ISB 5.9 325 HP - Fault Code 325 When driving in Wet Weather

[johnfr]

We have found that recently our rig has became a fair weather coach. Anytime we encounter a wet road we are getting a Warning Light indicating an engine fault. We thought it had been fixed back in April on a trip to Texas. This last week on a trip to Wyoming we hit a thunderstorm and within a few miles I felt the engine miss fire. Within another couple miles we had passed through the storm and it started running normally again. Then about 30 miles later we ran into a major down pour. This time the engine began to miss fire and the Warning light came on.

A little history first. We have a 2007 Monaco Cayman with the ISB 5.9 325 HP engine with about 30K miles on it. On a recent trip as we were rolling through Weatherford, TX, I felt the engine miss fire and stutter as I rolled up to a stop light at the giant round about in the center of town. I looked down to see the check engine light come on. When the stop light turned green I stepped on the accelerator and had almost no power. It was pouring rain and we had been driving in rain all morning. I managed to get through the round about and found an empty parking lot a few blocks further down the road.

Thinking I might have water in the fuel I went back and checked the fuel filter and found no water in the bowl. The engine was shaking violently and miss firing and sounded like it was only running on two cylinders. I ended up calling a mobile mechanic that finally showed up some 1-1/2 hours later. He connected his diagnostic computer and it indicated the cylinders 5 & 6 were miss firing. The computer detected a Fault Code 325. See this link for more info:

ISB/ISBe Series Engines - FAULT CODE 325 - Diesel Engine Troubleshooting

His diagnosis was that we had a wiring harness inside of the valve cover that was damaged. He explained that this harness was held in place with plastic tie wraps that would occasionally break and allow the harness to get into the valve train and get chewed up by the motion of the valves.

I was stunned to learn that there were wires that ran internally inside the valve cover and held in place with tie wraps. (The attached photo shows this harness once the valve cover was removed.) He told us that we could drive it with this problem and it wouldn't damage the engine but we would be low in power. He even told us we "might" be able to make it the 600+ miles back home to Colorado but would not recommend it because we might get stalled in Ten Buck Two. Unwilling to take that risk, I had Him get us scheduled into their repair shop 5 days from the day we had our issue. We limped it to a campground a couple miles from the repair shop and waited out the 5 days.

The day of our appointment to get into the repair shop I drove from the campground to the shop and it ran normal. No check engine light or lack of power. When we got to the repair shop the mechanic connected his computer and it had no current code. It showed a previous 325 code indicating a defective injector and/or injector harness. He pulled the valve cover and found no issue with the harness. He measured the resistance of the injector solenoid and it read normal. Unknown to me the newer diesels have a solenoid valve that opens to spray the fuel into the cylinder. Apparently failure of these wire harnesses is a common failure on the ISB 5.9 engines. There are 3 harnesses. Each one controls 2 injectors. Not wanting to experience this again I told them to replace all 3 harnesses. They had to order in the new harnesses overnight.

The next morning the mechanic replaced all 3 harnesses. He found none of the harnesses damaged except the failing one which had a damaged grommet seal where it passed into the valve galley. I asked him if this damage grommet could of allow rain water to get into the wire harness and cause the issue. (Remember, it ran fine driving to the shop 5 days after the incident, having 5 days to dry out.) Unaware our issue started while driving in a rain storm, he acknowledged that that could very well have been the cause of our problem. He commented that because our engine had never been opened up before, this damaged grommet may have been installed improperly at the factory.

With the new harnesses installed he reinstalled the valve cover with new gaskets and started it up. It ran fine and it threw no codes. We took it for a test drive and it seemed to run as good as new. So some $2800 later, $380 for the parts and $2420 for labor and roadside diagnostics we were on our way to Colorado.

Based on the fact that the internal wire harnesses are brand new I am convinced that the problem involves the wire harness between the ECU and the plugs that plug into the valve cover. I am curious if anyone has ran into this issue and if so what was the fix?

I am fairly convinced the issue is on the connector at the ECU. There are 2 plugs (see second and third photos) on the ECU which are a bear to reach. I managed to get a couple of phone photos of the plugs. There is what appears to be a bolt that goes through the center of the plug. I can't tell if it is an allen socket or a small bolt head. I assume that if I can get this unplugged I could remove the plug, inspect and clean it. Has anyone tried to unplug these plugs and if so how did you do it?

Does anyone have a document that tells what the pin out of these connectors is?

 

Edited Tuesday at 03:25 AM by johnfr

[Ivan K]

Usually the bolts are hex head on the ECMs I had. The Injector leads should be on a 60 pin connector, 10x6 pin configuration, the other should be 10x5. You say there was history for misfire on 5, 6. These are on the same harness pair, possibly flaky mating connector on that harness.

I hate when someone takes advantage of us, it took me an hour to replace the harness on ours. Different engine but it included jake wiring. Harness ~ 100 bucks.

Good luck! 

[PeterSchweizer]

On 7/1/2024 at 9:54 PM, Ivan K said:

Usually the bolts are hex head on the ECMs I had. The Injector leads should be on a 60 pin connector, 10x6 pin configuration, the other should be 10x5. You say there was history for misfire on 5, 6. These are on the same harness pair, possibly flaky mating connector on that harness.

I hate when someone takes advantage of us, it took me an hour to replace the harness on ours. Different engine but it included jake wiring. Harness ~ 100 bucks.

Good luck! 

I had the same issue but with my transmission not shifting past 4th then 3 gear during a wet drive. Removed the I think 5 connector plugs on the trans cleaned them silicon sealed all the wires going into the back of the plugs added di-electric grease to connector/pins. no issues the past 3 years