adf111

2001 E320
88K miles

When I initially got the car (22K miles ago), I experimented the MPG read on the instrument panel. I noticed that when I reset the reading while driving ~70MPH on the fwy, the initial reading to appear had always been 17.x MPG, that quickly climbed up to 25-28 MPG (At the top, I reached 31.4MPG, @ an average of 71MPH, on a 41 miles trip).

Now, after replacing spark plugs and wires, when I do the same, the initial reading is @ 15.7 MPG, climbing to 22-24 MPG.

Any idea how can it change that much (over 10%)?
Is there something to check or re-adjust?

vettdvr

The only question I would ask is did you use identical plugs and gap on installation? Sometimes plugs are close but not the same. Years ago plug mfg's would advertise you could lose 10% on fuel mileage if your plugs were bad. So in this case they might not be bad but just different. Are you using the same brand of fuel and is it the same. I noticed you mentioned freeway so I assume you are on the west coast. There at times when the blend of gas is changed for air quality and this also can cost you 10% in fuel usage without you knowing it. Part of the "mikey won't notice he will eat anything" from the gas companies. The federal mandate on fuel production has also produced variation in fuels so don't be too quick to jump on the car as the issue. Switch brands of fuel and try again. Best of luck. Jim

adf111

All 12 brand new plugs are Bosch.
California fules....hmm... a reduction in quality and thus MPG in addition to $4.15/gl for 91 (as of this morning in Los Feliz!), I don't know guys.

We probebly can afford it or else, why aren't we all out in the streets?

I'd still say it might be the car, merely for the reason of the first number to show: Used to be over 17 MPG and now it's 15.7.

MBTech21

Did you notice if this changed in a hurry, or over the last 22K? If you are using the same Bosch platinum plugs and they gapped right, then there is nothing that could have changed the mileage. A gradual change in the car's adaptations would impact it.

vettdvr is right on with the fuel too- the companies have been mandated to add more 'non-petroleum' products to the fuels, and it's making a difference. Up here in the cold states, this is almost normal to us- winter to summer fuel switch over is noticable almost instantly with some cars (4-cylinder C-Class and diesels seem to be the most obvious). Suprisingly, for some cars (seems to be hit and miss), regular fuel rather than premium, is the far better fuel for both performance and mileage. I had a engineer try to explain this to me, something about flash-points, etc, but decided I didn't really need to know the whole chemical analysis....

mleskovar

Were they the same Bosch as were taken out? Same part number and electrode type?

adf111

Yap, these were the same Boch Platinum.
The change wasn't gradual, it all happened onces the CATs and wires gone bad. But now, with new CATs, new wires, new K&N air filter, new oil & filter, so what esle should I replace if a new MAF refuses to cooperate (see above or my other thread about MAF Adaptation")?

Vic_E55_2001

15.7 MPG on 320? You got led foot or major problem with your car. No way sparkplugs can affect that much without misfire detected.

MBTech21

Do you have any way to read the adaptation data? That would be my next step.

adf111

Vic_E55_2001 - if you read the 1st message on the thread, you'll notice your question is irrelevant.

I am talking here on the INITIAL read, after RESET, WHILE cruising on the FREEWAY, at ~70 MPH.

It used to start @ 17.3 MPG and now it starts @ 15.7. This signifies ~10% increase in consumption OR(!!!!), could be just the initial read. This is the big question.

The MPG climbes after that to the "normal" consumption. which is @ 28-31 MPG.

MBTech21 - I wish I had a way to be connected while all processes. Purchased the EPC/WIS DVD's on eBay, but was never able to get them running.

MBTech21

The wis DVDs aren't going to help you anyway, if you can't read data via a scan tool. Without reading adaptation data, MAS readings and O2 voltages, we might as well throw stuff at a wall and see what sticks.
Just as a question, have you changed the cluster during this for any other reason? The newer ones calculate differently and it has caused some problems with customers.
When the CATs were replaced, did the O2 sensors get changed too? They can impact fuel mileage a lot- however like I said, with out data stream, this is shooting into the dark.

adf111

MBTech21 - Just as a statement, I'm not a techie. I'm trying to understand processes so that I can avoid getting ripped off by stealerships.

The O2 sensors were not replaced with the CATs, but as you say, it's shot in the dark.

I heard of a wreck yard for new cars only ('00 and up), here in SoCal. I drop there today to see if they have such sensors (and other stuff as well). I guess any E, CLK or S would do; am I right?

MBTech21

Most people on here aren't, and explaining processes is easy, but to blanket the dealers will names like that tends to shut off the help that these forums were designed to address. I can't count the number of times I have seen guys spend hundreds, if not thousands on their car, due to some conception that because we have to charge money in order to cover the costs of our special tools, MB enforced fancy buildings, training, etc,etc, that we are ripping them off. And in your situation, up here at least, based on the info I have, we would charge you $95 to tell you exactly what is up with your mileage. Cost me $125 for 20 minutes at the physical therapist the other day (to help with the aches and pains of being a ripoff artist) , so I wouldn't call it highway robbery.

Seeing as an O2 sensor is a consumable item I would never buy a used one, and the three cars you mentioned are all different chassis, from our smallest to the largest, so I doubt it (although , all O2 sensors are the same, with the exception of the new bandwidth versions, so technically, you could wire in one from a 88 560SL, or a 99 Ford Windstar for that matter).

MBTech21

Most people on here aren't, and explaining processes is easy, but to blanket the dealers with names like that tends to shut off the help that these forums were designed to address. I can't count the number of times I have seen guys spend hundreds, if not thousands on their car, due to some conception that because we have to charge money in order to cover the costs of our special tools, MB enforced fancy buildings, training, etc,etc, that we are ripping them off. And in your situation, up here at least, based on the info I have, we would charge you $95 to tell you exactly what is up with your mileage. Cost me $125 for 20 minutes at the physical therapist the other day (to help with the aches and pains of being a ripoff artist) , so I wouldn't call it highway robbery.

Seeing as an O2 sensor is a consumable item I would never buy a used one, and the three cars you mentioned are all different chassis, from our smallest to the largest, so I doubt it (although , all O2 sensors are the same, with the exception of the new bandwidth versions, so technically, you could wire in one from a 88 560SL, or a 99 Ford Windstar for that matter).

adf111

MBTech21 - I accept your educating explanation and do apologize. Your help on this forum is valuable and I meant no offence.

I do use the dealer from time to time, but mostly would go thorugh and indie to save some bucks.

As to the MPG start point, it seems there's still no other choice but to run the SDS. I visited the dealer this morning on other issues and suggested to run an SDS for $125, while the indie does it for $75.

I decided to run it on the forum, in the attempt to avoid an SDS, that is if somebody had encountered this issue and found a solution.