slowrideCX Posted January 18, 2010 Share Posted January 18, 2010 I am working on a friend's 01 Jeep Wrangler with the 4.0 motor. 168k on it. It is showing a (Po300 code) which is a multiple cylinder misfire. He has already changed the coil back and spark plugs. It seems to be backfiring through the throttle body when under load/ acceleration. They say that the fuel filter/pressure reg. are not serviceable. ( located on top of the tank) I tested the fuel pressure and it holds steady at 45psi ( according to the book that is ok.) I am leaning towards the injectors causing a lean condition under load. :icon_think: Am I heading in the right direction????? Any thoughts would be greatly appreciated. Quote Link to comment Share on other sites More sharing options...
wrgoudy Posted January 18, 2010 Share Posted January 18, 2010 Makes me wonder if there is a valve timing issue from a worn timing belt or whatever the Jeeps use, but I'm probably in the wrong ballfield. Quote Link to comment Share on other sites More sharing options...
slowrideCX Posted January 18, 2010 Author Share Posted January 18, 2010 Makes me wonder if there is a valve timing issue from a worn timing belt or whatever the Jeeps use, but I'm probably in the wrong ballfield. That is a possibility. I was thinking that also but it seems to have started over the last couple of days. Quote Link to comment Share on other sites More sharing options...
cbrbear Posted January 18, 2010 Share Posted January 18, 2010 I am working on a friend's 01 Jeep Wrangler with the 4.0 motor. 168k on it. It is showing a (Po300 code) which is a multiple cylinder misfire. He has already changed the coil back and spark plugs. It seems to be backfiring through the throttle body when under load/ acceleration. They say that the fuel filter/pressure reg. are not serviceable. ( located on top of the tank) I tested the fuel pressure and it holds steady at 45psi ( according to the book that is ok.) I am leaning towards the injectors causing a lean condition under load. :icon_think: Am I heading in the right direction????? Any thoughts would be greatly appreciated. Had this with my friends jeep and it was the cps, crank shaft position sensor or whatever its called... the wire housing had worn through and it would ground out and cause it to backfire and run like what your saying. Quote Link to comment Share on other sites More sharing options...
HANKSXXX Posted January 18, 2010 Share Posted January 18, 2010 A second guess would be distributor cap and rotor...next plug wires... That is, of course, if that motor still has them...LOL Quote Link to comment Share on other sites More sharing options...
jon haney Posted January 18, 2010 Share Posted January 18, 2010 Intake manifold leak? I know, it's a long shot. Quote Link to comment Share on other sites More sharing options...
Peepa Posted January 18, 2010 Share Posted January 18, 2010 Check the Crank sensor or Cam sensor Quote Link to comment Share on other sites More sharing options...
The Krypt Keeper Posted January 18, 2010 Share Posted January 18, 2010 Not on a Jeep, but my borther in law just had his cam sensor replaced on his F150. Ran pretty decent at idle but under acceleration it would spit and sputter. Thats what he gets for having a Harley Davidson F150 Quote Link to comment Share on other sites More sharing options...
slowrideCX Posted January 18, 2010 Author Share Posted January 18, 2010 Thanks for all the input. The 2001 4.0 motor does not have distributor cap and rotor Hank. It has the cam sensor with a coilpack over the top of the spark plugs. I will check all the sensors mentioned. Thanks Also I will check on the wiring to see if anything has worn through. I knew I could count on this group for ideas... Thanks again guys!!!!! Intake manifold leak? I know, it's a long shot. Already checked for that it all good there. Quote Link to comment Share on other sites More sharing options...
XXNUTZ Posted January 21, 2010 Share Posted January 21, 2010 Check the Crank sensor or Cam sensor I'm with Outlaw on this one...a PO300 code that keeps coming back, even if all other ignition parts are good can be either one of these sensors...if the sensors are OK then go with a very worn timing chain...at 168k it's very possible that the chain has slack in it and it's causing the crank and cam sensors to get out of sync causing the PO300 code...very common on high mileage engines and have seen it too many times...hope this helps...cheers. EDIT:I'm an ASE Master Tech, got good feeling on this one. Quote Link to comment Share on other sites More sharing options...
slowrideCX Posted January 21, 2010 Author Share Posted January 21, 2010 Check the Crank sensor or Cam sensor I'm with Outlaw on this one...a PO300 code that keeps coming back, even if all other ignition parts are good can be either one of these sensors...if the sensors are OK then go with a very worn timing chain...at 168k it's very possible that the chain has slack in it and it's causing the crank and cam sensors to get out of sync causing the PO300 code...very common on high mileage engines and have seen it too many times...hope this helps...cheers. EDIT:I'm an ASE Master Tech, got good feeling on this one. Thank you for the tip that is our next course of action checking those 2 sensors. Quote Link to comment Share on other sites More sharing options...
Iceman_40 Posted January 22, 2010 Share Posted January 22, 2010 http://www.jeepforum.com Lots of good jeepers on there that would likely be able to point you in the right direction. But it is likely the sensor mentioned. Quote Link to comment Share on other sites More sharing options...
BackStreet Posted January 22, 2010 Share Posted January 22, 2010 Old trick but a goodie - start the engine at night and in the dark see if it is sparking anywhere. I've seen sparks around the coil, distributor (if you had one), and between plug wires or to ground. Even if there are no sparks, that will tell you the wires etc. are OK. Quote Link to comment Share on other sites More sharing options...
slowrideCX Posted January 30, 2010 Author Share Posted January 30, 2010 Well we finally got it squared away. This was one of those defective replacement parts biting you in the ass!!!! Never assume that just cause it is new it is good!! My buddy had already changed the coilpack and plugs before he brought it to me.So I dismissed that as a possibility. Low and behold The Jeep was really running bad on his way home one night earlier this week and he popped the hood when he got home only to see #'s 1 + 2 cylinders Sparking like mad from the coilpack to the head . After removing the coilpack he found that those 2 cylinders were missing the spring that makes contact with the top of the spark plug and it had burned the top of the plug off. This is why the multi cylinder misfire code kept coming up. He went back to to where he originally bought it and they made good on the coilpack and the 2 new plugs. Now he is back up and running like new!!! Just wanted to say thanks for all the thoughts and help. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.