stuwie911

Hello All,
As stated this is my first post and this problem is killing me.


Vehicle: 2001 Jeep GC Laredo w/ 4.0 I6 automatic


Problems: Runs Rough (Vibrates) at idle IN neutral and park. The vibration is much worse while in gear and idling.
It has low acceleration until it hits around 1500-2K rpm in 1st gear, it struggles to get there.
While driving, if I hit 3K rpm, it will cut out. The engine doesn't die, it almost seems as if the transmission disengages until the RPMs drop below 3K
Popping sound if I slam the gas, doesn't sound like its from the throttle body, but possibly could be.


DTC's: P0353, P0300, P0303, P0304


Things I've checked/replaced:
All sensors on the throttle body (IAC, TPS, MAP, IAT)
Cam position sensor
Crank Position sensor
Coil Rail
Plugs
Vacuum at manifold is 15, with a little fluctuation. (less than 1Hg)
Fuel Pressure is good


I have also cleaned the throttle body and ran seafoam to do a top end clean and ran fuel injector cleaner.


I know the coil rail is good.
Where I would like to start, if someone here can help me, is......How do I test the 4 wire connector that runs from the PCM to the coil rail? And also, could a bad ASD relay cause a primary circuit driver malfunction for the C coil? (P0353)


I'm pretty sure if I can find the cause of P0353, the other codes should clear up.


Thanks in advance!

dave1123

Welcome to CF!

The only thing I can tell you is check the wiring harness connector for the coil rail. The plug has been known to melt and loose connection. The connector has 4 wires, one is power and the other 3 are grounded thru the PCM. There are only 3 coils and they fire 2 plugs at the same time, one spark is wasted on the exhaust stroke. A common problem with the coil rail is a short internally between #1 and #6 cylinders. This causes spark to go places it's not supposed to. It sounds more like a wiring problem to me.

Go to pacificcoastmanuals.com and download the FSM for your vehicle for $7.99+tax. It's the best investment you'll ever make.

stuwie911

Thanks for the reply.
I'll do my best to check the harness, I'm assuming I should see 12 volts to each coil?


Also, Ive been thinking there might be a vacuum leak causing a lean condition. Which may be causing the misfire. Ive checked all the vac lines around the engine, but reading through the forums I noticed there is a vac reservoir by the radiator. Ill be checking that tomorrow as well.

Ill definitely be getting that FSM
Thanks for the input!

dave1123

Actually, on your vehicle the vacuum reservoir is a rectangular box underneath the passenger's front headlight support. I have a picture of the access to the fan relay which I have posted and the reservoir is just in front of the relay. The reservoir holds vacuum for the heater controls and cruise control servo. The supply pipe comes off the manifold by the brake booster. I would think a vacuum leak would result in a high idle, not a rough one. Remember there is no fuel in the intake system until the injectors put it there.

The ASD relay energizes the ignition and injector circuits and the PCM controls them by grounding their supplies as needed. The ASD relay is pulled in by the PCM when it gets a crank sensor signal. The PCM monitors all the sensors and if the data doesn't match parameters needed, it drops out the ASD or sets a code.

I was thinking cam sensor, but your code is for ignition coil driver which tells me the cam sensor is sending a good signal, but the coil isn't firing properly, hence connection between the PCM and coil rail. There is a Youtube video on this problem, just Google "P0353 jeep cherokee". I doubt it's the PCM itself.

In case you haven't noticed, I drive a 2000 myself. 198K miles.

stuwie911

Thanks man,
Ive seen that video before. I just dread chasing down wires but I guess it has to be done.


I found the hose to the vac reservoir was disconnected, after plugging it back in, my selector switch works and my vacuum reading is now steady at 16. (still a little low maybe?)
I also noticed my radiator fan isn't working properly, so ill have to fix that as well.

Ill be checking the wires from the pcm to the coil on sunday. and probably the fan circuit.


Ill let you know what I find

Bustedback

Sounds like a fuel pressure problem to me. What were the readings when you checked it?

stuwie911

Sorry, forgot to state in my first post that the fuel pressure is good. a steady 49 psi.

dave1123

Your 2001 has strictly an electric fan, correct? That fan relay I showed you is a pulse-modulated relay activated by the PCM. On high, it's given a full 12 volts, and on low the supply is pulsed to reduce the speed of the fan. This system proven to be problematic so in 02 was changed to 2 relays and a fan motor with 3 wires.

My fan doesn't run at all until the engine gets to operating temp. Then HIGH cuts in a 210* and drops to low when the temp gets down to 195*, stays running on low until you shut off the engine. If it engine temp gets up above 210* again, it runs on high until it's back down.

You can see where that fan relay doesn't last long being pulsed at millisecond intervals.