hi everyone! I have a 1986 f150 with the 5.0l engine I have recently put a new gas tank, fuel pump(s), fuel filter, injectors, plugs, plug wires, rotor button, rotor cap, act sensor, etc sensor, and tps sensor. All NEW parts. The only thing I could find was the knock sensor wich is broke off. I have a knock sensor from the 300 inline 6 in the vehicle as of right now. I do not know if this is the cause of my problems. The truck starts up in the morning and goes through its warmup and then runs great. It might not be perfect but how much perfection I expect from this old of a truck. But once it's warm and I shut it off and then come back to crank it (still warm) it cranks idles up and then dies and does this unless you continue to crank after various attempts or give it some throttle. The truck also shifts hard at cruising speed if you let off the throttle and coast and then accelerate again almost like it jerks in to gear. I don't know if this is associated with my running problem. I know this is a lot but hope you all can help!

 

There are a lot of things to consider.
Is the Idle Air Control (IAC) solenoid working properly? Do you have a vacuum leak?

Have you cleaned the throttle body?
I would start by cleaning the throttle body, then running the EEC diagnostic test (Key On Engine Off test). See what codes come up (if any). You can google how to do it. For example:
Here's a good description on how to do the tests: http://www.tomco-inc.com/Tech_Tips/ttt6.pdf In this description an "analog voltmeter" is used.

After the KOEO test a Running test will check the IAC and EGR (among other things). See what that test reveals.

Regarding the Knock Sensor - I don't think a 4.9 sensor will work properly in a 5.0L engine. I know the part numbers are different for a 4.9 and a 5.0.

These sensors are tuned to specific frequency. It seems knock Sensors are getting hard to find for some reason. This is supposed to be a replacement: More Information for AIRTEX/WELLS 5S2211 but I doubt that sensor is the cause of your problem.

 

I hand pulled codes recently and just get the one for the knock sensor. The link you sent no longer has that part available. The idle air control is just about the last sensor I have not replaced. I have had the throttle body off and replaced the gaskets but it didn't seem to dirty. Do you think the iac could be the cause? And I have tested for vacuum leaks and there doesn't seem to be any.

 

Certainly the IAC could be a problem. It was not uncommon for them to get gummed up and stick (the crankcase fumes (oil mist) is going through it via the PCV). You may be able to clean it by spraying "throttle body cleaner" through it with the engine running. If you do this you will want to replace (or at least clean) your spark plugs afterwards.

I recall that the later model Throttle Bodies had a coating on them (Teflon I think) to help prevent oil-gum from sticking - so you had to be sure to use a "coating safe" throttle body cleaner. But I don't remember if that was on the 5.0L trucks too.

On the Knock sensor, if it is not working (not correct p/n) it could cause computer to think engine is knocking which would then retard timing. That wouldn't result in the problem you posted about but it would make the truck run like crap. Maybe a salvage yard would have the correct part. Otherwise keep looking/reading about it - someone must have a solution or source for this part.