View Full Version : T1N Fuel Contamination, 2006 51k MH, what now?

04-16-2019, 04:03 PM
I thought I could tackle this myself, but I need help, here are the facts and history to date, it reads like a book…
1) Over the last 2-3 months I noticed increasing audible humming noise coming from floorboard area under driver seat.
2) A month ago: threw CEL on a grade, went into limp mode. Autel 802MD = P0087 Fuel Rail/System Pressure too Low. I changed the fuel filter, reset the code. Upon hard accel, engine shuts down, Code returns….Humm Me thinks… NOT FILTER. -$50 & 1 hour of enjoyable labor…
3) 3 Weeks ago: Because of the sound under the floorboard, I begin to investigate LP fuel system. I come across the well documented problem of T1N Fuel Line vibrations/floorboard noise due to Fuel Quality Valve at the HP pump… I think I have it nailed, upon touching the lines, one of the them is vibrating wildly! I purchase a new Fuel Quality Valve from europartsSD. A couple days later, I replace and test drive after, but CEL returns, again on hard accel. Nuts! me thinks… NOT FUEL QUALITY VALVE -$230 and 3 Hours of puzzle-solving but enjoyable labor (that bugger’s not easy to get at)… SHAME ON ME FOR THROWING PARTS AT IT!
4) 2 Week Ago: Further research (here) leads me to a proper LP fuel pressure test, that weekend, it takes me about 3 hours to rig up a T before the filer and get a good quality gauge. My LP pressure from the tank is 34-48 PSI (well below the required 48-65 psi). On test drives, when it drops below 40psi, the CEL is thrown… OK, it’s the lift pump or plugging in the LP system… I drain and drop the tank, I pull the pump, I find the inlet grid on the suction tube plugged solid! (see picture) CONTAMINATION, HA!! I think I have it nailed! I clean the little grid, I clean the entire tank, and I put it back together. Upon testing the CEL returns, MH in limp mode, LP fuel pressures still in the 35-45 PSI range. SOB!! -7 hours of messy, upside down, neck and core fatiguing work, MY WIFE WON’T EVEN LET ME IN THE HOUSE BECASE I SMELL LIKE A DISEL REFINERY… Drinking my beer alone, Me thinks, “I like the smell of diesel…Failed Lift Pump? Must be. That “*^(*%!” tank must come back down…”
5) Last week, I drain and drop the tank again, easy this time, 1 hour out to the ground… I remove, blow out and verify the fuel supply line is clear…it is… (another hour), but before buying a new lift pump assembly, I think “What the Hay… lets tear this apart and look inside”. This begins a 3 hour long surgery on the Lift Pump Assembly that was obviously never intended to come apart. I take my time, I enjoy the work. I find an entirely plugged inlet screen on the bottom of a perfectly good pump! (see pict below… I partially cleaned the screen for comparison…) HA HA HA!! I found it! Me thinks!! - I put it all back together, I take a deep breath before turning the key… THIS IS WHERE IT GETS INTERESTING… - 6 hours of lift pump surgery and tank reinstall…
Upon Starting it immediately throws a different CEL, Autel802MD = P0088 Fuel Rail/System Pressure too high.
a) The LP pressure is now 55-60PSI at idle
b) The code is thrown about 5 seconds after starting, when CEL is thrown it immediately goes to LHM.
c) When the code is thrown, LP pressure spikes to 63. Drops back to 55-60 after LHM
d) When code is thrown, FRP builds to 9-10k drops back to 4-5k after LHM.
e) During the first 30 seconds of start, I can reset the code repeatedly, the above pressures will build repeatedly, throw the code and return back down.
f) After the first thirty seconds or so, the code will not return, the engine idles fine, the pressures are stable at 55-60psi LP and 4-5K HP.
g) Why this issue only during the first 30 seconds of start?

Aqua Puttana
04-17-2019, 02:20 AM
First. Good job not giving up. Thanks for all of the information. :thumbup:

g) Why this issue only during the first 30 seconds of start?
There is a 30 second delay upon starting in which the "normal" fuel pressure controls are out of the picture. I don't recall the details, but that should explain your delay. A search should find more info regarding the delay.

My guess is that some of the crud got past the filter and has affected other control components in your fuel system. There are parts in the High Pressure Fuel Pump and fuel rail which wouldn't like the crud. Perhaps the fuel rail pressure sensor is partially plugged?

:cheers: vic

04-17-2019, 02:32 AM
Curious if Biodiesel loosened the crud?

04-17-2019, 02:36 PM
Too late now, but a tip for dropping the tank: Get a motorcycle jack from Harbor Freight for $90. https://www.harborfreight.com/automotive-motorcycle/lifts-stands/1500-lbs-capacity-atvmotorcycle-lift-61632.html

This makes life super-simple. Just raise the lift/jack against the tank, loosen the straps and everything you can get to when in position, then lower partially in order to release the connections at the pump, then lower to the ground and roll it out from under the van.

Installation becomes a snap, too, as the tank remains steadily in position when rolling back under the van and lifting in place. I like to lift it all the way up to ensure its in the right spot, then engage the wheel locks on the jack, lower it a bit to fasten the pump connections, then lift back up and strap in place.

If you're going back in, try this method, and good luck!

04-17-2019, 06:55 PM
Thanks Vic, Im researching how the pressure solenoid at the back of the rail works in the first 30 seconds.
Bob: I never used Bio-diesel, but the debris found is soft and gelatinous, like bio-diesel precipitants... Perhaps breakdown of 20% bio blend...IDK??
DRTDEVL, thanks for the tip, that would have indeed helped!

As far at the issue at hand...the CEL P0088, (high FRP), but only triggered during the first 30 seconds of cold start. I did some more testing...more observations...perhaps they will help.
1) Temperature plays a role, if the engine is hot, I can actually start it, and if I wait 30 seconds before driving, it will not throw the CEL&LHM.
2) On hot starts, if I drive or advance the throttle during the first 30 seconds, it triggers the CEL&LHM.
3) Once the CEL is cleared and after the first 30 seconds, it will not come back, FRPs seem normal, MH drives fine, the issue will only return after restarting.
4) The CEL seems to be triggered by FRP in the mid 9-10k range while at idle in the first 30 seconds of start.
5) Why are my FRPs getting so high during idle in the first 30 seconds?

04-17-2019, 09:28 PM
Have a slow read through the HP Fuel delivery section of the service manual.
The “Fuel Quantity Control Valve” is a HP Fuel Pump component that is inactive during the first 30 seconds after start.
During that period rail pressure is controlled entirely by the “Rail Pressure Relief Solenoid” being held partially closed by the ECM. This dumps the bulk of the fuel pumped into the rail, which releases a lot of heat, so after a time the ECM begins to close the Quantity Control Valve to reduce the amount of fuel entering the HP Fuel Pump, and simultaneously closes the Rail Pressure Relief Valve (or more correctly: increases the signal pulse widths controlling its closure) to maintain the desired pressure at the reduced HP flow rate.

BUT: If the Quantity Control Valve doesn’t close, the pump bores fill with fuel and the rail gets a full shot of HP fuel, overwhelming the (now closed) Relief Solenoid and the pressure overshoots the expected rail pressure for the rpm, FQCV, and Fuel Rail Pressure Relief Solenoid setting.

So my money is on contamination of the Fuel Quantity Control Valve. (FQCV)

It wouldn’t take much of the sludge pictured on your fuel screens to prevent it from closing properly... you may have allowed contamination to enter at some point working on the filter or on the HP Pump?

I would degrease then remove the HP Pump, then remove and back-flush the FQCV with filtered diesel fuel. (actually I might just throw a new one in?) While the HP pump is off, run the LP Pump to flush the LP fuel delivery line with filtered fuel.
Then reassemble, being compulsively paranoid about maintaining system cleanliness.

Edit: Sorry... I misread your symptoms. The overshoot when the engine is rev’ed during the first 30 seconds, and absence of symptoms after 30 seconds suggests a partially clogged Fuel Rail Pressure Relief Solenoid. Once the FQCV kicks in (which would spike the LP line pressure) the solenoid is able to pass enough HP Fuel to control the pressure. A bad solenoid valve would mean replacing the fuel rail, but you may be able to back-flush the valve to remove contaminants?

A wiring fault may also be the root cause, but the goop on your filter screen is compelling evidence of a physical blockage.


ps: There is no ‘Fuel QUALITY Control valve’ - though I’d love to find a supplier for one! The LP pump screens would suggest your fuel supplier may need one too? :cheers:

04-17-2019, 11:03 PM
algae? I have heard this can be a problem with some fuels.

04-17-2019, 11:17 PM
Any prayer that a fairly high level of BG244 might break down the offending bits?

04-17-2019, 11:22 PM
Good point: I used to often see algae blooms in marine fuel... damp, warm, long sit times.
I haven’t seen it in highway diesel in years. A biocide on your next tank can’t hurt?


04-17-2019, 11:55 PM
It may be worthwhile to check the Y diverter on the fuel cooler coils. If there is a bunch of junk in there, the whole HP fuel system may need purged/flushed, and a few parts replaced.

04-17-2019, 11:58 PM
Nautamaran, Thanks for taking the time and effort, your post makes sense. So lets suppose that some sort of obstruction in the solenoid valve is the cause. In keeping with, "first do no harm" how could one clean/flush it without risking damage to other components?
1) take the fuel rail off and attempt to clean? Without the electromags holding down the solenoid, how much pressure is required to open the seat?
2) fuel treatment in tank?
3) higher dose of fuel treatment in LP line after filter? (like rollerbearing is suggesting)
4) How could I attempt to backflush?

A proper functioning fuel quality valve would have prevented all this!!! (HA! HA! :0)

04-18-2019, 01:24 AM
The tank pump flows LP fuel through the rail solenoid valve during pre-start to prime the system, so it doesn’t take much to overcome the relief valve spring. Pulling the connector off the solenoid would guarantee flow at tens of PSI... Certainly not hundreds. At those pressures there is minimal (zero?) flow through the injectors, so a cleaner would keep to the rail.
Get good advice on chemical choice (keep the gunk from your tank to experiment) and ensure it will do no harm.

Removing the rail or flushing in place are both viable options.
A diesel shop can also perform a proper cleaning for you.

Were you able to view the interior of the fuel tank?
The interior is likely to be fouled... paying to have the system cleaned may be cheaper than repeatedly replacing your fuel filter (been there, done that... algae bloom in a 1000 gallon marine tank after seawater came down the tank vent - then swapping Racor filter elements every ten or twenty hours until we could get enough down time to have the tank cleaned. Good times!)

My sympathies... it’s not an easy situation to remedy.


04-19-2019, 03:54 PM
OK, after the suggested slow read through the fuel system and an in-depth search on the fuel rail solenoid operation during the first seconds... I developed my initial cleaning plan which required minimal time and money, here was first the theory, followed by the results;
1) I will have the fuel tank very close to empty, 1-2 gallons
2) I will use SeaFoam cleaner as there was ample literature verifying that even full strength concentrations will not harm engine
3) I will add 40 ounces of Sea Foam directly to the tank
4) I will unplug the fuel rail solenoid so that only spring pressure keeps the solenoid closed, that requires 870 psi. ( 2900psi is what is required to start engine)
5) I will crank the engine for about 10 seconds or so the fuel is pressurized to the rail and is ejected back out the return to the tank. Perhaps a several times
6) The intent is to send the seafoam directly to the rail and flush around the solenoid, possibly cleaning any fouling.

The Results
1) Nothing...with the fuel rail solenoid unplugged, the fuel Lift pump does not operate. The ECM must see no sig from the solenoid (at the rear of the rail) and immediately shuts down the lift pump on LP side. On my LP Gauge, even before cranking and immediately turning on the key, the pressure increases for a 1/2 second and immediately drops to zero. Im assuming no fuel is cycling through the HP pump, rail, or anything. When cranking, the engine does not start with the solenoid disconnected, I'm assuming because no fuel is getting to the rail? So the easy idea of flushing the solenoid without starting can't work the way I'm attempting it.

04-19-2019, 04:33 PM
Sounds like a well considered plan.
Since you only require LP fuel pressure and a spinning engine, you could simply hotwire things?

The fuel pump relay supplies the tank pump, and is located on the side panel of the driver’s seat (next to the starter relay).
You can jumper the relay (term 30 to 87) to energize the pump, then crank the engine with the key.
If the ECM won’t authorize cranking, you can also jumper the starter relay, or (since that power comes from the ignition key being in crank pos’n) inject Bat(+) into the correct terminal to activate the starter without holding the key.
Be aware that Sprinter wiring often feeds power into relay terminal 87 and draws from 30, so check the Starter wiring diagram. Feeding the wrong terminal is safe (it connects back to the key’s crank terminal and the ECU’s start authorization pin), but would be ineffective. 50/50 you get it on the first try...
(Standards are great! Everyone should have their own!!)


04-19-2019, 06:48 PM
Dave, your breadth of knowledge on the subject is impressive, I'm considering your suggestions. In the meantime, I've decided to simply plug the selonid back in and run the MH with seafoam through the rail and engine as suggested by Seafoam. The injectors, sensors, valves etc could prob benefit from the agents. Thanks, big help.

04-19-2019, 07:36 PM
Hah! Thank you... I spent a lot of time in my teens and twenties crawling around dark engine spaces trouble-shooting half-a**ed marine setups (undeserving of being called “systems”).
As poor as the T1N wiring is in some ways (lack of mechanical/corrosion protection, vulnerability to back feeds, exposure to rodents and vermin, etc.) at least we have some reliable documentation. Those yachts were often built back in the ‘50s and ‘60s, perhaps refit in the ‘70s, then had stuff grafted on after that. Throw in salt water, humidity, mildew... it can be ugly.
The rise of the MMNA standards helped tremendously, and new builds are now usually to a high standard, but diving into old equipment to isolate and correct a fault always required a methodical approach or you could chase your tail for days... not for the impatient or the faint of heart.
I’ll return the compliment: You certainly seem to be taking a patient, well-researched approach to your problems. Well done, and happy to offer help! :cheers:


Aqua Puttana
04-19-2019, 08:03 PM
Dave, your breadth of knowledge on the subject is impressive, ...

I’ll return the compliment: You certainly seem to be taking a patient, well-researched approach to your problems. Well done, and happy to offer help! :cheers:



Anyone have a match to light the campfire?


Sorry. Couldn't resist.

The amount of help available here is impressive. I know I'd be working a bunch harder to keep my Sprinters going if it weren't for the information and help gleaned from here.


This is more likely for my campfire.


Back to topic.

:cheers: vic


04-19-2019, 08:06 PM
Were it not for a bunch of bored/desperate engineer types on the internet, we would all be at the mercy of MB dealerships... A terrible thought.

04-19-2019, 08:44 PM
Which reminds me: how do I send $20 out in support of this invaluable collection?


04-20-2019, 04:35 PM
Ha Ha, IDK Dave, Vic is both SMART and FUNNY, my affections are shifting, our bromance is in jeopardy...

So I put 30 miles on the rig in hopes the seafoam mixed with the 2 gals would work miracles on the fuel system (so that organization could become my new infatuation); but no such luck. -$20 and 3 hours of interesting research, the same P0088 CEL persists within the first 5-10 seconds of start. I can afford no further time this weekend.
Here's the next question, I was planning on taking this thing to Sedona for a couple days next weekend; since all indications are pointing to a fouled solenoid seat or ball that manifests problems only in the 18% of initial startup opening and before the fuel quantity valve is in play, (because after such, the MH has no issues regulating rail pressure) is there any foreseeable damage that can occur driving like this? Starting it up, waiting 30 seconds, and clearing the code...
Second question, what exactly is the ECM limp mode doing to modulate FRP back down to 4-5k during the first 30s of startup after FRP has climbed to 10k and triggered the CEL? Is it opening the quantity valve? opening the solenoid further?

04-20-2019, 04:55 PM
I don't see any harm in what you propose.

With regards to the ECMs fuel pressure control, it has a few options. It can disable one of the three pump elements in the HPFP, it can change injector duration, etc. It is probably just opening the rail pressure solenoid a bit more.

The P0088 code appears to be a generic OBDII code. What menu are you using to read the codes? The right path is scan->euro->sprinter->901/902/903

04-21-2019, 04:13 AM
I doubt damage to be likely, but have no data...
I agree with MWD.
The spike in LP Fuel pressure that you observed as the code sets suggests that the fuel flow is interrupted - like a water hammer in plumbing, which suggests that the FQCV is being closed in response to the high rail pressure, and the rail solenoid valve is being opened, but I’m guessing about that. A scope on the leads or a live data stream from the ECM would confirm it (I think the valve duty is visible on the actuator menu?) If the pressure remained uncontrolled the ECM would likely dump open the rail solenoid, close the FQCV, and hault injection, stopping the engine.
(I am not aware of a piston control scheme in the HPFP? I believe it simply pumps whatever fuel is able to enter, which the FQCV modulates)


04-22-2019, 11:50 PM
without all the insight that Nautamaran shares here, but having crawled around lots of bilges...
and having operated peugeot and veedub diesels that encountered shi_ty fuel....
methinks you ought to drop the tank and clean it/ hose it out thoroughly,
since if there's s__t growing in there, there's no way in hell you'll be able to clean it out with biocides
or ANY kind of fuel additives.

it's also why i tend to buy fuel at the same station(s) every time i fill up (costco usually)

04-23-2019, 04:36 AM
(I am not aware of a piston control scheme in the HPFP? I believe it simply pumps whatever fuel is able to enter, which the FQCV modulates)

-daveToday I learned that the OM612 (-2003 models) does use a solenoid to disable one piston in the fuel pump to reduce the amount of HP fuel produced and to reduce fuel heating. The OM647 (2004-2006) uses the fuel quantity control valve for this function, reducing the effective stroke of any pump cylinder attempting to draw in fuel while the fqcv is closed.


04-23-2019, 05:20 AM
Outbound, thanks for reading my post, the initial post was long, apologies, I already dropped my tank twice, cleaned it the first time, and blew out the fuel feed line from the filter to the tank. MWD, I have not looked into the return lines or the Y, and I'm using a autel802MD to read codes and live data. I also replaced the fuel quantity valve for reasons explained.
Dave, your post on water hammer relating closing the FQV firmly supports what I'm seeing in the data as the event happens. You really do have a good mind for this.
My only fear at this point, is a full obstruction of the solenoid valve and fuel only being regulated by the quantity valve after startup and whatever potential issues that might pose. I know my LP system is clean on the supply side.
Thank you all for reading and taking the time to care and respond.
MATES, ILL update when I dig back in, after I sail this thing 1000 miles to sedona, if things continue with the same symptoms, methinks that rail has got to come off and cleaned best mecan....
Appreciative...Chris, Four corners

Aqua Puttana
04-23-2019, 03:48 PM
MATES, ILL update when I dig back in, after I sail this thing 1000 miles to sedona, if things continue with the same symptoms, methinks that rail has got to come off and cleaned best mecan....
Appreciative...Chris, Four corners
A nice long drive.


My question would be whether to try another dose of yum yum juice or leave things as is. Adding a can of BG245 fuel conditioner over long run time might help to loosen things and clean... :thumbup:
or it could loosen things and cause a different problem. :thumbdown:

I'd be tempted to throw a can in and roll the dice. I have no data.

:cheers: vic

04-23-2019, 03:57 PM
I know my LP system is clean on the supply side.

However supply and return are constantly looped so any contamination from the return side will then contaminate the supply side. Just wanna say to make sure you're packing a spare fuel filter for that long drive because it doesn't take a whole lot of gunk to fatally plug a filter, especially with a known issue of contamination possibly containing algae.

Good luck and happy trails.

04-23-2019, 04:08 PM
I was watching my gauges last night...
My FQCV settles in at 41% after warmup then doesn’t move much.
The rail solenoid then varies a LOT, anywhere from 20% to 60% depending on LOD, RPM, and rail pressure (4,500-19,500psi)
Your AutelMD802 can display these too... if your FQCV duty % is a lot higher that supports the theory that your rail solenoid is partially blocked.
Have a good trip - and I too would pack a fuel filter.