Cold miss on a 90' RENIX

I've been fighting this problem for a couple of weeks. I have a miss/stumble only on cold mornings and only on acceleration. After the engine warms up it runs fine. When I bought this XJ a few months ago the engine was blown and it was partially torn down and missing a few parts. The 4.0 has been rebuilt(by a local engine builder), it was bored 40 over and the head was milled and the block decked. Here is a list of what is new, some of which was replaced because they were not on the Jeep.

TPS, O2, CTS, IAC(Holly)
I've replaced and/or cleaned the grounds.
I've tried 3 different sets of plugs(Champions/Autolights) and wires, I'm running NGK right now.
New cap and rotor
I've double checked the distributer indexing, its on #1 TDC.
New injectors.
New fuel filter.
The intake and TB are clean.
Its pulling 18hg vacuum
I've checked the fuel pressure and it is in spec both at idle and with the vacuum disconnected.
EGR is blocked.
There are no vacuum leaks.
I'm getting 18 mpg city.
I've got a CPS and a MAT on order and will install this weekend. I've checked the sensors before replacing and they were all good, but decided to change them anyway(I'll keep the others for spares).
This XJ is being restored to original since it belonged to my dad before he died and it got sold and then I found it and bought it back. I would really like to get this mechanical problem fixed so that I can move on with the resto.

Anybody have any ideas?

You've covered just about all the usual problems.
I would also check:
plug wires
MAP sensor
distributor

There comes a point when it makes sense to get a second opinion and take it into a shop where they have the diagnostic equipment and expertise with the Renix (87-90 years) systems. I enjoy doing almost all of my own maintance and diagnosing problems as they come up, but sometimes I resort to a good mechanic to help me out. Cool deal on getting your Dad's Jeep backeace: Good Luck

What you described is a classic EGR issue with renix, and yours is blocked, How exactly is it blocked? Once you get it unblocked, make sure the pintle moves in the bell shaped thing on the manifold, and that you are pulling vacuum on the line to the firewall and the solinoid on the firewall is working. Good Luck

I forgot to mention that the MAP is new also. All sensors are OEM except for the MAT which the dealer no longer carries, I got it from GP Sorensen.

I've tried three different sets and brands of plug wires and have checked the resistance on each and every wire.

The EGR is in working order and is clean, I have the vacuum plugged off from it right now. It misses the same with it plugged or unplugged.

The thermactor hose is removed due to fact that it will not fit back in that tight spot due to the tranny cooler lines.

I have not checked the Sync sensor yet but I doubt that is the problem.

I wouldn't think the CPS is bad since it starts quick and runs fine warm. It checks o.k. anyway.

CPS is tricky critter, the ohms change with the temp.
My CPS is at the edge of the allowable tolerance 200 ohms plus or minus 75. Mine reads 278 cold. The motor hits a certain temp. around 140 degress and she refuses to start. Noticeable miss at certaint temperatures. I've also had a CPS test at almost exactly 200 Ohms and still not work. The wiring for the CPS, often has excessive resisitance at the connectors between the CPS and the ECU.
I actually poured a bottle of water on my CPS (to lower the temp.) to get the old XJ started the other day. It's due for a change, I'm holding off till I replace the rear main seal, don't want to put in a new CPS and then have it get oil soaked.
You may have a weak spark condition. just on a hunch, seperate the coil from the ignition module and clean the contacts. Check the ignition module connectors (at the module and also the down stream connector) for moisture, which can cause a bit of voltage bleed, which can weaken the spark a bit. I've had line bleed (from water or mud) and dirty connectors, noticeably lower my ignition module voltage, causing a weak spark. Yellow spark is often weak, sharp blue spark (you can hear the pop) is best.
Stock resistance igntion coil to distributor cap wires seem to work best.
Check for moisture, condenses when cold and vaporizes when hot. Especially in the high voltage parts of the ignition system. Avoid WD-40 or other sprays, some are highly resistive. Any kind of coolant leak can cause all sorts of grief, coolant is a relatively good conductor, better than water alone.
Plug off all the vacuum lines to the manifold except the MAP, they connect often at one end or the other and in open loop operation, when they leak, can cause noticeable differences in how the cylinders fire, acts almost like a miss. Uneven compression can also cause, what acts like a miss, seems to get better (or sometime worse) depending on the engine temp.
I had an 87 with a cold miss, I reduced it, but never did completely eliminate it, learned to live with it.

8Mud, I checked all of those connections before but will do again. My CPS arrived today so I will put that in tomorrow and try again. I can get a EGR for about $30 locally may try that if the CPS doesnt help. The only other thing is the distributor, I can get a Reman for $45. I really hate just being a parts changer but even with 20 years mechanical experiance this one has got me stumped, I'll keep throwing money at it untill it fixes itself!!
The wierd thing about this problem is when I had the distributor retarded a tooth(dumb mistake, don't wanna talk about it) it didn't miss only had a low idle and slight off idle hesitation. I advanced the dist. one tooth(trailing edge of rotor on #1 terminal at #1 TDC) and the idle picked right up and the stumble went away, but now the cold miss, I can't win!

Thanks for everyones help. I'll repost if I find it.

Its official, this Jeep hates me! I replaced the CPS this morning and found that the old original one was bent at the very end. I thought I had finally found the problem. I also added another ground to my OPTIMA, I went from the un-used side post to the chassis.

I went for a test drive(it still missed cold) and started smelling gas. It turns out that #2 injector was pouring gas out of it where the plastic and metal body meets, no problem just replace it, they are under warranty. So after replacing the injector I go for another test drive, (still misses cold, but not as bad).

Then when I get home I pop the hood to check for fuel leaks since I had all the injectors out, then the dang coolant bottle cap blows off and soaks me in hot coolant!
I've not had one single cooling problem with this XJ, the bottle was only slightly swollen, about normal. I think the cap just slipped off the threads. I recently replaced the CTS and had to drain the system but I did burp the system good. I hope I can find just a cap locally or I will have to order another bottle.

If this Jeep didn't have so much centamental value to me and such low mileage(140k) I'd sell it.

I just had to rant! I'm still looking for the problem!

Seems I'm talking to myself, I guess that happens with old age, but just in case anyone searches this topic, I will update.

After cleaning every single connector in the engine bay and under the dash, and replacing a leaky injector that was a suprise, I've just about got it completely out.

It only slightly misses when I first start it(cold) and pull out on a hard accel. I can live with that. I still have one sensor on order(MAT) that I will install for the h@# of it.

Bottom line is: When you think you have checked everything and its good....Check it again, it will probably be something simple.

XJTrailRider,

Sounds like you have been having a miserable time with your Jeep. I had some similar problems recently and I changed quite a few sensors, a MAP, TPS, IAC, Ignition Coil, Fuel Pump Resistor (all from a local junkyard). New Fuel Pump, engine and fuel line cleaned, on and on....and it still was missing and bucking at low speeds. I switched my plugs form Autolite Platinums to Champion regulars and there was a huge difference but still some bucking. I then pulled a Renix from a 90XJ (like mine) and that seemed to do the trick. Although I have not heard that the Renix computers go bad I think that might have been the problem for me.

The odd thing is that a lot of other things were going on as well, my overfill bottle began leaking, my injectors would stay on etc.

Good Luck,

LTK

Now that you got it all close, do a flash on your ECM, Then maybe that can learn and erase the miss, Can't hurt. Heres one way to do it.
http://www.mhjcontherocks.com/Community/TechWriteUps/196.aspx

Itkaknm, Its been a journey for sure, but I think I've turned the corner on this problem.

XJING, Mine is a RENIX so it doesn't store codes, it resets with every key off. That trick will work well for OBD I/II, but thanks for the advice and help.

Almost everytime I go through the connectors and clean everything up, there is a noticeable improvement in idle. People say it is a waste of time, but unhooking the battery and then reconnecting, does seem to do something for my old Renix on occasion (it can't actually hurt much). There is a constant power supply to the ECU and a switched power supply. I believe some information is saved as index info for the next start, possibly atmospheric pressure or some other stuff. The programing almost has to be slanted towards emissions and not effiency, smoothness or performance. IMO some info is saved, the difference after disconnecting my battery isn't real subtle and is noticeable and does change as the vehicle is driven. Just an oppinon.
Take the distributor cap off and gently push the rotor shaft to the side, wiggle it a little, any noticeable side play will cause flutter. There seems to be a lot of up and down play in most distributor shafts. Many have the spacer or shim (above the gear) on the shaft completely worn away and gone. The drive gear teeth also wear.
Funny, I just put on a new fan clutch, heavy duty which improved idle. I'm guessing the extra load on the timing chain, took some of the flutter out.
Easier to see on a scope, but if you have a timing light you can see the flutter just by aiming the light at a dark patch on the motor. It's rough trying to get anything constant out of a Renix, while looking at the timing marks. You can also hook the timing light up to the spark plug cables, one at a time and point it at a dark spot and see a single cylinder misfire.
Most times it has turned out to be a combination of little things, that just add up and cause a rough running motor. Grounds seem to be sores pot, with sensor connectors as a close second and general power supply as a close third (resisitance adds up).
Irrelevant but interesting was my habit of putting a big block oil pump into a small block Chev motor. The tighter tolerances in the pump, took out a lot of the flutter (harmonics) that could be seen on a scope as somewhat erratic firing of the plugs.