Troubleshooting 87 4.9L EFI F-150

[dzertracer]

I'm having trouble with my 1987 F-150 4.9L EFI/C-6. During idle it is running very rich (exhaust smells like fuel). Off idle the motor hesitates and stumbles, then begins to pick up. I just recently replaced spark plugs, wires, rotor, checked cap (o.k.), replaced the coil pickup, and TSP sensor. All of these were done trying to fix the poor idle and low end performance. At first it seemed to help, but now the truck is running poorly.

What areas can I look into that would create a very rich idle?

Thanks for any help.

 

[fordconvert]

Have you checked to see that the base timing is set right? When setting the base timing and throttle settings you have to put the computer in the proper modes. I think the fords have a 'spout' connector for the timing that needs to be unhooked. Im not sure of the procedure for base thorttle.

Other thing to check is the fuel pressure regulator. Its located on the one end of the fuel rail and will have a fuel return line and a small vacuum line going to the intake or throttle body. Pull the vacuum line and see if its got fuel in it. If it does its bad. It will be sucking fuel straight into the intake and running the fuel pressure higher than it should. Other sign is hard starts.

 

[dzertracer]

The base timing is correctly. The fuel pressure at idle is around 55 psi. I don't know what the psi is when driving. I will check the fuel pressure guage for a fuel smell.

If the FPR checks out o.k. what should I look into next? I am stumped on this one.

Thanks for any help.

 

[fordconvert]

Exhaust restriction like a plugged cat?

 

[dzertracer]

Still haven't checked the FPR. I will this afternoon.

I doubt the cat is clogged. It is about four years old, and a 3 inch high flow one.

I have read that the EGR valve causes poor idle if not functioning correctly. I thought about making a EGR block off plate. What do you think?

 

[fordconvert]

You could try unhooking it for a few test runs to see if its maybe its not seating sometimes. You have to be careful what you mess with or the computer wont like you. If its the type with a multi wire connector on the valve itself you pretty much have to keep it because the computer monitors its position and wont like it if it doesnt see it move. If its the older type that just has a solenoid to control it you should be able to unhook and plug the vacuum to it and the computer shouldnt mind that much unless it sees an issue in the o2 readings.

 

[dzertracer]

The FPR passed my sniff test. I adjusted the idle a few hundred rpms. It was around 700-800 rpm, now it is around 1,000. The idle is much better and does not smell rich at all. I wonder why it runs so rich if the idle is turned down?

 

[fordconvert]

Just like the timing the idle on an efi engine is not really adjustable especially if it has an IAC motor (which most multiport systems do). Im not sure about you car but most of the time there is a specific procedure to get the IAC in the right position before setting the throttle stop. If its not set right the computer gets confused.

 

[Does10s]

The base timing is correctly. The fuel pressure at idle is around 55 psi. I don't know what the psi is when driving. I will check the fuel pressure guage for a fuel smell.

If the FPR checks out o.k. what should I look into next? I am stumped on this one.

Thanks for any help.

55psi is to high at idle. It should be around 35psi.
Will

 

[dzertracer]

50-55 psi is how the EFI 300's came from the factory.

I was not aware of the IAC and throttle stop procedure. Maybe they mention something about it in my Haynes manual.

Thanks.

 

[Anonymous]

also check your coolant temp. sensor - make sure it's not out of range ( like reading -40* F, thus driving the mixture rich)