bumpy Posted January 1, 2013 Share Posted January 1, 2013 Hey guys, its been a while since ive had a MJ and in the meantime ive had 3 XJs since... all the same but i missed the truck and came across one on here and gl4x4, anyways shes got a issue right now and I'm not sure if its lack of compression or lack of fuel or lack of spark... just hoping that someone else has had the same symptoms as me and can help. ive searched and read up on a few threads but no real luck... The Jeep is a '87 4.0 5spd 4x4, d44/d30.. the issue besides no CEL... I was driving down the highway and its kinda like it started to backfire in a sense, a hiccup if you will, it bogged down and slowed down, won't hold over 2000rpm makes a bunch of loud pops and bangs in the motor, finally died completely about 4 miles down the highway.. it would still drive, will no go over 2000 rpms in any gear and when its in a gear it will drive, it just will not speed up at all. I'm not really sure where to start besides buying a new motor and swapping it in, not too big of a fan of finding the problem and fixing it thing now a days lol! i know its not real descriptive on the issue, but I'm sure if someone else has had this stuff happen to them before that theyd be able to help me pinpoint my problem!! thanks guys in advance!!! Link to comment Share on other sites More sharing options...
cruiser54 Posted January 1, 2013 Share Posted January 1, 2013 New motor? Whoa. Soundsl like a loss of fuel pressure. How mechanically inclined are you? Link to comment Share on other sites More sharing options...
87MJTIM Posted January 1, 2013 Share Posted January 1, 2013 Have you check the catalytic converter? Sounds like it might be clogging up. Link to comment Share on other sites More sharing options...
bumpy Posted January 2, 2013 Author Share Posted January 2, 2013 Fairly mechanically inclined, have swapped 3 XJ motors in the past 2 years... I know nothing about renix motors tho that's why I figured swapping a motor may be easier than trying to figure out the actual problem... 6ish hours of labor to swap a motor or a lot more in frustration?? Fuel pressure could be the issue as the first time it happened, the fuel light was on, I filled it up and it ran fine... The next day it hated life tho... I will disconnect the exhaust before the cat and see how it runs but the cat appears to be fairly new? Thanks for the insights fellas! Link to comment Share on other sites More sharing options...
cruiser54 Posted January 2, 2013 Share Posted January 2, 2013 The motor is probably not the issue. Renix is not voodoo for crying out loud. Good chance you compromised the fuel pump by running a 20 plus year old tank low on gas, allowing the pump to suck up debris. Do a fuel pressure test first. Link to comment Share on other sites More sharing options...
Biotex Posted January 2, 2013 Share Posted January 2, 2013 Cruiser, First off, i'm not disagreeing with your prognosis. We've all seen it many time when someone lets the tank go near dry, the fill up and the problems begin. What i'm trying to understand is what exactly happens. Is it debris? Is it the pump got hot? Both? Here's my logic: Fuel floats on water, so when the truck sits overnight, all the trash is settled to the bottom. The sump is on the lowest part of the tank, so theoretically every time you start up you should be cleansing the water/trash out by burning it, or trapping it in the filter. How do you see it? Curious.... Link to comment Share on other sites More sharing options...
bumpy Posted January 2, 2013 Author Share Posted January 2, 2013 cruiser how do you go about a fuel pressure test?? Link to comment Share on other sites More sharing options...
gogmorgo Posted January 13, 2013 Share Posted January 13, 2013 Here's my logic: Fuel floats on water, so when the truck sits overnight, all the trash is settled to the bottom. The sump is on the lowest part of the tank, so theoretically every time you start up you should be cleansing the water/trash out by burning it, or trapping it in the filter. I concur. Long story short, I dropped and drained my tank into a bunch of gallon pails (all I had). The tank got knocked around a lot on the way down, and then it sat a few hours while I was trying to figure out why Napa sent me an XJ tank. I jumped the relay to pump the gas out. The only pail with $#!& in it was the first one out of the tank, and I had the pump going until nothing came out. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 13, 2013 Share Posted January 13, 2013 First off change the fuel filter. If no joy do a fuel pressure test at the fuel rail. You will need a fuel pressure gauge connected to the fuel rail test port. Plenty of info here on the forum for the correct PSI specs, and I'm not sure about the Renix specs. I suspect you will be reading low because the filter sock on the in-tank fuel pump inlet is clogged or collapsed. Link to comment Share on other sites More sharing options...
relyt120 Posted January 13, 2013 Share Posted January 13, 2013 Sounds similar to an issue I had a few months back, not saying its definitely the fix, but after replacing numerous parts it finally stopped after replacing the fuel pressure regulator. Link to comment Share on other sites More sharing options...
ComancheKid45 Posted January 13, 2013 Share Posted January 13, 2013 Definently sounds like a fuel issue. I experienced a very similar situation when the hose between the fuel pump and the sending unit came loose inside the tank... Link to comment Share on other sites More sharing options...
88mjgilley Posted January 13, 2013 Share Posted January 13, 2013 i had one a few years ago do this if you figure it out fill us in i still scratch my head to this day about that thing Link to comment Share on other sites More sharing options...
JeffN Posted January 13, 2013 Share Posted January 13, 2013 I had the same problem about a year ago, it turned out to be the hose inside the tank that was leaking the fuel back into the fuel tank, the one from the pump to the sending unit. a new piece of hose and haven't had a problem since Link to comment Share on other sites More sharing options...
JFAComanche6 Posted January 14, 2013 Share Posted January 14, 2013 Cruiser, First off, i'm not disagreeing with your prognosis. We've all seen it many time when someone lets the tank go near dry, the fill up and the problems begin. What i'm trying to understand is what exactly happens. Is it debris? Is it the pump got hot? Both? Here's my logic: Fuel floats on water, so when the truck sits overnight, all the trash is settled to the bottom. The sump is on the lowest part of the tank, so theoretically every time you start up you should be cleansing the water/trash out by burning it, or trapping it in the filter. How do you see it? Curious.... Ha, so are you saying I need to jump up and down in my truck's bed every morning to slosh all the refuse out of the way? Jk, but I agree with what you're saying, the first thing I bought for my $200 Comanche was a brand new $150 gas tank (rockauto.com) because the old one had rusted out. Link to comment Share on other sites More sharing options...
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