in a White heat sink or not. If that were the problem would a cause miss fires like that? Because the car doesnt overheat and shut off like it did before so i know that isnt the problem. im wondering if it is a faulty distributor?

So that's a, "No".
 
Well i have a MSD distributor so that doesnt even have a heat sink or anything like that just the TFI which i already replased. So i dont see the point of doing it again . Most of the threads i have seen with missfires like mine they all have MSD distributors
 
Well i have a MSD distributor so that doesnt even have a heat sink or anything like that just the TFI which i already replased. So i dont see the point of doing it again . Most of the threads i have seen with missfires like mine they all have MSD distributors
That's a piece of information I failed to pick up in your first post. MSD stands for "May Suddenly Die". You may want to dump the codes and look for code 14, which indicates a PIP problem.

The distributor body IS the heat sink: no fancy fins or protrusions. The heat sink compound is a must have for all TFI installations.

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

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If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
 
That's a piece of information I failed to pick up in your first post. MSD stands for "May Suddenly Die". You may want to dump the codes and look for code 14, which indicates a PIP problem.

The distributor body IS the heat sink: no fancy fins or protrusions. The heat sink compound is a must have for all TFI installations.

Pulled the car into the shop this morning and i DO have a Heat Sink. Is it possible that a brand new distributor went bad?