bucketheadben Posted December 10, 2007 Share Posted December 10, 2007 Hey guys. My 90 XJ 4.0 Auto has had a long starting problem since I've owned(couple of months.) I think it has something to do with the pump or pressure regulator, but I'm uncertain because priming it doesn't help the long start. It will take about 5 secs until the engine spins over. The start time will be cut to about 3 secs if it was running recently and I try to start it up. Today for the first time it stalled out on me in traffic. Once at a red light and twice decelerating around MPH. It would run rough right before dieing and it would start up like normal afterwords. Once i got it in the driveway i started it up and would idle fine, then i restarted it and it died immediately twice and on the third try it was fine and took it around the neighborhood with no problems. So do you guys think this is a fuel issue or could it be a sensor(TPS,CPS,IAC?) I'm going to clean the TB and IAC while I wait for some input. Thanks in advance for any help. Ben Link to comment Share on other sites More sharing options...
Wildman Posted December 10, 2007 Share Posted December 10, 2007 I would check the fuel pressure first, you can get a 'cheep' gauge for this, and see if the pressure is up to spec's, And if you have not changed the fuel filter in some time, will not hurt to change that out. Check the body ground, that grounds the tail lights and the fuel pump. In fact, check all the grounds, battery to engine - engine to body. Check the ballast resistor on the left front fender, even by-pass it to see if this is causing your problem. Check the CPS at the connector, the wires and do a reading on the CPS, and even go as far as replacing the sensor. A real pain, but something is causing you to cut out. Leave this for last. Link to comment Share on other sites More sharing options...
bucketheadben Posted December 10, 2007 Author Share Posted December 10, 2007 I would check the fuel pressure first, you can get a 'cheep' gauge for this, and see if the pressure is up to spec's, And if you have not changed the fuel filter in some time, will not hurt to change that out. Check the body ground, that grounds the tail lights and the fuel pump. In fact, check all the grounds, battery to engine - engine to body. Check the ballast resistor on the left front fender, even by-pass it to see if this is causing your problem. Check the CPS at the connector, the wires and do a reading on the CPS, and even go as far as replacing the sensor. A real pain, but something is causing you to cut out. Leave this for last. Sorry, I forgot to mention that i changed the fuel filter, plugs, wires, cap and rotor button when I bought the XJ. I just finished pulling and cleaning the IAC and using Sea foam but it doesn't seem like it did anything noticable. I actually left it running while i was washing my hands and when i walked outside it was not running any more. So i pulled the cap on the fuel rail and pressed in the shcrader valve and got what i thought was very little fuel. I'd say no more than a couple tablespoons of gas. So i'm realy leaning towards the fuel pump. Does anyone else agree. Ben Link to comment Share on other sites More sharing options...
bucketheadben Posted December 11, 2007 Author Share Posted December 11, 2007 I think i found the problem. It was not the pump because i wired it directly off of the the battery and it pumped. So i disconnected the outlet hose on the pump so i could see if it would pump when i turned the key. Nothing in the 'on' position, but when i started it i got fuel. So after checking the ceramic resistor again i found the female connectors were in rough shape and i did not had a good connection when i tried to jump the wires together the first time. So i cleaned them up real good and shorted the wires directly together and i got fuel to pump in the 'on' position. So I hooked the hose back up, started it up and drove it around for about 15mins and no problems. I'm pretty confident this will solve my long starting problem since it wasn't priming in the 'on' position. I think I've read before that some people have just left the resistor bypassed and have not have problems, or am i remembering incorrectly? Does it do anything other than quiet down the pump. Thanks for all of the help. Link to comment Share on other sites More sharing options...
Wildman Posted December 11, 2007 Share Posted December 11, 2007 Yea.....aways the simple things.....like the ballast resistor :brows: From what I remember, you should replace the ballast resistor, It's like a $7-9 part, it is designed to make the pump run quieter and last longer than having full voltage applied all the time, after start up. although, '87's did not have the ballast resistor installed. Does this make a big difference :dunno: Well, glad to hear you had a simple problem to fix......this time :D Link to comment Share on other sites More sharing options...
1986Comanche Posted December 12, 2007 Share Posted December 12, 2007 Yea.....aways the simple things.....like the ballast resistor :brows: From what I remember, you should replace the ballast resistor, It's like a $7-9 part, it is designed to make the pump run quieter and last longer than having full voltage applied all the time, after start up. although, '87's did not have the ballast resistor installed. Does this make a big difference :dunno: Well, glad to hear you had a simple problem to fix......this time :D Yes, 1987s do have a fuel pump ballast resistor. I have a 1987 Comanche SporTruck 4x4 with the 4.0L I-6 sitting here right now and it has a fuel pump ballast resistor on the drivers side front inner fender. Link to comment Share on other sites More sharing options...
Oizarod115 Posted December 12, 2007 Share Posted December 12, 2007 Yea.....aways the simple things.....like the ballast resistor :brows: From what I remember, you should replace the ballast resistor, It's like a $7-9 part, it is designed to make the pump run quieter and last longer than having full voltage applied all the time, after start up. although, '87's did not have the ballast resistor installed. Does this make a big difference :dunno: Well, glad to hear you had a simple problem to fix......this time :D Yes, 1987s do have a fuel pump ballast resistor. I have a 1987 Comanche SporTruck 4x4 with the 4.0L I-6 sitting here right now and it has a fuel pump ballast resistor on the drivers side front inner fender. but he's right you should still replace it, cheap part, makes the pump quieter and supposedly last longer so it can't hurt. but don't be afraid to drive it like that for a while if you've got to Link to comment Share on other sites More sharing options...
Wildman Posted December 12, 2007 Share Posted December 12, 2007 Yes, 1987s do have a fuel pump ballast resistor. I have a 1987 Comanche SporTruck 4x4 with the 4.0L I-6 sitting here right now and it has a fuel pump ballast resistor on the drivers side front inner fender. Yes, It could have, There was a Service Bulletin latter that added the Ballast Resistor to the '87, Thru the Dealer Service. 2 '87 MJ's I parted out this summer, nether had the Ballast Resistor. The one '87 MJ I have parked now, No Ballast Resistor. The '88 and '89's have the Ballast Resistor. Link to comment Share on other sites More sharing options...
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