99XJake

Hoping someone has experienced the same thing and can chime in.

99
150k
4.0

NO CODES
Recently fixed exhaust leak
New IAC, O2 sensors are new, IAT cleaned, new MAP, new crank position sensor.

Fuel pressure unknown at the moment
Plugs, wires, cap rotor are new enough accel kit
Need to try throwing copper plugs in there its got NGK iridium plugs right now.

Could it be timing?
Idles a little high on starts then sits a LITTLE choppy 700-800

It will hesitate off the line under 3/4 to full throttle acceleration and when coasting around 40 if I have to accel it will SOMETIMES backfire thru the intake.

I hate this **** lol
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99XJake

I'm desperate for this sex box to run right

MonacaYankee

My 99 would do that during the first acceleration. If I gave it gas it would backfire then take off. It was the front o2 sensor.
I found this thread for ideas. https://www.cherokeeforum.com/f2/bac...intake-101294/
Coolant temp sensor can cause it too.

99XJake

They're both pretty new NGK sensors. But they were in for a bit while I still had a manifold leak so MAYBE that fried em. Just annoys me to have to replace something so new maybe. It doesn't make sense that there are no codes... Is a shop diagnostic gonna be able to tell me more? I don't wanna waste money being told nothing

MonacaYankee

It would be cheaper to throw parts at it then to go to a shop.
The only o2 sensor that could make it backfire is the front one anyway.
My rear one is original.

Evilpopcorn

It kinda sounds like what my old 2000 was doing, although mine just stopped working at all by the time we found out it was the Camshaft Position Sensor.

DFlintstone

My 90 Renix, (somewhat if a different cider), blew the mouse nest in the air cleaner right out the front grille. Drove through the confetti! No sign of the mouse. I could accelerate gently, but much throttle, then bogging and backfiring out the intake.

For a year nothing helped, then I found one of the wires to the lower sensors grounding on the heat shield. Problem solved, no doubt about that.

Was before I joined CF, I didn't note the color code. Went back, pulled my tape and couldn't duplicate the backfiring, here in the driveway anyway.

It's suggested being lean is the cause. Temp sensor is a big player there, besides fuel pressure. You might split the loom and take a really good look at your temp sender wires. (and the O2 wiring)

The sensor can be checked ;



Coolant Temperature and Manifold Air Temperature Sensor Resistance Values
Approximate resistance your meter should show at the temperature shown in the chart.
NO resistance indicates a 'short' to ground - can be the sensor but will usually be a wire where the insulation has been abraded.
INFINITE resistance indicates an 'open / broken circuit. Can either be a broken wire or a bad sensor.
Degrees Fahrenheit l Resistance in Ohms
40* - 7,5000 ohms
70 - 3,500
100 - 1,600
160 - 456
212 - 185

An unfortunate truth, it's rare that threads on this end with a solution. Posters just fade away, do hope you post your solution.

99XJake

Coolant temp sensor causing lean fuel condition am I reading that right? I'll recheck O2 wire... Both O2s were shorted I believe when I changed them and I thought they were being overloaded by the exhaust leak so maybe they're actually grounding somewhere.

DFlintstone

Yea, due to how it evaporates-atomizes, it needs more fuel cold and less hot. Supper, yea check all those wires good. Looks like it goes to less fuel with less resistance....Idk if the 02 has the power to do that or not, being it's for the final fuel trim after the MAP, bet hey Idk.