i need help

[BenDiesel]

so im tired of my jeep doing what its doing and need some help trying to figure out whats wrong.

whats wrong.
cruising around 2000 rpm it falls on its face backfiring on what seems to be every piston. but let off the throttle a little or push it a little it goes away. it will accelerate just fine like it always did and idles fine. when i cruse at speeds were the rpm is around 1500 it wont do it.

some one mentioned fuel pressure. i dont think thats it but dose any one have a efi fuel pressure tester?

im also open sunday if any one wants to come over and help. Little Caesars will be in volved lol

 

[fubar XJ]

Someone should move this to the tech section. Sorry, I don't have any ideas off-hand what's causing your issue, but you'll get more feedback in tech.

 

[TORX]

Moved to OEM tech.

 

[NW-ZJ-SCOTT]

A couple of educated guesses from me would be:

Fuel pressure. sounds like a bad pump/filter
Throttle position sensor
Dirty air filter
Possible bad spark plug wires.

Last time it had a tune up?

 

[McQue]

Sounds like a bad spot on the throttle position sensor... when you are above or below it, it works fine...when you hit that spot where you normally cruise, around 2k rpm it has a bad spot...kind of like a bad spot on a volume control.

 

[BoringDave]

I was told that a bad egr system will stumble at cruising speed.

Dave

 

[jujuscisyn]

There is a little hose on the fuel pump that can and will come loose or off all together. It is real easy to check, I'd start with a pressure test at the rail. If its low, start at the source (fuel tank) and work your way up and I highly recommend checking that hose. good luck

 

[joe_peters]

Just for grins pull the distributor cap and see if there is sideways play in the distributor shaft.

 

[BenDiesel]

i thouht about the tps. it dosent do it when i cruse around at 1500 rpm at the same spot in the throttle. i even played with the throttle to check for that.

its wierd i had a dieing batt in it when i whent wheeling and broke the 02 sensor off. the bat died completely and sat for 2 or 3 days then i put a bat in and it started doing this. i put a used o2 in and still dose it. im guessing the computer lost its fuel map when the bat died and the o2 i put in is bad.

i dont know if this matters but its got a bad rod knock as well. and it dosent have the factory intake or exhaust. i put a 99+ intake and a apn headder. only vac lines go to map, break booster and fuel rail.

 

[cruiser54]

Your computer ain't that sophisticated, my friend. This is Renix. You are offererd sound advice about checking fuel pressure with a gauge. I like Joe's suggestion of pulling the distributor cap and checking side to side play in the distributor shaft.

 

[BenDiesel]

Ok I checked the fuel pressure. And like I thought it was fine. Key on engine off its at 40psi engine at idle its at 31psi. Haven't checked the dizzy yet ill do that here after the engine cools down

 

[BenDiesel]

figured out the problem. the bolt that holds the plate that holds the dizzy down was loose. thanks for the help guys. i feel like a noob now

 

[cruiser54]

Congratulations. Now that you found the bolt, you ought to look at indexing your distributor properly. Renix works best with this procedure performed.

 

[ptf18]

Gee...I like it when the fix is sooooo simple!

 

[BenDiesel]

oh k how dose one index the distributor?

 

[winterbeater]

With the #1 cylinder at the timing mark, the rotor should line up with the distributor tower for the #1 spark plug wire. Mark the housing directly down from the cap #1 post and take the cap off. Turn the engine in the normal running direction until the timing mark lines up on the crank pulley. If the distributor is pointing 180 degrees away, turn the crank around on more time. If it is not lined up good, rotate the distributor base until it does and tighten the bolt back down. Don't overtighten and break it off. (I know someone that did.)

 

[cruiser54]

There's a write-up somewhere you can search for. It's late and I'm tired and I'm sure someone else did a great job on a write-up once or twice. Worth doin by the way.

 

[JJacobs]

Actually the trailing edge of the rotor should be at the #1 plug tower. If they're centered up, it may still be off a tooth.

edit: I also give the rotor a twist, just a side to side wiggle isn't enough as I've seen several roll pins start to break apart.