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DonAltman3 10-04-2013 06:01 AM

I'm at my wits end need some ideas
Hello all.. I have a 1988 YJ 4.2 Automatic..
35 inch tires
Little background... This jeep has had the nutter mod done to it.. the ignition system has been updated (new dizzy cap rotor and msd blaster and I have the stuff to do the rush upgrade)
New fuel pump about a year ago or less.
MC2150 a year or two ago... never really ran right.
EGR deleted vacuum lines all cleaned up.
Timing around 8btdc.

Well I recently got tired of my jeep stalling out. I was having some issues with idle and felt like I had some problems with my
The mc2100 I original had was a 2100 that I made work.. it never was great and since I rebuilt it I was never fully confident in it being 100% correct (jets and pump ect)

I decided to take the plunge and get one from gronk the ebay guy.
Installing it took very little time since my jeep had already been converted.. initially the jeep crank right up and idled perfectly.. I was thrilled. Driving around it drove pretty well at first... I noticed that when taking a corner from speed when you let off the gas to coast the corner then pressed down again to resume acceleration I would get a hesitation.. or a stumble.. if I feathered the fuel it would be fine.. if I pushed it more.. it would bog to the point of stalling out.

The jeep is now doing this even more now.. I could be driving with low rpms.. just keeping the jeep maintaining a constant speed it it start to stumble if I give fuel it cuts off or hesitates and does nothing... if I let completely off the fuel rpms will drop down and it will go to ideal rpm and run smooth as a champ. then slowly feather back up some speed and it drives fine. sometimes this not being able to accel lasts merely seconds and sometimes it lasts for minutes or longer. I can slowly from 45 all the way to 15 mph and get little surges of speed enough to keep me rolling if I don't touch the pedal at all. eventually it will "catch up" or "work itself through it" and I can touch the pedal and start driving like normal.

I've looked for vacuum leaks and I haven't found any. (I only have two lines ported to dizzy and manifold to PCV)

I'm thinking this is a fueling problem as the jeep doesn't seem to cut off it seems to stall.. it doesn't skip at all and idles as smooth as I could hope for. The idle rpm when col is around 1000 then after warm its around 800ish

Could the sending unit be a culprit? My fuel pump is mechanical and as I stated earlier it has been replaced once already. The carb has been changed and other than the idle being better it has the same exact symptoms as before the carb change. Filters have all been changed as well.

I looked at Orieles and ... neither list the sending unit for my yj...

yzjwk 10-04-2013 06:27 AM

I have never been able to get my YJ to run properly at 8*BTDC since i changed the dizzy years ago , IIRC i had the same symptoms as you .I've been running ~10-12* since then . Could be caused by too heavy of a spring or weak vacuum at/just off idle.

Que89YJ 10-04-2013 06:36 AM

If it is a fuel issue then get a pressure guage on it and find out. You can get one from any of the big parts store tool loan program. x2 with the timing. 8 is a starting point to set it, most people end up around 12. Did you run the distributor ground on the nutter bypass? It is easy to overlook. Full tune up is always a good thing too.

DonAltman3 10-04-2013 07:11 AM

tune up has been done.. I guess I could measure fuel pressure driving down the road??? As it will run fine in the driveway in neutral.

I did the nutter so long ago I do not remember the ground actually.. can you give me a little more info and I can run out to my jeep and check it.

OMG QUE.. I'm still dealing with this same problem from 2 years ago.. you tried to help me then.. lol

I thought for sure it was the carb so I just stuck it out.. finally saved up 300 bucks and got another one from the ebay guy.... NO BUENO..

Where can I find a replacement pick up.. and is that the same thing as the sending unit???

superj 10-04-2013 07:16 AM

when i ran one of those, i found i had to move the accelerator pump linkage to one of the other holes, not the middle one.

DonAltman3 10-04-2013 07:21 AM

Que.. after doing the nutter is there a chance the ICM is still causing me problems and I might need to get a new one and nutter it as well?

I thought the nutter totally bypassed the ICM?

Que89YJ 10-04-2013 10:51 AM

The computer it's bypassed the ignition coil module is still needed. You basically eliminate the ground control from the computer as well as the advance. The distributor ground wire needs to be ruin to a good ground because the ground control is eliminated from the computer and the coil. There have been a few no starts and intermittent from the distributor ground not being run after the mod.

yzjwk 10-04-2013 10:56 AM

Nutter by passes the computer and feedback to the ignition module, but not the ignition module itself . they generally work or they dont or they get intermittant and the engine will stall over bumps and such. one thing you can try is pull and plug the vacuum advance to your distributer and then set your timing to about 16 or 18* . If it runs better then the problem is in your ignition timing, if it runs the same then it's probably fuel related .

DonAltman3 10-04-2013 11:31 AM

I really thought the nutter eliminated the ECU and the ICM.. perhaps that was my problem the whole time... is that even plausible to think the icm could be intermittently shorted for years?


rambo3489 10-04-2013 08:59 PM

I doubt it would be intermittent for years. Eventually something would have to give and you would be stalled out. You only have one of two main problems. Fuel and spark. I would double check your nutter setup and then move on to fuel.

Old4X 10-05-2013 10:50 AM

You need to do some basic troubleshooting before replacing parts willy-nilly.

What is your fuel pressure doing at idle and when it stumbles?

How much slack is in your timing chain?

What readings are you getting on your vacuum gauge at idle? Steady needle? At your elevation you should have over 21" of vac if your engine and carb is properly set up.

DonAltman3 10-05-2013 12:32 PM

I'm not sure pressure when it stumbles because it is random and only when driving. Never at neutral just running..... I guess I could run a remote somehow to watch as I drive.

I haven't replaced parts willy nilly it's been to three mechanics. Each one gave up. I've taken advice from people here and tried to figure out the problem. That being said though there isn't much else to change Lol. Icm and sending unit and that pretty much everything.

Old4X 10-05-2013 03:33 PM

There aren't mechanics working today on the line that are familiar with the YJ and their systems. Anyone will take your money for a looksee.

You need to do some base line assessment work and correct deficiencies that are discovered.

First, do fuel pressure tests to see if you are within needed fuel supply for your carb, must be done and recorded at all RPM ranges you will use.

Next, hook up your vacuum gauge and see what the engine's health is.

Next, go to NAPA and get a timing tape kit. Map your engine timing from idle to 3500 rpms.

Next, check slack on your timing chain, if over 6 degrees, replace chain and gears.

Next, what vacuum source are you using for your vac advance. Try the other one and se if the problem persists (ported vs manifold).

Next, set the vacuum advance to factory default (8 turns out from the stop) and se if any improvement.

Next, from your timing map you did, are you getting proper ignition timing advance (and not too much) in the trouble range? Both too little and too much ignition timing causes bogs and misfiring.

Next, check phasing on your distributor if no solution yet. Instructions available on this site via search. The dizzys were not set up for non-smog use, and the phasing on some is off when the computer is removed.

Next, test pressure drop across your cat and muffler looking for restrictions.

These engines are not a mystery, but they are antiques that were designed 70 years ago. Modern computer troubleshooting is of no use with these motors. Did any of your shops have an old Sun ignition analyzer and flow bench that they used when working on your engine?

Old4X 10-05-2013 03:39 PM

Also, how is your carb set up and where did you get the settings to use. When you put an off brand carb on an engine it was never set up for, you get to be the field engineer for fuel flow, fuel pressure, idle settings, jet size, power valve size, air filter CFM rate, etc. I can get you right on the money with the OEM carb, but do not have a clue with what you bolted on.

Have you modded the carb to work with gasahol, or are you running alcohol free fuel?

Old4X 10-05-2013 03:55 PM

Are you running 8mm wires? What gap are you using on your plugs? Why did you go with the MSD ignition? Is it set up as a stand alone ICM, or is the Duraspark ICM firing it?

How is the ignition grounded?

NVM, I see the blaster is just a coil, has to be fired by an ICM

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