I've got a weird issue with my 2000 ML320 (70K miles) and I'd appreciate any suggestions or advice. I like the truck, but if I can't solve this problem, I may have to sell it.

The problem is that the engine will abruptly and completely lose power when climbing long mountain grades. It is exactly like it is running out of gas - it will be humming along at 75 mph one second and totally and completely lose power the next.

It never completely dies; I always am able to limp along at reduced speed with the engine cutting in and out until reaching the top of the grade, where it will regain power and be fine. The problem is fairly intermittent - I've had long trips over mountain passes where the problem didn't occur, but other trips where it has occurred several times. It never happens driving around town or on level terrain. The amount of fuel in the tank doesn't seem to matter. What brand or grade of fuel I use doesn't either. I get no CEL, temps are fine, the engine runs fine otherwise.

The MB dealer has taken a run at the problem, but since it can't be duplicated in the shop, they're just guessing. I have tried to convince them its the fuel pump since this is problematic area on the truck, but they say it checks out fine. The first two times I had the problem, it was very hot, so I thought high ambient temps were a factor. The dealer thought they could intermittently replicate the problem with high underhood temps as a crank position sensor which they replaced, but the problem has since occurred in winter conditions so this was a red herring.

On my most recent trip (in winter temps), the problem was particularly bad in one stretch. A friend with me suggested that we loosen the fuel cap in case it was a tank venting problem. This solved the problem for the remainder of the 1K-mile trip over numerous mountain passes. I've had the problem go into remission several times so I don't consider this definitive. But a tank venting issue would be consistent with the fact that the problem only occurs after a long climb at high power which would pull a lot of fuel over a long period of time - if the tank wasn't venting well, this could start to pull a vacuum in the tank that would prevent the fuel pump from working properly. Having said this, I've never noticed a "whoosh" when opening the gas cap.

Another interesting item is that with the fuel tank cap loose over thousands of miles, I don't get any kind of CEL. Shouldn't I get a CEL with the tank cap loose? This would suggest some kind of problem in the tank venting system.

Final piece of info consistent with a tank venting problem. With the fuel tank gauge bottomed, the truck used to take about 18.5 gallons to fill when new. Recently, I ran the truck to the absolute bottom of the fuel gauge (I was worried I would run out), but I could only get about 16 gallons into it. Either the gauge calibration has changed dramatically or something has happened to drastically reduce the fuel capacity. Could this be the tank collapsing due to lack of venting?

This is a real puzzler.

- Mark

 

Have the dealer change the fuel pump and fuel filter.....

 

I'd either fix the cap or replace it. I had a cap seal up on my truck (non MB) once, it ran fine, but I noticed the plastic tank was all caved in. It never recovered either, I'm permenently about 3 gallons smaller.

 

Thanks for suggestion, but I'm pretty sure the gas cap is supposed to seal so that vapors stay in the tank and are taken care of by the evap canister. That's what the "clicker" does - torques the cap to a value that seals it. Since no cap seems to help the problem, I doubt it is a bad cap.

- Mark

 

Oic, I guess I missed the part where you said you replaced it. But still, a loose cap solves the problem right? I'd "fix" the cap.
I fixed mine with a one way valve meant for a Holley carb. It allows air in, but not out. Home fixes are a way of life for me.
If the dealer can't figure it out then you need to at least consider it.
So far my local dealers have been nothing but 100% useless. Good at taking money, tho

 

This sounds very much like my ML430 apparent power loss posting (see 31 Jan timeframe). I have heard the fuel pump solution from the dealer and from the forum, but I haven't replaced it... yet (as it has not been a problem recently). On my last long journey I added a bottle fuel injector cleaner to the tank when I topped off. It seemed to do the trick as I had no issues at all that trip, but I'm not convinced. I'm still waiting for it to reoccur.

 

Yes, the problem appears similar.

Since I wrote this, I did some research and discovered a service bulletin called "Installing Supplemental Lines for Large Capacity Fuel Filter with Pressure Regulator" (TSB T-SI-47.10/13 SB 621564 dated April 2001):

http://www.whnet.com/4x4/pix3/ML_fuelfilter_tsb.pdf

According to this TSB, this retrofit should be preformed "at the next service visit" on MB's dime. In fact, unless you do this update, you can't use the replacement fuel filter currently being made. I could find no record of this being done on my car.

I took the car in today to the dealer. I got a different service advisor who immediately volunteered that there was a TSB for the problem and produced the above document. He even said that the retrofit was designed to prevent "fuel delivery problems at high altitude" which is exactly my issue with going over mountain passes. Surprisingly, it took some arguing to get them to do the retrofit - he said they normally do it at the 60K service and since I hadn't used the dealer for service since the 50K warranty period expired, that was the reason they hadn't done it. Which is a bit of a crock since the TSB says "next service visit" and they had the car on two separate occasions already with me complaining about a fuel delivery issue that supposedly this TSB is designed to address.

In any event, we agreed that I'd cover the cost of a new filter since this is a routine maintenance item and they'd cover the cost of the TSB retrofit and they'd check my tank venting system and fix any issues they might uncover. I'd still feel more comfortable if they'd just replace the fuel pump too, but they continue to insist that the pump checks out Okay. This is starting to get to the point where I'm just going to trade the vehicle for a Honda Pilot and be done with it.

In any event, on your ML430, I'd check to see if this TSB has been done and if not, I'd start with getting it done. The intermittent nature of this problem makes diagnosis difficult, but I doubt fuel injection cleaner is the solution - it certainly wasn't for me. Good luck,

- Mark

 

Been there done that almost two years ago..... Thats why I said change the fuel pump and filter..... If they wont change the pump I would pay to have it done at the same time...... Are they the same dealer that said they could not find the problem???? HHMMMM......

 

Sell it! :v

 

Your comments illustrate the issue: Do I invest $700+ of my own money to replace a fuel pump that may or may not need replacing by a dealer that may be borderline incompetent for a SUV I may or may not keep?

I'm surprised MB is digging in their heels on replacing that damn pump - it's been revised umptempt times. They replaced the whole damn transmission at the drop of a hat a year ago, but now I can't get them to replace a known-problem fuel pump that probably costs them $150 or less. I had to wrestle with them just to fit the new fuel filter/regulator.

- Mark

 

Got the car back. The mechanic said the fuel filter was the likely cause - fuel delivery was under spec and fuel pressure was low. They did the TSB with the new fuel filter/regulator. Thereafter, fuel pressure and delivery came up to spec. They also checked the evap and venting systems - nothing unusual. There was a fault in the computer for my leaving the cap loose with no explanation why I didn't get a light on the dash.

I paid $100 for the fuel filter (which was due under normal maintenance) and they covered everything else under goodwill, which is fair (although it seems odd to have to use "goodwill" to finally do a TSB that they missed in multiple service visits and that was specifically designed to address exactly the symptoms I was complaining about 20K miles ago while the car was still under warranty). Still would have liked to get a new fuel pump, but such is life.

The acid test is the next trip across the mountains. When I make that trip, I'm carrying the title to the car, and if it stutters again, the first Nissan, Toyota, or Honda dealer along the road is likely to get some business from me.

- Mark

 

Does the dealer "have" to do a TSB, or is only if you have the problem? Can one insist to have a TSB performed if it has not?

The text of this one reads as if it must be performed on all vehicles within the VIN range. Our ML430 is within the range, but I do not recall them having done the TSB, unless they did it without telling me explicitly. I will ask my service advisor on Monday, when the car is going in.

 

They did mine at the time of the very first 10K service (back in 2001 when my ML was just 8 months old).

They just informed me that it would take them a day longer to perform the service, since MB had notified them to replace the fuel filter/lines on the truck..

 

The TSB is not a recall, so they do not proactively contact the consumer and have them bring it in. But the TSB says that it is "recommended at the next sevice visit". Further, it must be done to use the new fuel filter and MB is discontinuing production of the old fuel filter. So I read this as one of those things that the dealer should take care of the next time they see the car and should do it free if the car is in the warranty period.

My dealer says that they don't typically do the update except at the 60K fuel filter maintenance or when the customer requests it. (Note that 60K is conveniently after the 50K warranty period is up unless you have an extended warranty.) That's why I had to push them - in their minds, my complaining of a fuel delivery issue within the warranty period didn't constitute my requesting that they do the TSB. Which, of course, is a crock and that's why when I pushed back they backed down and did it.

The TSB doesn't say why they made the change, but my service advisor said it was specifically do improve fuel delivery at high loads and high altitudes.

If your car is in warranty, I'd print out a copy of the TSB and simply go in and say that you want it done even if you've had no issues, if for no other reason than you want to be able to use a current production fuel filter. Out of warranty, I'd still push, but I suspect they might say to go fly a kite.

- Mark