View Full Version : Engine Bogg, Backfire Through Intake

March 29th, 2005, 20:26
I just yesterday started having a problem with my jeep above about 2500 RPM. When I step on it hard it gets to about 2500 - 3000 and starts to bogg down and backfire through the intake. It looses a ton of power and almost feels like the same thing as when im low on gas and go around a corner and it dosent get gas and boggs down. the only thing is it is just on the street going straight. It is a 90 with the 4.0 and the fuel filter is about 10,000 miles old. Also if I down shift it into first and gradually speed up through the RPM range it seems fine as long as I dont step on it hard. Im thinking weak fuel pump but dont have a fuel pressure gauge I can get access to right know. I put it under modified because it is built and sees offroad use about once a week so maybe the beeting on the gas tank is stiring up stuff to.


March 29th, 2005, 20:59
i dont mean beeting by the way, i mean just the shaking and vibration stirring stuff. lol


March 30th, 2005, 05:29
I noticed no one answered you. So I'll try and make you feel better.
I would say you are on the right track. Backfire through the intake is most likely a lean condition. I would start by getting the pressure checked.

March 30th, 2005, 05:50
Thanks, haha, now I feel better. lol. Has anyone else had this same kind of problem with there cherokee?


March 30th, 2005, 06:37
if its not the fuel pressure causing the problem it could be a weakened fuel line collapsing onto its self when you accelerate (is your engine fuel injected or carburated??) not sure if any XJ models had any soft (not hard metal fuel lines in the system but with other vehicles i've seen that sorta thing happen (on low pressure rubber fuel lines)

maybe your question would have better response from these Gurus ;) (http://www.naxja.org/forum/forumdisplay.php?f=86)

good luck

also i thought maybe a clogged cat, but i'm really not sure

March 30th, 2005, 07:22
I just got my 93 XJ up and running yesterday afternoon following problems much like you have described. The culprit turned out to be the fuel pump...running and producing pressure, just not enough. I swapped in the pump from my 89 organ donor and all is well again. I hope its that simple for you.

March 30th, 2005, 07:52
Like most said, the likely culprit is fuel starvation. In the older rigs, I would have said change the fuel filter, but I think yours may be the one in the tank.

A bad MAP or O2 sensor can cause the same issues as well.

The way to really tell is to do a spark plug reading. From that you can tell if the engine has been running too lean. Go out and find a nice long hard hill. Try to accellerate hard up the hill and force the problem for as long a possible. Then kill the engine as quickly as possible and coast over to the side of the road. Give it a few minutes to cool down so you don't burn your self, then pull the plugs. If you don't know how to read the colors and such on the plugs, grab a digital camera and take some nice closeups and post them back here.

If you like spending $$$, take it to a dyno and stick a tail pipe CO sniffer in it and simulate the issue there. They will be able to give you the straight info.