w124 230te Poor Mpg

[Weeble]

My 1990 230te auto has 120000miles and is running great, but I have noticed a big increase in fuel consumption recently. On a 200 mile mostly motorway trip, gentle on the throttle, the car returned 23.1mpg. Usually I get between 29-30 on same trip, with a best of 32.1mpg. With a lot of town work I get somewhere around 26mpg. A short run out into the New Forest (40mph) today and never going over 65mph on the M27 returned 19.04mpg! I have had the car a year, and it has never been this greedy. I know the old girl is never going to be an economy car, but I know it can do much better.

I have noticed the tailpipe has black deposits around the outside of the end, which I would take to indicate the car is running rich. I am confident there are no fuel leaks. The car is a non cat model. The car had bit of a misfire and an erratic idle a while back, this was cured by new HT leads. I have noticed the car does wobble a little at tickover.

Any ideas please? What should be checked first? Any advice gratefully received thanks.

Another unrelated thing, the tappets are quiet on startup from cold, but when the car is hot and been stood, say 10mins, it rattles (sounds like a drumroll!) for a few seconds, until the oil pressure gauge climbs up. Is there a fix for this?

Thanks and over to the experts...!

 

[Will]

If the ignition side of things is okay, it sounds like a fuel related misfire (wobbly idle?)

It might be overfuelling due to a problem with your fuel distributor/metering head or related parts?

Does it feel spluttery at all, or hesitant when it's been left idling?

Have you checked the plugs to give an idea of how it's running - you could let it idle for a short while then take a quick look at each one.

How does it start from cold/warm etc out of interest?

Will

 

[Weeble]

Hi Will,

The car fires up from cold after a second or 2, with no pedal. From warm a little longer, but haven't noticed anything untoward there. The car does seem perhaps hesitant when driving away, but then the pedal has always needed a hefty shove to get things moving. Maybe a little more so at the moment though, as I did think the car seemed to be difficult to pull away smoothly today. Power seemed to be either on or off. I recall my previous 200 had quite a heavy accelerator, put this down to being normal on a 124.

I haven't checked the plugs, as away from home at the moment, but I have noticed black around the exhaust which I don't recall before. Car is going in for the prop coupling doing shortly, so am hoping to get this sorted at the same time. My mechanic is good, but not a Merc specialist, nice to give him some pointers if I can, as (garages)time is money as they say!

Thanks for your suggestions.

 

[Weeble]

Steady run from Hants to Yorks, gentle on the car, no traffic, 22.4mpg....about 10 down on my usual figures, so def have an issue.

 

[scooter]

i had the same problem with my 230te when i first bought it i read through this forum of what mpg should be mine didn't add up £20 was getting me 45miles so i checked it over i checked everything i found out it was my back box it looked brand new but on the join of the box itself the weld/wrap had actually split letting out alot of carbon replace it back to normal i hope it helps also on a previous car my fuel filter had no filter in it it was basically flushed out

 

[Weeble]

Thanks for the suggestion Scooter, will look at that when it stops raining. Never considered the exhaust. will post when I have checked....

 

[Weeble]

Thanks for the suggestion Scooter, will look at that when it stops raining. Never considered the exhaust. will post when I have checked....

 

[Will]

I'd be surprised if a ~ 25% reduction in fuel consumption would be due to a slight exhaust leak on the rear silencer?

My bet is on a fault with the K-jet system. Perhaps a faulty metering head (fuel distributor) or airflow meter.

Worth getting it looked over by a specialist if you're not sure, either an MB expert or Bosch service centre etc.

Will

 

[scooter]

hi will i see you point of a slight exhaust leak i would agree but with my exhaust it was a 8 inch split you would not of notice it or heard it how i found it was the carbon on the inside underneath the car in front of the rear box and the exhaust was brand new 600 miles ago by the previous owner because i found the receipt of the purchase in folder that came with the car

 

[vin230]

Some might argue this is a scattergun approach, but on my recently acquired my 230 CE was running very rich (about 20 mpg or less) I did the following:

replace engine temp sensor for fuel injection
replace theromostat and temp sender/fan sensor (now warms up quicker and stays at just over 80 deg C)
replace O2 sensor

each item gains a few more miles per tank, but most noticeable was the o2 sensor. The old one looked like, as stick of charcoal, and looked like a cheapo ebay one as it had not MB, Bosck or NGK markings anyware, and the wires tisted in place rather than useing the correct connectors.

Each replacement gained a slight improvement in performance and smooth running, but replacing the O2 sensor made the single biggest difference so far.

will keep you posted, but hopfeully will get 300 miles out of a tank rather than 200!

Booked in for a proper tune once I fit the thermo vacuum valve that opens and shuts the vauum going off to the ECU.

I also used Winns injection cleaner, which got me an extra 20 miles from a tank.

My logic - I don't care about diagnosing which of those items was at fault, after 120K miles, and a gap in ther service history and no receipts in that time, I am betting all those items are outside spec and require replacement.

Lucky for my car it has now found an owner willing to look after it properley.

 

[Weeble]

Just a quick update, been ages since my original post. My mechanic replaced the fuel metering unit, and now the car is back up to 28 mpg on a run at 70 mph, and 26 mpg on mixed driving, which is a lot better than the 19mpg I was getting.

Thanks for your replies. The thermostat was replaced about 12 months ago. Didn't realise how faulty the old one was, car never warmed up fully unless in traffic! May investigate further at some point, but our c220d has died, runs for about 20 mins, EDC light comes on and cuts engine!