Saturday 7/30:

Swapped the 3/6 plug wires at the new coil. Started it from cold and let it warm up to temperature. No codes. Slight detectable miss.

While continued idling, sprayed ether under the plenum with a straw on the nozzle. Sprayed both banks from the sides, front, rear, no quick rpm jump so I'm ruling out a vacuum leak.

Put it in drive, barely out the the driveway and P0306 sets and Service Engine Soon light on. Drive to NAPA to order a intake to plenum gasket and bought one new matching plug. Gasket won't be here till Tuesday. My understanding is these gaskets are not supposed to be reused. If I have to take it apart, cylinder 6 will get a new plug (vs Hunters' recommendation to swap plugs between 4 & 6 to rule out a coil issue and possibly move the problem to cylinder 4, but then I would have to take it apart to fix cylinder 4 while knowing without a doubt that the plug was it).

Left Napa, got out of city traffic, rest the codes, and drove for 30 miles or so with speeds ranging 45-75 and no code set, but did get a pending P0431 Warm Up Catalyst Efficiency Below Threshold Bank 2. Continued to drive another 6 miles with stop and go traffic lights, still no set codes only the pending P0431.

Sunday 7/31:

Start up and drive away. Intense rain storm last night vehicle parked outside. Start it up this morning and drive away no speedo and no check engine light. Drive for about 30 minutes (about 25+ miles) no stored codes but a pending P0500. Park for about 1.5 hours then drive for about 45 minutes (about 35 miles) still no stored codes. Restart engine after 15 minutes and service engine soon light comes on and now P0500 is stored. No pending P0431 either.

Slight miss at idle detectable.

Electrical problems....

 

Still have not resolved the P0306, but also have not had a chance to work on it either. Speedo also comes and goes setting a P0500, so there is another short in the wiring somewhere.

Changed the oil and filter from startup at about 400 miles (Shell 5w30 non-synthetic). I say about, since when the speedo quits so does the odometer, so mileage is a bit higher (maybe 150?). I had intended to do this at 250 miles, but did not happen.

Oil on the dipstick was still slightly golden, but getting dark. Frankly, I was surprised at how dark it had gotten at 400+ miles. No unusual smell to the oil. The Dimple magnetic oil drain plug had captured quite a bit of fine metallic fuzz which I'm assuming is the rings from seating. Wiping the drain plug with a rag, the metallic fuzz completely was absorbed by the rag with no debris evident, so the particles were extremely fine. I did not have a cutter to open the oil filter to look for debris, so that was discarded.

There was surprisingly quite a bit of sludge that had settled on the drain plug, very slippery. I was extremely thorough in cleaning the engine, so I'm thinking the sludge is the Lubriplate assembly lube that perhaps does not fully dissolve and go into solution (engine was warm for oil change but not "road hot"). Put on a Napa Gold 7092 oil filter and filled with the same Shell 5w30 oil (non-synthetic) and back on the road.

 

Continuing to drive the Montero and putting on the miles.

Performed 2nd oil change at 1900 miles since the rebuild, and about 1500 miles on the 2nd oil change.

Oil still had an amber tint to it although starting to get black. The magnetic drain plug had a slight amount of sludge on it with material in it. The material could not be discerned and smeared off on a towel and was still not visible. No off smell

Still have the P306 Cylinder 6 misfire. I purchased a remanufactured injector and when time permits, I will pull the plenum, put in a new spark plug for cylinder 6 and the reman injector. I'm thinking about doing a compression check while the plenum is off as well.

Couple of oil drips on the exterior of the lower oil pan which was puzzling so I retorqued the oil pan bolts.

Coolant level has been rock solid with no loss. When I prepped the motor for first fire, I just used water as no freeze concern this summer and the water only has been in place for the past 1900 miles. This weekend, I drained the radiator and siphoned out the overflow bottle and put in coolant. On these engines, draining the radiator does not drain all the coolant (about 50% remains in the block). There are drain plugs on each side of the block which need to be removed so as to drain all the coolant out. However, these plugs are not real accessible with the exhaust manifolds in place. Accordingly, I simply drained what I could, installed pure coolant, ran engine to blend the coolant, allowed to cool, checked, bled, and readjusted.

Overall, quite pleased with this rebuild and its nice to have the vehicle back in the fleet.

 

Tried to address the P306 Cylinder 6 misfire this weekend.

Removed the intake manifold, installed a remanufactured Denso injector, and installed a new spark plug all on cylinder 6. The removed plug had more soot than I would have expected for so few miles (sorry for the blurry cell phone picture). I checked all of the other plugs and #6 was clearly the worst of the bunch.

I was surprised how "loose" the plugs felt when removing them with socket wrench as they all had been properly torqued at installation.

While I had easy access, I performed a compression test. The engine was cold and the test was done by cranking with the key and all plugs installed (crank and cam sensors disconnected as part of manifold removal, so no signals to fire the injectors). I have a Sears/Craftsman compression tester which has a Schrader valve in it so it holds the peak reading from cranking.

1 - 150 psi
2 - 175 psi
3 - 175 psi
4 - 170 psi
5 - 175 psi
6 - 100 psi

The manual specifies 171 psi standard/127 psi minimum with 14 psi max spread with the engine coolant temperature 176 − 203°F and all plugs removed; I had all plugs in and a cold engine maybe 70F.

Clearly cylinder 6 was measured way low and cylinder 1 was low as well. Real pisser given the work I have done on this engine. Interesting that the low cylinders are consecutive in the firing order.

Adding oil to cylinder 6 and repeating the test showed no change, so not ring related. I do not have a leak down tester so was not able to charge the cylinder with compressed air at TDC firing to discern if the loss is intake valves, exhaust valves, or head gasket. Engine has not lost any coolant since rebuild and no leaks on the left bank so I am inclined to think that the head gasket is also not the issue.

With no other choice, I put the engine back together. Fired right up, nice idle, and no code thrown while idling in driveway for 10-15 minutes. Shut it down, cleaned up, then drove it for 1 hour going 50 miles or so on country roads. Shut engine down several times, restarted, and continued. No codes set although a pending P0431: Warm up catalyst Efficiency Below Threshold (bank 2) was shown on the scanner (I have had the P0431 before and I have all new O2 sensors).

Time will tell what is next. Not interested in pulling the head and we will drive it as-is for now.

The reman injector I got from Mike's Carburetor Parts. Perfect match Denso 195500-3300. Promptly shipped, $21 plus $3.50 shipping. Cheapest I could find on the net.
Welcome to Mike's Carburetor Parts - Your Number 1 Carburetor Parts Store

While the intake manifold was off I tightened the valve cover bolts as the right bank had a slight leak by cylinder 5 on the outside of the vee which was dripping on the exhaust manifold.

 

Still driving the the 2002 3.5L Sport and have almost 4k miles on it since the rebuild.

Still has a miss at idle, P0306 Cylinder 6 misfire.

From other posts, I was thinking that perhaps the ignition control module might be the problem, although cylinder 6 is down in compression (many older vehicles at best had 100 psi cranking, so I think it should still run better than it does).

Attached excerpt is the testing procedure for the ICM. The ICM makes or breaks the circuit powering the primary side of the coils. The procedure has you briefly apply 1.5V to certain pins while checking for continuity on other pins. With voltage NOT applied, the procedure says I should not have continuity for the pins which drive the coils.

The pins are very small and I was not able to apply voltage and check for continuity by myself. I did check the pins without application of voltage and was surprised that I have continuity on all coil driver pairs.

Am I reading the procedure wrong?

 

You are reading it correctly - no applied voltage should equal to no continuity between 4-13, 4-12 and 4-11 pins

 

HunterD - thanks for the sanity check. Seems like a simple enough test to perform yet something is not right. My meter is set on resistance to check for continuity as confirmed by touching leads and observing swing of analog meter then separating leads to see infinite resistance and no meter movement.

With no 1.5V battery applied I get the following:

1/4 Coil Check
Negative probe on Pin 13 - I have continuity on Pin 4 yet also on all of the other pins

2/5 Coil Check
Negative probe on Pin 12 - I have continuity on Pin 4 yet also on all of the other pins.

3/6 Coil Check
Negative probe on Pin 11 - I have continuity on Pin 4 yet also on all of the other pins

Have not been able to check it via application of 1.5V power yet, but given that this part of the test is no good, would you bet money the ICM is bad? They are about $100 on the aftermarket. Anyone have any good luck (or bad luck) with aftermarket ICM's?

 

That's puzzling. Not sure if it will help, but I'll throw a meter on my Monty tonight to see if i get different readings.
As far as experience with rebuilt or aftermarket ignition control modules, unfortunately I don't have experience with that.

 

Thanks Hunter - interesting to see how yours tests.

 

Ok, ran the same test on my Montero ('01) - I have continuity on 4-13, 4-12 and 4-11 WITHOUT applying 1.5v to 3-4, 2-4 and 1-4. That doesn't make sense. I'm starting to wonder if we are missing something.

I've found this thread on the interwebs with a similar misfire issue like the one you described:
2002 montero sport: 3.0 v-6 rough idle..misfiring..firing..plug wires
You may want to go through the tests to see if this helps to verify ignition module faliure