I've got a 69 f100 that I put a 91 5.0 and aod trans out of an old ltd and I am having some issues. First off it always starts right up when cold, but as soon as it gets warmed up enough to go into closed loop it will stall when throttle is applied. It runs great until warmed up. When it starts to stumble you can really hear the motor sucking air through the intake.


Here is what I have done so far. Base timing with spout disconnected is 10* when you plug the spout back in it advances like it should. New distributor and tfi module, cap and rotor. New ect, map and iac valve. I pulled the air temp sensor out of the lower intake last night and tested it there is no resistance between the prongs so I bought a new one and will install it tonight. Plugs and wires are new all of my sensors get the required reference voltage from the computer. I had an extra computer and have tried that as well. The fuel pump is new and pressure with the vacuum applied is around 38psi. I have around 20" of vacuum.
Tps voltage is right around 1 volt.


I ran the codes and have a few but the only one that I think would affect the engine operations is the code 18c. which was something like spout to ground or no reference from idm. So I ohmed out my idm to pin 4 on the ecm and came up with nothing. Then I ran a wire from the idm wire on the tfi harness to the 22k ohm resistor then re ohmed to pin 4 and had resistance but it wasn't 22k ohms. There was like 5 ohms. So I plan on getting a new 22k ohm resistor today.


So my question is what do you guys think? Im new to the 5.0 eec iv game and any input would be appreciated I would really like to drive this truck. Its been about a year long restomodoration. Thanks!

 

Forgot to say that this is a speed density motor.

 

Stalling when throttle is applied could be a few things. Weak spark could cause that, as well as poor ignition wiring.

Please post all the codes, as they might not seem relevant, but they can be.

 

Code 18c 81 82 85 33 . Egr is blocked off.

 

Also code 75.

 

Ok I believe I have figured it out. My fuel pump which is about 9 months old and has maybe 2 hours of run time is getting extremely hot. When it gets hot my fuel pressure slowly starts to drop off with the engine running. I have to keep priming it with engine off to build up pressure. Once its primed it starts right up and then the pressure slowly drops. This is an inline summit pump. What's a good aftermarket one to get? Or could the regulator be returning too much fuel there for not allowing a suitable amount of pressure to keep it running?

 

Do you have a lift pump in the tank? A lot of inline pumps don't do well if they have to lift from the tank as well.

Ford has an OEM inline high pressure pump that was offered on the ~86-89 (possibly later) Rangers, F-Series, etc...

It's unlikely the regulator is failing when hot, but not entirely impossible.

 

No lift pump but it is gravity fed so I don't see that being an issue. I built the tank to go between the rails and have a sump.

 

Thinking about it, if it builds pressure by "priming" a few times with the key, the regulator is likely fine.

The fuel pump could indeed be failing. Another thing to consider is that getting too powerful of a fuel pump will excessively heat your fuel, which could lead to other issues.

 

I looked on orielys web page for the inline ford pump. I think ill go with that. Thanks for the help.