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1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
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Discussion Starter #1 (Edited)
:confused:Hello out there: I seems to have an issue with burning too much fuel? I've noticed within the last 2-years I've gone from getting an average of about 20mpg to getting around 16mpg? I've noticed a few things and taken a few steps. It seems my tailpipe used to have a dark gray to black soot look to it. Now it looks like I've cleaned out the tailpipe...not much of a "Soot" look at all. Some mechanic told me it look like I may be running a little to rich??? I thought these engines were nun adjustable when it comes to setting rich vs lean? I put in new spark plugs, spark plug wires, 02 sensors and Crank & Cam sensors. I'm still around 16mpg? Is there some setting they need to do with the Computer or something? Or, 'am I expecting too much from a 1999 ML430 with TOP maintenances?:bowdown:
Any help would be greatly appreciated.
Thanks "V"
 

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Outstanding Contributor - Always Remembered, RIP
Zotye Auto 1.5T T600 2016
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52,804 Posts
You may find the air mass meter is bad. Also known as the MAF sensor.
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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Also with what Eric posted as the catalytic converters start to give up efficiency will drop as they create
more back pressure.
Not sure how many miles are on your truck and if they are the original cats.
 

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Outstanding Contributor - Always Remembered, RIP
Zotye Auto 1.5T T600 2016
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52,804 Posts
Also with what Eric posted as the catalytic converters start to give up efficiency will drop as they create
more back pressure.
Not sure how many miles are on your truck and if they are the original cats.
Good point Noodles, both bad cats and bad MAF do not always throw fault codes until they are way out of whack so you have two possibles to look at. The computer has parameters pre set, and I do not think the ECU is a problem, rather something else throwing fuel injection out with bad signals such as maf or cat back pressure.
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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What kind of spark plugs did you put in?

I am assuming you are running it on 91 octane or higher.

The injectors may not be working at peak efficiency. The only additive to help clean them up to use would
be Techron. Do not get the Techron Fuel System Cleaner. Just get the Techron 20oz bottle and
pour it in before a fill up and run entire tank of fuel through it.
 

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1990 190E 2.6,.... 1998 ML320, 2005 ML500SE
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3,103 Posts
The correct Techron bottle is labeled "Techron Concentrate Plus" but it also says "Fuel System Cleaner" at the bottom of the label.
As Noodles pointed out there is another Techron labled "Techron Fuel System Cleaner". I almost bought the wrong stuff a few times.
I buy the 20oz bottles for the ML's and the 12oz bottles for my 190E. Watch for the 2 for 1 sales at Advance or Autozone.
Mike
 

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03 ML350
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250 Posts
The correct Techron bottle is labeled "Techron Concentrate Plus" but it also says "Fuel System Cleaner" at the bottom of the label.
As Noodles pointed out there is another Techron labled "Techron Fuel System Cleaner". I almost bought the wrong stuff a few times.
I buy the 20oz bottles for the ML's and the 12oz bottles for my 190E. Watch for the 2 for 1 sales at Advance or Autozone.
Mike
i used this on my last fill.
this is the first time i'm using fuel additive and i can't say it feels any different.
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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That is made by BASF and sold under the name Keropur. You see it is also on the label. It is not bad
as far additives go, but Techron will clean varnish and carbon up better than Keropur.
 

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1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
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153 Posts
Discussion Starter #9
Hello Eric, Noodles, Mike's ML and Gotca: You'all have been very helpful with my questions. First, my ML have approx. 230K miles on her. I kind of thought my Cat's may be a factor, but didn't want to go to that extreme... off the bat...not cheap! I think my MAF is ok since I put a new one in about 20K miles ago. I'm most definitely going to try the Techron (Techron Concentrate Plus) that Mike's ML recommended. Run it a while and see if there's any difference. Given my milage, how likely is it that my Cats are causing high back pressure? Oh, by the way I installed Mercedes Dealer brand spark plugs, and always run 91 octane or higher. My ML runs very smooth, no misfires...that I can tell, and when I floor it, it responds.
Thank You'all for your reply
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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It is good to know quality OEM or equal parts have been used.

You and I have very similar mileage. I get about 20mpg hwy and 17.7 mixed driving and 16 city mpg.
It used to be a 1 MPG better across the entire range. Mine is due for plugs again. First set was changed
at 126k miles.
I will be doing the plugs and wires in the next few weeks as son as the kids are back in school.
 

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1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
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153 Posts
Discussion Starter #11
It is good to know quality OEM or equal parts have been used.

You and I have very similar mileage. I get about 20mpg hwy and 17.7 mixed driving and 16 city mpg.
It used to be a 1 MPG better across the entire range. Mine is due for plugs again. First set was changed
at 126k miles.
I will be doing the plugs and wires in the next few weeks as son as the kids are back in school.
Yea Noodles, that's about where I was approx. 2-years ago...20 mpg hy. I could sometimes get 21 mpg on long flat open roads not pushing too hard. How dose your tailpipe look? Is it dark or clean? Its good to have someone with the same truck...to make some comparison with. What type of plugs do you use? Have you done any Major work on yours yet? Thanks
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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I use the Bosch 7422 plugs.
The tail pipe is clean, not much soot or carbon at all.
No major work by me. MB picked up the cost of a replacement transmission after a tech at a dealer
said the fluid was fine and he never checked it.
Both cats were replaced about 4 years ago with MB OEM parts at a huge discount from MB. My
VIN did not meet the recall range, but the seams did fail so they charged me about $280 per side.

I did a steering pump, shocks all around twice, ball joints, tie rod ends, rear wheel bearing and have
always been on top of the fluids. Almost forgot, I did the AC condenser and the air blend motor also. It drives very well.
 

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My ml 430 1999 will be running very well in the morning, but once the temperature is at 80 it starts vibration and movement won't be smooth any more. Please can somebody tell me what to do in this kind of situation?
 

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1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
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153 Posts
Discussion Starter #14
My ml 430 1999 will be running very well in the morning, but once the temperature is at 80 it starts vibration and movement won't be smooth any more. Please can somebody tell me what to do in this kind of situation?
Well, your problem sounds close to what was happening to my ML430 about a year ago...except mines would shut down. I had my entire intake system cleaned out...the throttle and other parts in the intake had started to clog up and a couple of rubber tubes replaced. After that clean, no more problems. But mines would run good cold, but after heating up, it would stop at idle...most always.
Hope this may help
 

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92 400se, 01 ml320, 83 280SL, 79 6.9, 72 300sel 3.5, et al
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91 Posts
you might want to check your fuel pressure, if the pressure regulator fails sometimes by getting stuck and causes excessive prssure and hence forces more fuel to the injectors, you would think the o2 sensors would correct it, but ive experienced it. the fuel pressure should nt be mor than 45-55 psi, i think. worth a look
 

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2000 ML430, 2000 C280
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Just as another data point, here is my situation:

2000 ML430 with 135000 miles/217000 km. 15-16 mpg on average. Used to be a little better, but not much better.

The ML has had new Bosch plugs (OEM equivalent), MAF, catalytic converters (dealer recall), frequent new air filters. Also replaced some wires, coils and engine sensors as required. I drive conservatively and the engine seems to run very smoothly, it just uses a lot of fuel.

Our 2000 C280 with 125000 miles continues to get 26 mpg in city driving as always with MUCH less maintenance). I haven't even bothered to change the C280 spark plugs yet and the cats, MAF and wires (and just about everything else) are original. We bought this car brand new.

You can't blame the California fuel. Both vehicles get the same Shell premium gas from the same gas stations. It all comes down to this:

V8 engine + heavy SUV = lousy gas mileage
V8 engine + heavy SUV + old age = even worse gas mileage

Especially with all the questionable parts used in the ML to keep the price down.

DelJ

ps I'll try the injector cleaner fluid mentioned in this thread.




:confused:Hello out there: I seems to have an issue with burning too much fuel? I've noticed within the last 2-years I've gone from getting an average of about 20mpg to getting around 16mpg? I've noticed a few things and taken a few steps. It seems my tailpipe used to have a dark gray to black soot look to it. Now it looks like I've cleaned out the tailpipe...not much of a "Soot" look at all. Some mechanic told me it look like I may be running a little to rich??? I thought these engines were nun adjustable when it comes to setting rich vs lean? I put in new spark plugs, spark plug wires, 02 sensors and Crank & Cam sensors. I'm still around 16mpg? Is there some setting they need to do with the Computer or something? Or, 'am I expecting too much from a 1999 ML430 with TOP maintenances?:bowdown:
Any help would be greatly appreciated.
Thanks "V"
 

·
Registered
1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
Joined
·
153 Posts
Discussion Starter #17
Just as another data point, here is my situation:

2000 ML430 with 135000 miles/217000 km. 15-16 mpg on average. Used to be a little better, but not much better.

The ML has had new Bosch plugs (OEM equivalent), MAF, catalytic converters (dealer recall), frequent new air filters. Also replaced some wires, coils and engine sensors as required. I drive conservatively and the engine seems to run very smoothly, it just uses a lot of fuel.

Our 2000 C280 with 125000 miles continues to get 26 mpg in city driving as always with MUCH less maintenance). I haven't even bothered to change the C280 spark plugs yet and the cats, MAF and wires (and just about everything else) are original. We bought this car brand new.

You can't blame the California fuel. Both vehicles get the same Shell premium gas from the same gas stations. It all comes down to this:

V8 engine + heavy SUV = lousy gas mileage
V8 engine + heavy SUV + old age = even worse gas mileage

Especially with all the questionable parts used in the ML to keep the price down.

DelJ

ps I'll try the injector cleaner fluid mentioned in this thread.
DelJ, Hi,
I like the way you think...at least on this subject...Ha Ha Ha. Yea I realize the truck is in-fact-A-Truck. But I have known others (beside this site), including myself, that have gotten approx 20mpg. Soooo, something must have happened to decrease that milage...or we are in error in our calculations? Anyrate, I'm gonna go through the process of elimination and see what I come up with. Thanks for your input.
 

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1999 Benz ML430, 1997 Benz E320, 2006 Toyota Avalon, 2002 Jag. S-Type (sold), 1985 Benz 380-S
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153 Posts
Discussion Starter #18
you might want to check your fuel pressure, if the pressure regulator fails sometimes by getting stuck and causes excessive prssure and hence forces more fuel to the injectors, you would think the o2 sensors would correct it, but ive experienced it. the fuel pressure should nt be mor than 45-55 psi, i think. worth a look
Hi cronix1, can you tell me where exactly, is the Fuel Pressure Regulator located on the ML430? I think I have an idea, but not sure?
Thanks
 

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2000 ML430
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@delJ
Did you ever try a different brand of gasoline. I was told that I should stay away from Shell gas and only use it if I can't make it to a different station.
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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22,145 Posts
Hi cronix1, can you tell me where exactly, is the Fuel Pressure Regulator located on the ML430? I think I have an idea, but not sure?
Thanks
Remove the engine cover. You will see a rail that wraps around the engine.
On the passenger side there is a plastic cap that looks like a tire valve cap.
The is the fuel pressure test point on the fuel rail. When you remove the cap
you will see a Scrader valve that looks like a Schrader valve in a tire stem.
Screw the fuel pressure gauge on to that and read the pressure at idle.
Let us know what it is.
 
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