BByler

I have a 99 xj 4.0 with 150000 miles on it. Runs great but when I'm trying to hold a speed, it backfires through the intake. If I accelerate it stops until I try to maintain a speed again. Here is everything I've done, check fuel pressure at rail - holds at 50, change both O2 sensors - twice, changed IAC, TPS, MAP, WIRES, DISTRIBUTOR CAP, COIL, INJECTORS, BATTERY, checked for vacuum leaks and Cleaned all my grounds. Spark plugs were replaced about 6 months ago. Check engine light hasn't come on yet. Does anybody have any advice or know what is causing this.

97grand4.0

Welcome to the forum. As you have learned, first change all the part$ you can see, then do some trouble shooting. Rotor did you change the rotor? Crank sensor? Cam sensor? Do you have a scan tool? Does the fuel pressure bleed off? Am I up too late?

BByler

I don't have scan tool but I've had it done. It just comes up as fuel to rich, replace O2 sensor which I've done twice. No codes come up since the last time i changed them. I haven't changed the rotor or the crank sensor or cam sensor. And I'm up way to late researching this.

97grand4.0

So my guess is, based on your codes, that your fuel is too rich.

BByler

Just changed the distributor, cap, rotor and spark plugs. Still popping through the intake. Bout ready to burn it.

BByler

So I decided to take the so called upgrade 4 hole injectors out and put the factory injectors back in. Now the XJ runs like a champ. No more backfire through the intake, starts a lot easier. 4 hole injectors went straight to the garbage. Worst upgrade I ever did!!!

Cummins93

Take them back out of the trash list up the part number and where you got them. If they are Ebay injectors list the vendor name. It may help someone else down the way.