87 Basket Case Posted July 24, 2019 Share Posted July 24, 2019 Just picked up an 87 with 4.0, BA10/5sp 2wd shortbed and ive got a fuel problem. Previous owner screwed up the wiring real bad, its a mess. When Key is on, I hear the pump running constantly. When I press the brake, I hear the pitch of the fuel pump sound change, like its getting less power. Ive got no pressure at the rail, And I don't have any fuel or even positive pressure coming from the supply hose before the filter. Not sure if I have a bad pump or a wiring issue on my hands. Possibly a fuel pressure regulator? What is the test procedure for the Fuel pump/pressure regulator/ballast resistor? Link to comment Share on other sites More sharing options...
Pete M Posted August 2, 2019 Share Posted August 2, 2019 On 7/24/2019 at 1:03 AM, basket case said: Just picked up an 87 with 4.0, BA10/5sp 2wd shortbed and ive got a similar problem. Previous owner screwed up the wiring real bad, its a mess. When Key is on, I hear the pump running constantly. When I press the brake, I hear the pitch of the fuel pump sound change, like its getting less power. Ive got no pressure at the rail, And I don't have any fuel or even positive pressure coming from the supply hose before the filter. Not sure if I have a bad pump or a wiring issue on my hands. Possibly a fuel pressure regulator? What is the test procedure for the Fuel pump/pressure regulator/ballast resistor? sounds like part of your issue could be a bad ground at the drivers side taillight. the fuel pump and the brake lights ground to the same spot back there. also I moved your topic to Tech so more eyes will see it. Link to comment Share on other sites More sharing options...
87 Basket Case Posted August 2, 2019 Author Share Posted August 2, 2019 Ok Ill give that a shot, ive got all day tomorrow to work on in. Ill check my tail light ground and probably drop the tank. I found a pin hole leak that I'm going to try and weld up Link to comment Share on other sites More sharing options...
fiatslug87 Posted August 2, 2019 Share Posted August 2, 2019 If the pimp is running and nothing is coming out before the fuel filter, the hose to the pump could be off or the tube is corroded or the sock is clogged or... When you pull the pump apply power to it to see if it's really pumping. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 4, 2019 Share Posted August 4, 2019 Do this while you're at it. CRUISER'S MOSTLY RENIX TIPS IMPROVING THE FUEL PUMP GROUND JANUARY 3, 2016 CRUISER54 49 COMMENTS The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ. Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture. Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire. Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering. At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces. Link to comment Share on other sites More sharing options...
87 Basket Case Posted August 4, 2019 Author Share Posted August 4, 2019 Thanks Crusier, that's a solid idea. I pulled the tank and bench tested the pump and confirmed it is bad. I've got a new pump, pick up sock, and filter. I also found a handful of pinhole leaks in the tank. I have cleaned the tank up and washed it out, now I'm letting it sit out outside for a few days, trying to let it air out and get the fumes out of it. The plan is to put a couple tac welds over the pin holes. When my tank is sealed up and leak free, I'll install the new pump, add the new ground, and see if I've got good pressure at the rail. Once it's running on its own power, I'll start working my way through the rest of Cruisers mostly renix tips Link to comment Share on other sites More sharing options...
Jeep Driver Posted August 4, 2019 Share Posted August 4, 2019 15 minutes ago, basket case said: Thanks Crusier, that's a solid idea. I pulled the tank and bench tested the pump and confirmed it is bad. I've got a new pump, pick up sock, and filter. I also found a handful of pinhole leaks in the tank. I have cleaned the tank up and washed it out, now I'm letting it sit out outside for a few days, trying to let it air out and get the fumes out of it. The plan is to put a couple tac welds over the pin holes. When my tank is sealed up and leak free, I'll install the new pump, add the new ground, and see if I've got good pressure at the rail. Once it's running on its own power, I'll start working my way through the rest of Cruisers mostly renix tips Save yourself the grief......and you'll likely burn through anyway. https://www.partsgeek.com/gbproducts/DC/2237-05487211.html?utm_source=google&utm_medium=ff&utm_content=DN&utm_campaign=PartsGeek+Google+Base&utm_term=1987-1992+Jeep+Comanche+Fuel+Tank+Spectra+Premium+JP5B+87-92+Jeep+Fuel+Tank+89+88&fp=pp&gbm=a&utm_source=google&utm_medium=ff&utm_campaign=PartsGeek+Google+Base&gclid=Cj0KCQjwhJrqBRDZARIsALhp1WSVNhEUsOaxbg1zZCbn3D-e-wP1pMfHzov2uyVCjT6WAI9QRyonu0QaAnyZEALw_wcB Link to comment Share on other sites More sharing options...
DirtyComanche Posted August 4, 2019 Share Posted August 4, 2019 1 hour ago, basket case said: Thanks Crusier, that's a solid idea. I pulled the tank and bench tested the pump and confirmed it is bad. I've got a new pump, pick up sock, and filter. I also found a handful of pinhole leaks in the tank. I have cleaned the tank up and washed it out, now I'm letting it sit out outside for a few days, trying to let it air out and get the fumes out of it. The plan is to put a couple tac welds over the pin holes. When my tank is sealed up and leak free, I'll install the new pump, add the new ground, and see if I've got good pressure at the rail. Once it's running on its own power, I'll start working my way through the rest of Cruisers mostly renix tips Just buy a tank. If there's pinholes in it now, there will be more later. EBay, Rockauto, etc all have them. Link to comment Share on other sites More sharing options...
Warren Mohler Posted August 16, 2019 Share Posted August 16, 2019 does any one know what fuel pressure should be, 89 Comanche 4.0L renix I have 39 psi at key on 29 at idle and about 37psi when revved I don't seem to have throttle response I had 20 years ago, still runs well and great mileage just not as snappy has 5 spd trans Link to comment Share on other sites More sharing options...
Ωhm Posted August 17, 2019 Share Posted August 17, 2019 Fuel pressure numbers seem good allowing for a little slop in the gauge. Ideally would be 39psi at KEY ON and 31psi at IDLE. Maybe time for a secondary tune up. Plugs, wires, rotor and distributor cap. Link to comment Share on other sites More sharing options...
87 Basket Case Posted September 15, 2019 Author Share Posted September 15, 2019 Wanted to update the thread... I ended up buying a new tank, pump, filter and sock. I added the extra ground and attached it to the fuel filter bracket. When it was all said and done, I still couldn't get the fuel pump to kick on. I tried applying 12v straight to the pump harness and I could get good pressure at the rail when I did that, but the pump wouldn't kick on when I was Key On. I tested voltage at the pump harness and was getting 0v at key off, 2.8v key on, and 1.8v cranking. I tested the fuel pump relay (I believe it is the middle relay of the 3) and it was good. I moved on to the starter relay. While messing with the rats nest of wires, I could hear the fuel pump kick on! I think the orange wire coming off the B+ terminal on the starter relay runs to the fuel pump and has a bad connection somewhere down the line. I also believe my starter relay is bad because the previous owner bypassed it to put a push button starter in it, but I would like to know the proper way to test the unit. Does anyone know a testing procedure? I have the 4 post relay, the one with out the lead for the ballast resistor. Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 15, 2019 Share Posted September 15, 2019 29 minutes ago, 87 Basket Case said: I also believe my starter relay is bad because the previous owner bypassed it to put a push button starter in it, but I would like to know the proper way to test the unit. Replace it. It's $20 Link to comment Share on other sites More sharing options...
87 Basket Case Posted September 16, 2019 Author Share Posted September 16, 2019 10 hours ago, Jeep Driver said: Replace it. It's $20 I'm not a big fan of throwing parts at problem and hoping it fixes it. Fiatslug87 gave me the electrical diag manual for 1987, I found testing instructions incase anyone is interested Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 16, 2019 Share Posted September 16, 2019 24 minutes ago, 87 Basket Case said: I'm not a big fan of throwing parts at problem and hoping it fixes it. Fiatslug87 gave me the electrical diag manual for 1987, I found testing instructions incase anyone is interested OK, I sit here everyday I read the same post over and over and over.........same problems, over and over. By your own admission- You have a mess, you have a Basket Case. I didn't suggest you throw $2000 part at a $2 problem. If you want to drive the truck and you want the truck to be reliable.......at some point you need to start cleaning up the mess. It's a 32 year old relay. Here is mine, NOS Mopar, IIRC I paid something like $13 for it on ebay. Link to comment Share on other sites More sharing options...
87 Basket Case Posted September 16, 2019 Author Share Posted September 16, 2019 You're not wrong Link to comment Share on other sites More sharing options...
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