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Ron
Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 23001
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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Have 1988 f150/ 5.0L/ 2wd/auto. have had intermittent

Customer Question

have 1988 f150/ 5.0L/ 2wd/auto. have had intermittent problems for two (2) years with hi press fuel pump failing to engage. this usually only occurred during the winter, in cold temps. 1 week ago it just quit while driving, and now, it wont engage at all. control computer replaced, along with frame fuel filter, fuel pump relay. if I bypass the electrical system and wire the HP fuel pump directely to the battery, it operates normally, and the truck will run normally. the next thing to try is remove the HP fuel pump electrical disconnect and replace it. sure could use some help with this one, it has me stumped!
Tim. Montana
Submitted: 10 months ago.
Category: Ford
Expert:  Edward replied 10 months ago.

Hello Tim, You have a 4 pin fuel pump relay, When the pump doesn't run, (which I am assuming is at all times now?) Do you have power on the YELLOW and RED wire at the fuel pump relay with key ON? Do you have a volt meter or 12 volt test light to do some tests with? thanks.

Customer: replied 10 months ago.
l have meter. already tried. however, wire colors are different. have 5 pin relay, however, pin five is not used. have intermittent power on pin one and two, some times I have power, and at others none. right now, no power. on pin 1 and 2. no power between 3 and 4.
Expert:  Edward replied 10 months ago.

You only have 4 wires in the harness going to the FPR. correct? that is the wiring diagram I'm looking at. did you jump the inertia switch or check power there when cranking just to see if it makes that far?

Customer: replied 10 months ago.
pin 1 and 2 are for the coil. 3 and 4, when energized, are supposed to operate the fuel pumps. have looked at every fuel wiring schematic I can find. none show the wiring for the hi pressure fuel pump, only the in-tank low pressure fuel pump; so dont know where the power originates. and yes, did check inertia switch; operates correctly. removed and tested it. and correct on 4 wire, pin 1 has a second wire joined with another, feeds power further down the line, if I read the schematic rigjht
Customer: replied 10 months ago.
can only work for a short time tonight. been working on this PITAPOS since 10am outside at 20 degrees. and now its getting dark. but can continue tomorow. only thing left is to replace the electrical disconnect at the fuel pump. thats for tomorrow.
Expert:  Edward replied 10 months ago.

Alright, Is this the diagram you we're looking at? If you don't have duel tanks don't look at the tank selector switch, just the part that goes to the high pressure rail pump.

Expert:  Edward replied 10 months ago.

You we're looking at the green relay, correct? that is the Fuel pump relay, black is PCM relay.

Customer: replied 10 months ago.
nope, dual tanks. dash apart, but tank select switch installed. still none of my schematics show the hi pressure pump. as I said, pump and truck operate if pump wired direct to battery. rear tank not used in multi years. bad pump electrical connector. only front tank used. any ideas?
Expert:  Edward replied 10 months ago.

The green relay out on the drivers fender well is the fuel pump relay, it doesn't have a YELLOW and RED wire going to it? If not, I don't believe it's factory wiring.

Customer: replied 10 months ago.
no, was black relay, left fender by hood hinge. that is where manual said it was. if thats not it, where is it located? still have time to check it.
Customer: replied 10 months ago.
no yellow and red wires. 1 black 1 brown 1 white/red stripe. the others I dont remember.
Customer: replied 10 months ago.
it appeared to be factory. jumpered wires were a factory type. think we are talking about the same relay. may have been replaced in the past prior to me owning the truck
Expert:  Edward replied 10 months ago.

Look between the master cylinder and the air cleaner box, on drivers fender, should have a green colored connector there with 4 pins in it, that is the fuel pump relay. the green connector will look like this one.

Customer: replied 10 months ago.
let me go down and check. will get back with you in about 20 minutes
Expert:  Edward replied 10 months ago.

Sounds good. take your time.

Customer: replied 10 months ago.
okay, made it. here is what i found Ed. only one relay on left side. pins; 1-black 2-brown 3-black with white/red stripe tied togather 4 black with white stripe. like you, cant find it in any schematic i've looked at. but thats whats on the truck.
Expert:  Edward replied 10 months ago.

Alright, did you look around there, down around the fender well, they fall out of that cover sometimes.

Customer: replied 10 months ago.
yeah, i did. that was the only relay I found. will you be available tomorrow? will try and look in the daylight. damned cold out there now. down to about 10 degrees. enough to make ya say: "Its KKKKKKKKOLD. OUT THERE!!!" lol hopw to talk to ya soon, and hope to get this figured out.
Expert:  Edward replied 10 months ago.

I gotcha! That sounds good, lets try again tom. in the daylight. Let me know if you find it.

Customer: replied 10 months ago.
awesome! just found schematic that shows the HP fuel pump. operates off the relay. but like yours it shows red and yellow as power. will try and find the relay in the morning. nite
Expert:  Edward replied 10 months ago.

ok. sounds good.

Customer: replied 10 months ago.
Edward, if your there, found some interesting things. 1- the fuel pump relay wiring harness has been changed, thats why none of the wire colors match! 2- i have power to the fuel pump relay with the key on, and power from the relay toward the inertia switch. HOWEVER, i only have 6 volts of power at the inertia switch. l will have attempt to find where the resistance is, by tearing into the harness junctions, and remove the bad stuff, OR just replace the wire from the fuel pump relay to the inertia switch. lets see what ya think about the tentative plan of attack? Tim D. De Borgia Montana
Customer: replied 10 months ago.
I am going to head back down and give stuff a shot. its getting late, and only have about an hour before i have to quit for the day. will relay what find and did in about 90 minutes. talk to ya soon. Tim
Expert:  Edward replied 10 months ago.

Alright, sounds good. I will have cell only access this evening, but let me know what you find.

Expert:  Edward replied 10 months ago.

Tell me some good news!

Customer: replied 10 months ago.
okay, here is the news. have constant power on pin #3, which it is supposed to have. unfortunately with the key on, I have no power to pin #1, which it is supposed to have, to energize the fuel pump relay. am unsure it is in the spot where the new harness was wired in. I thought I had power thru the relay last night and some today, but now have no voltage at all. am suspecting an intermittent short in the relay wiring. will have to tear into it tomorrow. again will keep you up to date. if you have any ideas, they are welcome!
Customer: replied 10 months ago.
question for ya. if I am reading the schematic right, the power for the fuel pump relay is routed through the ECC power reoay, is that right? if so, can you please tell me where the power relay is located, so I can make sure I have power leavimng that point, and downstream of the fuse link. any other suggestions you can thinks of? now gotta start at the power supply and work toward the fuel pump.
Expert:  Edward replied 10 months ago.

Ok, was it a green connector at the relay ? Or is it still missing?

Customer: replied 10 months ago.
no green connector. the entire harness has been replaced, including the connector. its now a grey connector. but think it is supposed to be wired the same, though with completely different colored wires. until i get power supplied to the fuel pump relay coil, am dead in the water. so gotta start from the EEC power relay. from there to the fuse link then to the relay wire harness. can you tell me where the EEC power relay is?
Expert:  Edward replied 10 months ago.

Should be right there, on the fender well, That was the factory spot.

Customer: replied 10 months ago.
yeah, it was in the right spot. but the harness has been changed. the original harness has been changed out, and a replacement was installed. that is why I am having trouble. the replacement harness has a different wire color code. and until I can strip off all of the electrical tape, i cant tell what the colors are. but still need to know where the EEC power relay is located. need to start there and work toward the fuel pump relay. with no power to the relay, nothing will work.
Customer: replied 10 months ago.
am callin it a night. 5am comes awful early. gotta feed the criitters by 6 am. will work on it again tomorrow, unless its snowing like crazy. if you would let me know where the EEC power relay is, will open this dialog in the morning, and get on it as soon as i can. thanks- TIM
Customer: replied 10 months ago.
am still waiting for a response for the location of the EEC power relay. have asked multiple times. I know where the test test site is located at. is the EEC power relay next to it? where is it? from the schematic, once the ignition switch is on, power energizes the EEC power relay coil, which in turn energizes the fuel pump relay circuit. as if now I have no power to the fuel pump relay! this means I HAVE TO START AT THE EEC POWER REOAY! my manual does show the EEC power relay, nor does it show oar tell where it is located. this is the information that I need at continue diagnosis of the lack of electrical power. the electrical schematic also shows an fuse link after the EEC power relay. without knowing the location of this power reoay, I am unable to locate this fuse link, and to test it! PLEASE tell me the location of the EEC power relay!!!!!!!!!!!!!
Expert:  Edward replied 10 months ago.

The EEC power relay is right next to the fuel pump relay that is in a factory cover where the EEC self test connector is on the left fender well. At least that is the factory spot. Now if you say the wiring harness has been replaced. I don't think they would have moved it far, but, I can't be sure. Does the check engine light come on when you turn the key on? If so, the EEC power relay is working.

Customer: replied 10 months ago.
ck engine light comes on. snow n rain all day, so havent had a chance to work on trk today. if it is only snow tomorrow, will work on trk. now that I know where power originates can start checking power from the ECC power relay forward toward the fueo pump relay. will keep in touch as I make progress to fixing the PITAPOS!!!! If your wondering what PITAPOS is - it stands for Pain In The Ass, Piece Of Shit!!!!!!! hope ya got a good laugh at my expense! and the next time you work on one, you will remember this conversation! thanks for the info on sathe location of the power relay
Expert:  Edward replied 10 months ago.

bwahaha, that is good. lemme know what you find there.

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