95 5.2L back firing through intake

Curtis_H

Curtis_H

Well-Known Member
Joined
Sep 17, 2008
Location
High Point NC
I installed a 95 5.2L from a grand cherokee in my cj 5 project. Engine fires right up and seems to run great until u try to give it throttle quickly then it hesitates and backfires back through intake. Once u pass that point it will take the throttle and run fine.
Project is not road worthy yet so only been running in back yard for now.

I installed new crank sensor, plugs, wires, cap rotor button, when I installed motor. I cleaned up vacuum lines replacing any rotted lines, replace pvc valve and grommet, re indexed distributor per all data instructions with a volt meter, and swapped map sensor with a used one i had with no change on how motor runs.

Any ideas what I need to check or where to start.
 
I was thinking maybe plenum gasket, might try it next. I've tried spraying starting fluid around base of plenum, engine don't rev up. Any other way to test it.
 
Guessing no way to check timing chain other then tear it down and look? When I bring it up to tdc, the mark on the balancer matches up with mark on timing cover.
 
Did you mess with the distributor at all? Initial timing does need to be set properly or it will run crappy. Ignition and fuel timing rely on that dist. being set properly.
 
I brought motor up on tdc and hook volt meter to wires going into distributor. Then turned distributor until I reached close to 5 volts as possible. This is what I read on all data to index the distributor without a scanner.
 
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hmm, Does the TPS voltage sweep properly from closed to open throttle? (~.5ish V to ~4.5ish) If the TPS isn't working right it could be a lean back fire.

I would check the TPS voltage and put a timing light on it and blip the throttle, see where the timing goes and go from there.
 
Idk havent checked tps. I'll check it. I tried to put timing light on it but mine decided it didn't won't to work. I'll get one and see what I got. Thanks
 
You don't need a scanner to set sync on a Magnum, lucky for you. I copied this from another site (because I don't have time to type it all out right now). It is important to follow the oil pump drive and dizzy install to a "T".
Here goes:
3. Set the motor to TDC cylinder no. 1 compression stroke. Turn the crank clockwise until you feel air coming out the spark plug hole of cylinder no. 1. Stop when the 0 degree mark on the balancer lines up with the TDC mark on the timing cover. You will notice both valves are closed on cylinder 1 (if the timing gears were installed right ).

4. Install the oil pump gear. Make sure the slot points at the No. 1 cylinder or 11 oclock. Do this before you install the intake manifold because you will need several tries, and pulling the gear back out of the motor is easy with the intake manifold removed, and almost impossible otherwise. The oil pump gear meshes with the cam gear, and it rotates as it slides down and meshes.

5. Install the distributor. Use a new o-ring. It can only go one way (idiotproof thankfully) due to a recessed area on the distributor neck where the distributor clamp rides. If you slide the rotor on, it should point at cylinder no. 6.


Also, what is your fuel pressure? A lean condition can cause an intake backfire as well.
 
Jody Treadway said:
You don't need a scanner to set sync on a Magnum, lucky for you. I copied this from another site (because I don't have time to type it all out right now). It is important to follow the oil pump drive and dizzy install to a "T".
Here goes:
3. Set the motor to TDC cylinder no. 1 compression stroke. Turn the crank clockwise until you feel air coming out the spark plug hole of cylinder no. 1. Stop when the 0 degree mark on the balancer lines up with the TDC mark on the timing cover. You will notice both valves are closed on cylinder 1 (if the timing gears were installed right ).

4. Install the oil pump gear. Make sure the slot points at the No. 1 cylinder or 11 oclock. Do this before you install the intake manifold because you will need several tries, and pulling the gear back out of the motor is easy with the intake manifold removed, and almost impossible otherwise. The oil pump gear meshes with the cam gear, and it rotates as it slides down and meshes.

5. Install the distributor. Use a new o-ring. It can only go one way (idiotproof thankfully) due to a recessed area on the distributor neck where the distributor clamp rides. If you slide the rotor on, it should point at cylinder no. 6.


Also, what is your fuel pressure? A lean condition can cause an intake backfire as well.
Click to expand...
I didnt think my engine was a magnum. Would process still be same? Also was thinking this is same thing I was doing with volt meter and indexing distubtor. Is that an incorrect statement?

Distributor has not been removed so oil drive gear should all be right still. But not knowing what I was doing tried to turn distributor to changed timing and later found out all computer controlled and ran across how to index so reset that. So hopefully I'm back to where it started before I moved distubtor.

Definitely need to check fuel pressure, didn't realize low fuel pressure could cause backfire through intake. I have a rci fuel cell gravity feeding a e2000 fuel pump. Maybe not doing the job for some reason. Thanks for help.
 
Yours is a Magnum. Jeep just didn't call them "Magnum" like Dodge did. Same engine, same electronics, etc.
If the dizzy has not been removed, you can ASSUME it was synced correctly when you got it. Then it could be as simple as minor tweaking IF it is a sync issue.

Check the fuel pressure and report back. I just solved a lean backfire issue on my own truck that was the result of low pressure. You know how an engine hiccups and backfires as it is running out of fuel? That's a lean backfire...
 
OK only had about 15 minutes to mess with it yesterday but idling only had about 30psi fuel pressure. When I would hit the throttle it would jump to 40 but then go back down while i holding the throttle. From what I read need 35-45 psi. I unplugged vacuum line from fuel pressure regulator and it would hold a steady 40 psi and ran much better. So think found problem but now how to fix. I'm going to try and test incoming pressure to regulator tomorrow. If pressure is good going in then guessing fuel pressure regulator is weak and needs replacing?
 
Alright think I got it fixed today. Think when I unplugged the regulator to increase pressure seemed to run better but still wasn't right. Changed out tps with used one I had and now running great. I was zeroed in on timing wasn't thinking any thing about fuel. Thanks for everyone's help.
 
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