SubSonic Posted February 15, 2011 Share Posted February 15, 2011 Well it's a tech question, and for all intents and purposes we'll pretend said XJ is an MJ for forum of course... :no: I've dealt with plenty of H.O.s and even rebuilt and replaced one in my Comanche, but this renix motor in this jeep I picked up is giving me fits. It's so familiar yet so far from home. Here's the background: picked up 1990 XJ, 4x4, AX15, 140k, hadn't been started in 5 years. Towed off guy's land, went to gas station parking lot, worked for 3 hours and got it *running (oil change, connected gas tank, intake, stearing column, clutch lines) enough to make the 50 mile trek home... recieved tickets on way home.... continued... made it home. SKIP TO HERE IF LAZY! OK as it sits tranny is good, 4x4 is good, susp. is good, and motor itself is good (no knocks, taps, raps, or craps etc.) However it runs like absolute crap. Finally got all the vacuum lines connected and got the MAP hooked to the throttle body, which all the sudden made the idle sound right, and even the revs sounded good with no load. (still dies occasionally with no foot on gas) but as soon as you try to drive it there is a whole lot of no power and a bunch of intake firing... ie. can't really get anywhere. So I replaced the MAP same deal... unplugged the MAP vacuum and the idle turned to $#!& again and it sounds and runs like crap but becomes drivable (this is how I drove it home, mind you). Perhaps the richness with the map unplugged allows it to run and with it plugged in it runs too lean. I've replaced the fuel filter, and the pump seems to prime every time the key is turned. So I'm stumped, this was supposed to be a parts jeep so it's not a huge deal but I've spent too much time now, so I atleast need to assuage my curiosity. Thanks for any input guys. Link to comment Share on other sites More sharing options...
JeffN Posted February 15, 2011 Share Posted February 15, 2011 Check for moisture inside the distributor cap and also look for arc lines in there, they aren't expensive to replace Link to comment Share on other sites More sharing options...
Eagle Posted February 15, 2011 Share Posted February 15, 2011 Google "Distributor Index" Link to comment Share on other sites More sharing options...
SubSonic Posted February 15, 2011 Author Share Posted February 15, 2011 I have already checked the cap, rotor, and looked for arc on the wires, and all seemed fine. While it never hurts to replace those things, I don't believe that's the root of the problem. Thank you very much for the insight, though. Link to comment Share on other sites More sharing options...
SubSonic Posted February 15, 2011 Author Share Posted February 15, 2011 Google "Distributor Index" Yes, I had considered that it may be a tooth, teeth, off. But the idle, and revving in neutral seem as if it is firing correctly at times... but it's probably worth restabbing for assurance. Thanks! Link to comment Share on other sites More sharing options...
ComancheKid45 Posted February 15, 2011 Share Posted February 15, 2011 Check the o2 sensor and pull the #1 spark plug as well... Link to comment Share on other sites More sharing options...
SubSonic Posted February 15, 2011 Author Share Posted February 15, 2011 Check the o2 sensor and pull the #1 spark plug as well... I've replaced all the spark plugs... they were blackened, but not fried. I should tow it to the stealership to replace the O2 sensor since it still has that as an unperformed recall :D I have however unplugged the O2 sensor so it will go into limp rich mode, but it fixes nothing, so I don't believe thats the issue. Thanks! Link to comment Share on other sites More sharing options...
Eagle Posted February 16, 2011 Share Posted February 16, 2011 Clogged catalytic converter? Link to comment Share on other sites More sharing options...
sinkrun Posted February 16, 2011 Share Posted February 16, 2011 Check and clean all the grounds to the block and firewall. Link to comment Share on other sites More sharing options...
SubSonic Posted February 16, 2011 Author Share Posted February 16, 2011 Great, new things to try! I'll unbolt the exhaust before the cat and see if that helps. And while I'm checking grounds, it probably wouldn't hurt to check the ground on the fuel pump... maybe even pick up a gauge and check my fuel pressure. Thanks so much for the responses! Link to comment Share on other sites More sharing options...
500 MJ Posted February 16, 2011 Share Posted February 16, 2011 FYI - This may come in handy. viewtopic.php?f=9&t=12517 Link to comment Share on other sites More sharing options...
cz777 Posted February 16, 2011 Share Posted February 16, 2011 a bunch of intake firing back firing ? and no power ? too lean and /or ignition cap carbon tracked - i seen intake vacuum leaks around the injectors etc also look at the fuel pressure regulator which is overlooked a lot -see if its leaking fuel and psi of the system ! Link to comment Share on other sites More sharing options...
veritas4156 Posted February 16, 2011 Share Posted February 16, 2011 Or just spray foaming glass cleaner all over the intake near any connections and watch to see where it gets sucked in while its running. Its pretty much just alcohol and we all know the 4.0 can take a bit of abuse so it shouldn't hurt. Then wipe it up after and watch it shine. Link to comment Share on other sites More sharing options...
SubSonic Posted February 16, 2011 Author Share Posted February 16, 2011 Or just spray foaming glass cleaner all over the intake near any connections and watch to see where it gets sucked in while its running. Its pretty much just alcohol and we all know the 4.0 can take a bit of abuse so it shouldn't hurt. Then wipe it up after and watch it shine. So that's like the visual version of carb and choke cleaner on the vacuum lines, interesting concept. Link to comment Share on other sites More sharing options...
jeep10 Posted February 17, 2011 Share Posted February 17, 2011 Well it's a tech question, and for all intents and purposes we'll pretend said XJ is an MJ for forum of course... :no: I've dealt with plenty of H.O.s and even rebuilt and replaced one in my Comanche, but this renix motor in this jeep I picked up is giving me fits. It's so familiar yet so far from home. Here's the background: picked up 1990 XJ, 4x4, AX15, 140k, hadn't been started in 5 years. Towed off guy's land, went to gas station parking lot, worked for 3 hours and got it *running (oil change, connected gas tank, intake, stearing column, clutch lines) enough to make the 50 mile trek home... recieved tickets on way home.... continued... made it home. SKIP TO HERE IF LAZY! OK as it sits tranny is good, 4x4 is good, susp. is good, and motor itself is good (no knocks, taps, raps, or craps etc.) However it runs like absolute crap. Finally got all the vacuum lines connected and got the MAP hooked to the throttle body, which all the sudden made the idle sound right, and even the revs sounded good with no load. (still dies occasionally with no foot on gas) but as soon as you try to drive it there is a whole lot of no power and a bunch of intake firing... ie. can't really get anywhere. So I replaced the MAP same deal... unplugged the MAP vacuum and the idle turned to $#!& again and it sounds and runs like crap but becomes drivable (this is how I drove it home, mind you). Perhaps the richness with the map unplugged allows it to run and with it plugged in it runs too lean. I've replaced the fuel filter, and the pump seems to prime every time the key is turned. So I'm stumped, this was supposed to be a parts jeep so it's not a huge deal but I've spent too much time now, so I atleast need to assuage my curiosity. Thanks for any input guys. Considering, it runs if you unplug and enrichen it, seems to me if it was a firing problem it might get worse. You said it sat for 5 years, is it a possibility the injectors are gummed up ? And under load it is actually a fuel starvation problem. How nasty was the fuel... like varnish I would think in five years. Just things to toss around and check. Link to comment Share on other sites More sharing options...
SubSonic Posted February 17, 2011 Author Share Posted February 17, 2011 I just checked the fuel pressure, it's only at 17 psi, pinched line at rail and ruled out pressure regulator... So I pulled the pump, and the rubber line on the pump was in pretty bad shape. It had a very minor leak as well. I don't feel like throwing a new pump at a title-less parts vehicle, but I may try putting a new hose on the pump and checking the psi again. Link to comment Share on other sites More sharing options...
dakal Posted February 17, 2011 Share Posted February 17, 2011 mine sat quite a while. gave me fits until i replaced the fuel strainer in tank. its a flat one now. problem gone. strainer looked ok, but replaced it since the pump was out. the hose looked ok but replaced it also. Link to comment Share on other sites More sharing options...
SubSonic Posted February 17, 2011 Author Share Posted February 17, 2011 mine sat quite a while. gave me fits until i replaced the fuel strainer in tank. its a flat one now. problem gone. strainer looked ok, but replaced it since the pump was out. the hose looked ok but replaced it also. Any specific hose you guys like to use on the pump in the tank that's most resistant to gasoline degradation. Or shall I just go with regular hi-pres. fuel line. Link to comment Share on other sites More sharing options...
dakal Posted February 17, 2011 Share Posted February 17, 2011 i used german fuel line. the kind that goes in bmw or merc's. my mechanic says it holds up better than the others. so good for me. Link to comment Share on other sites More sharing options...
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