500 MJ Posted December 13, 2007 Share Posted December 13, 2007 My G/f has a '90 XJ with the renix 4.0L/AW4/242 setup in it with 170,000. The Jeep is getting horrible gas mileage, like in the single digits. We have alot of hills around town but it shouldnt be that bad in my opinion. Whenever the Jeep is put in Park or Neutral with it warmed up, the darn thing revs up to around 2 grand. I know that this isnt right. Any thoughts on the problem? I've already cleaned the throttle body all up. Also, it sounds like it misses right after its been started up and then a few seconds in, runs just fine. I doubt that there is a problem with the headgasket but there could be a small leak. I'm thinking it might be a fuel injector related issue. Anyone have the injector number's off hand that should be in the Jeep? Thanks - Brent Link to comment Share on other sites More sharing options...
offroader461 Posted December 13, 2007 Share Posted December 13, 2007 My XJ did that when i bought it..and only averaged about 11MPG..here was my solution: Tune up (plugs, wires, cap, rotor, air filter) cleaned the CCV and all breathers cleaned the IAC and set the TPS replaced the Oxygen sensor my XJ now avg about 19 MPG now and idles like a champ Link to comment Share on other sites More sharing options...
Eagle Posted December 13, 2007 Share Posted December 13, 2007 The oxygen sensor is the one that's most likely to put the fuel mileage in the toilet. A tune-up never hurts, but won't usually flush the mileage THAT badly unless it gets to the point that the engine hardly runs. A bad O2 sensor, on the other hand, just leaves it running rich all the time. Fast idle is usually the IAC or the TPS, but it can also be rust in the throttle linkage bellcrank on the driver's side of the engine, down below the master cylinder. Try spraying that with a good penetrating lubricant (NOT WD-40). Link to comment Share on other sites More sharing options...
Confedneck Posted December 13, 2007 Share Posted December 13, 2007 fast idle could also be a faulty CKP... i would start with a full tuneup Link to comment Share on other sites More sharing options...
fiatslug87 Posted December 14, 2007 Share Posted December 14, 2007 Whenever the Jeep is put in Park or Neutral with it warmed up, the darn thing revs up to around 2 grand. Also check for vacuum leaks, especially aroung the intake manifold. Link to comment Share on other sites More sharing options...
ejndssn Posted December 14, 2007 Share Posted December 14, 2007 the issue that corrected my fast idle egr valve its a quick fix and if that this the original its about time to get it replaced :brows: . it was around the 175k -185k mile range and now runs pretty dam good Link to comment Share on other sites More sharing options...
dfreeman616 Posted December 14, 2007 Share Posted December 14, 2007 try checking if it has a recall on it for the o2 sensor, i just got mine replaced in my 88 cherokee recall #561. not sure if her's is covered, but might be worth checking. you can do it on the chrysler site just be sure to use the full vin in the comment section. Link to comment Share on other sites More sharing options...
comanchekidwa Posted December 15, 2007 Share Posted December 15, 2007 I'd check for a intake leak and if thats ok... then more and likely the O2 sensor and don't buy a cheap one buy a Bosch O2 sensor.... Link to comment Share on other sites More sharing options...
carnuck Posted December 15, 2007 Share Posted December 15, 2007 clogged hose (or cracked) to the MAP sensor. I jumped up to 18 mpg with 3.73 gears, 5 speed and 33" tires. Link to comment Share on other sites More sharing options...
TajMan Posted December 16, 2007 Share Posted December 16, 2007 Bosch 02 sensor from different vehicle compatible if it uses the same # of wires etc? I've got 2 ok used ones in my garage I believe. Link to comment Share on other sites More sharing options...
500 MJ Posted January 27, 2008 Author Share Posted January 27, 2008 We replaced the O2 sensor with one from another Jeep I had lying in reserve. It solved nothing. My roomate thinks its the ECU. Any thoughts on that one? Yes/No It also should be brought forth to mention that the exhaust manifold is cracked and has a pretty good leak to it at startup. Once it warms up it quiets down some. I have a good manifold, I just need the time to replace it. Is there a chance that the manifold could contribute to the fast idle. Its been cold out these past few days. I went out and started the Jeep the other day just to see if I could hear any vaccum leaks. No luck there. BUT - and this might help you all diagnose the problem - without even getting into it or driving it - touching the gas in any way, it revved up as it would get warmer. It was really weird, about every 30 seconds it would up itself about 200-300 rpms. I think its posessed. :popcorn: Link to comment Share on other sites More sharing options...
Eagle Posted January 27, 2008 Share Posted January 27, 2008 (1) Swapping in a used O2 sensor is a total waste of time and energy, because the used one you swap in may be as bad as or worse than the one you're replacing. (2) A cracked exhaust manifold allows air to get into the exhaust stream. This makes the O2 sensor see a much leaner exhaust than what the engine is really putting out, so it richens the mix to compensate. I'd say that's your problem, right there. Link to comment Share on other sites More sharing options...
500 MJ Posted February 10, 2008 Author Share Posted February 10, 2008 Ok. Got the new manifold on and whoopie, the engine runs so nicely now and idles right back down around 600 range. Very Nice. ;) Just for good measure I take the Jeep out and run it down the road and the AW4 doesnt want to shift out of 1st gear. :mad: Here we go again. If its not one thing its the other. Some Notes: - I found that the manifold was NOT cracked, rather the stud on the rear of the head broke off so the exhaust was leaking around the gasket which toasted the old gasket right out. As we were cleaning the head to mount the new gasket I noticed that the CPS connector was melted a bit, but it still worked. I plan on replacing this next weekend (I didnt have a scrap male connector on hand when I was in there and I wanted to get the Jeep running ASAP). I wouldnt think that this would be related at all to the trans problem but I might be wrong. Also, while I was under the hood I swapped in a different starter as the one we had was giving us some issues and a complete set of fuel injectors (the previous set was mismatched and I wanted a entire set that I knew was good, were OEM parts and were uniformly used). However, this new uniform set DID come from a I6 with a manual trans. Again I don't think that it would matter but I might be wrong. - Any thoughts on why it won't shift? I don't see anything that I forgot to hook up and I've had lots of people look at it with no luck. Fluid level is fine and it shifted like a charm prior to taking the manifolds off to swap in this new gasket. Kick-down cable and everything is hooked up as far as I can see but I know somewhere is probably a simple connector that I missed. One more reason to dislike automatics. :hateputers: Link to comment Share on other sites More sharing options...
Twisty Posted February 10, 2008 Share Posted February 10, 2008 Make sure that both TPS plugs are connected. The TPS also controls shifting of the tranny. Link to comment Share on other sites More sharing options...
Wildman Posted February 11, 2008 Share Posted February 11, 2008 X2 on the TPS The trans not shifting out of 1st is almost always the TV cable (what you call the 'kick down' cable) On the 4.0, it is adjustable, you might have it hooked up, but not adjusted just right, double check that first. Link to comment Share on other sites More sharing options...
500 MJ Posted February 11, 2008 Author Share Posted February 11, 2008 How do you go about adjusting it? Link to comment Share on other sites More sharing options...
500 MJ Posted February 11, 2008 Author Share Posted February 11, 2008 It clips in here and here ..................................................................^ and goes through the square hole? Thats the kickdown cable right? Link to comment Share on other sites More sharing options...
Wildman Posted February 11, 2008 Share Posted February 11, 2008 This should help, it's also in the Haynes book ;) http://www.lunghd.com/Tech_Articles/Tra ... ostics.htm Also click on the link for the ' cable replacement' and it will give you a little more details. Link to comment Share on other sites More sharing options...
500 MJ Posted February 12, 2008 Author Share Posted February 12, 2008 So I readjusted that thing and it did nothing. Seems to me that the only other possibility is the TPS? If it worked fine before, why isnt it now? :hateputers: Link to comment Share on other sites More sharing options...
Eagle Posted February 12, 2008 Share Posted February 12, 2008 Have you tried a diagnostic run on the tranny itself? I don't have the book in front of me at the moment and I'm a 5-speed guy, but I believe I recall that if you pull the fuse for the TCU the tranny should operate in "manual shift" mode -- the low position on the shifter should give you 1st gear, there is no 2nd gear, the "3" position gives you 3rd and the "O" position gives you 4th. You should be able to take it on the road and drive it like that. If you can't make it shift up manually with the TCU disabled, you probably have a tranny problem. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 12, 2008 Share Posted February 12, 2008 So I readjusted that thing and it did nothing. Seems to me that the only other possibility is the TPS? If it worked fine before, why isnt it now? :hateputers: Eagle is basically right on the tranny diagnostics. They are simple to do and will tell you if you do in fact have a tranny problem and if it's electrical and/or machanical. If you shoot me a PM with an address I can send you the AW4 diagnostic manual. Link to comment Share on other sites More sharing options...
LEAD_NOT_FOLLOW Posted February 12, 2008 Share Posted February 12, 2008 http://www.greatlakesxj.com/tech/TPS.html Link to comment Share on other sites More sharing options...
LEAD_NOT_FOLLOW Posted February 12, 2008 Share Posted February 12, 2008 Oh and here is the AW4 Manual... http://www.greatlakesxj.com/tech/AW4_manual.pdf Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 12, 2008 Share Posted February 12, 2008 Oh and here is the AW4 Manual... http://www.greatlakesxj.com/tech/AW4_manual.pdf Dayem! Is there any manual you DON'T have on your site? :D BTW, I need an engine manual for a 1965 Saab Monte Carlo with the 850cc two-stroke engine. Can ya post it up? :cheers: Link to comment Share on other sites More sharing options...
LEAD_NOT_FOLLOW Posted February 13, 2008 Share Posted February 13, 2008 Dayem! Is there any manual you DON'T have on your site? :D I'm missing a few year FSM's. :cry: I also have been looking for the NP242 service manual (have the 231 though!). But besides that, got just about everything else. :D Link to comment Share on other sites More sharing options...
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