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Brad, ASE Certified Technician
Category: Ford
Satisfied Customers: 2366
Experience:  ASE Certified Master Technician
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1986 ford f150 runs fine util it warms up the the idel ...

Customer Question

1986 ford f150 runs fine until it warms up to normal opertating temp, then the idel slowly drops and the truck dies. It will not start again until it has cooled off. If you catch as it starts to die and hold the gas peddle to the floor it will clear out and rev up but then it starts caughing and sputtering until it evetully dies. let it set for a while and it will start and run fine until warmed up agian.
Replaced the module on the side of the distrubutor, replaced the air idle contorl (or some similar name, it sits on top of the throttle body) and replaced the map sensor. No difference.
Submitted: 10 years ago.
Category: Ford
Expert:  Mike V. replied 10 years ago.
Hi there! I suggest looking at the egr valve.If it is sticking open it will give you running problems when hot.It is designed to open when the rpms are high.If it is sticking open when they are low it is almost like an intake air leak.You can take it off and clean it with carb cleaner.Make sure you check any vaccum sources going to it as well,if the vaccum is staying on when it should be off then a switching solinoid could be the problem.Hope this helps!Thanks
Customer: replied 10 years ago.
Changed EGR valve same thing, runs about 15 - 20 minutes idel drops, it dies and wont start until it cools off.
Expert:  Mike V. replied 10 years ago.
OK,Next step should be the coolant temp sensor.If the pcm thinks the engine is cool even when it is hot it will give the truck a rich mixture that may be flooding it out.The coolant temp sensor is located in the upper intake to the left of the distributor behind the water outlet if this is a 5.0 v8.
Customer: replied 10 years ago.
It's a straight 6 - Where would it be on that engine?
Customer: replied 10 years ago.
Relist: No answer yet.
Expert:  Marc replied 10 years ago.

See the diagram below for engine coolant temp sensor.

Customer: replied 10 years ago.
Reply to Marc's Post: Hello hope your fourth was good. I disconnect the engine coolant tempature sensor as indicated in the drawing above, unfortunitly no change. Runs fine until it warms then starts to sputter and dies and wont start again until cooled off.
Expert:  Marc replied 10 years ago.

Disconecting it isa not going to do anything You need to determine if the temp sensor is sending the correct signal to the ECM

You have to back probe the plug at the white and black wire and check the voltage with a volt meter.

Normal voltages

Cold engine (70 degrees F) voltage should be about 3.0 volts

You can also try conecting the pins together when engine is hot if the engine clears out and runs better replace the sensor.

Full warmed engine 190 degrees Voltage should be 0.7 volts

Customer: replied 10 years ago.
Reply to Marc's Post: I don't have a volt meter so I used two allagater clips and a peice of wire as suggested above. Did'nt make a differnce still died.
Expert:  Marc replied 10 years ago.

Is the engine warming up to full temp? if it is not you may have a stuck open themostat.

Is the check engine light coming on?

If so you need to get the codes .

Customer: replied 10 years ago.
Yes it warms up to normal operating tempature before stalling. Although today the temperture gage barly regigstered before the idle begin to drop and it stalled. I don't know if it had anything to do with it but it was 98 today.

No engine lights come while running or druing the stalling.
Expert:  Brad replied 10 years ago.
You may have a restricted exhaust... (such as a plugged catalytic converter).. try removing the oxygen sensor when it is hot and start it back up.. it will be very loud, but if your power has been restored significantly, it will prove a restriction exists.

Usually when the converters get plugged, it'll run fine when cold, but gradually lose power as it warms up (especially under load) until it just won't keep running anymore.

Good luck!
Customer: replied 10 years ago.
I borke the oxygen sensor lose, re tighted let the truck run until it sputtered and died as usual, took it out and tried restarting, After it cooled off enough to start I let it run with the sensor removed until it again sputtered and died. Since it runs the same as before I reinstalled it.

Next I took the muffler off and rammed a metal rod down the catalytic to punch a hole in it. Now if I ever get the truck running right I'll have to replace it but I'm sure it's not pluged anymore if it was. In anycase, it still runs fine until normal operating temp then the idel drops and it slowly sputters and dies. as before if you catch it at the right time and hold the gas to the floor it clears out for a 30 - 40 seconds then sputter for a while and die.
Expert:  Brad replied 10 years ago.
I think your next step is going to have to be checking the fuel pressure. You'll have to install a fuel pressure gauge (you can usually borrow one from a parts store with a deposit) and run it until it acts up.. if you see your fuel pressure drop when it acts up, you're going to need a fuel pump. Hook the pressure gauge up to the schrader valve (like a tire valve) located on the fuel rail.. that is IF this is fuel injected.

If it is carburated.. hrmm i don't know.. a clogged jet maybe?