I have a 1990 F150 with a 5.0L 5 speed 4x4 that I'm working on. When I rev it up, it stumbles and takes a bit and then revs quickly and easily up and is fine. Sometimes if multiple revs higher and higher or just a big throttle jump, it will make a pop noise. Driving it takes a bit. I have to rev it pretty good to let the clutch out all the way and then its very slow increase of throttle or it just bogs down. I was checking vacuum hoses, the previous owner had a T in the brake booster line and it went out the front to the front of the truck with a ball valve???, so I got new line and replaced that and others, but actually just capped the vacuum tree. I tried to start it to see if it would be any better. It took some throttle to start (assuming since it didn't have data) but it idled great with my foot on the pedal a bit. It revved up great and and 0 hesitation at all. I haven't tried to drive it like that but revving up just sitting there is like it supposed to be. I narrowed it down from removing vacuum lines and retrying and it came down to the MAP sensor. I had a 92 F150 that has been sitting for a few years but ran good when parked. I took that MAP sensor off and switched it out and no change. When vacuum line connected, hesitation when revved; disconnected, needs a bit more throttle to idle but revs up great. I got a 89 F250 with this F150. I wouldn't think trying a 3rd sensor would probably change things though. I also have checked the wires at the MAP sensor with my Power Probe. I get a 5v, flashing ground(assuming the Hz since it can't detect that), and then ground. So I think the connection from the computer is good. Any ideas on what it could be? Something masking with the MAP sensor removed?

 

You should check your fuel pressure at idle at the rail.

 

Fuel pressure with vacuum on regulator.



Fuel pressure with vacuum line off.

 

Codes while off: 61 84 95
Codes while running: 61 98

 

KOEO

61 - engine coolant temp sensor fault or circuit grounded. Was this an active or stored fault?
84 - EGR vent fault
95 - fuel pump secondary circuit fault. Was this active or stored?

You need to fix these before doing the KOER faults.

 

How do I tell if it was active or stored? Im guessing the coolant temp sensor is the one by the thermostat and not the one by the fuel rail port since the coolant gauge works in the dash?

 

Active is displayed first then the separator code ( I think 11 if watching flashes ; 10 on the Innova code reader ) and last will be stored codes.

 

Both active then I guess. It went through the same codes twice and then I shut it off, unless it would flash 11 after a second cycle.

 

Few things
I checked on the coolant sensor. It was broken off so I got one from the other truck and swapped it. Maybe a bit better but no change. There is no check engine light when its running now. I hooked up a vacuum gauge and it was 18" at 5-600rpm.
The fuel pump circuit is interesting. They ran a wire to the fuel pump and it is connected to the wire that comes from the EEC Relay that turns the fuel pump relay on. Whenever I take that wire off, I have 7 volts at the inertia and tank switch. When I ground out the pin for the fuel pump test, it then has the full 12V at those spots.

 

Any ideas?

 

You have a vacuum line connected to your MAP sensor? I think it just ports to atmospheric pressure under the hood, i.e. open.

 

No. It is connected to manifold vacuum

 

I might try and swap throttle bodies, I have a spare one so.

I'm somewhat worried that the other truck I got will have this problem too. I'm guessing this vacuum T with a ball valve on the end off of the brake booster line was to reduce vacuum so whatever sensor could change the parameters. Both the trucks have this T. It was ran out to the front of the truck to the end of a ball valve. The other one has the T but haven't found the ball valve to it yet, but the upper intake was off of that one.

 

I also noticed that the sensor that comes off the throttle body isn't there. Im talking about the vacuum lines that goes to the sensor/evap. The vacuum lines are just in a U on the throttle body. I can't seem to find the connector/sensor wherever it might be. Would this affect the truck this much??

 

Any ideas?