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Cylinder misfire, vacuum leaks and . . . ?

SuzysJ

NAXJA Forum User
2001 4.0/AW4 2WD with 122,000 miles. I've searched every thread here and other JEEP forums, and am looking for anything I might have overlooked; thanks for any help.


Have had 0301 code awhile, and now has worsened. I changed the sparkplugs (stock Champ 12's), cleared codes and had a smooth idle. Fluids and filters are new or close. Took it for a gentle 12-mile highway run, and, on return, really stood on it and wound it out. Back to flashing CEL and rough running. This JEEP, though bought used, has had excellent maintenance. BUT, due to underhood heat, everything has gone crispy brittle. You touch it, it breaks/crumbles. (Finally raised hood rear with spacers and trimmed weatherstrip awhile back, no longer have to use gloves to open hood). Have replaced one vacuum line that was history, and taped over terminations that were dry-rotted on another.

Went by Autozone and the mighty ACTRON scanner pulled, in this sequence:

0201
0300
0301
0304

(info from the site: http://www.obd-codes.com/)


0201 Cylinder 1 Injector Circuit Malfunction

FUEL OR AIR CIRCUITRY

The symptoms for this code will likely be a misfire and a rough running engine. Poor acceleration. The MIL will also be illuminated.

The causes could be any of the following:
• Bad injector. This is usually the cause of this code but doesn't rule out the possibility of one of the other causes
• Open in the wiring to the injector
• Short in the wiring to the injector
• Bad PCM


0300 Random/Multiple Cylinder Misfire Detected

IGNITION CIRCUITRY

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.

• the engine may be harder to start
• the engine may stumble / stumble, and/or hesitate
• other symptoms may also be present

A code P0300 may mean that one or more of the following has happened:
• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Burned exhaust valve
• Faulty catalytic converter(s)
• Faulty camshaft position sensor
• Defective computer

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor.


0301 Cylinder #1 Misfire Detected

IGNITION CIRCUITRY

0304 Cylinder #4 Misfire Detected

(Same as above)


None of this appears unusual, the "problem" I am having is that in order to make inspections I have to count on doing replacements of about anything I touch. No joke. I want to minimize the items I check.

After replacing spark plugs I checked/jiggled wire connections to injectors. Now for questions:

1] Should injectors rotate easily, or is this evidence of O-ring deterioration? I have no leaks.

2] Injector wiring has a red stay-clip. I moved it up and expected to be able to remove from injector. Seems the harness termination is welded in place. Tried several methods of removal, but no luck.

3] I would like to be able to examine the injector harness under the long plastic cover, but it won't survive being removed. Any point in checking? I examined a photo from another site where a wire was chafed, appeared to be on harness back near firewall and had rubbed on an engine fastener. My harness has no interference at that spot.

4] I assume I will be replacing the injectors at some point soon (5.0 Motorsports) and may have to replace the injector harness as well. PCM, too? (Crunchy connectors)

4] Vacuum leaks. Hate them, almost as much as electrical shorts under the dash; been chasing them nearly forty years. I know to check the lines connected to intake manifold. Have replaced fuel purge solenoid line/harness. Any other "weird" places to check? I don't really want to disassemble entire system if a known place is problematical.

5. When this JEEP was purchased [4] years ago last month, I pulled/cleaned TB and replaced MAP and TPS as preventative maintenance. I am leaning towards heat degradation here, and wonder if anyone has insight to this area as to leaks. I'll try fogging it, as the vacuum leak are the worst problem being experienced.

6. I have seen the MOTORAGE .pdf on re-aligning the cam position sensor, somewhere it was suggested that this may go whacky based on some timing chain stretch. I "might" do this as preventative/good practice, but assume will buy new as, again, anything I touch crumbles.


Your insights appreciated.

:worship:
 
A big write-up, very thorough. What did the spark plugs look like when you pulled them? It just seems odd that it ran good for such a short time after you changed them. Have you ever checked your compression? This is probably not the issue, but always something easy to rule out before breaking more parts. Verifying the cam sensor timing seems like something that can be done with minimal likelihood of breakage.
 
You've got misfires on 2 or more cylinders. Because of that, I doubt that it is plug or injector related. You probably have a "common" source for all the misfires. And you are on the right track with suspecting a major vacuum leak.

Adopt a "testing" strategy to isolate this. Don't throw parts at it.

1. If it were mine, I would start with a comprehensive check for vacuum leaks; if you know your way around a vacuum gauge, this would also be helpful. Check that intake very closely; I've seen a leak here be responsible for "random" misfires more than once.

2. Test fuel pressure at the schrader valve on the fuel rail with a gauge. You're looking for 49.2 psi plus or minus 5 psi Easy to do and in the process of elimination game, something you should verify

3. Testing camshaft position sensor as mentioned, wouldn't be a bad idea. It is responsible for fuel injector timing as well as other things. Can be tested with a manual and a meter.

BTW, a flashing check engine light indicates a "serious misfire". Failure to resolve may result in the trashing of your catalytic converter.

You really do want to get under this quickly. Good luck and let us know what you find!
 
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Thanks, as my garage and tools are 300-miles away. I own everything and then some, but can't take this vehicle there, nor, at present, afford a shop until there is no other choice. Nothing new (after a few decades of driving, wrenching), but I'm not in a position to easily check and replace broken items if they aren't needing examination.

I see I wrote MAP. Meant IAC.

Vacuum leak check, as said, is the main thing. I'll be thorough about intake manifold gasket (and TB mount) as a serious leak is present. This engine has been running hot for a long time (out of state, and out of my control until recently). I believe the leak "worsens" as vehicle warms up. I know where I can borrow a propane torch (Note: always make friends with maintenance man).

Spark plugs all looked good, and, though boots are rotting, I believe they'll hold up a while longer.

Appreciate fuel pressure numbers to verify.

I'll have to borrow or rent any/all testing equipment unfortunately, and agreed that a compression check is called for (don't know how old vacuum leak or leaks have been, but underhood heat tells me that the motor has been leaned out a long time. You wouldn't believe how crispy everything is on such a young car [what I've seen on Southern cars after twenty years] I'm hoping not too much damage was done by dirt ingestion). Having screwed myself as a younger guy by poor maintenance practice, it is no fun to have one come back into my possession as evidence of such. Rant on

I searched, but did not find FSM numbers for vacuum at steady idle and at 2,000 rpm (or what is noted). Anyone?


I won't do injectors just now. That one will wait a little, but, do injectors rotate quite easily? (I own a diesel, my last gasser was a '71 Chrysler a few years back). What about red clip and harness disconnect on injectors? Mine seem welded, and I'm already to replace entire harness from PCM to injectors (after some $$ comes free).
 
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I searched, but did not find FSM numbers for vacuum at steady idle and at 2,000 rpm (or what is noted). Anyone?


I won't do injectors just now. That one will wait a little, but, do injectors rotate quite easily? (I own a diesel, my last gasser was a '71 Chrysler a few years back). What about red clip and harness disconnect on injectors? Mine seem welded, and I'm already to replace entire harness from PCM to injectors (after some $$ comes free).

Injectors can rotate freely, as its not a sign of anything. The red clip pulls up (if it just doesn't clean break off), then you push in on the socket release button. That can break too. I usually just use a pick to go from the bottom of the connector (near the injector) and lift up on the clip.

Stock fuel rail pressure is 49.2psi +- 2psi

It would be a good idea to reindex the cam sensor and its easy to do.

If the spark plug boots are cracking it would be a good idea to replace them as it can cause arcing.

The recommend plug for 00+ dis less systems is an NGK, not Champion, but that isn't your problem now.

Common vacuum leaks: emissions solenoid (thing that clicks on the passenger side fire wall), hoses going to the charcoal canister in the rear near the gas tank. 90* hose under map sensor, the 3 90* connectors on the side of the intake manifold tend to dry rot, hose going to resovoir chamber behind front bumper.

I think the cylinder #1 issue could be an injector issue as you have two different codes for #1 misfire. #4 could be something else.

When do the misfires happen?
 
Injectors can rotate freely, as its not a sign of anything. The red clip pulls up (if it just doesn't clean break off), then you push in on the socket release button. That can break too. I usually just use a pick to go from the bottom of the connector (near the injector) and lift up on the clip.

Excellent, thank you. I hate breaking things (that are old) just to learn how it is supposed to be. And thanks on "normal" injector fit.



The recommend plug for 00+ dis less systems is an NGK, not Champion, but that isn't your problem now.

I guess it changed, huh? The Champ 12-series is what I've used for over nine years on these. I'll try the NGK's next time.



If the spark plug boots are cracking it would be a good idea to replace them as it can cause arcing.

I pulled rail again yesterday, and boots aren't as bad as remembered. I can put that one off (understand about arcing).



I think the cylinder #1 issue could be an injector issue as you have two different codes for #1 misfire. #4 could be something else.

Agreed. #4 is, I think, leaning out to far from unconfirmed vacuum leak. #1 is also affected, but more by injector not working properly. Have run quality injector cleaners most of last 40,000 miles.


Common vacuum leaks: emissions solenoid (thing that clicks on the passenger side fire wall), hoses going to the charcoal canister in the rear near the gas tank. 90* hose under map sensor, the 3 90* connectors on the side of the intake manifold tend to dry rot, hose going to resovoir chamber behind front bumper.

That's the ticket!! I've replaced the hose set from the vacuum purge solenoid, and have been looking at others. The three intake connectors are new or poor, but couldn't tell a difference when plugged off. I am hoping it is not the intake gasket, but need a tester to play around with.


Does anyone know vacuum gauge recommendations? FSM gauge readings under stated conditions, or good practice on all-stock motors?


Thanks for all the help in looking at this. Knowing how is one thing. Knowing how on a particular vehicle is another, and that is real help to this boy.
 
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due to underhood heat, everything has gone crispy brittle. You touch it, it breaks/crumbles.

I have never seen something like this on a modern vehicle, Why is it getting so hot under the hood?
I worked in a powerplant for decades & we had heat related failures on the older stuff, But the modern stuff seemed to hold up to heat just fine!
If your underhood wiring on your 2001 XJ is in bad condition like you describe I think this is where you will find your problem.
 
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I have never seen something like this on a modern vehicle, Why is it getting so hot under the hood?
I worked in a powerplant for decades & we had heat related failures on the older stuff, But the modern stuff seemed to hold up to heat just fine!
If your underhood wiring on your 2001 XJ is in bad condition like you describe I think this is where you will find your problem.

I know on the injector plugs tend to break quite easily with age along with the injector wiring becoming brittle. . Its all the heat coming off the manifold. Plus things just age and deteriorate. It is a 9 year old vehicle.
 
Excellent, thank you. I hate breaking things (that are old) just to learn how it is supposed to be.
Don't go any where near the rear upper shock mounts than! Lol.
I guess it changed, huh? The Champ 12-series is what I've used for over nine years on these. I'll try the NGK's next time.
Yes, they changed around 2000 and IIRC there was a TSB one it. The Champions aren't bad, but the 00+ 4.0L were prone to heat soak and other assorted misfires. The NGKs seem to handle this issue better. I have verified that myself. The system just likes the NGKs better.

That's the ticket!! I've replaced the hose set from the vacuum purge solenoid, and have been looking at others. The three intake connectors are new or poor, but couldn't tell a difference when plugged off. I am hoping it is not the intake gasket, but need a tester to play around with.
Using a propane torch (unlit!) will help find vacuum leaks. Just crank it open full, run the engine and wave it around where you think the leak is. If it finds a way into the engine the idle will change. Also, I have heard of people spraying WD40 at various points to find leaks. A smoke machine works best, but they are pricey.
 
I have never seen something like this on a modern vehicle, Why is it getting so hot under the hood?
I worked in a powerplant for decades & we had heat related failures on the older stuff, But the modern stuff seemed to hold up to heat just fine!
If your underhood wiring on your 2001 XJ is in bad condition like you describe I think this is where you will find your problem.

Nope, won't hold up to it at 9-yrs/6-mos and 122,000 on a Texas XJ. I don't dare pull any plug/connector I don't plan on replacing both ends of. Until I shimmed hood hinges with washers and trimmed hood/cowl weatherstripping, it was -- no exaggeration -- necessary to have gloves or rag to open hood after running. This includes anything at manifold level or higher underhood as to being ready-to-crack. I'm irked that I can't take things apart for examination, but that's the breaks until $$ comes in.

All coolant hoses were replaced some time ago, thermostat is a ROBERTSHAW HD 195F, coolant gauge shows sub-210F temps (not so hot for mpg), usually at thermostat temp all the time. No problems with exhaust I'm aware of.

I believe that it is at least one or more vacuum leaks causing engine to run lean and hot. As I said, car was out of my control for some time, so problems accreted.

I've been wrenching on cars for several decades and have some experience in getting high compression engines to run on the cat piss gasoline we've had for about twenty years now: heavy cars, low numerical gears, hotter than stock thermostat, re-jetted carb and completely new ignition advance curves. WIth ice cold A/C. In 105F weather, in stop-and-go. With weakened compression. But higher mpg. I can find my way around with test equipment.

I read the link to vacuum problems. On cars from the 1960's we could pull 19-21 IN/HG at idle; with '70's cars -- depending on make and emissions equipment -- we had lower numbers given by manuals. Etc.

That's why I wondered if the I6-242 had numbers set by the FSM.

The car is sitting for a time. I really do appreciate all the help, gentlemen. Will update as I learn something. At some point I'll bring my test equipment from home, and I'll probably have a shop do a lookover as well. (I'm old enough I prefer to have someone look over my shoulder to check things. Cheap at twice the price if rapport can be established).
 
with '70's cars -- depending on make and emissions equipment -- we had lower numbers given by manuals. Etc.

That's why I wondered if the I6-242 had numbers set by the FSM.


Those '70's cars gave EXACT vacuum numbers to search for, is the point. While the vac gauge stuff online is great -- basics -- I can promise that when one has an older car, SEVERAL problems may show up on the vacuum gauge!

I used to shoot for 19-20 In/Hg in tuning older cars as any less or more was not ideal in the sense of best performance/fuel economyexcept where the FSM gave an exact number [stock vehicle].

Am heading "home" to bring back tools among other things.
 
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The correct answer is the timing advance will be whatever the ECU/PCM decides it should be based on sensor input.

I would expect a healthy 4.0 to have a steady 15-17 inches at idle.
__________________

Mine idles at 16.5 with a 0.2 fluctuation. Mine is a 2000.


Thanks, Winterbeater for a number on a closely-related model year. I found that mine -- cold idle -- was the same with some steady fluctuation given a misfiring cylinder. An "emissions idle" vacuum reading.

The cars from the sixties -- big block motor, high compression weighing the same or less than 4WD Cherokee with winch, trail-ready, etc would really leap off the line to 40 mph +. But the timing and fuel curve to support this caused high emissions at idle. You younger guys missed out on cars that simply, effortlessly accelerated to road speed with no noticeable work involved. Catch a ride in one some day (I don't mean a muscle car).

I put off vacuum leak investigation, fuel pressure test and compression test at this point as the gauge was indicating a response consistent with a single cylinder misfire.

I re-examined vacuum connectors (soft, rotted), taped them with black electrical tape, and used tiny zip-ties on them once re-installed on manifold.

After some wire jiggling and the use of some 1/4" i.d. ATF hose as a stethoscope I found that while I could hear something (clicking) it was decidedly different than the other cylinders (2-6). I could not tell if it was a wiring problem or a malfunctioning injector. As my one day of being able to work on the car was closing I went ahead and installed an O'Reilly-sourced DEKA replacement injector ($47).

The four bolts holding the fuel rail were removed after disconnecting battery, the rail de-pressurized with a screwdriver and a mechanics rag as a "catch", and -- using more force than I expected (the heat problem I imagine) -- the rail with injectors was pulled loose after some v-e-r-y carefully applied force. Sort of wiggled it out. The retaining clip on the upper end of the injector was pried off.

I installed the new piece after lubing with some petro jelly on rings and a bit in rail. Wiped excess. All went back together fairly easily.

No leaks were observed at startup -- super smooth idle -- and after a long hard hot run winding it out (tached out twice) on a 14-mile turnaround.

With any luck, no more problem. I'll do a compression test at some point, etc, blah, blah now that I have my tools from home.

Thanks to all for your suggestions and help!!
 
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OMG. There are 2 service bulletins related to this. One has a software update for the PCM and the other for insulating the #3 injector (though I think all could use it). There is also a recall for a exhaust manifold debris shield. The later models have several issues due to smaller plastic bodied fuel injectors and cast exhaust manifolds both of which mean hot soak problems. Use of either plain Champion or NGK plugs are recommended. It can't hurt to run some kind of decarb cleaner through the engine too.
 
Vehicle has had fuel additive since we bought it. Same as with all our other vehicles.

No hot soak problems, TSB done (I never noticed an improvement or change on either of our 2001 XJ's the past nine years before or after; debris shield is in place). The "heat problem" is lack of airflow out of engine compartment. That has accelerated degradation of everything plastic. Corrected that by trimming hood rear weatherstrip on pass side and shimming hood. Vacuum leak made lean running engine that much hotter.

Stock spark plugs used. I'll try NGK's next time.

What PCM flash? I'm reluctant to change anything that may affect fuel economy (18/19 city, 24+ highway).

As it stands, the correction of one major and a couple of potential minor vacuum leaks took care of the worst of the problem.

Replacement of the #1 injector eliminated the CEL and brought engine performance back to normal.

Now, "normal" might be improved (the usual slight rough idle on a 4.0), so?
 
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What PCM flash? I'm reluctant to change anything that may affect fuel economy (18/19 city, 24+ highway).

Part of a TSB for rough idle after hot restart and misfire codes. There will be a reflash label underhood and/or on the PCM if it's been done before. It basically makes the PCM less sensitive to a hot start misfire preventing codes I believe it was.
 
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