I'll start with I should have asked earlier! 2004 GC 4.0 power. I completely rebuilt the engine 12k/miles ago. Its been a beautiful thing till a few weeks ago when my wife called saying it shut off at 2 stop lights and studdard or bogged down once. I pulled into our shop and ran scan. Scan gave o2 sensor, o2 sensor wiring short, and evap. Replaced o2 sensors (4). Will not start and backfire through throttle body. Here goes, I have replaced o2 sensors, fuel filter, crank position sensor, cam position sensor, throttle position sensor, ecu, plugs etc.. i have toned every engine bay wire, I have moved to TDC and checked for cam position sensor for proper position, pulled timing cover to inspect cam/crankshaft gears for proper position and finally pulled valve cover checking valves for proper movement rockers for tight. No change. I'm not a DIY guy but skilled engine builder taking an *** kicking from what should be a simple repair. Could someone more skilled bail me out?

 

Hmmm. Backfire is usually a timeing issue, but you seem to have that covered. Since it's a 2004, you have coil packs, not distributor, correct?

And the cam sensor lives where the distributor used to be on older models, correct?

What brand of sensors did you use? Aftermarkets are famous for being bad out of the box or soon afterwards. Even normally good brands like Echlin or Bosch don't do well with our 4.0s.

 

yes to both, coil packs in single unit and cam sensor does live where distributor would be. I bought Bosch sensors. I once believed the machine I couldn't fix was yet to be built but!

 

In all honesty, there is a really good chance the aftermarket Cam or Crank sensors could be the reason to cause this type of problem for you. Many many people have had this same type of thing happen with new(er) aftermarket CkPS in particular is one of the worst with poor quality magnets. Because the sensor(s) are being thought of as recently new and having just been replaced.. people can go chasing every which way in all directions trying to find the problem somewhere else... before coming back to and replacing the sensor again, to finally fix the issue. It seems like it often happens just like this a lot of times in all honest reality.

Have you looked down into the combustion chamber to see if any oil has made its way up into the spark plug wells? It is just another area to investigate for a failure at, or with something to do with the piston? A failure in this area is known to be able to cause an engine to spit and cough out the intake like that too. It may not be the most common thing to look for with something like this. But, it is a rebuilt engine to look after and into now too..

 

Yep. One these 4.0 engines, whether Cherokee, Grand Cherokee, or Wrangler, use ONLY Mopar (NTK/NGK) sensors. Too many people have had exactly your problem because the new sensors were bad out of the box, or failed within days, weeks, or months. It's frustrating because you tear your hair out looking for some other problem, because it couldn't be the brand new sensor you just installed!

But, sometimes it is.

And yes, sadly, this is even true of a quality name like Bosch.

 

Thanks for the input. We have loved our GC sometimes help from experience is required!

 

Just for jollies, remove the cats. They may be plugged.

 

Yep, and that's not good.



Plugged cat.

 

Y'all are crazy. I wonder what it was though? If the reason has been discovered or corrected?