FSS ground issues
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4wd Low
Joined: Nov 2024
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FSS ground issues
hey just got this 87 f250 with a 6.9 idi and been figuring it out, never really worked on a diesel before so this is me fixing and learning. i’ve been trying to get this thing going for maybe about a month now and just have been fighting things. this is along with one of the things. with this truck i haven’t had a key so ive been hot wiring the FSS in the IP and it has been working from running a wire from the positive side of the battery and connecting it to the spade with the wire. today i finally decided to take the cover on the IP and when I put it back on the FSS wasn’t clicking anymore at all. i knew i was getting power to it with that wire but couldn’t figure it out why it wasn’t clicking and working like before. figured it was a ground issue because i took the cap off again and put the ground to the negative battery post and put a wire to the same spade connector and the positive side of the battery and it worked. would really appreciate some info from some guys who have worked on these/ owned these for a while. thanks - Cayden
i ain't rite
Joined: Mar 2005
Posts: 65,564
Likes: 5,601
From: Marlboro Mental Hospital.
when you take the cap off the injector pump to access the fuel shutoff solenoid, you need to place it down on the pump with the cover forward an inch or so then slide it back over the pump to properly seat the actuator lever. if you just drop it down on the pump, you will jamb the fuel full open and will have a run away engine you can not shut off if you try to start it.
there is no "ground" to the injector pump, it is grounded through the engine block.
there is no "ground" to the injector pump, it is grounded through the engine block.
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4wd Low
Joined: Nov 2024
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I got it on there correctly but now it’s just not even powering on or clicking when i put a wire from the battery to the FSS but before i took the cap off it was powering on and working. so maybe i have a bad ground on the block?
Tuned
Joined: Jun 2013
Posts: 441
Likes: 61
From: Craigmont, Id
Tom can correct me if I am wrong and my truck is parked away from the house tonight so I can not go out and look, however it seems to me that there is a ground strap on top of that cover on the right side of the pump that goes from the electrical terminal to the front cover screw on the right, the power lead connects on the left side terminal. Are you sure that is all connected back up? You did not by chance leave off that ground strap. If it was working before you pulled the cover and is now not I would believe your issue is right there at the pump. Recheck where you have been before tearing into something else.
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4wd Low
Joined: Nov 2024
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will do, i reput that little ground strap back where it was i just am stumped why it just quit on me but i will look at the pump tomorrow and try to clean some stuff up on that cover. seems no one else has had this issue everywhere i check. Just trying to get this old truck runnin lol last step basically.
Tuned
Joined: Jun 2013
Posts: 441
Likes: 61
From: Craigmont, Id
A few things you can check. You will need a volt ohm meter. Harbor Freight one will work if you have to buy one. The two terminals on top of the cover lead to the solenoid. Disconnet the power wire, take a ohm meter and read the resistance across the terminals. Then leaving the lead on the power terminal move the other lead to the battery neg terminal. Reading should be the same for both test. From what I can see online the reading should be 3.5-4.5 ohms.
If when measuring across the 2 terminals you get a correct reading but when you go to battery neg you do not have same reading then you have a bad ground, couple of tenths I would not worry about but if you see several ohms difference then you have a problem. If you are not in the correct range then I would assume the solenoid had gone bad. Also measure and make sure you have battery voltage at the power terminal. Check that when plugged in so there is a load on the circuit. Again should be within a couple of tenths of what you read right at the battery. This time you are reading volts so make sure you set the meter for that.
Report back what you find if you need more help.
If when measuring across the 2 terminals you get a correct reading but when you go to battery neg you do not have same reading then you have a bad ground, couple of tenths I would not worry about but if you see several ohms difference then you have a problem. If you are not in the correct range then I would assume the solenoid had gone bad. Also measure and make sure you have battery voltage at the power terminal. Check that when plugged in so there is a load on the circuit. Again should be within a couple of tenths of what you read right at the battery. This time you are reading volts so make sure you set the meter for that.
Report back what you find if you need more help.
i ain't rite
Joined: Mar 2005
Posts: 65,564
Likes: 5,601
From: Marlboro Mental Hospital.
i dont remember seeing the injector pump ground strap on my 88. but then again, i have not messed with the pump in a good 20 years as the truck is relegated to backup snow plow service now.
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Fleet Owner
Joined: Jul 2006
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From: Mi'kma'ki
Take right back off and test it. If you know how to make sure to put it back on without causing a runaway, just take it back off and test it.
I just had one go bad, by not being able to turn off. I turned the key off and the truck kept running. I unplugged the FSS and she still kept running! haha. I grabbed the fuel line and kinked it. The IP just kept sucking, even with the electric pump off. I didn't know........or least, I don't remember they could fail like that.
You can run a little ground wire to the IP with a ring terminal.
Hey, I just thought of something. I could have the perfect zombie apocalypse truck right now. I could swap this bad FSS back in, swap an old mechanical lift pump back in, and all I'd need is a quick little shot of 12v and my truck will run over zombies all day!
Oh dang, no that's not true. I'd still need a manual trans.......Oh well, theoretically.
I just had one go bad, by not being able to turn off. I turned the key off and the truck kept running. I unplugged the FSS and she still kept running! haha. I grabbed the fuel line and kinked it. The IP just kept sucking, even with the electric pump off. I didn't know........or least, I don't remember they could fail like that.
You can run a little ground wire to the IP with a ring terminal.
Hey, I just thought of something. I could have the perfect zombie apocalypse truck right now. I could swap this bad FSS back in, swap an old mechanical lift pump back in, and all I'd need is a quick little shot of 12v and my truck will run over zombies all day!
Oh dang, no that's not true. I'd still need a manual trans.......Oh well, theoretically.
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