nauss85

Like I've stated before, I have had the issue of my fuel gauge not working. Either tank registers above full on the gauge. So I thought both def of units need replaced. The other day on the rear tank(the one I can use), the needle bounced around sparatically. Well today, it seems to work. Currently tells me I have about 1/8 tank which seems to be pretty accurate. Switch to front tank reads full. I do in fact have a full front tank. I can't use it because either the pump is bad, pickup is clogged, or its bad gas. The truck was sitting for some time. How can I tell if the pump is bad? I can't hear it running. I can't.t hear the rear either, and that seems to work. TIA guys. Ill report back when I get some gas after work.

qdeezie

I've always heard that if you fill your tank up with gas and pour a bottle of Techron in it and let it sit for a week, it would clean the contacts up on the sending unit.

Whether or not it's any truth in it, I don't know, but I've heard of people doing this quite often with good results.

sylver91

I sometimes get jobs for a fuel pump/sending unit, car won't start so customers have em towed to the shop. By the time they get here, no more issues, normal pressure etc. Same as banging on the bottom of the tank to free up the pump and it magically works again lol.

Some customers get it fixed, others drive away and come back later that week paying the towing company twice

5Rangers

C'mon man!!! You, a jet engine mech should know stuff won't fix itself. And more then likely not a magical fix other then getting there with a meter and troubleshooting. You could have an intermittent ground, dirty or bad connector, or a problem with the sender itself. As far as the pump goes, put the test ground on the vip connector and disconnect the supply line at the DFR and check for flow. Check for correct volts back at the pump, the electrical system on these pumps will drop volts all the way back all over the place so you only end up with 9v at the connector. Get a print and trouble shoot it. I have a print for an 88 and a 90, they should be applicable, if you need it let me know.

nauss85

Lol I know it doesn't really fix itself. I have heard (and witnessed) that filter clog, and no go, then after sitting, starts right up, stuff like that. I haven't filled it up yet, but could it possibly be a bad reading when it is above 1/4 tank? maybe corrosion on the top 3/4 of the sending unit connection?
5Rangers- the '88 print should work. I would really appreciate it. I will PM you my email. Ill have to see if I can get to it tom. Thanks fellas. Will post results/findings.

5Rangers

Got your pm but it’s easier for me to just put them up here. The top picture is from my 1990 factory print book. It matched exactly with my 88 and was the most helpful. The 2nd picture is of an 89 without as much detail, it is courtesy of "Subford" , a member here and on some other sites. The last is the VIP connector with the pin A to bypass the ECM and allow the entire system to be energized for testing without the truck running .

I found problems all through my electrical with pumps and indication. I had low volts at the pumps (5-9v), should be 12+. I just took a meter and started following the wires, starting at the relay, checking volts at connectors and fixing as I went. I had problems with the relay socket with poor connection on the underside (replaced the socket and pins). I was dropping volts at the firewall connector C202, its a big round connector dense with pins/sockets, I pulled it apart and cleaned with a brush and contact cleaner. I was dropping volts at the inertia switch connector (cleaned it) and the selector switch itself (replaced it). Then the connectors going to the tanks were nasty and needed to be cleaned. Verified that I had good grounds there. My in tanks were crap as the truck had been sitting for years. I dropped the tanks and cleaned them out and replaced the in tanks first with Federal Moguls, (they failed after a month), then I put Airtex in, no problems with them since. I also had to replace the rear sender since there is a 38 gallon tank back there and it still had the stock send which wouldn't reach the bottom of the tank. I replaced the front sender too as long as I was there. My DFR would not switch states, (fwd to aft) so I had to replace it too. And the connector to my frame rail pump was crap so I replaced it and put a FoMoCo frame rail pump in. After I did all of this I could finally get the truck started.

Basically I replaced the entire Low pressure fuel system other then lines, wires and tanks. On the high pressure side I didn't need to do anything other then the pump.

I’ve have been running the truck for a little over a year and the fuel system is amazing. I can fill both tanks and go along ways and then come back. The indication system works as advertized and keeps me apprised of the fuel level.

Oh, and here's a picture of Seans toolbox.

Somethings jacked with the site today as it wont post pictures correctly...

nauss85

Thank you so much! This will definitely aid in my troubleshooting!

I filled up the rear last night. The needle read just slightly above "E". To my surprise, it only took 15.1 gallons... I think I am going to have to drop, inspect, and clean both tanks as well. I am only an E4 (still...the most senior at my entire command :/ ). And I am the only income with a wife who goes to school and 2 boys. Needless to say money is tight, I think I am going to have to wait for my taxes and just knock it out then... I know total cost for everything is pretty cheap in comparison, but I can only do what I can! Lol. Thank you again 5rangers!

5Rangers

Roger that.. when I got out in 86, I was an AT2... I wish I would have stayed active for 20 to get to the retirement. Coulda been a triple dipper..

nauss85

^+1,000,000

They are downsizing as you probably already know...If I cant pick up 2nd, Ill have 8 years in Sep...Then I hit the road. Hoping to become a cop, and still do the reserves.

In 18 days, I will be the most senior E4. I have been in 7 years and 3 months. I have been a 3rd for almost 6 years...FML lol