OM642 Will Not Fire After Oil Cooler Seal Replacement - PeachParts Mercedes-Benz Forum

Graplr · #1 03-27-2020, 11:50 AM

Hi everyone,
It's been a long time since I had Mercedes diesel so I've been off the board for awhile. I have a w164 2009 ML320 Bluetec. Knew what i was getting when i bought it but got it at a good price and it is cosmetically in awesome shape.

Anyway, figured house lockdown for COVID would be a good time to do the 20 hour oil cooler seal replacement. Took my time, cleaning everything took the longest. Everything is back together except for air filters and foam on top of injectors as I wanted to check for leaks after it fired.

Replaced fuel filter while I was doing it and didn't fill the filter with diesel as I didnt have any sitting in the garage. Figured it would eventually purge after cycling the key for 20 seconds multiple times. But it just won't fire. Cranks. Have fuel at one injector at least. Still no luck.

Any suggestions?

Graplr · #2 03-27-2020, 01:10 PM

Some more info.

It seems the fuel rail is not filling with fuel. I took the return lines off the injectors and turn the key to on and fuel was pouring out of the return lines. That seems backwards? So it took an injector line off and it seemed like it had no fuel in the line or in the rail. How does the rail get fuel? The high pressure pump? Anyway to troubleshoot the high pressure fuel pump?

Something probably unrelated but possible.. the wire connection for what I assume is the AC compressor broke when I thought it needed to come apart during removal. I can't get it back together. currently. It is the next wire plug on the harness after the HPFP so I guess there is a slight chance it is affecting it.

Vehicle was running perfectly when I parked it for maintenance.

Graplr · #3 03-27-2020, 02:06 PM

Some more troubleshooting...

Low pressure fuel pump works great. Unhooked hose at HPFP inlet and turned key to on. Filled a 12oz bottle in a few seconds. Fuel does not come out of HPFP during this time. I assume this is normal operation. During cranking, fuel does come out of HPFP but volume seems low. Perhaps normal? Maybe I just need to crank more to fill the rails and purge air? I've been charging battery and cranking after it comes back to full voltage for awhile now.

engatwork · #4 03-27-2020, 03:17 PM

Quote:

Maybe I just need to crank more to fill the rails and purge air?

Sounds about right.

Graplr · #5 03-27-2020, 05:50 PM

Quote:

Originally Posted by engatwork

Sounds about right.

Thanks Jim. It's definitely possible. But I've been trying for almost a day now. I get about 2 10 second cranks before it slows down and I charge it. Maybe I should wait longer to fully charge before I attempts start. I burned up a charger I had (was really old, inherited from a barn on my old property) so I stopped at HF to get a new one while I was getting groceries this afternoon.

I didn't fill with coolant yet as I just wanted to get it started quick in case I had to tear back into it. Doubt low/no coolant matters, but maybe?

jay_bob · #6 03-27-2020, 06:11 PM

Hmm

When I did mine, I let it sit with the key on for about 20 seconds to let the LP pump run and fill up the filter.

I then had my wife hit the starter while I watched over everything. It took 3 full auto crank cycles and it hit on the 4th. A little rough at first but it smoothed out quickly.

I took it out for a drive and the first couple times I gave it gas it hesitated slightly (I think it was still passing air) and then everything was normal.

I did not have to crack injector lines or do anything other than what I said above to get it to start.

I would double check you plugged in the cam position sensor. It is on top of the right bank about the mid point. If you don't have this signal you will get no fire on the injectors. It needs this sensor to know where the engine is at in the cycle to properly inject each cylinder at the right time.

engatwork · #7 03-27-2020, 06:20 PM

That is correct, it should not take long to charge hp rail. I did not pick up on fact you've been working with it that long.

Graplr · #8 03-27-2020, 08:28 PM

Thanks guys. I definitely think something is happening which inhibits it from firing. I never unplugged the camshaft sensor. I only took the drivers side fuel rail off. But I double checked the plug just to be sure.

I just put the bottle of diesel from checking the filter inline at the lone coming off the HPFP and hooked a hand pump with container inline on the passenger rear cylinder. I pulled out exactly as much fuel as came in. So the rails must be full.

Any specific fuses to check? I can't find a fuse diagram.

Graplr · #9 03-27-2020, 09:05 PM

I checked fuses using a diagram from the interweb. Pulled and checked l ones labeled fuel pump and tried to look over al others. Found no obvious blown fuses. Relays weren't labeled in the boxes so I have no idea which one is D Fuel Pump relay.

It really is acting like the injectors just aren't opening. Absolutely no attempt to fire or sputter. Just cranks.

pawoSD · #10 03-27-2020, 09:54 PM

Is it cranking at a normal speed? You mentioned only getting two 10 second cranks from the battery before slowing down, should get way more than that from a healthy charged battery, whats the voltage?

Graplr · #11 03-27-2020, 10:51 PM

Quote:

Originally Posted by pawoSD

Is it cranking at a normal speed? You mentioned only getting two 10 second cranks from the battery before slowing down, should get way more than that from a healthy charged battery, whats the voltage?

I ran the battery down and wasn't waiting long enough and the result was the 2 10 second cycles. If I let it charge fully yes it will crank at full speed for at least 20 seconds a couple times. The battery is labelled 11/17 but I know the label doesn't mean it's good. I measured the voltage once after it was worn down and it was 12.2 or something. I have a load tester but it's packed up in storage. We relocated from SoCal to NorCal recently and a lot of stuff is sitting in storage.

It really seems in good enough condition to start the engine. Maybe if more than one thing was going on but I cant imagine it is the battery exclusively.

engatwork · #12 03-28-2020, 07:40 AM

Quote:

Replaced fuel filter while I was doing it and didn't fill the filter with diesel as I didnt have any sitting in the garage.

hmmm, this does not help but my gut tells me something did not get reconnected properly.

pimpernell · #13 03-28-2020, 09:37 AM

Please don't take any offense, but if you replaced the oil filter, are you sure that you put the rubber seals in correctly?

Graplr · #14 03-28-2020, 10:02 AM

Quote:

Originally Posted by pimpernell

Please don't take any offense, but if you replaced the oil filter, are you sure that you put the rubber seals in correctly?

Haven't touched the oil filter yet. Was waiting until after I could check for leaks.

Graplr · #15 03-28-2020, 10:09 AM

I'm going to start today by fixing the only wiring connection that I can find that isn't plugged in. This is what I assume to be the AC compressor. I've retraced the wire harness multiple times and can't find anything wrong other than this connection. It will need to be fixed sometime so may as well start there. Doubt it will help, but who knows at this point. Willing to try almost anything reasonable.

It's definitely not the battery. After letting it sit for a full charge engine spins as it should for long periods of time. Checked the exhaust after this and can't smell any fuel. It really seems like the injectors aren't opening as there is no attempt to start. Just crank.