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Backfiring...

13K views 231 replies 15 participants last post by  mike_breaker_5 
#1 ·
Ok, so I've always wanted a wrangler and I finally got one. It's a 93 2.5 5spd. It's not perfect but I always like a project! I already plan on swapping a 4.0 in it and have already bought one. I'm sure ill be asking tons of questions when I get around to doing that:)

But my post for today is about it running bad. It runs fine until its warmed up and then it starts bogging down and backfiring bad! I'm talking downshifting to 2nd on the highway to get it to move. Never overheated or got close to being hot. I've already changed the plugs, wires, dist cap, rotor, oil and filter, and air filter. It was pretty nasty underwood so I cleaned her up a bit.

Any ideas?
 
#73 ·
C2tuck said:
No...everything is tight as far as the dizzy and the rotor and cap. Already replaced them with no change. Yes it happens at night too. Coming back from the movies the girls were cold...it was fairly cool out that night and it did it just the same. I mentioned the cam and crank sensors in this thread and no one thought that was relevant. Is there a way to check them or are they cheap as I don't want to really throw parts at this thing. No one has ever had this problem before??

I'll try the water thing when I get home this evening.
There is a way to check them. It's in the fsm you will need a multimeter. There is a link on here somewhere to the fsm but I don't have it on here. A quick search could find it or hopefully someone on here will post it. I am really thinking the pick up the coil should cause a miss not a backfire when it starts to go.

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#74 ·
C2tuck said:
I already tried the I coil and it didn't change anything. So I put the old one back on and am going to go get my $50 back. Where is the pick up sensor located and how much if a pain is that to change?
The pick up is I side the dizzy take the cap and rotor off and it's that flat plastic piece with the connector coming out off it. It just pops out.

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#77 ·
Checking the cam pick up on a '95 YJ. Your '93 should be the same:
Got to eliminate things or you will go in circles forever. Wait until it is running bad;

http://home.comcast.net/~laybackman/95_cam_sensor_test.pdf

Questions for the OP and this is a shot in the dark. When it happens again what is your speedometer doing? Jumping around a bit? Then if it is unplug the VSS sensor on the transfer case. It is screwed into the transfer case and supplies info to your speedometer. It is on the same 8 volt supply circuit as the crank and O2 sensor. If it begins to fail it causes issues until it shorts out completely and you do not get anything. Again just a long shot.
 
#79 ·
Nope speedometer is always steady. The problem with checking it when it runs bad is that if I stop on the side of the road for literally 2 minutes, it starts run I g if e again for a few more miles. Then I have to stop again. I'll grab a pickup today when I grab the fuel filter (they didn't have one last night) and slap them on one at a time and see if it helps.
 
#80 ·
Usually when the VSS start acting up the speedometer can get jumpy since it controls it. At this point the only alternative to testing is to replace the cam sensor.

A fuel filter replacement is mandatory if you do not know when it was changed last.

Good Luck!

One more thing to think about. If the coolant temp sensor is not sending the right value to the ECM you will run like crap also. It is often overlooked as a problem with a warmed up engine problem. I''d swap that out first since it is a lot less expensive.
 
#84 ·
Ok. I'll check that when I get the driveshaft back in it. Rear of the tcase was leaking so I dove into that. I tried the water in the throttle body trick and it didn't work. Pulled it off and cleaned all the carbon off of it. Intake was pretty nasty too. Cleaned what I could and sprayed the crap out of it. Changed the fuel filter too and no change.
 
#88 ·
#90 ·
Ok. Went and ordered the stator today...should be in tomorrow. Got my seal replaced on the tcase out shaft. Need to fix a leak on the front axle as well. Want to tear into it and broke my half inch extension...can't say I've ever done that before. That's thing is on there! Looks like I'm taking the night off:)
 
#91 ·
Ok. I took the dist cap off and took the rotor out, removed 2 small bolts and took off the brass colored plate. There is not a shiny metal plate that I can't get to budge. The pickup is under that. Is there a trick or do I just pry it off? Don't want to mess anything up. Please let me know ASAP. Thanks
 
#93 ·
Now you have to pull the center shaft so it seems. Never done one myself but the picture tells the story. MAKE SURE you mark how it came out. If you do not then it could go in 180 degrees out.

hold off on this fix
 
#96 ·
OK, pull the cap pull the rotor unplug the wiring and lift out the cam sensor says the manual. Maybe it is stuck in there. You DO NOT have to remove the shaft like it showed in the picture that I deleted. Like you need me to run you off on the wrong path to add to your woes.....:eek:
 
#97 ·
More information; these guys came with one of two different sized distributors.
I happen to have the small one on my '95 4.0.

Some of the information I have says the distributor has to be pulled and yet other information says you do not need to pull it to swap out the camshaft position sensor.

It has to be because of the two different diameter distributors.
 
#98 ·
That is for the 6 cyl. The one I have on an engine stand in my garage is simple just like you described. Mine has cap, rotor, two little bolts, brass colored cover plate, shiny plate that is "pressed" onto the stud, and the sensor lives under that. I can't get the shiny plate to "pop" off. Don't know if I need a puller or what but I know something has to give...
 
#103 ·
If you want to try the smaller dizzy I think I still have a spare one around here and its got a good pick up in it. I won't be able to send it until monday though. Thats the best I can offer. They are $65 new at autozone with the pick up. I am 99 percent sure you can just switch them. I just sent one to que for his 89. You would need to get cap and rotor for a 95 from here on out is all thay would change

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#106 ·
Yes it looks like that.

Siva283- is there a difference in performance or is one better than the other? If you really don't mind that would be awesome. I can pay shipping, it's no big deal. How hard are they to pull and install? Always been kinda nervous about pulling the dizzy...you have to set the timing once you replace it?
 
#107 ·
I will get it from storage Saturday and can send it Monday we can PM the details. I get further discounts if there is a business address I can send it to but if not no worries. I dont think there is any performance increase its just easier to replace parts and it seems to be liked better than the older bigger dizzy for this reason.

Changing it isnt hard. The bottom is slotted for the oil pump drive so if the slot is oriented different you may need to use a screw driver to spin the oil pump shaft a little at a time until it lines up. So before you start look at where the rotor is pointing. Orient the new one to point in the same spot thats all there is to setting the timing part of it. Once you have the rotor oriented correctly on the new one mark it. Now take the old one out and slide the new one in. Tighten the bolt on the hold down and hook up the sensor and wires. I am still half asleep so if this doesnt make sense let me know and I will try to explain it better with more detail.
 
#108 ·
Actually if you pull the old distributor you do not need to bring the engine up to TDC.
#1 Remove the cap.

#2 NOTE GENERAL POSITION OF THE ROTOR...VERY IMPORTANT! MARK THE BASE OF THE DISTRIBUTOR.

#3 Once pulled note where the rotor ENDED UP. It will move a little bit while disengaging the helical cut gear at the bottom of the distributor from the matching gear on the camshaft. MARK IT AGAIN. Make sure you make a different mark a second time.

#4 Position the rotor in the new distributor in the same position your old rotor was after you pulled it out.

#5 GENTLY slide the new distributor in. When it begins to engage the oil pump shaft the helical cut gear will also engage the matching gear on the cam shaft. The rotor will move forward a little.

#6 Pop on the cap.

Keep in mind an engine is always in time but not necessarily on TDC of #1 or any other given cylinder for that matter. As long as you do not disturb the engine during the distributor swap and you orientate your new distributor rotor like the old one was will be OK.
 
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