Jeep wont exceed 1500rpm without backfiring badly

Hey guys I need some help. My 97 cherokee hesitates to start. Once it does start it idles okay, but when i give it some gas it will not get over about 1500rpm and backfires a lot. It has a new distributor with cap/cam sensor. Ive already tried the cps. I think its running lean. Atleast thats what it sounds like. My O2 sensor code just popped up after it warmed up. But i dont know if that would cause it to run crappy even when the motor is still cold. Anybody have this same problem? Or have a solution?

Looks like distributor is off by a tooth.

old_man said:

Looks like distributor is off by a tooth.

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I had it at TDC on the intake stroke. Set the oil pump at 11:00 and installed the distributor. The rotor pointed directly at #1. is this the correct way? or should the rotor be pointing just right before #1?

The crank should be pointing at roughly 14 BTDC when the rotor is pointing at the #1 plug contact.

I just went out there and turned it one tooth back. that didnt help at all. So my timing is right now. Im still in the same situation as earlier.

Can we assume that all your tune-up parts are fresh and that your battery is in good condition ?


Starting hesitation is common, is related to the fuel pump check valve or leaky injectors, and should not effect the running and driving.

Google SCAN TOOLS, O-SCOPES AND TOOTHPICKS . This is the correct way to check distributor/Cam Position Sensor alignment on an OBD-II Jeep.

Fix the O2 sensor problem. How can you diagnose an issue with an existing known fault ? O2 sensors ( and their malfunctions) have a direct effect on the drive-ability.

Test the Throttle Position Sensor.

thanks a lot guys. I have a volt meter. What is the correct way to test the tps with that?

TPS TEST

You should have 5 volts going into the Throttle Position Sensor (TPS). It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The other wire will be the ground and should show no voltage.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced.

Thanks a lot Tim! Ill try that tomorrow. Ive got neighbors and a loud jeep.

dubstepxj said:

I had it at TDC on the intake stroke. Set the oil pump at 11:00 and installed the distributor. The rotor pointed directly at #1. is this the correct way? or should the rotor be pointing just right before #1?

Click to expand...

i think it should be just after number one, so like 4 or 5 oclock.

search a bit and try to find out.

jeeptorino68 said:

i think it should be just after number one, so like 4 or 5 oclock.

search a bit and try to find out.

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As viewed from the passenger side fender.

Well its in the shop now. I always told myself id never take anything to a shop, but i had to. Atleast i know who's working on it. But I had timing dead on, new plugs and wires, new ignition coil, new cps, new tps, new distributor, all valves are moving, fuel pressure is at 49psi even when i rev the motor up. We will see what the prob was in a few days. i know its gonna be something stupid.

dubstepxj said:

Well its in the shop now. I always told myself id never take anything to a shop, but i had to. Atleast i know who's working on it. But I had timing dead on, new plugs and wires, new ignition coil, new cps, new tps, new distributor, all valves are moving, fuel pressure is at 49psi even when i rev the motor up. We will see what the prob was in a few days. i know its gonna be something stupid.

Click to expand...

I was chasing down a similar problem forever. Even took it in to a shop. I accidentally moved a vacuum hose and the jeep died. That hose had a leak and fixed the problem.

Sounds kinda obvious, so don't take this as a jab at you, but is it possible you mixed up the number 3 and 4 cylinder spark plug wires? Sounds like you are getting ignition on the intake stroke...