Intake BF

Hey all,
Got a situation here Ive been plagued with for a while now and could really use some advise. Let me start out from the top.
89 Cherokee Pioneer
4.0 I6 105+k
Work done by me in last 6 months:
Flywheel, TPS, TorqConverter, EGR Valve, Upper and Lower PCV Harness, Wires, Cap, Rotor, Brakes, Fuel,/Air Filters, Waterpump, Distributor Chain adn Gear and tonite Distributor itself.
Problem:
Intake Backfire. Was only under load and only when up to temp (200o)
Put in a new distro after haveing it suggested it might be the syncsensor. Seems that only made the problem worse, now it IBF's under any throttle level except full bore. She runs strong, just as soon as its up to temp it starts acting up.
From what I understand it is a computer controlled timeing and is non adjustable.
Any suggestions??

Yes, the timing is computer controlled, but just like in the old days the distributor has to be sync'd with the cam gear in the correct position.

I'm sure you got the #1 piston TDC to insert the dist, then made sure the rotor is pointing at the #1 plug wire position - the trick is the helical cut gear requires you to be a little off to screw the distbutor shaft in and wind up at the right place.

I spent three hours and trip to the parts counter to get it right the first time - on a Ford 300 - 6 - really frustrating, then I still had to rotate the dist to set the timing.

How much advanced is it when you put the timing light on it?

TiRod said:

How much advanced is it when you put the timing light on it?

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You can't count on the timing light to tell you, though. I had a similar problem with my 87, in which a mis-indexed distributor (one tooth advanced) caused hard starts, but once it was running the computer got the timing right. Of course, the computer can't correct the rotor position, though, so it could spit even though the spark timing is dead-on.

As I recall, when I got the right position it was not exactly lined up like the pictures. I think there's a little variation there. It might be worthwhile to experiment with displacing the distributor by one tooth either way to see if it makes a difference. Mark the current location of the rotor on the body before you remove it, and you can always put it back if it doesn't get you anywhere.

I dont have a timeing light . I put it in the same way everything came out. When i started, the rotor was pointing at the 6o'clock position / #1 piston ad when i got the new distro in it was closer to 7o'clock i tried backing off a hair but it would just end up at about 5 o'clock

Im pretty much learning to be a mechanic as i go, so i dont have alot of knowledge about these things (Thank God for the Net!)
What i dont understand is why it dosnt start happening until it gets warm When cold she runs fine, mabey a little mistep at about the same time the IBF kicks in when its warm, but otherwise its strong, with no IBF.
I dont have a tach but its under "normal" city acceleration (or "load" if I understand the terminology right) from 0-35mph, after that it was fine. Since I installed the distro it will do it reguardless of speed. I can also reproduce the problem by manually manipulating the throttle under the hood when warm.
Another symptom ive noticed recently is it will stall for a second when turning and catch itself as soon as I give it a slight amount of fuel. This is a rare incident, but its happened a couple times. i thought I might have been low on fuel and the gage was just wrong, but its reading correctly. Whether thats related or not I dont know, but I have a feeling it is. Also in the morning sometimes it will stall after i first start it up, not all the time but occasionally. When warm she fires right up every time. Of course with the typical Jeep cranking time (2-3seconds of cranking)

Sorry for makeing this a novel of sorts. Ive just been spending thousands of bux and a helluvalot of time trying to get this heap going and inspected (damn emmisions laws) and need some help.
I'll play with the distro somemore adn advance/retard it a tooth if possible adn see if that makes any difference

Thanks Alot for the assistance so far!!!

Well ive tried playing with the distro more, moveing it a tooth or so in either direction and that just made it run worse, or not start at all. Threw in a new O2 sensor as well, as the one in there hadnt been replaced ever by the looks of it, basically a solid blob of rust. She runs alot stronger now, but still the same ol' PITA problem.
Its got to be something stupid, just wish I could find out what

This is a pretty long shot but MAYBE the CPS might be acting up???

When my CPS went crazy I'd get some backfiring through the intake manifold.... Also, my CPS seemed to be angered by temperature changes (mainly when cold and then after it finally got going it would get angry becasue it was hot).

Probably wrong but I'd be willing to bet you'll need a new one soon anyway...

I´ve got a similiar problem on my 88 4.0 I6. Seems to thunk thunk thunk pop at around 2000 RPM, with the throttle open (accelerating)(low vacumn). It´s slightly noticeable in all gears, less when the motor is cold, but most noticeable in high gear at 2000 RPM.
Intitial timing recommendations for the 88 are in a recall notice (driveabilty problems), don´t know if the problem was also in the 89.
Sounds primative, but take an old distributor cap, cut a hole so you can see the number one electrode inside the cap, TDC1, 0 deg. advance, check and see if the rotor is slightly past the electrode. I believe the recommendation was .020 past the electrode from the trailing edge of the rotor. Said you had to cut the locking tabs off to adjust it.
I´ve got some other issues, with mine, broken intake/exhaust stud. Possible plugged cat. leaky exhaust, probable gummed up idle motor, probable loose timing chain, questionable 02 sensor. I´m gonna fix some other stuff first, before I start messing with the timing.
I wonder if a loose chain would show up with a timing light, the timing might jump around some, at a steady throttle, at certain RPMs.?
Had a sticky EGR valve in a 87 (you mentioned you changed yours, new doesn´t mean good), that would cause it to stall at low speeds, usually when going around a corner, just when you need the power steering the most.
A cold crank vacume test, might tell you something, hook up a vacume gauge, unhook the coil, crank it over, with the throttle closed and see what you get. Steady throbing rythem, above 5 inches of vacume, is what my book recommends.
Let us know what you find, most all of us, are on a learnig curve around here. Good luck.

Had a few more thoughts. The EGR is controlled by a solenoid, plug up the vacum line to the EGR and see if things improve with the stalling and such.
If your temp. sensor/switch is messed up, it will mess with cold idle (stall). Also controls the temp. when many other sensors are supposed to kick in.

I just looked up what the temp. sensor conrols and some of the items listed were the EGR solenoid, cold idle, and timing advance.

Well, in the old days too much advanced timing caused backfiring through the carb - so the old school solution was time it, tach and dwell. MPFI complicates that, reading off the CPS, and making it up as it goes, so to speak.

My '90 still has a timing mark on the pully and chain cover - I don't have the FSM with me, so I am just assuming that there is a procedure to set it precisely. Having watched a buddy work on starting a 350 in a Buick for 45 mins hand setting the distributor, I think timing it with a light might help get it right. It sure would have been faster for us.

(Note to self - look up procedure tonight.)

The way I understand the Jeep timing and others is. With imput from the CPS, the cam position sensor (ignition pickup), the knock sensor, the MAP sensor, the temp sensor, the throttle position sensor, the MAF sensor and maybe a few others, it sets it´s own timeing. The only adjusting point, is a beginning index point, from TDC, number one cylinder.
I havn´t experimented much with my XJ. But my Chev. with a closed sensor loop (operating temp. sensors good) you could turn the distributor a long way and the timing didn´t change a lick. To set the initial timing, there is a plug that can be unplugged (for the Chev.), that cuts out much of the imput to the computer, I assume it puts the computer into a open loop, allowing adjustment of the initial timing (with a light) without much of the sensor imput.
Maybe someone with a whole lot more knowledge than I, can figure out what to unplug, from the motor management system, to allow setting initial timing with a light, in an XJ with the Renix computer.

Thanks for the suggestions. Im going to take a look at the CPS tomorrow. It seems the previous owner rerouted it somehow, and when CheapXJ was cool enough to come down a couple weeks ago he mentioned something about it. I figure its as good a place to start again at any rate.
I also found some cut wire that was stuffed under my washerbottle. no clue where they go, but its heavy guage red/black combo about 4' long. comes out of the firewall left of the master cylinder as you face the engine

Thanks for the suggestions. Im going to take a look at the CPS tomorrow. It seems the previous owner rerouted it somehow, and when CheapXJ was cool enough to come down a couple weeks ago he mentioned something about it. I figure its as good a place to start again at any rate.
I also found some cut wire that was stuffed under my washerbottle. no clue where they go, but its heavy guage red/black combo about 4' long. comes out of the firewall left of the master cylinder as you face the engine

Pioneer89 said:

Work done by me in last 6 months:
Flywheel, TPS, TorqConverter, EGR Valve, Upper and Lower PCV Harness, Wires, Cap, Rotor, Brakes, Fuel,/Air Filters, Waterpump, Distributor Chain adn Gear and tonite Distributor itself.

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"Distributor Chain and Gear"? Are you perchance referring to the timing chain? If so, question #1 is how certain you are the new one was correctly aligned (indexed) when it was installed. Remember that there is a domino effect here -- the timing chain controls the relationship of the camshaft to the crankshaft, but since the distributor is driven by a gear on the camshaft having the timing chain off by a tooth or a link would also affect timing. (Maybe that's whay they call it a "timing chain.") I know it's a royal PITA, but unless you know absolutely beyond any shadow of a doubt that it was indexed correctly when installed, I would recommend removing the front cover to confirm.

Now we get to where you wrote that the new distributor would not align to the same point as the old one. PROBLEM. The process of "indexing" the distributor came out as a TSB to address issues that occur when after-market cams don't have the distributor drive gear oriented exactly the same as factory cams. The same could apply to an after-market or remanufactured distributor -- if the drive gear isn't pinned at exactly the same orientation as the stock one, the distributor won't be indexed.

You are correct that the distributor as designed cannot be "timed" because there is a locating lug to prevent turning it. The TSB on indexing tells you to gind that off. Then you take an old (or new) sacrificial distributor cap and cut away the side around the #1 turret. Make certain that the #1 piston is at TDC on the compression stroke, pop on your newly-modified diagnostic distributor cap, and look at the relationship between the tip of the rotor and the contact in the cap. The distributor rotates clockwise. The trailing edge of the rotor should be just beyond the contact, with an air gap of 0.020". If it doesn't measure that, loosen the lock screw, rotate the distributor body until you get 0.020" of gap, then tighten the clamp screw.

Lastly, I didn't notice any mention of oxygen sensor on your "Done" list. If the O2 sensor goes bad, once the engine warms up and starts looking for input from the O2 sensor, the ECU will receive false data. This can lead to an over-rich condition. That's what happened on my '88 when the O2 sensor went bad. Once it warmed up, I would get little "POP" backfires whenever I let off the throttle. Too rich, and the ECU wasn't getting reliable data to cut back the mix when I let off the throttle. The unburned gas went down the exhaust and backfired as soon as it hit the hot catalytic converter. A new O2 sensor and 5 minutes on my back to install it solved the problem.

"Distributor Chain and Gear"? Are you perchance referring to the timing chain?

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Yes, I think it was late when i typed that up and probably got ahead of myself from what i was thinking and what my fingers were typeing The mechanics I took it too specilize in transmissions, so i would hope that they could put in a new timeing chain correctly. I dont have the tools or know-how to check that, but i'll make a point to have it looked at. Mostly all of the work done has been to correct this ssue. It had the problem when it went in, and came out with no change. Leads me to believe that everything was put in correctly just didnt address the problem.

Ive read about that TSB for indexing before, I suppose thats worth a shot. I'll have to goto the boneyard and see if I can swipe an old one.
QUESTION: You refer to the "locating lug" where exactly is that on the distro?? When i recall inpecting my new one (ReManufactured) there was only the retaining "ears" on the right side were you mounted it to the engine. Are thoes the tabs refered to? Im assumeing so as they are the only "tabs" i can recall being on there. Also when I pulled the old distro out, just above the helical gears where the post "thickens" it looked as tho someone had put it in a lathe and ground down a very small amount of the shaft. My "new" one had very shallow raised "slots" that made it verry difficult to slide the distro into the hole. I didnt do any grinding, but i lubed it up a little with some dio-grease. It takes some muscle to get it in and out to realign, is this normal? The old one will slip right it and out, with little effort, it wasnt loose by any means just nothing like this refab one i have now. Could that be the tabs being referred to?

Threw in a new O2 sensor as well, as the one in there hadnt been replaced ever by the looks of it, basically a solid blob of rust. She runs alot stronger now, but still the same ol' PITA problem

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Thanks for the suggestions! Any sorry for being fairly ignorant to terminology and mechanics in general

I'm jumping into this thread a bit late, but you may also want to check your coil. A faulty coil will often show these characteristics particularly when your engine warms the coil. Check the primary and secondary resistances when the coil is cold and hot. Should be a couple of ohms on the primary and in the +10K range on the secondary. Better yet, try to swap the coil with a known working one.

Feel free to jump in anybody.
I`ll try and explain so even I can understand.
Distributor, as your standing at the front looking to the rear, number one is at 7 O´clock on the distributor cap, all I´ve seen have a 1 molded in the cap.
Look on the vibration damper (bottom pulley middle of motor) find the small notch or mark on the inside (motor side) of the pulley (takes some searching and maybe moving the damper around some). Mark it with a white crayon (I also mark the outside of the pulley).
Pull out the number 1 sparkplug (front plug)and turn over the motor in little spurts until you feel pressure coming out of the sparkplug hole with your thumb.
Turn the ignition off, and turn the motor by hand (or ratchet/wrench) until the timing mark is aligned with the 0 notch on the timing index marks ( right end )(use a flashlight).` If you have to back up, go past the 0 and make your final turn to the right (takes the slack out of the chain).
Find the number one pole at 7 Oclock and mark the side of the distributor housing in line with the pole/electrode. Remove the distributor cap and see where the rotor is pointing, should be somewhat to the left of your mark on the side of the distributor.
If your rotor lines up with (a little past) the number one pole/mark at 7 O´clock. Make sure the number one spark plug cable is also going to the number one pole at 7 O clock. Then down the line in a clockwise rotation on the distributor cap starting at one, second is 5 spark plug wire, 3 rd wire is 3, 6, 2, 4.
I´m trying to explain it, just like I think myself through the process. Like I learned it (works for me).
If you get this far and everything checks out. I´ll try another blurb. Or somebody else can jump in.

Possible reasons for intake backfire.
Ignition Timing, possible wrong starting point (distributor index) (number one cable on the number 4 or 5 distributor pole), possible faulty sensor imput, possible faulty module.
Fireing order. possible cable crossed
Valve timing, timing chain, usually makes for low compression and/or vacum (on all cylinders).
Sticking or bent intake valve, same as above, vacum gauge needle will take some wild swings. low compression on affected cylinder (or cylinders).
Sticking, bent or burnt exhaust valve. Same as above
Excessive fuel in the intake. Weak spark, flooding/excessive fuel
On carburated motors, sometimes low vacume (causes puddleing of fuel in the intake), among other factors. Hung open EGR, wide open throttle, valves.
I´d guess a hung open EGR, could ignite fuel mix in the intake, unlikely but possible.