jerky acceleration and coasting

87/4.0/puegot Recent tune up, new cps, swapped icm and coil from the jy didn't help, adjusted tps and tried a new tps, new fuel pump filter and relay, new alt battery cables and upgraded grounds with old battery cables as well as upgrading the alt charging wire and the wire that goes to the power distrobution thingy from the battery, and pretty much did everything in the renx files. It feels like the jeep hickups. It happens mostly during light acceleration/cruising but occasionally happens during hard acceleration. It used to do it really bad to the point that the jeep would stall for a second or two and if I got into the gas pretty good it would turn back on. It's turned off completely maybe a dozen times in the year and a half I've owned it. After all the upgrades I've done it hasn't turned off all the way in a while, it does just slight hickups now. It used to do it more in the summer but now it pretty much does it the same in the cold weather as much as the hot weather. Today I unlpugged the o2 sensor and drove around like that and it feels exactly the same as plugged in. It goes up and down in idle maybe 100 or 200 rpm's when it's cold and it pretty much goes away when it's warm. It doesn't have a tach so I can't tell the exact numbers but that doesn't bother me that much. The hickuping/jerking while driving is what bothers me. I haven't tested the o2 sensor yet but it looks like it's possibly been replaced by the po. When I first got the jeep I figured it wouldn't pass smog legitimately so the guy that bootlegged it told me it was running rich. The cat fell to pieces soon after and it's just straight piped now until I have to smog it again in July. I would really like to get rid of this hickup. It bugs the hell out of me. I've had two other renix xj's and they didn't do this to me. I wouldn't be opposed to taking it to a mechanic if anyone knows of a mechanic that can scan a renix xj or that can give me some guidance I would appreciate it. I'm thinking to get a complete set of map, distributor, cts, iat from the jy on half off day and swap them one at a time to see if it helps and bypassing the c101 connector but that seems like a bear. The grounds seem solid. All the sensors are reading 2.5 ohms. Please give me some guidance!

You need to check all your vacuum lines and CCV hoses for cracks or being plugged.

Next, the sensors: CTS,MAT,TPS should have 5volts with key on. the Ohms reading on the CTS and MAT should be less than 1000 ohms on a warmed up motor.

Check the o2 wiring for burns from exhaust since unplugging it didn't change anything.

my2monkeys said:

You need to check all your vacuum lines and CCV hoses for cracks or being plugged.

Next, the sensors: CTS,MAT,TPS should have 5volts with key on. the Ohms reading on the CTS and MAT should be less than 1000 ohms on a warmed up motor.

Check the o2 wiring for burns from exhaust since unplugging it didn't change anything.

Click to expand...

What he said and I've had my 88 do that for various reasons. Once was low voltage to the fuel pump through a partially cooked connector. Another time it was my TPS ground. Most times it was something to do with the O2 sensor or the CPS. If a new sensor doesn't cure it, you have to check the wiring. I've found O2 sensor, CPS, injector, fuel pump, CPS, TCU and TPS wiring issues in my 88 and still have many of my OEM original 1988 sensors.

If all else fails you may have to reindex your distributor, I had to on my 87. Bucking at low RPM's was my issue. My 87 would also hunt at idle with a vacuum leak. 87's have a cam grind issue, that sometimes messes with the initial timing.

8Mud said:

.....
If all else fails you may have to reindex your distributor, I had to on my 87. Bucking at low RPM's was my issue. My 87 would also hunt at idle with a vacuum leak. 87's have a cam grind issue, that sometimes messes with the initial timing.

Click to expand...

Good idea.

You can check the timing by marking the #1 terminal on the distributor base, and looking at where the rotor points
with the engine at TDC. It should be aligned with a bias
toward the CW side of the mark. This allows for the timing
spark to advance and the rotor to still contact the terminal.

my2monkeys said:

You need to check all your vacuum lines and CCV hoses for cracks or being plugged.

Next, the sensors: CTS,MAT,TPS should have 5volts with key on. the Ohms reading on the CTS and MAT should be less than 1000 ohms on a warmed up motor.

Check the o2 wiring for burns from exhaust since unplugging it didn't change anything.

Click to expand...

Which one is the mat? The one on the fire wall?

Runnin'OnEmpty said:

Good idea.

You can check the timing by marking the #1 terminal on the distributor base, and looking at where the rotor points
with the engine at TDC. It should be aligned with a bias
toward the CW side of the mark. This allows for the timing
spark to advance and the rotor to still contact the terminal.

Click to expand...

Sre you describing the same thing as in the renx files with cutting a hole in the cap?

This may help. Go to post 13 in the following link.
http://www.cherokeetech.com/VBull/s...uiser-s-Mostly-Renix-Tips&p=103796#post103796

EJXJ said:

Sre you describing the same thing as in the renx files with cutting a hole in the cap?

Click to expand...

Yes, that's what Cruiser54 is describing in his excellent
post and pics.

EJXJ said:

.....It happens mostly during light acceleration/cruising but occasionally happens during hard acceleration.....

Click to expand...

Cruising is when the engine
would be at maximum spark advance. Under acceleration
the spark would be retarded at first, then increase as the
speed increased and the 'load' on the engine decreased.
If the distributor is indeed off a tooth, then the coil is
sparking before the rotor reaches the cap terminal and
causing the misfire (during advanced timing situations).

This scenario is easy to check. Just turn the crank to TDC
on number 1 cylinder, and see if the rotor is to the CW
side of the number 1 cap terminal. If it's to the CCW side
of the terminal then the distributor is one tooth off.
(Remember the rotor turns CW when running.)

Runnin'OnEmpty said:

Yes, that's what Cruiser54 is describing in his excellent
post and pics.

Cruising is when the engine
would be at maximum spark advance. Under acceleration
the spark would be retarded at first, then increase as the
speed increased and the 'load' on the engine decreased.
If the distributor is indeed off a tooth, then the coil is
sparking before the rotor reaches the cap terminal and
causing the misfire (during advanced timing situations).

This scenario is easy to check. Just turn the crank to TDC
on number 1 cylinder, and see if the rotor is to the CW
side of the number 1 cap terminal. If it's to the CCW side
of the terminal then the distributor is one tooth off.
(Remember the rotor turns CW when running.)

Click to expand...

Thank you for the clarification. Thank you cruiser54 I've been following you renix guidance! I've been following you information since my first cherokee. This is the first one that has stumped me. I'll fix it tomorrow and we'll see how it goes!

I just drove eighty miles without it happenning!

So the dizzy indexing fixed it?

Yes. When I first did it I didn't have the number one cylinder at tdc. There are no markings on the balancer to go by. I drove it a little and it did it once. Then I tried again by turning the engine over in smaller increments until pressure stopped coming out of the cylinder and reset it. Hasn't done it since! Thank you very much!

how did the cap/rotor look? might want to pop for new ones if the terminals look worn. Other than that, enjoy your properly functional heep!

PS: don't forget to plug your O2 sensor back in

It needs a new cap and rotor. I plugged the o2 sensor in that day.