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deproson
November 24th, 2017, 14:14
So a little back history to what got me to this point.

I have a high mileage 4.0 with 260,000 miles. The other day I was driving to work and it started to have a slight miss. I continued to drive and then it develop a severe miss and had almost no power and felt as if the throttle would cut in and out. So I pulled over hooked up my OBDII scanned and pulled four codes.

1. P0300 Multiple cylinder misfire
2. P0301 #1 misfire
3. P0306 #6 misfire
4. P0122 Throttle/Pedal position sensor A circuit low input

So I took note of these and erased them and continued to drive to work. As I pulled back onto the highway and as the motor went above 2000 RPM the CEL illuminated so I pulled back over checked what it was again and it was the same as above. At this point I was close enough to work so I limped it along until I made it to work.

Got to where I work hooked up my fuel pressure gauge and have about 48 PSI. Pulled my fuel rail out and pressurized the fuel rail and three injectors were seeping. So I ordered new ones and replaced all six.

I also replaced my spark plugs with OEM spark plugs at that time.

Reset the PCM and drove it home with no issue. The problem seemed to have gone away. Until the next morning I take it to work and not three miles down the road I get the same symptoms as before. I continue to drive to work and do some further troubleshooting.

At this time I start to troubleshoot the coil. I pulled the coil and spark plugs and turned the motor over. All plugs had a nice blue arc and I also checked the spark plug gap. All were in spec.

So the next thing I did was check the harness from the PCM to all sensors that are in the engine bay. The engine harness is pretty crispy but checks out with no problems. PCM voltage to sensors is right where it should be the injectors are pulsing and have the correct voltage. I have a buddy with the same year XJ as mine and borrowed his PCM to see if would go away. I put his PCM in and have the same issue.

Now this is where things get weird. I put everything back together and have a code for the CPS along with all the other DTCs listed above. I DID NOT BUY AN OEM CPS SENSOR, I know this is most likely the culprit. The thing that is weird is that now when you crank it over it seems as if the motor is trying to fire at the wrong time and sounds like it is backfiring in the intake and is fighting itself while trying to start. If you unplug the CPS and or the Cam position sensor it turns over like normal. I replaced the NON OEM CPS with a replacement from the company I bought the last one from with the same symptoms. To me I find it hard to believe that I got to bad sensors. Anything is possible though.

Now I'm waiting on my OEM Crank sensor, Cam position sensor and a TPS sensor to hopefully fix this issue. The only reason I bought a part store crank sensor was to try and get it home. If this OEM one fixes my issues then lesson learned.

If it doesn't fix it my next step is going to be to check the timing chain, I dought this is the issue but if the replacement of the sensors doesn't fix it I'm at a loss as to what the issue is.

Since it has been down while waiting for the parts to come in I have since pulled the engine harness and cleaned it up fixed a few broken connectors and re loomed and pulled apart all the crispy wires. Put it back in the jeep problem is still there.


Has anyone else had these same issues?

Tim_MN
November 25th, 2017, 18:25
Cheap crappy Chinese clone CPS that don't work right ? Yes, that is a very common problem.

Install a genuine Jeep CPS, and solve the TPS trouble code, and it should be fine.

deproson
November 25th, 2017, 18:26
Cheap crappy Chinese clone CPS that don't work right ? Yes, that is a very common problem. Install a genuine Jeep CPS, and solve the TPS trouble code and it should be fine.



I hope so. Iíll have all the parts Monday. Iíll post an update.


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deproson
August 9th, 2018, 20:23
I have been chasing multiple issues for months now and still I am not any closer to solving the issue.

I have a loss of cam or crank sensor code along with ignition coil circuit A B C performance.

My xj will run for about 30 seconds and then stall. When I say it runs I mean it runs at an idle fand fluctuates from about 300 rpm to about 850 rpm and dies after about 30 seconds. I have replaced the cam and crank sensor with Oem parts. That did not resolve the issue. I replaced the coil assembley, that did not fix it. I have continuity tested the whole engine harness and have found no issues with it.

I found a good deal for a engine harness and a known good ecm and I bought those and swapped them out and still no change.

I have also changed the timing chain set due to the higher mileage of my xj (260,000) miles.

I am a diesel mechanic by trade I know that the timing set was done correctly.

I know that the cam and crank are in sync. (Verified with snap on Zeus)

I did however make an observation while I had it connected to the snap on scanner, it would show while KOEO a status window that would say “sync ok” then switch to “not in sync”. I’m not that familiar with Jeeps and how they do things but to me that does not seem correct.

I’m running out of ideas and where to look. I feel like I’m chasing my tail. Any help with this would be greatly appriciated. I love my Jeep but after almost nine months of chasing this issue I’m about to give up and find a different Jeep.

CJR
August 10th, 2018, 05:57
What was the day's temperature when the miss-firing began? If a hot day, it's possible you had vapor-lock in the fuel bar. Are the injector wires hooked up correctly to provide the correct injector firing order?

Best regards,

CJR

deproson
August 10th, 2018, 06:20
What was the day's temperature when the miss-firing began? If a hot day, it's possible you had vapor-lock in the fuel bar. Are the injector wires hooked up correctly to provide the correct injector firing order?

Best regards,

CJR



The temp was 105 but the Jeep was cold. It never runs long enough to get to operating temperature or to closed loop. When it ran before it didnít have the heat some issue.

deproson
August 10th, 2018, 06:33
What was the day's temperature when the miss-firing began? If a hot day, it's possible you had vapor-lock in the fuel bar. Are the injector wires hooked up correctly to provide the correct injector firing order?

Best regards,

CJR

Yes the injectors are correct.

RCP Phx
August 10th, 2018, 07:14
Have you individually checked the wires (point to point) with a megger?

deproson
August 10th, 2018, 07:23
Have you individually checked the wires (point to point) with a megger?

Yes I have continuity tested the whole engine harness. I have no short to grind anywhere in the harness. The harness seems to have checked out. Iíve checked it now multiple times.

I was able to find a used harness that is in good shape and swapped it out and still have the same issue. Also have a spare ecm and that also had no change.

Iím about to lose it on this one.

CJR
August 10th, 2018, 12:05
Deproson,

In my 00XJ 4.0L engine, the intake manifold and hot exhaust headers are right under the fuel rail. Vapor-lock, in the fuel rail, can occur quickly on a hot day and before the coolant temperature reaches normal operating temps. Kits are available for Insulating the fuel rails, wrapping each injector, and/or wrapping the exhaust headers. Likewise, spacers at the hood hinges, to lift the back of the hood up slightly, can increase air flow out of the engine bay and keep the engine bay cooler during operation. Also, there are time-delay relay circuits that can be installed to keep the electric fan running, after shutdown, for about 3 minutes to quickly cool the engine bay down. This also helps to reduce fuel rail vapor-locks caused by heat soaks after shutdowns/quick restarts. A 105F day is a warm day for an engine bay with poor air flow. When I bought my 00XJ, the entire underside of the engine bay had a factory-installed thick plastic sheet which effectively boxed-in the bay. That thick plastic sheet was one of the first things I pulled and chucked.

Best regards,

CJR

deproson
August 10th, 2018, 12:10
Iíd think that might be the problem but the hood is up and the intake is still cold. So at this point Iím not to convinced that itís a heat soak issue. I appreciate the response.


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Heavyopp
August 10th, 2018, 19:06
Have you done a compression test on this thing? -- Is it possible that you have a valve problem that doesn't show till it gets a little warm?

Compression test is cheap and easy -- why not? Do it with a cold engine and then once again right after she acts up -- gonna cost you 30 minutes

My 2000 had a stuck #2 exhaust valve , bent the pushrod -- ran but ran badly -- threw all sorts of unexplainable codes -- I wasted a ton of time and money chasing what I thought was an electrical gremlin -- Just saying...

deproson
August 10th, 2018, 19:08
Iíve done a compression test. 160 across all cylinders. Tool valve cover off checked the over head. Nothing appears to be out of place.


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CJR
August 11th, 2018, 05:26
Years ago, I chased a miss-firing issue on my 88XJ for quite awhile. I thought it might be a slight crack in my intake manifold, but couldn't find it. Then one day, while looking at the intake manifold, my son spotted a very fine crack. Apparently, the PO had carefully applied aluminium epoxy to the crack and blended it in perfectly. Then over time, the heat cracked the epoxy patch and my miss-firing problems started. A new intake manifold solved the problem for me. I suggest you carefully checkout the intake manifold for cracks/leaks.

Best regards,

CJR

Tim_MN
August 11th, 2018, 07:04
I know that the cam and crank are in sync. (Verified with snap on Zeus)


I am not familiar with this tool, does it display waveform like an oscilloscope ?

Have you seen this >> http://jeep.blackonyx.net/pdfs/jcss.pdf /

I have also read a forum thread where the XJ owner had the Dealership set the synchronization correctly with the DRB-III scan tool, but when tightening down the clamp, the crank sensor assembly would physically rotate slightly throwing the synch off again.



... Vapor-lock, in the fuel rail, can occur quickly on a hot day

Heat Soak is a starting issue that clears up in less than 30 seconds. Actual vapor lock seldom, if ever, occurs with fuel injection.

deproson
August 11th, 2018, 08:19
Yes the Zeus is also a scope. I have looked at the waveforms and they appear to be where they should be. Iíll take a look at the link you posted. Thanks.


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CJR
August 11th, 2018, 08:53
Tim MN,

With all due respect. Heat from the exhaust manifold can indeed cause vapor-lock in the fuel rail(i.e. liquid fuel gassing off to form a bubble of gas to block liquid fuel flow and/or flow of a mixture of vapor and liquid to the injectors). Mixtures of vapor+ liquid to ejectors randomly screws-up the fuel delivery to each cylinder. In some cases, some cylinders can randomly run lean because less weight of fuel is being supplied to them in a random fashion. I agree that a typical FI engine can clear vapor blockages quickly. But anytime you have a non-insulated fuel rail positioned over the very hot exhaust headers(i.e. XJs), on a very hot 105F day, vapor-lock/vapor flow is going to cause fuel supply issues. Also, the term "heat-soak" is normally used to define heat-flow into starter motors after shutdown which then cause hard-starting during a quick restart. The "heat-soak" I'm talking about is the heat flow into the fuel-rail to vaporize the liquid fuel.

Any way, we'll have to agree to disagree on this point.

Best regards,

CJR

Tim_MN
August 11th, 2018, 12:12
Heat Soak is the phrase commonly used by XJ Cherokee owners to describe a specific start-up behavior in 2000-01 Cherokees.

My 2000 runs well, as does another 2000 and an 01 in my local Jeep club. All three have a faulty check valve and will loose fuel line pressure on hot days when not running, both on the road and on 4x4 trails, but none have any running issues after starting and clearing the small amount of vaporized fuel in the fuel rail. None of the three set trouble codes either. All three also will idle evenly for long periods of time under the same conditions.

YMMV.