Priming

[Mello]

All i did was changed the fuel pump and sending unit on my 1987 foxbody. Tried to start it and no luck. However the pump keep priming with the keys out of the ignition.

 

[90sickfox]

The relayay be stuck...or the ground wore from the computer to the relay is shorted to ground. There is a fuel pump test connector under the hood behind the drivers strut tower. Little single wire plug. There are two of them over there. One is 12v for the underhood light the other is FP test connector. If it's grounded the pump will stay on.

Check the electrical ignition switch on the column.

Why were you changing the pump ? Something else jas to happen for the pump to start running all the time. The fuel pump circuit isn't wired that way. The relay has to get 12v from the ignition switch and the computer has to ground the relay in order for that to happen. Relay is located under drivers seat.

 

[Mello]

Thanks you ,thank you for the great advice. Here is the story- I was due to change the sending unit and decided to get that done. Two days ago i turned the key and didnt hear the pump priming, took the tank down and change the sending unit and pump. got everything done and it started going crazy. Got a new fuel pump relay and still no start.

 

[Mello]

The relayay be stuck...or the ground wore from the computer to the relay is shorted to ground. There is a fuel pump test connector under the hood behind the drivers strut tower. Little single wire plug. There are two of them over there. One is 12v for the underhood light the other is FP test connector. If it's grounded the pump will stay on.

Check the electrical ignition switch on the column.

Why were you changing the pump ? Something else jas to happen for the pump to start running all the time. The fuel pump circuit isn't wired that way. The relay has to get 12v from the ignition switch and the computer has to ground the relay in order for that to happen. Relay is located under drivers seat.

Can the pump be wired wrong and still priming. I pretty sure i put back the wires right. Thanks

 

[90sickfox]

Not generally. The pump has to get 12v from somewhere to stay running even with the key off. That means something is giving the pump 12v all the time. You have an electrical problem somewhere. I'd start at the ignition switch like I stated before. You'll need a multimeter, a test light, and schematics. http://www.veryuseful.com/

 

[Mello]

Thanks 90sickfox. Changed the fuel pump relay ,So it is priming as usual now . However its not starting. going to buy a fuel pressure tester to see if im getting enough pressure with the new pump.

 

[Mello]

Can the fpr be the culprit.

 

[slow84lx]

Can the fpr be the culprit.

The fpr has no electricity going to it. It cannot be the culprit for the fuel pump not working correctly.

Edit - it seems like you got the fuel pump pumping now. Have you checked the fuel pressure?

 

[Mello]

just came home with a fuel pressure gauge. Thats my next test

 

[chrlsful]

grounds in ol cars? Actual 'correct wiring' to fp? (hard to do wrong unless changing sender too).
I'd start at ' the begining' (as above, from both 'ends', continuity, key & w/long test jumper, inertia switch, etc)?

 

[Mello]

Morning good citizens, Now that my 87 GT convertible is running good , I want to thank all the guys who gave me really good advice.

 

[Mello]

It Wasn’t the pump that was giving me the business, it was the relay and because I don’t know how to test a relay , I assumed it was the pump.

 

[Mello]

Now for the sending unit- the new sending unit is not working. It does the same thing that the old one did. When I start the car , the needle goes ‘ past the full mark on the gauge.

 

[General karthief]

Unplug it, turn the key to on (no start), does it do the same thing?

 

[Praetorious]

Sounds like you may have a electrical issue,on another note i went thru about 4 of those new sending units back to back a few years ago (dropping a tank 4 times is living large,lol), the black float part after a month or 2 would disintegrate, one time clogging my fuel pump sock and burning up my pump,bought a spectra one from auto zone or advance and never had a problem again,the new sending units from ole china are really really bad, the spectra one is too of course but i think is a little better quality than the ones most vendors sell,finding a oem one is akin to winning the lottery pretty much.

The gauge rarely goes bad, could the amplifier in the cluster be causing this? i know when my floats kept disintegrating it would read empty i believe because nothing was on the wire since the float was gone and it would go down with the weight of the fuel but not sure why it would be measuring full?

 

[Mello]

Thanks for the heads up. I’ll start with the continuity test . I got this sending unit from LMR, they are supposed to sell quality parts, The old sending unit was rusty, this one is new but I get the same reading. Oh well , I’m hoping that it’s a ground or something simple. Thanks again.

 

[chrlsful]

"...start with the continuity test..."
ideal, but make sure it's the right part too.
Any thing else changed? (yup, relay, but gauge, something else?)
Hooked up backwards, bad grounds? Not sure related but my 15 yr older rig hasa
IVR. Also is neg / positive leads reversed on back of gauge? HTH, automotive ele is my nemesis.

 

[Mello]

I’ll try to get under the dash this weekend and check for any loose wiring.

 

[Mello]

Anti-Slosh Module?????

 

[General karthief]

https://lmr.com/item/LRS-10849/90-93-Mustang-Instrument-Voltage-Regulator#:~:text=The%20slosh%2C%20or%20anti-slosh%2C%20module%20is%20a%20circuit,brake%2C%20or%20even%20go%20up%20and%20down%20hills.