No start efi
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4wd Low
Joined: May 2024
Posts: 13
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No start efi
Well it’s been about 8 or more years sense I have posted but long story short I have a 1986 f150 302 short box reg cab lariat with a np435 4x4 that will not start after sitting for a couple of years. The truck will crank fine but will not start , I hear no fuel pump or anything. I did try to bypass the fuel pump relay and the pump started then I checked for pressure at the fuel rail and got a good blast from the port on the rail. The truck will fire on starting spray but I believe the injectors are not firing . So no fuel pump with key on and the injectors won’t fire. What would cause that? Maybe bad pcm from sitting? Any help would be greatly appreciated! This truck and me have been through so much I really want to drive it again
Lead Driver
Joined: Jun 2013
Posts: 5,668
Likes: 1,159
From: Tolland, CT
So you bypassed the relay, and you got fuel...could it be a bad relay ?
https://www.garysgaragemahal.com/ Look under the Documentation link for info on the system.
https://www.garysgaragemahal.com/ Look under the Documentation link for info on the system.
Moderator
Joined: Jan 2001
Posts: 56,992
Likes: 2,741
From: Virginia
If the ignition system has a problem and the computer does not get any signals from the distributor, the computer will not fire the relay to turn on the fuel pump. But, the fuel pump should prime when you initially turn the key to run. The pump should run for 2 or 3 seconds and then quit. If the computer see's signals from the distributor, it will turn on the fuel pump relay again.
Is the fuel pump priming? Have you pulled any codes from the computer?
Is the fuel pump priming? Have you pulled any codes from the computer?
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4wd Low
Joined: May 2024
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So the fuel pump dose not prime when I turn the key, the only why I can get the pump to come on is to jump out the relay, I need to find my old code reader so I can check for codes but the truck will run on starting spray so idk if the ignition system has any problems
Moderator
Joined: Jan 2001
Posts: 56,992
Likes: 2,741
From: Virginia
Not priming is a clue. The computer signal is not getting to the relay, or the computer is not generating the signal. They feed the relay with a key-on hot wire, and the computer grounds the relay to turn it on. If you look it up, there is also a terminal on the test port where you hook the code reader. If you ground that terminal the pump should run with the key on.
Moderator
Joined: Jan 2001
Posts: 56,992
Likes: 2,741
From: Virginia
Here is some info and it shows the fuel pump terminal also on the port. Forget the check engine light part, your truck doesn't have one usually.
https://www.therangerstation.com/tec...ipped-engines/
https://www.therangerstation.com/tec...ipped-engines/
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Cargo Master
Joined: Sep 2006
Posts: 2,120
Likes: 390
From: Evansville, Indiana
@Gibsontraditional86 Check the main ECM ground. It runs from the ECM connector under the dash above the accelerator pedal to the battery negative terminal. It is a 18 gauge mostly black wire. In stock form it has a connector about a foot away from the battery. This connector is notorious for corroding. Most have been cut out and replaced with a butt splice connector by now.
The ECM has other grounds as well. On the ECM, pins 20, 40 and 60 are all grounds. Besides the battery itself, terminations are located at a screw under the dash near the ashtray and on the driver's side rear of the lower intake manifold.
The ECM fires the injectors in much the same way as it does the fuel pump relay, by grounding them.
The ECM has other grounds as well. On the ECM, pins 20, 40 and 60 are all grounds. Besides the battery itself, terminations are located at a screw under the dash near the ashtray and on the driver's side rear of the lower intake manifold.
The ECM fires the injectors in much the same way as it does the fuel pump relay, by grounding them.
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4wd Low
Joined: May 2024
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Update
So I did find that black wire that grounds the ecm for the injectors , the wire was unhooked due to probably me when I changed the battery. Now the injectors do click and now I can jump out the fuel pump relay and get the truck to run. My question is why am I not getting the hp fuel pump to run and prime when I turn the ignition? I did change the relay but still nothing
Moderator
Joined: Jan 2001
Posts: 56,992
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From: Virginia
On the relay you should have a red and a tan/lightgreen wire, besides the yellow and pink/black. When you turn the key on, make sure you have 12v on the red wire. When you touch the tan/lightgreen with the key on, it will probably have 12v also. While holding your meter or testlight on the tan/lightgreen wire, get someone to cut the key off, then turn the key on. The tan/lightgreen should have no voltage, and then voltage. If it does,, the computer is working. The computer grounds the tan/lightgreen to activate the relay, since there is always 12v on the red wire when the key is on. Supposed to be anyway.
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4wd Low
Joined: May 2024
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Update 2.0
So I was poking around under the hood an was trying a bunch of stuff like continuity on grounds an found out that the ecm was not actually grounded, so I did some digging on the main ground for the ecm the one 8 inch cable that goes from the hood to the firewall near the blower motor and hood hinge . The ground was completely broken in half! So I replaced it with a nice new cable and now she fires right up!! Goes into high idle for a few seconds then right down to normal idle. This is the first time in 4 years that it runs , I’m now super motivated to get this truck back on the road now all I need to do is to bleed the brakes due to all new be pre bent brake lines I installed from bronco graveyard . then get a new exhaust bent up . Thanks again everyone for the help and good advice !
FTE Legend
Joined: Nov 2015
Posts: 30,935
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From: Angier, NC
Good to hear you are moving forward and not backwards as that is never good 
Yea grounds are pretty important and can cause all kinds of stupid things to happen.
FYI battery to motor, motor to frame, motor to cab are the big grounds.
Some will add bed to frame too.
Dave ----
Yea grounds are pretty important and can cause all kinds of stupid things to happen.
FYI battery to motor, motor to frame, motor to cab are the big grounds.
Some will add bed to frame too.
Dave ----
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