4.9 EFI fuel HELP!
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New User
Joined: Aug 2003
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From: New Braunfels
4.9 EFI fuel HELP!
Have a 1989 F150 SC 2wd 5spd, The fuel pump relay is not working, the relay has voltage from the fusable link and from the red wire, not getting a ground from the ECU. Also, the Injectors wont fire, pulled them, cleaned and tested each one, they work good. New fuel pumps (intank and on frame) have good pressure at the test port on the rail. Pulled spark plugs, cleaned, gapped, and tested, they fire. The truck will start on Ether, the problem is Injectors, right? I need help,
thanks
thanks
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
You would not have fuel pressure at the test port on the rail without the fuel pump relay getting a ground from the EEC Computer.
Note that this ground only happens for one second when you turn on the key.
Also the EEC Computer will not ground the fuel injectors without the PIP pulse train.
Note that this ground only happens for one second when you turn on the key.
Also the EEC Computer will not ground the fuel injectors without the PIP pulse train.
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New User
Joined: Aug 2003
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From: New Braunfels
when i jump the fusable link (yellow) wire to the brown wire the pumps come on, thats how i get fuel pressure. The module on the distibutor is new, (I know that doesn't matter) I will try the pick up.
Elder User
Joined: Jun 2006
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Have you checked the TPS?
If it's failed shorted, or if the SIG RTN wire is broken, it will be putting a full 5V on the position feedback, which indicates WOT. The ECU will not fire the injectors during start if WOT is detected. This has two purposes. 1, it allows you to mitigate a flooding condition if caused by poor performance, but won't do diddly for a leaking FPR. 2. It will let you find out if you have leaky injectors. Nifty little test. Floor the throttle pedal, and see if it'll crank. It shouldn't.
If you have dual tanks, check the tank selector switch. Even though mine has a single tank, it is wired for dual tanks, and simply uses a jumper embedded in a plug on the dash bezel to replace the tank switch. If the fuel pump doesn't run when you turn on the key for 1-2 seconds, it may well be that connection. The switches on dual tank systems are notorious for failure, and I found out the hard way not to unplug that harness from the bezel. One symptom of this on my truck though, was the fuel gauge pegged out.
Happy hunting, but before you pull the dizzy for a PIP, check the TPS, as well as the tank selector switch.
If it's failed shorted, or if the SIG RTN wire is broken, it will be putting a full 5V on the position feedback, which indicates WOT. The ECU will not fire the injectors during start if WOT is detected. This has two purposes. 1, it allows you to mitigate a flooding condition if caused by poor performance, but won't do diddly for a leaking FPR. 2. It will let you find out if you have leaky injectors. Nifty little test. Floor the throttle pedal, and see if it'll crank. It shouldn't.
If you have dual tanks, check the tank selector switch. Even though mine has a single tank, it is wired for dual tanks, and simply uses a jumper embedded in a plug on the dash bezel to replace the tank switch. If the fuel pump doesn't run when you turn on the key for 1-2 seconds, it may well be that connection. The switches on dual tank systems are notorious for failure, and I found out the hard way not to unplug that harness from the bezel. One symptom of this on my truck though, was the fuel gauge pegged out.
Happy hunting, but before you pull the dizzy for a PIP, check the TPS, as well as the tank selector switch.
Elder User
Joined: Sep 2007
Posts: 624
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From: Kalamazoo, MI
Originally Posted by dabshr
when i jump the fusable link (yellow) wire to the brown wire the pumps come on, thats how i get fuel pressure. The module on the distibutor is new, (I know that doesn't matter) I will try the pick up.
before you yank the distributor...
the fuel pump relay is going to have four wires going to it..
one is going to be "hot at all times"
one is going to be "hot key on"
one is going to be "ground at all times" (but it really isn't... it's the power feed for the fuel pump)
one will be a commanded ground from the ecm...
check your powers
check your grounds
note: one will only be "ground" for two seconds when the key is turned to the "run" position - this is the one we're looking for.
