04 Grand Cherokee misfire - JeepForum.com
 1Likes
Reply
 
LinkBack Thread Tools
post #1 of 20 Old 05-20-2020, 02:28 AM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
04 Grand Cherokee misfire

hi,

I have a 2004 Grand Cherokee Laredo. I started to get the error code P0305. I do feel some misfires time to time, however the vehicle runs a little rough from one or two exhaust leaks so I'm not sure how frequent the misfires really are. I don't have a scan tool that has an active counter. One exhaust leak is pretty far down the pipe where the two exhaust pipes join before the muffler

I've tried a bunch of things to fix the error code and have gotten the code to go away on its own twice for approximately a day or two. Each time I've made multiple changes so I can't pinpoint anything.

Anyway, here's a short list of things done:
6 spark plugs changed
Coil pack inspected and checked with multimeter and spark tester, appears fine
Fuel injectors checked with multimeter while cold and hot engine, no problems (#5 and #3 injector switched as well which did not help)

One day I cleaned out a bunch of debris in the air box and bought a new coil rail. This removed the light for a couple days, but then came back.

The other day I changed the air filter, cleaned out the throttle body, and cleaned out the idle air controller. I cleaned out the terminals on the 3 wiring connected to the throttle body. I also swapped a few of the spark plugs around including #5. This removed the check engine light for a day.

It should be noted the new plugs are already pretty dirty with a black/gray soot look. Also, previously the trim on the vehicle showed it was running rich, but more recently it looked more even. This leads me to believe a bit too much fuel is getting into the engine than needed.

Right now from my research, I think either the o2 sensors, map, or fuel pump/regulator may be bad causing too much fuel to get in. My main question is whether I sound like I am on the right track or not. I'm not very experienced, and if you know something I'm missing please advise. I'm in the process of buying some equipment to test the aforementioned possible problem causes. Thank you for your time and help!

JRowan8 is offline  
Sponsored Links
Advertisement
 
post #2 of 20 Old 05-20-2020, 03:20 AM
Waterluvr
Registered User
 
Waterluvr's Avatar
2004 WJ 
 
Join Date: Apr 2018
Location: South Bend, IN
Posts: 577
Garage
Shorts in the fuel injector driver wires are a problem on the I6's, when that happens it mimicks the signal supplied to the circuit from the pcm.

If you take the white plug off at the pcm you can test the driver wire on any suspect injector by probing the driver side of the two wire connector. All the injectors are wired hot off the ASD relay supplied by a green wire, and controlled by a different color at each injector.

For a 2004, #5 FI driver color is solid gray. Once the pcm end is unplugged, take the connector loose at the fuel injector ground the test lead on a DVOM set it to read Ω and probe the driver circuit.

If you get a continuity reading, there's a short to ground in the harness and your injector never shuts off.
Waterluvr is offline  
post #3 of 20 Old 05-20-2020, 05:36 AM
jtec
Registered User
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 10,457
Quote:
Originally Posted by JRowan8 View Post
hi,



It should be noted the new plugs are already pretty dirty with a black/gray soot look. Also, previously the trim on the vehicle showed it was running rich, but more recently it looked more even. This leads me to believe a bit too much fuel is getting into the engine than needed.

will your scanner show live data?
maybe take a look at - ECT, o2 sensor Voltages, Fuel trims, long and short.

did you look at pending and freeze frame?
Do not clear code as soon as CEL comes on lets see if another code sets

The airbag light is not on steady?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
 
post #4 of 20 Old 05-20-2020, 09:57 AM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
I found some time and will be checking out a few items mentioned. My scanner will do live data and ill double check the fuel trims. The ect seems fine. I only get the one error code, nothing else comes on, no airbag light.
JRowan8 is offline  
post #5 of 20 Old 05-20-2020, 09:56 PM
jtec
Registered User
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 10,457
ect is fine is not an answer - post Deg F.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
post #6 of 20 Old 05-20-2020, 10:13 PM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
Agreed. i had just woken up, definitely not a sufficient answer... I am not a mechanic. I tried to take some scan tool screen shots and freeze frame shots prior to disconnecting the pcm. I have attached the files.

In regard to the driver wires.. i am not an electrician either. I stuck my multimeter probes down in the injectors connections. I did not get any readings from the wires on any of the injector driver wires I tested. I used the beep (continuity?) Test and the omega symbol. With the injector wiring disconnected, I tested the part that powers the injectors and received i believe a 12.4ish consistent reading.
Attached Thumbnails
20200521_000448_1590034005381.jpg   20200521_000322_1590034013529.jpg   20200520_220737_1590034384436.jpg  
JRowan8 is offline  
post #7 of 20 Old 05-20-2020, 10:18 PM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
I should also note I am not sure why the live data and freeze frame sometimes shows different data. For instance, the ect was around 200F when the photos were taken. Also the fuel trim during the live photos showed 0 on 3 of them, but it usually has a value. I believe the scan tool software bugs out a little bit.
JRowan8 is offline  
post #8 of 20 Old 05-20-2020, 11:44 PM
rep-tile
Cash 4 clunkers survivor
 
rep-tile's Avatar
2004 WJ 
 
Join Date: Jul 2013
Location: bakersfield
Posts: 1,624
Quote:
Originally Posted by Waterluvr View Post
Shorts in the fuel injector driver wires are a problem on the I6's, when that happens it mimicks the signal supplied to the circuit from the pcm.

If you take the white plug off at the pcm you can test the driver wire on any suspect injector by probing the driver side of the two wire connector. All the injectors are wired hot off the ASD relay supplied by a green wire, and controlled by a different color at each injector.

For a 2004, #5 FI driver color is solid gray. Once the pcm end is unplugged, take the connector loose at the fuel injector ground the test lead on a DVOM set it to read Ω and probe the driver circuit.

If you get a continuity reading, there's a short to ground in the harness and your injector never shuts off.
^ This. 4.0 WJs have a well documented weakness of wire harness rubbing against the engine stud at the rear of the engine, causing wiring to either melt and short out or simply loose continuity, which many owners experienced including myself. This issue seems to specifically affect the injector wiring.

You know which injector is affected. Unplug injector #5's connector, unplug white PCM connector. Then check for continuity and short to ground for injector driver (the Gray wire) between the two connectors. Continuity should be about .02 ohm for that kind of wire gauge and the given length of wire. Your reading should be very close to that number. Then check for short to ground. You should have zero continuity between any end of the wire and a known ground. The negative of the battery qualifies as a known ground.

All you need is a $20 digital voltmeter of any brand. No live scanner on earth is going to tell you this.
Attached Images
 
Waterluvr likes this.

04 WJ 4.0 - Avital 4103, DB-ALL
91 XJ 4.0 - Avital 4103, Stage-2 aFe intake system, BBK high flow Throttle Body, 703s injectors, Jones Exhaust A3518M-5

2020 RECOUNT
rep-tile is offline  
post #9 of 20 Old 05-21-2020, 07:21 AM
jtec
Registered User
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 10,457
when doing the continuity check - I will shake and wiggle wiring harness* slightly to simulate engine vibration. Often you can feel the soft area in the loom rather than see it and further checking with a mirror confirms it.

I was hoping to see a code p0205 or any injector circuit code that might confirm suspicion.

A thought - you have 12v on the common injector 12v wire, put a noid light into injector connector and check that way to start... the connectors often fail and are available separate.

*as mentioned top of engine, rear where injector harness passes over and disappears down, it rubs thru on the STUDS.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
post #10 of 20 Old 05-21-2020, 08:58 AM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
So far no luck, but I'd like to thank you guys for continued help.

I just checked continuty on the driver wires and it all was good on all wires tested. I got continutiy on each wire, however I had to use different pins to get continuity (as designed..?).

I also did not get any continuity to ground so no problems there.

The wiring shielding is definitely ripped up behind the engine, but I don't see any damage on the wires.. yet. I still have only ever gotten the single cylinder misfire code.

I'm planning on fixing the exhaust leak(s) asap as I know they can throw the o2 sensors off a bit, but I'm thinking something else is in play with just cylinder 5. Like I previously mentioned, all of the spark plugs have gotten covered in soot, but #5 was slightly worse. I'm at a loss right now 😅
JRowan8 is offline  
post #11 of 20 Old 05-21-2020, 11:10 PM
Uniblurb
Web Wheeler
 
Uniblurb's Avatar
2004 WJ 
 
Join Date: Jan 2012
Location: Central
Posts: 10,592
Quote:
Originally Posted by JRowan8 View Post
The wiring shielding is definitely ripped up behind the engine, but I don't see any damage on the wires.. yet. I still have only ever gotten the single cylinder misfire code.
Define "ripped up" and do you mean chewed up? As one who's experienced rodent damage (bushy-tailed rats) many times you won't be able to tell if any wires are damaged/chewed until you open up the harness convoluted plastic tubing and check each wire closely. And I've had wires that barely had any teeth nicks in the plastic coating but the wires are cut in half internally when you bend them back/forth. Also I've seen copper wire corrode with a small nicks in the plastic/rubber sheathing.

I know it's difficult to get to those wires behind the engine but you best check them for damage. Good luck.

2004 4.7L WJ Limited, 96 4.0 ZJ


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Uniblurb is offline  
post #12 of 20 Old 05-21-2020, 11:29 PM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
The black plastic shielding protecting the wires is broken/torn in multiple locations near the engine. The shielding feels very thin/weak and could have been caused by just about anything that would have moved or shook the wiring harness. The parts of the shielding that are broken don't all touch the engine. Its kinda expected with how cheap the plastic shielding is in an engine bay of a vehicle of this age.

That being said, it does not look like an animal has gotten to it. And from my inspection, the wires appear fine. Following the diagnosing tests above, the wiring does not appear to have any problems anyway.
JRowan8 is offline  
post #13 of 20 Old 05-22-2020, 08:02 AM
jtec
Registered User
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 10,457
double check the inj connector..

Then without a P0205 lets take a quick look elsewhere -
any noticeable difference #5 and #4 or #6?
a compression test.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
post #14 of 20 Old 05-22-2020, 01:50 PM Thread Starter
JRowan8
Registered User
 
Join Date: Mar 2020
Posts: 9
Okay ill try to keep it short, but I have found part of the problem.

I double checked all wiring and still did not notice any problems using the multimeter. I pulled all the plugs and for the first time noticed a very small amount of what looked like a wet spot on one or two of the spark plugs ( I think it was plug 3 and/or 4) it was very light and I honestly am not sure if water dripped on them when I pulled them out as it rained on my jeep. The wet spot was only on a tiny corner of the top of the thread. Anyway I took a picture of the plugs to get an expert's opinion of the coloring. You can see the black soot by the threads and grayish white soot on the prong of the plug.. let me know how that looks in your opinion. Just FYI the plugs all look wet due to the camera flash, but all the soot was dry and crumbly.

I proceeded to due a compression test and found the following numbers:
#1 170
#2 175
#3 165
#4 160
#5 105
#6 165

I'm not sure if I messed up the test the first time I did it a few months ago, or if the problem got worse. Thats why I wanted to include all of the information on everything I've done so far as multiple problems may exist. That being said, I don't see any smoke coming out of the exhaust when it runs.

My next step is to stick a bore scope down inside and see if I can see anything noticeable. I'm not sure what I should do after that, but I won't be able to do anything until tomorrow afternoon. Thanks again
Attached Thumbnails
20200522_145220_1590177000653.jpg  
JRowan8 is offline  
post #15 of 20 Old 05-22-2020, 02:30 PM
speednjay
Registered User
 
speednjay's Avatar
 
Join Date: Oct 2015
Location: bakersfield
Posts: 250
Mine had a slight misfire before it ate the valves.
speednjay is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome