Well - call me what you want but I put a coil and a throttle position sensor in it tonight and that wasn't the problem.

 

Let me ask a question - could this be the IAC (Idle Air Control)? If this thing is bad and never letting more air move threw as you accelerate, stuck at zero %, could this cause a rich, bucking, cutting out condition?

If I understand correctly I can check this by unpluging it and the idle should change? If it doesn't that means it is bad. When unpluged the motor should stumble and stall. If it keeps running and there is no change in the idle it needs replaced or removed and cleaned.

 

let the engine run with a gauge on it for fuel pressure for say 30 mins or so, or just drive it a bit till its bucking and chugging, then check the fuel pressure. sounds to me like the fuel pressure regulator. those sometimes will stick after a while, and you will end up with a fuel pressure of 70 80, or sometimes 90 psi. does it run better around 3,000 than say 2000 rpms?*

 

No... it has no effect on engine operation above idle speed.

 

Yea the IAC is at 100% open when on the road, its ready position to take over engine idle control.
If it was closed "warm cruise" when it should be full open, your motor would stall, or would tend to try and stall every time you let off the gas pedal.

 

is the IAC why ppl in my drivethru sometimes have vehicles that seem like they're slightly revving every second? lol i've always wondered what was up with that

 

The computer is programmed to idle up the engine every time the AC clutch or electric fan engages, the smaller the motor the more it revs under this load.

 

It does seem to run a little better, (I said a little better) at higher speeds - rpms. It acts up the worse at like 30 - 45 mph. And after a 12 - 15 mile drive when I stop it seems like it is going to shut off - the idle (in park) goes way up and then way down and up and down......

Dam thing runs all but perfect for the first 2 - 3 miles and then crap. This is when the motor is dead cold.

 

It may need a new IAC, or at least cleaned but no its not the reason it runs like it does. I wouldnt do anything with it until the main problem is cleared up.

Its runs better going fast for the same reason it runs good cold, it needs all or most of the fuel its getting for those conditions.

 

I did clean the IAC a few months ago.

So could it be the fuel regulator? Is there any way to check it to see if it is operating properly? I did have the fuel pressure checked at a garage and it was ok. Is the regulator before or after the place you check the fuel pressure?

 

Well after reading a bunch of these, i feel a little better than i am not the only one having the same problem too. I have a 87 F-150 with 89 460 EFI. I rebuilt the the whole thing and it's making me mad. I have put everything new in it besides Coolant temp sensor and fuel pressure regulator. mine runs great for the first few miles as well. loses power and then when shut off won't start, it will just sit there hardly idle or die. if you give it more throttle it dies or do nothing. no check engine light has come on either. unhooked the tps and motor shuts off. so my last option is it's prolly the fuel pressure regulator. That's what i am going to try. all other trucks i have seen have bad O2 sensors never really ran that bad. heck my old build 302 i had in it before didn't even have one and i put a block off plate on the egr and ran just fine.

 

also i am running platinum plugs. didnt' know dad threw those in when i was out of town working. platinum plugs require a bigger coil. your stock coil does not burn hot enough unless you buy a accel coil or mallory.

 

throw out the plat plugs.

 

yeah for these engines copper is just fine

 

Yeah, I just wish I could figure it out with my 460. I am tired of working on it and I want to be able to drive it.

I did forget to mention my plugs are pitch black. so i know it's running rich. so what does everyone think.......try the coolant sensor or fuel pressure regulator.