2001 WJ misfire help?
 

Hello:

I'm asking for some second opinions here;


I have a 2001 jeep grand Cherokee 4.0 with 210,000 miles, I have been getting P0306, P0305, P0304, and of course P0300 for the misfires of cylinders 4,5, and 6. It has never thrown any misfire codes for the other cylinders. I wanted to confirm with other jeep owners that this could not be the fated crankshaft position sensor, right? all the threads I have read on the CKP sensor had indicated all cylinders show misfires, but mine are only the rear 3 cylinders that are showing misfires. all the plugs were replaced a few months ago with champions, of course. I performed a compression test; 175psig in all cylinders expect #2 had 165 psig long term fuel trips are close to zero at idle for both oxygen sensors. vacuum at idle is about 16 inHg steady. the CEL will flash at low throttle positions and higher than 3K rpm. full throttle performance is awesome. I have run a can of seafoam, intake cleaner, and some water spray as well. the light will still illuminate at the above conditions. I removed the coil rail and measured resistance of all the coils and they were 15K ohms and the primary windings were 0.9ohms right on target.


by the way, I have no misfire symptoms! the thing runs great! maybe the mpg is a little low (17mpg) but the thing rips right to redline with no codes, but when I let off the gas to about 20% the check engine light will start flashing and will not stop until I shift to get the rpms down or floor it.
weird?


I have come down to two things; valve spring issues or carbon build up. but if it were the valve springs would this thing run great at redline? I thought not but I have reasoned myself into circles here, so I am punting to you experts! help!

Update: I installed new NGK plugs and when I did a propane test with a hose, I found that the short term fuel trims would go negative when I went near the intake manifold gasket. So I replaced that. I tested it for leaks again and found none. Hooray!


Then.....I took it for a drive and the misfire codes appeared again! This time it was for #1 and #6 cylinders. Then I ran it at 3000 rpm and held it until the CEL flashed again, this time #4 was in the list of codes! Should I just buy the coil pack or the crank position sensor?

hey I also noticed something strange; when I have removed my intake boot assembly, I notice that I drain a half cup of water out of it. the crankcase breather hose does show some foam in it but I was thinking that this is from when I did the water spray carbon removal? I drained it multiple times though. I did a compression check and everything is good. Can I have a head leak and have good compression? thanks,

When you have a misfire on both 1 and 6 this screams ignition coil to me since they both fire off the same coil at the same time.

Like I had mentioned on my thread, I have a good and bad ignition coil. Walk me through what you would want me to test on a multimeter on each one and I'll do it for you.

As far as your water issue goes, check out your oil. As soon as I started getting these symptoms I took an oil sample and mine looked like chocolate milk.

Have you changed your O-rings and swapped around your fuel injectors?

I did swap the #3 and#4 injectors and the misfire stayed with#4 so that ruled out the injectors. My oil has no milk in it though. I think it's condensation since my commute is 9 miles. Thanks for your help

These misfire conditions reek of the fated bad ckp/cmp circuit. The ckp is most common to fail with these,followed by the cam sensor. Things you need to check before dumping cash. 1 the distance your ckp has from the flywheel matters critically. If it can move even a wiggle by hand. Then it's moving when you drive and needs tightened. Also follow the wires up from it. Check for damage on the yellow wire. Which is your signal to pcm. Move it back and forth with vehicle running to check for idle speed dump. Same with the wire off of the cam sensor. A lititle short in the signal wire to pcm loop, and it acts like junk. Mostly misfiring at idle 300-1100rpm spikes.. also make sure you are getting 5v signal throughout the whole loop from pcm. This includes cam,ckp,abs,map,iac,and tps. There is another 5v loop for the o2s and temp sense but doesn't effect the idle. Take it from someone who has dumped tons in including map,iac,tps,ckp,cam sens,fuel pump,asd relay new pcm, trips to jeep dealer who still didn't find it just replaced a c sens that I had already done. It was a short in a wire between ckp and cam. How I figured it out was it finally popped a p1391 code. (Intermittent cam sens/ckp) checked to.see if ckp had wiggled loose(it was a little) but no change. So reinspected wires... nothing visible. But when I moved the yellow by the pigtail off the ckp Viola!! 2 bucks worth of wire to fix over $1100 OF HEADACHE. jeeps are extremely intolerant of any type of weak or bad electric signal. And 90% of the crap is linked to each other. Please make sure you do a very thorough electrical inspection. $60 for your own live read obd scanner is worth every penny when it comes to these guys. Not the cheap flasher.type. get one that has live read so you can see what all parts are doing and compare to their specs

Words of wisdom, Brian. Well said. I'll 2nd what you said and throw in the K.I.S.S. principle (Keep It Simple Stupid).

Yes....most people don't realize these sensors operate on a 5 volt signal and good wiring and connections are critical. 12V can jump a gap and function anyway, but 5V, no way. How many times have you picked up a flashlight and it didn't work just because the batteries had oxidation on the contacts? Same deal. I have a 600 lumen LED flashlight with 3 D-cells in it. One day it stopped working and after checking the entire circuitry, I checked the batteries themselves even though they were only a month old. 2 of them showed 1.47 volts, but one only showed 0.32 volts. Brand new Duracells!

When working with solid state electronics, don't assume anything.

Thanks for the help guys. Yes I am slowly beginning to realize it could be the crankshaft position sensor. The transmission was replaced by the previous owner and i think the cps was never readjusted or was bumped during the install. I'm building an oscilloscope to test the cps right now. Much cheaper than a scan tool. I will update with the outcome

Are you also a member of the All About Circuits forum? Building an oscilloscope to trace and tweak Crank Position Sensor function?

That's an ambitious and admirable science fair project. Will it be virtual o'scope on a laptop (like Arduino-based) or a real o'scope. Have you heard of, seen or used Pico Tech (picoscope) - those things are amazing - they're getting better features and more functions via software upgrades every day. Sorry, I digress...

Good luck tweaking it. I wish I had your kind of tinker-time.

I'm still willing to test my old ignition coil if someone will explain how to. However I was only misfiring on the one cylinder the whole time.

Update;
I pulled out my crankshaft position sensor to inspect it and I think I have a non-mopar sensor. The magnetism of the tip is very weak. I ordered a mopar one and should be here soon. The interesting part is that I played around with the gap; at first I pushed it in and tightened it, this resulted in some rubbing noise when I started it up. I then adjusted farther out and when I revved the engine to get the misfire to show up, It didn't!


So I may have fixed it with the slightly larger sensor gap? I guess so? I will install the mopar though, can never be sure about the aftermarket, is there a better way to distinguish the two?

I've been told, although I haven't bought one yet, that the Mopar one that mounts with 2 bolts, comes with a paper wafer on the sensor end to space it from the flywheel. This wafer gets torn off on startup, but it sets the distance properly. The sensor is a Hall-effect switch that senses movement within it's design distance. The one that mounts with only 1 bolt sets it's own distance.

I spoke to a good trans shop and they said they install a new one anytime they install a transmission so it doesn't come back with problems. Sounds like a good practice.

I would replace the CKS first with Mopar as your currently doing.
If it stays I would move on to a new Coil Pack

update;
I replaced the crankshaft position sensor with a mopar sensor ($89 shipped) and I have not experienced a check engine light for misfire yet. I think I fixed it! Before I installed the sensor I noticed that the magnetism of the mopar tip was very strong compared to the one that came out. I suspect the one I removed was aftermarket. Also, I forgot to mention that before all this I also performed the exhaust valve rotation mentioned in the tsb. I wanted to include that for future readers. I know it was strange that the misfire only happened at low engine load and high rpm.......I haven't figured that one out yet. I would expect the crank sensor with a weak magnetic tip to lose granularity at higher rpms regardless of the throttle position, but I suppose I have learned more about my jeep in the process.