CaptainBob Posted October 17, 2007 Share Posted October 17, 2007 Hi, I am new to the forum and have a problem I cannot seem to cure. The fuel pump has no power to it. I have done extensive testing of sensors and have replaced the idle control valve, the throttle position sensor, all 5 relays, a bad ignition switch and key cylinder, the fuel pump, and traced the wiring back to the relay to be sure there was no fault. The truck was finally running good and idleing properly. After driving about 30 minutes on the highway, the new fuel pump died and would not start again The pump runs on the ground when tested. In the truck, the fuel pump relay clicks on and the pump starts for a second then stops...as it is supposed to. I understand the computer must sense the car is running or being started for the pump to run again. It never runs. Is there a fuel pump cutoff or an inertia switch on this truck? Does anybody know if and where a fuse link might be. What am I missing? There is nothing left but the computer that I can find. Thanks for any help you can give. Captain Bob Link to comment Share on other sites More sharing options...
1999MJ Posted October 17, 2007 Share Posted October 17, 2007 Have you checked the ground wire at the rear of the truck? That's what grounds the rear portion of the harnass including the fuel pump. I had a simmilar issue and that's what it turned out to be Link to comment Share on other sites More sharing options...
Wildman Posted October 18, 2007 Share Posted October 18, 2007 Did you check the Ballast Resistor that's on the left front fender?? Has a Orange w/black tracer wire, you can use a jumper between the two connectors to check if it's working or not. This was installed on '88 + vehicles and a very common cause of the fuel pump not running, or shuting off. Oh.....and Welcome to the ComancheClub :waving: Here......found a picture of it - Link to comment Share on other sites More sharing options...
Bacon Posted October 18, 2007 Share Posted October 18, 2007 Hi, The pump runs on the ground when tested. In the truck, the fuel pump relay clicks on and the pump starts for a second then stops...as it is supposed to. I understand the computer must sense the car is running or being started for the pump to run again. It never runs. your problem is the ballast resistor already mentioned. guaranteed. unplug those two wires, attach them to each other. start your truck up and drive to the parts store to buy a new resistor. happened on my truck a couple months ago. on startup, the ballast resistor is bypassed, giving your fuel pump a good jolt of power, which pressurizes the system. after your key is turned back to the on position, the power for the pump goes through the resistor. these are notorious for failing. i didn't know that info until mine died. now i carry a spare resistor in the tool box. hope this helps. oh, welcome to the forum! Link to comment Share on other sites More sharing options...
CaptainBob Posted October 19, 2007 Author Share Posted October 19, 2007 After replacing the ballast resistor, I now had power to the pump but no fuel pressure to the rail. Found it was the fuel pressure regulator and after replacing it, the truck runs great. Too bad the previous owner didn't do the repairs as he went along instead of letting them accumulate to create a nightmare. Oh well, I got a good deal on a rust free Larado that now runs like a top and life goes on.... A note: When I first started diagnosing the fuel problem, I pulled the pump mechanism from the tank and found that the hose between the pump and the supply line was almost disconnected. Looking back now, I am sure when the pressure regulator failed it caused the hose to blow off. I wonder if it was then that the resister was overheated too...... Appreciate the welcome to the club! Great place! Now that my son has his Comanche, I feel left out...maybe I will get one too...a 4X4 would be nice :D Thanks again, Captain Bob Link to comment Share on other sites More sharing options...
sinnaevd Posted October 19, 2007 Share Posted October 19, 2007 I have heard that you don't even need the ballist resistor at all, What the heck does it do? Link to comment Share on other sites More sharing options...
CaptainBob Posted October 19, 2007 Author Share Posted October 19, 2007 I have heard that you don't even need the ballist resistor at all, What the heck does it do? The ballast resister reduces the voltage to the fuel pump in the engine running mode to reduce noise and make the pump last longer. This I learned from one of the members here in a private mail. You can jump the resister to test for power at the pump but I wouldn't change the design of the system unless you don't want to spend the few bucks on a new one. Captain Bob Link to comment Share on other sites More sharing options...
Geonovast Posted October 19, 2007 Share Posted October 19, 2007 I just started having a problem with my pump too, it's making a loud groaning noise, and gets lower when i tap the gas. It's there while driving too, and its only there when the truck is running. Maybe the ballast resistor is letting too much current through? I'm not experiencing any loss of power, though. Link to comment Share on other sites More sharing options...
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