davidgelb

Hi all,

I have a 2002 Jeep Grand Cherokee (2WD, 4.0L). I was having a problem with intermittent engine stalling with no MIL. Usually it would restart no problem while coasting (shift into neutral and it would fire right back up). One time, as it stalled, I got wild tach needle fluctuation (0-4000rpm) althought the engine was off, so I know that was errant. That time, it was about 20 seconds before it would fire back up...cranked, but no start until I let it sit for a bit.

First, I cleaned throttle body and replaced IAC as it was pretty crusty and not cleaning off very well. Also replaced both (cracked) crankshaft vent hoses.

Re-assembled everything and it continued to stall so I decided to replace the CPS. Real PITA, but followed James Bond's instructions and it went OK. Got everything back together and it seemed to be working fine, no stalls.

One my way home last night on the freeway, the MIL lit up (alternating between steady on and flashing)...codes read P0300 and P0320, but no stalling and no start issues. Engine seemed to be running smoothly.

I reset the MIL which has been off for a while now, but wondering what the issue could be if the light comes back on...could it be a bad CPS (It is a BDW aftermarket sensor), or could it be the Camshaft position sensor?

Any suggestions would be greatly appreciated!

Thank you,
David

dave1123

P0300 is a misfire code and P0320 is no crankshaft reference pulses to PCM. Sounds like the CPS, but it may be in the wiring. Check the plug at the CPS and the connecter at the PCM. It also may be the CPS. This is a Hall-effect switch and mounting distance is important. Also it may be defective or poor quality.

davidgelb

Thank you, Dave.

Would you suggest I try replacing the CPS first again to make sure it isn't a bad sensor? I used an aftermarket sensor - should I try swapping it out with a MOPAR one first?

Just wondering if it is worth re-replacing the sensor (as it is not the easiest thing in the world to do), or check other things first.


Thank you for the advice!!

-David

dave1123

The OEM sensor comes with a paper spacer on the end to set the proper distance from the flexplate. This spacer gets removed as the engine turns. If the distance isn't set right, the sensor won't "feel" the magnetic pulses. This is what I've read, I haven't actually changed one myself yet. I know it's a PIA to get to. On the V8s, I've heard of guys who cut a hole in the floorboard to do it.

You should check your wiring first.

davidgelb

Dave, you were right on...thank you!!!

I pulled the new sensor out and replaced it with another new one (returned the first as I thought it was defective).

After I was done, noticed that the paper spacer was still intact on the first one I installed - I assume that means it was not installed close enough to the flexplate and never sheared off.

I installed this second one without the brass wire guide that was on the original one, as I couldn't get it to sit close enough with it installed. Without it, the sensor fit in perfectly and the check engine light went off. No more stalls or engine lights and it seems to run great!!!

One question - the only thing I notice is that it now idles around 600-700rpm. From what I can tell, that is about right, but it is a touch rougher than if it were at 800-1000rpm. Also, once or twice, I felt the rpm dip and get very rough (like it was going to stall) but it recovered itself and kept on running.

I have already replaced the IAC and cleaned the throttle body - might it just need adjusting?

Thank you again for your help!!

-David

dave1123

If the hoses were old and cracked, you might want to change the CCV. Also, check the MAP sensor hose for cracks. 750 rpm is normal idle speed. Obviously your high idle was caused by vacuum leaks.

IMO, the IAC is working because the engine recovers itself. IDK if the IS an adjustment. I quess I've been very lucky with my WJ because I haven't had any issues with it yet. My 97 ZJ, on the other hand, gave me all sorts of problems. It had been "ridden hard and put away wet" too many times before I was suckered into buying it. It was owned by many soldiers at Fort Drum and sold when each one deployed. I should have known better! The 4.0 never gave me a problem. Everything else did! What can I say? It was pretty and ran good, and the price was right.

davidgelb

Hi Dave,

Just to be sure I am correct, the CCV is the 90 degree valve, correct? I replaced both of them along with the grommets when I replaced the hoses (I broke one removing the hose, and figured if they were both brittle, would be worth doing while I was in there).

I will check the MAP sensor hose as well. If it is cracked, I will replace it.

Anything else I should be looking at?

Thank you so much!!

-David

davidgelb

Oh...and did I need to use RTV or anything when replacing the CCV? Or are they fine without?

Thanks!

dave1123

You sound like you have a handle on it. I would just like to pass on an tip from an old mechanic. If you have a suspected vacuum leak that you just can't find, like an intake manifold leak, you can use what's known as "propane enrichment". Take a small propane torch (don't light it!) and crack the valve open slightly. Play it around hoses and gaskets with the engine running. If the engine surges or speeds up, there's your vacuum leak. If the gas flashes, you have a spark causing it. I was astounded when I first saw this done!

A friend of mine worked at GM's Tonawanda engine plant. He said every engine leaving the plant was tested by using a propane snorkel over the intake to test run the engine.

davidgelb

That is a great idea! I will give that a shot. I guess that will tell me if I need to use RTV on the CCV.

I will do that and check the MAP hose this weekend.

Thanks!

-David

dave1123

If you're talking about using RTV on the grommet, no. The CCV just adds a negative pressure on the crankcase so it pulls in any oil vapors. The valve itself is the metering point and is controlled by intake vacuum. In extreme ring wear cases, the valve will be full of oil. This valve should be changed occasionally but most people don't. I was always under the impression that of it rattled or the engine speed changed with my thumb over it. it was good. Not so. When I worked at Valvoline, my boss convinced me to change mine and my idle was smoother and my fuel mileage improved! Live and learn, right?

Bustedback

The CCV has no moving parts, no parts at all really, it's just a small hole. A controlled vacuum leak really.

dave1123

Okay, Busted! I beg to differ. The CCV has a plunger on springs that controls the "leak" as you call it. Unless the CCV and a PCV valve are different, I can't see how a simple orifice would work. A PCV is designed to meter the flow of air but open wide during periods of high intake vacuum. Now, give us your opinion.

Bustedback

I've never dissected one, but it looks like it's just a small hole to me.