97 2.5 ignition problems

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Shane Jacob

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Joined
Sep 27, 2018
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12
Location
Cape Coral Florida
Hello everyone, I'm new to the forum,This is my fourth Jeep. I have been working on a body of frame project for Almost two years now. I have the body back on engine and drivetrain hooked up and harnesses and grounds connected. The problem I am having is starting. I will list all the information I can gather.
1.Timing of cam and crank comfired at TDC
2.distributor installed correctly
3.New Fuel pump, Spark plugs, Rotor, Cap, Coil, Cam sensor, Crank Sensor, Map, Intake Temp Sensor, coolant temp sensor, new upstream O2, Starter, battery, battery cables, clean grounds, Injector orings, fresh fuel, 150, 155, 160, 155 compression, brand new head, lapped Valves, no leaks, no bent valvetrain parts. Cleaned throttle body and IAC.

The Jeep turns over, I have spark, I have fuel, but it backfires through intake, and only starts when I have a vacuum hose disconnected, it will idle high around 2800 and the engine will die if I put the vacuum hose back on. It has me stumped. Also the cluster does not chime 5 times when key is turned to on anymore.
 
Hello. Just off the top of my head, maybe there is an air leak at the intake manifold since the head was just replaced. Try running a vacuum system test on it. If the local parts store doesn't have a loaner test set then they are usually pretty inexpensive to buy. A vacuum test might be able to tell you what's going on. Best of luck.
 
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Has me thinking it is a timing issue. Backfire through the intake usually only happens when the intake valve is open when the spark plug fires.
I don't know enough about the 4cyl. To help. But if you confirmed the timing chain and distributor. Im at a loss
 
I managed to get the engine to start again, I noticed smoke coming from the intake manifold/exhaust manifold area, I think the intake might not be seated properly, time to remove it again!
 
I had a friend with a similar issue on his XJ and it ended up being the intake/exhaust manifold gasket.

x2 for doing a vacuum test, they're pretty easy.
 
Boinked said:
Has me thinking it is a timing issue. Backfire through the intake usually only happens when the intake valve is open when the spark plug fires.
I don't know enough about the 4cyl. To help. But if you confirmed the timing chain and distributor. Im at a loss
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Yeah, people tend to use the word "backfire" to describe any loud pop or bang from a running engine. What's being described here is more likely "preignition" from the fuel-air mixture being too lean.
 
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It only sputters and pops through intake with smoke while attempting to start, when it does seldom fire up, it runs solid but at high rpm, caused by one of the vacuum ports being open to the outside air. If I plug, or attach a vacuum line it while sputter and die. New intake manifold/exhaust gasket torqued all bolts in sequence and factory spec. I'm going over distributor alignment with TDC right now. I'm aware the the PCM does spark timing, and the distributor coil pickup is for the fuel injection. Also, Ive heard these TJs don't like Bosch 02 sensors?
 
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This is where I'm at for TDC on Compression stroke. Is yheth Anybody with a 2.5l that can compare?

15382455012291281444120.jpg
 
Shane Jacob said:
It only sputters and pops through intake with smoke while attempting to start, when it does seldom fire up, it runs solid but at high rpm, caused by one of the vacuum ports being open to the outside air. If I plug, or attach a vacuum line it while sputter and die. New intake manifold/exhaust gasket torqued all bolts in sequence and factory spec. I'm going over distributor alignment with TDC right now. I'm aware the the PCM does spark timing, and the distributor coil pickup is for the fuel injection. Also, Ive heard these TJs don't like Bosch 02 sensors?
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You are correct. Our TJs will only run as designed with the correct NTK O2 sensor.

The correct upstream O2 sensor for your 2.5 is a NTK #23506.
 
Shane Jacob said:
I managed to get the engine to start again, I noticed smoke coming from the intake manifold/exhaust manifold area, I think the intake might not be seated properly, time to remove it again!
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I had loose intake bolts (missing bolts) a few months ago and it backfired a few times along with a high idle at start up. Replaced and tightened bolts, no further issues for now.
 
Had the engine rebuilt. Installed, with nearly all new components, sensors, injectors, plugs, wires, rotor, cap, CPS, CamPS, distributor ignition switch. Good compression, it is getting fuel. The jeep tries to fire but won't start and run. No codes. Engine is timed, distributor is timed. Tried swapping a programmed pcm. It's unbelievable. The only thing I've noticed is a weak spark, an orange spark. New coil. All circuits for starting, ignition, sensors have been ohmed and load tested. I took the harness off and tested every circuit needed to operate the engine and load tested. I have verified timing with the valve cover off and timing cover off to make sure it is mechanically sound. I am at a loss lol.
 
Shane Jacob said:
Had the engine rebuilt. Installed, with nearly all new components, sensors, injectors, plugs, wires, rotor, cap, CPS, CamPS, distributor ignition switch. Good compression, it is getting fuel. The jeep tries to fire but won't start and run. No codes. Engine is timed, distributor is timed. Tried swapping a programmed pcm. It's unbelievable. The only thing I've noticed is a weak spark, an orange spark. New coil. All circuits for starting, ignition, sensors have been ohmed and load tested. I took the harness off and tested every circuit needed to operate the engine and load tested. I have verified timing with the valve cover off and timing cover off to make sure it is mechanically sound. I am at a loss lol.
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I have the same issue did you figure out what was wrong with the engine?
 
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