wryork25

Please help I really need to get this truck runnning.

Hello,
I am new to the site so thank you in advance for the assistance that I get from everyone here. Here is the problem, I bought a 1990 F150 XLT Lariat V8 (not sure what size). It has spark, the fuel relay does ingage, The tank selector switch does switch from tank to tank, and the inertia switch is not tripped. The fuel pumps do not come on. I have shorted the test pin to ground to keep the fuel pump running for testing perps and it still does not run. I was able to reach the electrical plug on the foward gas tank and pull it off, I only read 7.5 volts which I asume is to low in a 12v system. I have not started tracing the voltage back to see where I am loosing it but my haynes manual is kind of vauage when it comes to electrical. My question is how many connection points are between the pump plug and the inertia switch? Is it a straight shot or are there a couple connections I have not found? Do you think that I am on the right track?

wryork25

I measured the voltage at the inertia switch last night before it started raining and it read 12 volts so i know that the full batt voltage is getting that far. I also measured the voltage on the red wire on the back of the tank select switch to ground and it read 10 volts?

5Rangers

Power for your pumps comes off a fusible link W (front RH fender apron) directly to the yellow wire on your pump relay. The EEC pulls the relay (or the test point) and puts 12vdc on the brown wire coming out of the relay. From there its goes through C202 which is the big round connector on your firewall to the brown wire on the inertia switch. It comes out of the inertia switch on pk/bk wire through a splice (S225) where it becomes R/Y then to connector C206 which is right there at the selector switch. The switch directs power to BR/W for the rear and R for the front back through C206 and then back through C202 then through C133 there on the inside rear of the driver’s front wheel well. C133 is interesting because for the front and the back it breaks each ones wires out on splice to 2 wires each maintaining color code, then back down to one wire each maintaining color code after the connector. ( I don’t know why they do that, but the schematic shows it, maybe one of the guru's know?) From there R goes to the front pump connector and BR/W to the rear pump connector. Front finds its ground on O and rear on O (orange) they go through S400, change colors to BK and find G100 (LH side of radiator support)


Your on the right track, just keep checking for power methodically going down the line. I was losing power at the cobbled relay wiring, the switch and had a dirty pin at C202. After I fixed all of that I had 12vdc at the pump connectors. It was time consuming but needed to be done.


My source is the 1990 Bronco and F series electrical and vacuum troubleshooting manual. (Its a Ford book) I used to have a schematic electronically but I think it's on my laptop(edit- found it) at work.

5Rangers

Here's a pic for an 89, it's close but with fairly significant differences.

This picture shows a frame rail pump which I don't think you have. I think in 90 it was no more and they just put high pressure pumps in each tank.

5Rangers

Here, I took a picture of my book.

ymeski56

Good job 5Ranger!

ymeski56

So you're testing the plug hot/ground? If you go plug hot to an alternate ground source & get 12V, then your ground return for that circuit is the problem.

wryork25

I do not get 12 volts witha alternate ground source at the pump switch. I get 7.5. Thanks 5ranger I am going to continiue to try and find the culprit. Yor explination and schematics will help alot!!!! I plan on getting the EVTM I just have not got gotten one yet I have only had the truck for a week. Haynes was the only thing I could buy locally. I will keep you posted on what i find. THANKS AGIAN

5Rangers

Dup....

5Rangers

Quote:

Originally Posted by ymeski56

Good job 5Ranger!

Thanks ymeski56, coming from you, that's alot. Just tryin to give a little back, been there done that and I know what the OP is going through, as many of us do. Life is so much easier with the right schematic. Hey, is that a quote for my sig line?

Quote:

Originally Posted by ymeski56

So you're testing the plug hot/ground? If you go plug hot to an alternate ground source & get 12V, then your ground return for that circuit is the problem.

Good point on the ground leg, I always test each side separately

You being a "guru" maybe you know why they split the power out at the C133? They don't do it on my 88 but on the 90 ya....