A Question for the Injection "Masters" - PeachParts Mercedes-Benz Forum

Diesel911 · #1 08-10-2009, 12:25 AM

Quote:

Originally Posted by katja

Has anyone referenced here all the possible causes of "nailing"? From what I understand, that annoying sound could be caused by (don't quote me, I'm observing, but don't really know):
-injector nozzles with poor spray pattern (dirty or worn)
-injectors that are sticking/not popping correctly
-air leak (where? supply lines?)
-bad fuel
-pump timing (too advanced? too retarded? I don't know)
-weak injection pump (?)
-excess carbon buildup in pre-chambers (?)

I've been trying to figure out how to tackle a periodic, random nailing I'm hearing....it happens most often under light throttle...goes away under heavy throttle, and not present at warm idle. Somedays it's really bad, other days, barely at all. Diesel purge didn't help, so I'm thinking it's time to replace the injector nozzles, but now I'm wondering if that's REALLY the problem (probably won't hurt though).

This is what I think:
I have not understood why yet but apparently some nailing can be caused by too advanced or too retarded IP timing. The Nailing/Knocking sound has to do with too much of the Fuel bruning at the wrong time and or place in the Pre-Combustion chamber.
Burning and the wrong time and place includes most of what you said.

You also left out low/bad compression.

Weak Injection Pump- I am not sure what you mean by this. Worn or abused IPs have erattic fuel delivery and deliver less fuel. I am speaking of the high pressure fuel that goes to the Injectors.

This can be caused by worn Elements/Plungers and Barrels (scratches on the parts due to bad fuel or poor filtration or some alternate fuels) or if the Rollers, Tappets, and Camshaft inside of the IP are worn (the makes the internal timing of the IP).

[On other vehicles with Rotary type Fuel Injection Pumps (like VW Rabbits, my Volvo and vehicles with Standyne IPs) the advance mecanism is built into the Fuel Injection Pump and as the pump wears the advance become retarded over time. The advance pistons are also at the bottom of the IP and that is where any water will also settle. If the water sits long enough the advance piston can stick.]

Aparrently on those IPs with O-rings that leak; when they leak it some time causes nailing (from what I have read in the threads).
Quite a few members have reported that after the O-ring changing job they experienced Nailing until they have driven 200 miles or so. The reason for this has yet to be explained.

I am not sure if a weak Fuel Supply pump will cause Nailing or not. I guess with the OP saying it was his filter there could be something but it is not clear to me what it is.

I have not read of the excessive Carbon explination for Nailing. I would be the result of another problem or problems like Oil burning, bad Injector Nozzle, Ball Ping damaged, damaged Pre-chamber, bad fuel and so on.

sasquatchgeoff · #2 08-10-2009, 02:58 AM

When air is in the lines, the spray pattern is disrupted. In my case, I have a rebuilt head (new valve guides, seals, rebuilt injectors) and the bottom end is in good shape. When purged of air, the engine runs like a new one. Slowly, over a period of about 3 or 4 days it would begin to show the signs of air creeping back into the fuel system (nailing, rough starts) but when it runs well, it really runs well, smooth smokeless starts - no nailing whatsoever under any circumstance. That was the real clincher evidence that the problem was air. Even when the car was nailing, I could drive it real hard - 75 or 80 mph on the freeway for a couple of hours always purged it enough to run smooth for a while.

During the head refurbishment, the IP pump sat for about 3 months with the injector lines off. The PO burned B99 for a year, and I used B99 for about 4 months after first acquiring the car. All the fuel lines were 5/16" Gates and were swollen and distorted when I replaced them. The IP poly-connectors to the fuel filter housing had become brittle, but did not seem to be leaking - I replaced them anyway. The IP has no outward sign of fuel leaks. Somehow air was getting in. Many times I pondered the possibility that air was getting by the delivery valve o-rings when the car was off. Possibly negative siphon pressure was slowly pulling air into the pump. However, if that were the case, then the air would be purged after running for a bit. I would be very receptive to any input on this theory.

Air infiltration is a peculiar beast. A ghost with no direct trace to its whereabouts. Whatever I did, the engine is better now - for how long will be the question where all of my (and other's) theories will be tested.

Dionysius · #3 08-10-2009, 09:58 PM

You are doing good work here Sasquat. Keep it up until it reaches a solid conclusion.

It is possible that it takes more than one cause occuring simultaneously to set up a nailing condition such as the intermittent type at low throttle. Revisit your theories with this in mind and see if you get further.

If you would not mind could you please redo the list you started after you get all of the input and try to prioritize it and organize it. You might also add valve adjustment as a potential contributing cause.

This nailing is an insidious condition that can do damage over a long period of time.

Basstrip · #4 08-28-2009, 01:46 AM

Diesel, do you think a leaking IP can losse compretion and may cause unbalance fuel delivering and nailing.

Quote:

Originally Posted by Diesel911

This is what I think:
I have not understood why yet but apparently some nailing can be caused by too advanced or too retarded IP timing. The Nailing/Knocking sound has to do with too much of the Fuel bruning at the wrong time and or place in the Pre-Combustion chamber.
Burning and the wrong time and place includes most of what you said.

You also left out low/bad compression.

Weak Injection Pump- I am not sure what you mean by this. Worn or abused IPs have erattic fuel delivery and deliver less fuel. I am speaking of the high pressure fuel that goes to the Injectors.

This can be caused by worn Elements/Plungers and Barrels (scratches on the parts due to bad fuel or poor filtration or some alternate fuels) or if the Rollers, Tappets, and Camshaft inside of the IP are worn (the makes the internal timing of the IP).

[On other vehicles with Rotary type Fuel Injection Pumps (like VW Rabbits, my Volvo and vehicles with Standyne IPs) the advance mecanism is built into the Fuel Injection Pump and as the pump wears the advance become retarded over time. The advance pistons are also at the bottom of the IP and that is where any water will also settle. If the water sits long enough the advance piston can stick.]

Aparrently on those IPs with O-rings that leak; when they leak it some time causes nailing (from what I have read in the threads).
Quite a few members have reported that after the O-ring changing job they experienced Nailing until they have driven 200 miles or so. The reason for this has yet to be explained.

I am not sure if a weak Fuel Supply pump will cause Nailing or not. I guess with the OP saying it was his filter there could be something but it is not clear to me what it is.

I have not read of the excessive Carbon explination for Nailing. I would be the result of another problem or problems like Oil burning, bad Injector Nozzle, Ball Ping damaged, damaged Pre-chamber, bad fuel and so on.

Diesel911 · #5 08-28-2009, 10:47 PM

Quote:

Originally Posted by Basstrip

Diesel, do you think a leaking IP can losse compretion and may cause unbalance fuel delivering and nailing.

Sorry I did not see your post yester day.

I believe I have read where other members have reported nailing when their Delvery Valve O-rings were seeping on the IP.

And, as other have said when the O-rings were replaced the IP continued to cause nailing for hudereds of miles afterwards.
In one of the threads I speculated that the Delivery Valves (the small valve in the middle) got shifted around and needed time to reseat themselves. But, I do not know for sure.

In the past when I did Fuel Injection work we would somtimes get IPs in that had worn Delivery Valves that needed replacing or relapping of the valve seating area.
However, our customers Mechanics were the ones who did the trouble shooting and removing of the IP (and almost all were from Direct Injection Engines). So, I have no clue if the worn out Delivery Valve issue was causing Nailing or not.

sasquatchgeoff · #6 08-31-2009, 11:02 PM

Well friends and neighbors I wanted to update this thread and get any input that may be slung my way.

Rebuilt lift pump and fuel thermostat today. Also replaced return relief valve. Lift pump and thermo o-ring seals were flattened and almost to the point of crumbling. Reassembled, cranked up and WOW! Major difference in power, idle, and overall running. In order to not jinx this great circumstance, I will withhold any definitive statement of resolution until a cold start tomorrow and 3 days of smooth performance without even an infinitesimal amount of nailing, but for now, it is literally running like a new car - far better than any of my previous post-air-purge "honeymoons."

stay tuned...

sasquatchgeoff · #7 09-06-2009, 12:38 AM

The lift pump and fuel thermostat rebuild produced improved performance, but after a couple of days the rough starting and rough idle came back. The next day the IP got air-bound again and the nailing came back.

I was stumped. I had replaced the fuel hoses, filters, nylon IP to secondary filter connectors, return relief valve, lift pump and fuel thermostat innards, had the timing checked by the local well-reputed indy, checked the tank strainer, blew out the goop in the hard lines from tank to firewall, checked tank vent lines, had the injectors pop-tested twice, and confirmed good fuel - all to no real change in the pattern of rough starting, rough idling, and eventual nailing due to the IP becoming air-bound over a period of 3-4 days after purging.

It was time to do what Mark at Diesel Fuel Injection Service in Portland (the folks who rebuilt my injectors) had suggested from the beginning. Replacing the seals and crush washers in my delivery valve holders was much easier than I had anticipated. I didn't even pull the intake manifold (unlike 617's, 602's and 603's IP pumps sit under the IM) - Mark had kindly loaned me the special socket and with a 3/8 universal, 8" extension, and a breaker bar I was able to get each one off after meticulously cleaning the top of the IP off w/brake cleaner and compressed air. The rubber o-rings were practically rectangular and literally crumbled while I pulled them off the holders. The original copper crush washers were flattened out pretty good, and I surmised that someone not so thorough had been in there and reefed on those holders once upon a time. The springs were a little tricky to get just right on top of the DV so that the holder could come down on it and allow it to fit up into the recess, but I managed quite well - if I do say so myself. This job was WAY easier than I expected, and I was able to feel confident that I had done a good job while I torqued the holders to the FSM specified 35 Nm.

Cranked it up and there was an immediate difference. Drove it on the freeway, got it up to about 85, and pulled back into my driveway with a big grin on my face. No post-o-ring replacement nailing that some have reported. It was almost as if the car could breathe where it had been choking for the weeks post-rebuild. After nearly two months of banging my head against my garage wall, my engine was running the way it was supposed to - and not reverting back to a sub-standard condition due to air infiltration.

SOOO...,
My original questions:

With no apparent fuel leaks, can worn delivery vales/sealing washers & rings be the cause of nailing? If so, how?

The answer to the first one is YES! Now, I have to understand how it happened. Maybe somehow the worn o-rings allowed microscopic amounts of air in as the element/DV receded, which over time collected in the secondary canister?

Thanks to everyone for their input. This has truly been an intriguing and educational process.

- geoff