Rough Running 4.0

[jpboyjeep]

I'm about a day away from taking the Jeep to a "real" mechanic!

106k mile 4.0L 2000 TJ Manual

Driving it at about 40mph steady throttle, engine warm. All of a sudden it turned rough, coughing and sputtering, it wanted to die when I let the throttle off, so I had to tap the throttle when I come to a stop to keep it running. However it sputters and coughs at all RPM ranges, smooths out a little at higher RPM. Its undrivable in its current state.

Check engine light on, codes said "misfire #5". I had a problem a year ago with a bad sparkplug. So I replaced the older plugs and the newer one with all new plugs with proper gaps. No change.

Checked the coil rail (DIS on this) with plugs in and have spark on all cylinders. I had a spare rail, swapped that in anyways and rechecked spark. No change.

Checked for any cracked or leaking hoses. Found none. Wiggled and pulled on hoses without effect.

I started checking the fuel system. I had an intermitant noisy fuel pump. I checked pressure without a gage, just put my finger over the line. It didn't feel like 60psi, so I went and replaced the pump. Definite pressure increase, again, I didn't have a real pressure gage, just put my finger over the line. While in there, the fuel filter was checked and much cleaner on the new one. No change.

Went to the gas station and filled up with midgrade, put in a bottle of injector cleaner. Drove back, no change.

Pulled #5 injector, cleaned it, looked fine visually. I pulled the rest and cleaned up them as well. Reinstalled injectors in a different order. No change.

While engine is running, I pulled a plug off a random injector and noticed very little change in the engine RPM or roughness.

Started on sensors even though I have not gotten any codes.

I checked the Crankshaft Position Sensor. I Ohmed it out and came within specs I recieved from a search on here. I went to the local auto store and checked a new one and had the same reading. I tested the old one with the engine warmed up and didn't have any unexpected readings. I left the old one in.

I tested the MAP sensor. I was told to expect a voltage reading of 1-2v at idle and gradually higher as the engine revved up. I tested the MAP at 3.8v-4.0v at idle. I got a new one and had no change in my engines performance. With the old one back in, I tested it by sucking on the rubber nipple ;) with the meter attached and the harder I sucked, the lower the voltage all the way down to 2v. I figure that the sensor is working. I cleaned out the port in case it was plugged, it was clean. No Change.

Tested the TPS and it passed with flying colors.

Made sure the valves on top of the valve cover are clear.

I tried unplugging the O2 sensor and it didn't make any change.

I cleared the #5 misfire code. Ran it around the block until it threw another code. Again #5 misfire.

I've gone through about 1/2 tank of gas in about 45 minutes of rough idling and maybe 8 miles of road driving. You can smell the gas and I end up with a black mark on the cement from the tail pipe. Also, the Jeep runs very loudly, like the fuel is burning in the tail pipe or something. I can rev the Jeep up to 4k without a problem, just I have bad sputtering and missing getting there, once there, it isn't too bad, but you can feel and hear it running badly. Only power I have on the road is at 3k+ RPM.

From my perspective, I have a sensor issue that is screwing up the fuel air mixture by telling the injectors to spray waaayyy to much. Is it vacuum? or electrical?

Anything else I can check? I'm getting frustrated and ready to throw in the towel. Thursday, I'm going to try to rent a pressure tester from an autostore, if I can, to test compression, but I've taken care of the engine and it has no mechanical noises I can tell, we'll see there.

Lucas

[Go_Vols]

Please keep us informed - I'm chasing the same gremlins on mine...

Thanks,
TN

[jeepdude1]

Have you checked the compression and performed a leak down test yet? Could have a blown head gasket or a leaky valve.

[jpboyjeep]

Have you checked the compression and performed a leak down test yet? Could have a blown head gasket or a leaky valve.

No, I've yet to get "mechanical" with it. It seems to just flood the engine with gas. The next step will be to do a compression test thou, tonight.

Lucas

[vorlando]

Lucas-

Just a though, but try replacing you O2 sensors. I know a few people that had similar problems and at the end of the day it was a bad O2 sensor. Since you just unplugged it, if it was bad, you would not have seen a change anyway. Mine has been doing the same thing more or less, but I still have not gotton around to fixing it cause I am lazy.

vince

[Bill99TJ]

Did your steering wheel get wet at some point? Could be a bad clockspring. One of the sensors (don't remember which runs through it).

[JohnnyJ]

I tested the MAP sensor. I was told to expect a voltage reading of 1-2v at idle and gradually higher as the engine revved up. I tested the MAP at 3.8v-4.0v at idle. I got a new one and had no change in my engines performance. With the old one back in, I tested it by sucking on the rubber nipple ;) with the meter attached and the harder I sucked, the lower the voltage all the way down to 2v. I figure that the sensor is working. I cleaned out the port in case it was plugged, it was clean. No Change.


It sounds like you have a vacuum leak.

The computer thinks you are putting a big load on the engine (high MAP, low throttle) and is trying to fuel to it. This would likely cause the misfire code, because it's gonna run really rich and have bad combustion, and likely foul the plugs.

You mention that the MAP sensor can read lower values (the suck test) so we know it's not a sensor issue. So you have to trouble shoot why it would read high values.. (biggest cause: vacuum leak)

Unless you have multiple issues, I doubt the compression test will show anything.

[BajaCherokee92]

It sounds like you have a vacuum leak.

The computer thinks you are putting a big load on the engine (high MAP, low throttle) and is trying to fuel to it. This would likely cause the misfire code, because it's gonna run really rich and have bad combustion, and likely foul the plugs.

You mention that the MAP sensor can read lower values (the suck test) so we know it's not a sensor issue. So you have to trouble shoot why it would read high values.. (biggest cause: vacuum leak)

Unless you have multiple issues, I doubt the compression test will show anything.


Another vote for vacuum leak.

If you actually have a blown head gasket, you'll probably be able to see steam in the exhaust....

[jpboyjeep]

Another vote for vacuum leak.

If you actually have a blown head gasket, you'll probably be able to see steam in the exhaust....

The exhaust doesn't have anything but a bad smell to it. And when it sits idling for a while it leaves a black mark on the cement...gas/carbon. My coolant level has remained constant and it has a nice green color, I just repaired a leaky radiator, so I had to refill it. It isn't tainted, if a blown head gasket would do something to the color of the coolant?

Any sure fire way to know a blown head gasket?

Any good way to check for vacuum leaks. I was going to put a vac hose on the intake tube, run it in reverse to blow air into the intake with a rag over the end and puff some foot powder around to see if I have any air leaks. Any better idea?

I wonder if I were to put a vacuum on the MAP sensor to lower the voltage if that could test for a vacuum leak, and test the MAP sensor at the same time. If it ran better, than I know its a vacuum leak somewhere and if it doesn't do anything...?

Thanks,

Lucas

[JohnnyJ]

The exhaust doesn't have anything but a bad smell to it. And when it sits idling for a while it leaves a black mark on the cement...gas/carbon. My coolant level has remained constant and it has a nice green color, I just repaired a leaky radiator, so I had to refill it. It isn't tainted, if a blown head gasket would do something to the color of the coolant?

Yes, more than likely, or you'll continually be low on coolant. Stop worrying about the blown head gasket, it sounds like you've got a vacuum leak.


Any good way to check for vacuum leaks. I was going to put a vac hose on the intake tube, run it in reverse to blow air into the intake with a rag over the end and puff some foot powder around to see if I have any air leaks. Any better idea?

Here (http://www.google.com/search?hl=en&q=find+vacuum+leaks+EFI) you go.


I wonder if I were to put a vacuum on the MAP sensor to lower the voltage if that could test for a vacuum leak, and test the MAP sensor at the same time. If it ran better, than I know its a vacuum leak somewhere and if it doesn't do anything...?

Just look for the leak, you said you did a suck test and it moved. Applying vacuum or adjusting the voltage on the MAP sensor isn't going to fix the problem, because you still have more air entering the engine than what the throttle would allow. If you "fix it" by tweaking the MAP sensor, you'll go lean and bad things can happen (like holes in cyldiner heads..)

Just fix the problem.

[Knoxville]

When I had the 2.5L in, the brake booster diaphram was leaking bad, and thus the engine was running like ass. You might want to try plugging the vacuum line to the booster coming off the intake and see if that helps. Like mentioned earlier, bad O2 sensors can cause this kind of thing too. Good luck with it, these things can suck.

[Blt2Krawl]

:mad3: I'm dealing with the same crap too, replaced and chaged most of the things your discussing to no surprise it's still messing up. Haven't checked the clock spring situation is there anyway to check this? Mine hesitates and it's only gotten worse, I rode around with a severely cracked exhaust manifold for awhile coudl this have hurt it. The hesitation has gotten worse since I put a new header on, the throttle and idle kicking start when I used to crank itup while it was cold now it's doing it all the time. It also pops in the back of the transfer case I duno if it's cause the throttle is making the shaft and all kick back or something in my transfer case or tranny is causing this. I do know I can drive down the road at 55 miles an hour and all of the sudden it'll die and I can let off and press the gas again and it'll pick back up or I can stomp and it'll accelerate. It's just so damn inconsistent it's hard for me to put my finger on it to fix it although it has gotten more frequent lately. Any suggestions?
Thanks in advance, Nic-

[chadlucky13]

i had the same exact problem with a 99 2.5L. i checked everything that was mentioned above and could not find the problem for the life of me. finally gave up and took it to a mechanic here in town which was a big mistake. they told me it was my computer and order me a new one. they put in the new computer, cleared the check engine light and told me it was good as new. on the way home from picking it up, same damn thing started happening, i turned around got my money back and told them to go #$% themselves. i then double checked everything again and finally found out that it was my battery causing the problem. the positive terminal post was loose on the battery causing the computer to intermintently screw up the FI, causing a code of "misfire #1 cylinder". I put a new battery in, cleared the code and the jeep drove like new and havent had the problem since. Soo, it took me about a week to find out i had a bad battery. long story short, check your battery. :eek:

[Blt2Krawl]

I haven't diconnected my battery and reset it I think I need to do that because maybe after I changed the exhaust manifold it started running right, so if I reset the computer it might run right again.

Anything elsE?
Thanks, nic-

[Bill99TJ]

The clock spring has two connectors going to it. One has the aribag circuit the other has the horn and part of the TPS circut running through it. Unpulg the connector with the horn and tps. If it runs better then your clock spring is shot. On a 99 I believe the connector is brown.

[jpboyjeep]

One thing that I forgot about the first day I was dealing with this problem was that even though I disconnected my top post ground wire, the winch was still attached to the side post and that was grounded! Oops! Just a note if you do try to reset the computer...

I will check for a vacuum leak tonight with some propane..... :mad3:

Lucas

[jpboyjeep]

Just look for the leak, you said you did a suck test and it moved. Applying vacuum or adjusting the voltage on the MAP sensor isn't going to fix the problem, because you still have more air entering the engine than what the throttle would allow. If you "fix it" by tweaking the MAP sensor, you'll go lean and bad things can happen (like holes in cyldiner heads..)

Just fix the problem.

Yeah, its starting to make sense, if the voltage is high at idle, and it should be low, but the MAP works, then its leaking in somewhere.

Lucas

[thenodnarb]

Has anyone considered checking the IDLE AIR CONTROL valve?!

I used to see this all the time at the auto parts store I worked at. Sometimes a nearly dead battery does the same thing. Check the battery with a load test at the parts store. its free and easy. if it tests good. replace the IAC valve.

[Schmozilla]

My jeep did something along the lines of yours. It ended up that the wireing harness had fallen back on the the exhaust header and had burned threw a few of the wires causing all sorts of fun stuff to happen.

[jpboyjeep]

I was under the impression that if I had only a rough idle, I would look into the IAC, or even stalling. But that is not my case. I get a crappy running engine at all RPM ranges.

The battery is strong, starts well, don't think that is an issue.

I did some tests tonight. I didn't have any luck with using Propane to detect leaks, nor did it do anything at all to the idle when inhaled directly into the intake. Does propane work? Or is it some other type of gas your supposed to use, cuz this didn't make the engine do even the slightest thing differently even with the propane being held directly into the intake!

I had some gages of my dads and I had him help hook them to the test port on the intake manifold. We read 6-7 inches at a cold idle and up to 20 inches at 3k RPM. This was roughly, they were refridgerant gages, so it wasn't made really to measure this!

I tried the brake booster, I unhooked the line and put my finger over the end. It sucks plenty, but it didn't do anything as far as the engine goes. I alternated putting my finger over the tube and off the tube, it made a slight drop in RPM before the engine adjusted and it went back to normal idle.

I hooked a vacuum up to the intake and held a cigar around every hose and I didn't notice anything. Maybe I'm supposed to light the cigar? :smokin: :) If I have to, I'll pick up a can of "smoke" somewhere....auto store?

But all tests, it still is coughing and sputtering badly.

I keep coming back the the MAP sensor. What voltages am I supposed to get from it at idle and then at high RPM? I read online somewhere 1-1.5v at idle and like 3.5-4 at full throttle. I get 4 volts at idle. I'm about ready to go and get another MAP sensor and reset the computer and double check my readings on the new MAP sensor. The first one I failed miserably to reset the computer and to check the voltages, I was in such a hurry to return it if it didn't work cuz the idiot at the counter said I could return it!! :flipoff2: But just plugging in the new one before didn't fix anything, maybe I needed to reset the computer? If I can't think of anything else, I'll have to try that again....

Thanks guys!

Lucas

[CJ-7traildriver]

Checking for vacuum leaks on intake manifold Jeep recomends spraying small streams of water in areas listening for changes. Never used this method but should work just don't go crazy with amount of water. I have always used carb cleaner spraying gasket areas, vacuum hoses etc. If there is a vacuum leak and carb cleaner finds it it revs up. Carb cleaner is also flamable so hot exhaust manifold, sparks etc can cause a fire. Be carefull if useing this method.

Have you ever put a vacuum gauge on it watching for radical changes? Alot of things can cause issue like worn/weak valve springs can cause irratic vacuum, backfires etc. Just some ideas take it easy and hope you get it figured out.

[jpboyjeep]

Whenever I spray anything that is supposed to cause the engine to race or change idle, it doesn't do anything.

I had a mechanic tell me to try and spray a little carb cleaner in the intake and if the idle picked up, then I could target the TPS and a few other sensors, but it made no change in the engine noise or RPM etc...

I tried propane to find a vac leak and even when putting the propane in the intake, the engine did not change RPM or noise etc...

I also think the info I found about MAP sensors is not right. This sensor, the harder I "sucked" on the inlet, the lower the voltage got. That leads me to believe that at idle I should have a high voltage and at WOT I should have a low voltage signal. FSM would be nice right about now!

I'm going to dive in again tonight and see what I can find.

Thanks,

Lucas

[jpboyjeep]

I ordered a FSM last night, so early next week I should see it.

This morning I bought a new CPS so I would at least have a spare if it didn't make a change with the engine. Sure enough, no change, but now I have a spare for when it does fail!

I'll update this thread once I get the manual and am able to test a few more things.

Lucas

[chadlucky13]

find anything out?

[jpboyjeep]

Yeah, I found out I still can't fix it!

FSM came, only its missing every single how-to test this and that. Apparently, they put that info in a different manual. So, I have a book on how my suspension used to work and come apart before I torched it off.

It may come in use if I need to rebuild the trans or something.

But, I pulled and tested the Camshaft Position Sensor, and it works fine. I get near zero volts without anything blocking the reading head and plenty of voltage when I block it...on a bench for testing.

FSM did mention something about a head gasket could leak between cylinders and cause misfiring among other problems.

I'm at the point where I'm going to start looking into mechanical problems. After I do a real vac. leak test, I'll start looking into something a mechanic said. One guy said my timing chain could have broke a tooth and skipped a link, throwing off my timing. I'll have to check my timing.

So, I've got timing off or head gasket problem...once I eliminate the vac leak.

I'm ignoring the O2 sensor, simply because the way I understand them, is that I'd only have bad gas mileage or a slight power loss if it did fail. Not this rough, loud, misfiring engine!

I've either tested, replaced, or swapped with a working one, the following sensors: TPS, CPS, CMS, MAP, & MAT...

Lucas

[Blt2Krawl]

Well researched a bit farther, and thought about the easy stuff first before I went and spent 300 on replacing all the sensors. This whole time i've been overlooking the fact my horn hasn't worked in some time :rolleyes: so do you think I need to break down and mess with the clock sensor?
Thanks, Nic-

[katarn444]

Did you check the torque on the intake manifold bolts? Those bolts are notorious for shaking loose.

Katarn

[ScottDeLano]

watch your tach when the engine miss-fires. does the tach jump wildly? or does it move smoothly? This will help diagnose the problem as electrical or mechanical in some cases.

Your problem is very similar to an intermittant CPS problem. Did you swap the new CPS in? Most of the time, a bad CPS will still Test as a good. Also when you put the new one in, make sure you get the sensor as close to the tone ring as possible. Use a business card as a gap tool.

[jpboyjeep]

watch your tach when the engine miss-fires. does the tach jump wildly? or does it move smoothly? This will help diagnose the problem as electrical or mechanical in some cases.

Your problem is very similar to an intermittant CPS problem. Did you swap the new CPS in? Most of the time, a bad CPS will still Test as a good. Also when you put the new one in, make sure you get the sensor as close to the tone ring as possible. Use a business card as a gap tool.

I'm not sure if this is derected at me or the fella above....I'll answer anyways.

My engine doesn't just misfire once in a while, it runs like crap all the time. There is no smooth running instance. Its at a cold start to full warmup it runs like shit. Tach doesn't skip around either, it twitches as it idles very badly and when you hold it at say 2k rpm, it twitches slightly based on how bad the engine is running at that rpm.

When I replaced the CPS, with a new one, on this vehicle the sensor has 2 bolts and you can't adjust anything. I suppose you could push hard down on it to maybe move it about 10 thousands or something closer to the tone ring. But this one isn't adjustable.

Lucas

[Go_Vols]

Gents - I bought a new clockspring from the dealership last night ($118 + tax - ouch). Installed it in about 20 minutes....no more misfiring, no more "backfiring" into the intake, no more sputtering, no more engine dying at stops, no more erradic idles....just a smooth running 4.0 with a vicious exhaust leak :smokin:

Cleared codes, drove it out to get a case of suds, came back to the shop...no codes (well, except a speed sensor malfunction...haven't hooked up the Atlas).

I am over-f'n joyed that it was such a simple fix... now I need a new exhaust manifold...

[sw_mi_xj]

as earlier stated , run a compression test and or a cylinder leak down test ,
one of our other tech's in the shop had this same thing on a newer grand
cherokee 4.0 liter , recurring cyl. #5 misfire .

it was a worn lobe on the camshaft , a little odd for 15k miles .

but since the cam was on back order i guess they are having a problem
with this .

[jpboyjeep]

After 2 weeks not working on it, I finally was able to bring my Jeep back home and put it into the garage over the weekend. Having it way out by my parents was a major PITA! My dad likes to give away all his tools to neighbors and anytime I need something, its at home!

So, anyways, I did go out and purchase a brand spankin' new compression tester. I didn't want to buy one unless I had to, well, I tested every single sensor and all checked OK, so this was the next thing.

I ended up with zero compression on #5, which was the same one giving me a misfire code. I pulled the cover and ended up with a broken valve spring.

So, in the end it comes down to having the right tools. At least now I can read my codes and check compression! The last thing I figured I'd have go wrong, did! 106k miles and a broken valve spring. I only wish I knew someone that had a compression tester about 3 weeks ago, my search for a problem would have been shorter!

I appreciate all the help on here!

Lucas