1989 MJ. 1100-1700RPM hesitation

Hey guys. I haven't really dove into the issue at all yet, I have a few ideas in mind to try, but I figured maybe I can tell you guys and maybe you've experienced these symptoms and have solved the issue quickly.

1989 MJ 5spd peugot 2wd (dana 35) 4.0renix STOCK 230k

I am a very detailed person. Deal with it.


THE SETUP:
I started by upgrading the master cyl/booster. from a 2000XJ. Well the reason for the upgrade is because I had a busted brake line that went from the junction block at the back of the truck to the prop valve up front. I had to take the gas tank loose to access the stock line, after getting the line off, I put the gas tank back and made the new line fit. So I will be going back and checking all the fuel lines and clean the fuel filter just to eliminate that possibility.

Up front I had to take the knee knocker panel off from underneath the dash to access the brake pedal area to remove the old cylinder and pedal assembly. There is a computer under there, not sure what it is for, but I am going to check all of my connections underneath that entire area to eliminate that possibility.

I then had to take the air cleaner off and stock vacuum line assembly off (which is all still in tact) to access the prop valve and master cylinder. I have checked for vacuum leaks with a can of brake clean, but it did not show any issue.

THE PROBLEM:
The truck will sit/idle and free rev with no issue, no hissing, bucking or jerking. When you shut the engine off I feel a shutter in the engine as it is shutting off (the entire engine shakes). While driving down the road at WOT I have no issue through any gear.

The problem I have is that around say 1100-1700 RPM the truck starts to buck like its choking out of fuel or lack of spark, my shift indicator/severe misfire light does not illuminate during the issue. This problem arrises when taking off from a stop light at around 1100 to 1500 RPM and then it will come back in every gear at the same RPM. Once at cruising speed in 5th gear you can still feel it doing the bucking, which requires more throttle input in order for it to cease. The truck really is struggling up hill in 5th gear.

THOUGHTS:
SO, what my intentions are to clean out the fuel filter and then take off the throttle body, clean it really well and check every single connection I could have possibly damaged. After that if it is not fixed I will take out the OHM meter and start ohming out my tps and check the operation of the IAC. I am not exactly positive if there is an actual test for that crank sensor (it either has spark or not).

CONCLUSION:
In conclusion I have "bucking" issue between 1100-1700 RPM in any gear, and in 5th gear at cruising speed 45MPH-highway speeds. I have been in the fuel cell area and fuel lines, under the dash on the drivers side and have removed the air box and air cleaner assembly, after doing all of that and putting it all back together, this is where the issue has come up.

Hopefully someone can maybe put this issue to bed really quick because this is my only means of transportation. I can still drive it, I just don't want this issue to really escalate much further than this.

muchos garcias senators!:us::cheers:

Fuel delivery problems tend to get worse as the RPM's go up, the motor needs more fuel.

Any difference between a cold motor and a hot motor? Reason I'm asking is a faulty O2 sensor can do what you describe, usually only on a hot motor (over 140-160 F or there abouts). The O2 sensor sends faulty data and the motor can lean out too much. Usually only happens at cruising (max fuel efficiency) RPM's around 2200-2400. But still a possibility.

Could be the beginning stages of CPS failure.

May be a faulty sensor, wiring or grounds. Just a guess, but ground issues kind pops out at me, you may be back feeding voltage into a sub system that should be without voltage with the ignition off. The same ground issue could be screwing up sensor values to the ECU.

Read this,http://naxja.org/forum/showthread.php?p=246160724#post246160724 , it may be your issue or it may not but if you plan on keeping the MJ your going to have to do it all anyway.

Thanks for the info. I would say it is temperature sensitive, but this morning it was about 19 degrees and it was being a real bitch until it got warm and then it smoothed out, but continued with the same symptoms once it warmed up

Click on the link below and do Tips 1,3,4, and 5.

http://www.naxja.org/forum/showthread.php?t=1115935

Back at it again here.

as of now:

I have inspected all the fuel lines and vacuum hoses around the gas tank. I then removed the fuel filter (which seems pretty dirty) and cleaned it thoroughly and replaced it.

I moved forward and inspected under the dash for loose wires etc. I did not find anything that could be causing an issue. I did notice however that the clutch master cyl is leaking down onto the main fuse panel. Obviously that can be an issue.

From that point I moved into the engine bay and replaced the ground cable from the cylinder head to the firewall. I also made a new ground from the negative battery post to the radiator support. I then removed the TPS and IAC sensors and took a good look at the throttle body. It was not very dirty so I just cleaned off the IAC and re-installed it. I did do a voltage sweep on the TPS, but it showed it was functioning correctly both going wide open and going all the way closed. I unhooked the 02 sensor, crank sensor and CTS connectors and cleaned them thoroughly and put some di-electric grease in each connector. I then sprayed all the vacuum lines and intake hoses with brake clean again while it was running.

No Change yet. Same issue still persists

After I let it sit over night I swapped the Ignition coil and module from my XJ over to it. I drove it and the issue was not any better.

After I swapped it back, I then swapped in the 02 sensor from my cherokee. The stumble GOT BETTER, but it was still relevant. So that leads me to believe that I have an issue that is resulting in bad fuel trim and its beginning to wipe out the 02 sensor.

I then completely went through every piece to the puzzle in the manual that was posted on here. I ohmed out the TPS and found that I had a steady .9 ohms of resistance until I wiggled the dipstick tube ground post, it then shot to about 5-10ohms I went as far as removing the grounds from the dipstick stud, replaced both of the eyelets and also replaced the entire negative and positive battery cables to a thicker gauge wire. I cleaned off all the grounds i could see to bare metal with my mini-sander. I took every spade loose and hit it with a scotch brite pad and re-installed it. The truck really has come back to life now, however the problem is STILL THERE! Its just not as bad now.

At this juncture I am going to be replacing the crank sensor with a good one that I have here and maybe just buying a new fuel filter for it. I will also inspect the entire fuse panel and remove every fuse just in case I did miss something in there. I will also be removing all the spark plugs, sandblasting and re-gapping them. I did remove the distributor cap to check for arching, but I did not see anything.

Any more thoughts, gentleman?

Joshooha said:

Back at it again here.

as of now:

I have inspected all the fuel lines and vacuum hoses around the gas tank. I then removed the fuel filter (which seems pretty dirty) and cleaned it thoroughly and replaced it.

I moved forward and inspected under the dash for loose wires etc. I did not find anything that could be causing an issue. I did notice however that the clutch master cyl is leaking down onto the main fuse panel. Obviously that can be an issue.

From that point I moved into the engine bay and replaced the ground cable from the cylinder head to the firewall. I also made a new ground from the negative battery post to the radiator support. I then removed the TPS and IAC sensors and took a good look at the throttle body. It was not very dirty so I just cleaned off the IAC and re-installed it. I did do a voltage sweep on the TPS, but it showed it was functioning correctly both going wide open and going all the way closed. I unhooked the 02 sensor, crank sensor and CTS connectors and cleaned them thoroughly and put some di-electric grease in each connector. I then sprayed all the vacuum lines and intake hoses with brake clean again while it was running.

No Change yet. Same issue still persists

After I let it sit over night I swapped the Ignition coil and module from my XJ over to it. I drove it and the issue was not any better.

After I swapped it back, I then swapped in the 02 sensor from my cherokee. The stumble GOT BETTER, but it was still relevant. So that leads me to believe that I have an issue that is resulting in bad fuel trim and its beginning to wipe out the 02 sensor.

I then completely went through every piece to the puzzle in the manual that was posted on here. I ohmed out the TPS and found that I had a steady .9 ohms of resistance until I wiggled the dipstick tube ground post, it then shot to about 5-10ohms I went as far as removing the grounds from the dipstick stud, replaced both of the eyelets and also replaced the entire negative and positive battery cables to a thicker gauge wire. I cleaned off all the grounds i could see to bare metal with my mini-sander. I took every spade loose and hit it with a scotch brite pad and re-installed it. The truck really has come back to life now, however the problem is STILL THERE! Its just not as bad now.

At this juncture I am going to be replacing the crank sensor with a good one that I have here and maybe just buying a new fuel filter for it. I will also inspect the entire fuse panel and remove every fuse just in case I did miss something in there. I will also be removing all the spark plugs, sandblasting and re-gapping them. I did remove the distributor cap to check for arching, but I did not see anything.

Any more thoughts, gentleman?

Click to expand...

It's not the crank sensor, but you can test it and modify it. Tip 7.

Replacing the fuel filter is a good idea versus cleaning it out.

Ever indexed the distributor per Tip 13?

What brand of spark plugs are in there?

I have autolite plugs in it now. They have approx 4 years and 40k on them my gaps are pretty good. .035 on cylinders 1 and 2. About .040 on 3, .038 on 4, and .040+ on 5, 6. Gonna blast them and re-install them.

I really am not sure if I want to work on it much more right now. I plan on driving it to Florida tomorrow morning. I will for sure do the fuel filter and plugs today and drive it around. If the problem is still really bad I suppose I will have to work on it a bit more.

Cracker had a very similar issue with his MJ, I hooked up my DRB and found the ECU was getting no sync signal from the distributor, we swapped out the distributor and the hesitation was gone and the truck ran better than it ever had.

Joshooha said:

I have autolite plugs in it now. They have approx 4 years and 40k on them my gaps are pretty good. .035 on cylinders 1 and 2. About .040 on 3, .038 on 4, and .040+ on 5, 6. Gonna blast them and re-install them.

I really am not sure if I want to work on it much more right now. I plan on driving it to Florida tomorrow morning. I will for sure do the fuel filter and plugs today and drive it around. If the problem is still really bad I suppose I will have to work on it a bit more.

Click to expand...

Really?

Put a new set of NGKs in there!! The 4.0s are due for new plugs, cap, and rotor every 30,000 miles. We always did wires while we were at it.

Unplug your distributor and see if that sync generator really makes a difference.

Okay today's progress. The stumble is still present, but I do feel comfortable in driving it to Florida.

I started by Pull out the plugs and blasting them, regapping and reinstalling them. It did not change anything at all. I the removed the IAT sensor and noticed how nasty it was. Cleaned it, reinstalled and drove it. The truck did run better with that. I figured I might as well do the same with the crank sensor. After removing the crank sensor I noticed it was still engraved "renix" so for $33 it was worth putting a new one in. It did help the truck s bit more.

Drove it home and decided I would swap the distributor and rotor from my xj to it. It didn't change a thing. Still stumbling. Mostly on take off and really low speed now. I then tested the EGR by pulling a manually vacuum on it with the engine running. The engine choked out and died as it should. I did however swap out the diaphragm from my xj to it, it helped start up a good bit, fires faster now.

I know this is an '89 model, but it was built in '88. I still have the c101. With that clutch master leaking down onto it, I suspect that will be my next place to dig in to. I will mess with that in a week or 2

Thanks for everything this far. All the tips have helped a lot. This truck really just needed a lot of refreshing!

Joshooha said:

Okay today's progress. The stumble is still present, but I do feel comfortable in driving it to Florida.

I started by Pull out the plugs and blasting them, regapping and reinstalling them. It did not change anything at all. I the removed the IAT sensor and noticed how nasty it was. Cleaned it, reinstalled and drove it. The truck did run better with that. I figured I might as well do the same with the crank sensor. After removing the crank sensor I noticed it was still engraved "renix" so for $33 it was worth putting a new one in. It did help the truck s bit more.

Drove it home and decided I would swap the distributor and rotor from my xj to it. It didn't change a thing. Still stumbling. Mostly on take off and really low speed now. I then tested the EGR by pulling a manually vacuum on it with the engine running. The engine choked out and died as it should. I did however swap out the diaphragm from my xj to it, it helped start up a good bit, fires faster now.

I know this is an '89 model, but it was built in '88. I still have the c101. With that clutch master leaking down onto it, I suspect that will be my next place to dig in to. I will mess with that in a week or 2

Thanks for everything this far. All the tips have helped a lot. This truck really just needed a lot of refreshing!

Click to expand...

I'm confused. The clutch master cannot leak on to the C101, only the fusebox.

Click on the link below and go to Tip 27 and see if we're talking about the same thing.

Sorry, I was using my crappy iphone last night, I didn't write that up correctly. Your'e right it is the fuse panel its leaking on. I don't know why I put C101.

Like I said. I will be driving it for 9 hours today, I did take it 20 miles down the interstate yesterday with no issues at all. Ill keep ya'll posted.

Progress as of now.

Brief Synapse:
MAP sensor-checked and swapped
TPS-checked
CPS-checked (new)
02-checked and swapped
coolant temp sensor-checked
IAT-checked and swapped
swapped distributor (not cap/rotor)
upgraded all engine ground circuits
swapped 02 heater relay
checked all fuses
checked EGR valve
swapped EGR relay/ballast
swapped ignition coil/module
swapped fuel pressure regulator
inspected all fuel lines/vac hoses
cleaned fuel filter
clean spark plugs/regapped
checked for exhaust restriction via vacuum gauge

...maybe more, can't remember it all

The problem still exists completely. It cranks fires idles and revs perfectly normal. Once under load under 1500 rpm on take off it stumbles horribly, it will clear out and take off above 1500rpm. At cruise in any gear if the RPM is below 1800 the engine bucks. On hard acceleration you can feel a stumble in all RPM range in any gear unless you are wide open throttle. Once speed has increased to 65mph or about 2000rpm the problem ceases.

The issue I don't think is heat related as much as time related. If I fire it up and just take off its good for approx 30secs-1 minute. After that period it will start and progressively get a little worse once heat gets into the engine.

It gives me all the thoughts of a damn 02 sensor if you ask me, or possibly a coolant sensor, but none of my results indicate that.

I have not pulled the fuel rail off to clean the injectors. I performed that service about 40k ago. I find it hard to believe that is the issue considering the symptoms

At this point I think I'll get with the snapon man and see if he has an adapter I can plug into my scan tool and maybe get some damn readings through the under hood diag ports.

No plug wires?

Have you indexed the distributor?

I haven't done those 2 yet. I'm really leaning away from the plug wire/plugs thing, I may swap them just to see if their is a difference

I wouldn't.

Tip 13 in the link below for indexing the dizzy. Tip 12 for making sure you're on #1.

#1 should be at the 5 o'clock position of the dizzy cap when viewed from the passenger side fender.

http://www.naxja.org/forum/showthread.php?t=1115935

If I read everything right, you might be over thinking this. You have not done any basic tune up parts ? Cap n rotor, new plugs and plug wires. You mentioned it in your original post, fuel or spark related. These are all spark related. Get you some stock Champion plugs and a good set of 8mm wires.

MACH90XJ said:

If I read everything right, you might be over thinking this. You have not done any basic tune up parts ? Cap n rotor, new plugs and plug wires. You mentioned it in your original post, fuel or spark related. These are all spark related. Get you some stock Champion plugs and a good set of 8mm wires.

Click to expand...

My thoughts exactly.

Ok, I think I may have a strong suggestion for you, as I had the same issue a few years ago:

Start out by checking pressure on the fuel rail, IIRC it should be about 40PSI, if it's less than this that's your problem.

Generally what happens here, is the tube that connects the fuel pump to the bulkhead connector rots out because of ethanol blended fuel and will become mostly disconnected. This results in the engine becoming starved for fuel at higher RPMs even if it idles fine. You will get pops, bucks and all kinds of other chaos.

Note: This problem usually starts slowly, with just an over-all feeling of sluggishness and eventually develops into a full blown (I can't get much above idle). The tube usually ends up kinda blowing gas up the line, but it never develops the pressure it's supposed to.

The other thing to check, if you have a bad fuel odor coming from the tailpipe is your fuel pressure regulator, pull the vacuum line off and look for evidence of gas (when mine had this issue, it looked like I disconnected a fuel hose)

Thanks Bulletmaker. I actually just jumped on here to see what was posted because I was headed this direction. I had an old Ramcharger that had the same issue, it was an '88 and it would sometimes just lose fuel pressure for no reason. Turns out a line was collapsing internally.

For my own piece of mind I did put some new NGK's in it, got a new cap and rotor. Also I made up some new 8.6mm wires for it.

So, I will do the fuel stuff next. I'm hoping my friends brother has a scan tool with an adapter on it.

Thanks again guys.