SAMM

Guys my Benz is taking so much petrol that I really dont want to drive it until its fixed.
just changed the head gasket, valve guides, head resurfaced and valves reseated. New Bosch injectors. New sparks, leads, dist cap, rotor arm. All Bosch items.
It is doing about 9.8 miles per gallon. US gallons that is. Its doing 12 miles to the UK gallon.
Somebody tell me that this is not right. Even the 560 SEL would do better than this.
This is the third m103 engine I have had. Previous two were 260E but all are 1991 models. The other two would average 19mpg US in city and 24mpg US Combined freeway and city. Mine is a SOHC just like the 260Es I had, and i really dont believe the extra 0.4 liter capacity difference would do this!
I have had the CO level adjusted 3 times at 2 different Mercedes independant garages. I have changed the O2 sensor and the CAT. The car still has a slight hesitation, as if there is too much petrol going into the engine, problem is it is very slight and Im finding it hard to believe this the issue.
Do you guys think that maybe there is a fuel LEAK somewhere on this car? Anyone with some input? I ve spent so much on this car trying to restore it. I bought it as a fixer upper. loads of problems when I got it, but I didnt mind because i thought they would be easily identifiable. Now I really am feeling down and out. The car is a replica of a w124 hammer, all factory fitted AMG things in 1991, black on black. I have had it physically restored too apart from centre caps (cant find them anywhere for AERO I 17 AMGs!). So it looks lovely but its killing my pocket. Im back at university doing post grad work at law school here in London, so I cant work and my money has to last me at least a further 8 months!
I hope you guys have some positive input here, cos im feeling down and out at the moment about this ride. May start cycing to university!
thank you ll in advance...

neanderthal

if you say youve changed your cat and your O2 sensor, and youve had the car smogged, then i can only assume that you have a leak.

the usual suspects, where there is a case of high fuel consumption, are;
*get a tuneup,
*check you dont have dragging brakes, or a faulty transmission/ torque converter
*check for leaks.

failing those, you have to check your emissions, the results can be telling (if youve done the tuneup youve eliminated several possible problems) and thats where you get the O2 sensor/ cat thing, which youve already done.

now is the time to look for leaks.

ps2cho

First get a mechanic to perform a smoke test on it to fully rule off vacuum related leaks.

After that I'd look into the following:
-- Replace fuel pressure regulator
-- Replace fuel distributor (get both used as you will notice a big difference right away. Its highly unlikely you will get a used replacement that will be an exact replication)
-- Testing how much fuel is getting through the system based on MB specs.

SAMM

thanks for the input so far guys...

Very expensive to get a fuel distributor even the regulator is serious cash...

Do you think a fuel distributor being faulty would account for such a drastic fuel consumption increase? You may well be right of course. Even though I just did all this work, especially renewing the valve guides at the machine shop because oil was seeping into the AIR intake of cylinders 4,5 and 6, the car still hesitates AFTER I have had the CO level adjusted at the Mercedes garage. New injectors in there too, and I found cracks in the rubber under the air flow meter and a crack in a rubber hose in tha area too. Of course replaced these parts.
Its not a misfire, more like there is too much fuel entering the combustion chamber and so would this cause the following:
-the car is ever so slightly sluggish on pulling away from a stop
-very noticable hesitation when you look at the engine, but car doesnt really shake at all (except when warming up from cold)

I was thinking there may be a fuel leak along the pipes from the tank to the engine. But I cannot smell gasoline from under the car or inside the car period. Would you guys expect to smell gas if there was a leak along the fuel lines? I must say that a Merc specialist who seems to always be working on the 60s 70 80 90s Mercs told me that the fuel distributor and regulator were most likely to be the faulty items. He said they seem to go all the time in the Mercs with this type of fuel delivery system. Now you have said it too. But I will not buy used things. Ive spent so much money on my car because it means a lot to me, I cant start going cheaper now, especially when I dont know whether the used parts are perfectly functioning or not. They may seem fine like my dist and reg, but in reality faulty...



By the way guys did the headgasket here in my driveway, as long as you pay attention to everything you take off and where you have put it, the job is very easy actually. You dont need an engine hoist, just you and a friend. Head weighs about 80 pounds or so. Be prepared to have to take the head to a machine shop to get your valve guides replaced and head resurfaced, that cost 250 pounds here. Did it at the same machine shop the Mercedes Main Dealer uses, so they know what they are doing.

SAMM

By the way can someone explain what a vacuum smoke test is? How can this relate to the ridiculous fuel consumption increase?

Thank you all...

SAMM

guys I was told that the fuel distributor has these rubber seals that wear out. They probably cost pennies. Why the hell should I hundreds on a reconditioned one just beacuse of these rubbers?? Cant I get these rubber seals from someplace?

Benz260Benz

From what I understand Mercedes fuel distributors are next to impossible to rebuild with any kind of success. they are very intricate and if you don't get everything exactly right, it will not end well. You are way better off getting a used one.

appatula

Try backing the adjustment screw out (CCW) of the EHA valve, that will reduce fuel delivery dramatically.

SAMM

thanks for sharing your thoughts so fsar guys!

APPATULA, which screw is that then? People have told me the EHA valve is where they would look to replace an item. However you are saying just turn a screw? im up for it if it works and saves me money!
Kind regards,

appatula

Read through the following thread and that should point you in the right direction http://www.mercedesshop.com/shopforu...&highlight=EHA

If you need me to clear anything up after you read through that thread I'd be happy to help.

berti_00

hey will doing this help the gass milage? and how do you know when its right? just by hearing it or how?

what should the rpm stay on idel? 5thousand? or higher

SAMM

Hey Appatula!

Very handy thread, particularly the part where the EHA valve operation and purpose are explained. I always wanted to know this and not just be told by Merc Mechanics to just change the EHA!

However, These adjustments seem to be too inaccurate for me so I may actually just buy a new Bosch EHA, for about 150 pounds. Obviously I still have slight hesitation even after having the CO level adjusted so this may be due to the EHA being out of tune. But do you think it could be causing my ridiculous gas consumption too?

Really appreciate all your input,

SAM

appatula

A new EHA will need to be adjusted to factory specs, whereas your current EHA may just need a small tweek, no harm in playing as long as you make sure you remember where the screw seated originally. The EHA is essentially a very accurate solenoid valve from what I believe and adjusts the 2nd chamber fuel flow accordingly via varying current. Your EHA may be so out of wack that it isn't metering fuel flow and is rather pouring fuel into the distributor. This is just a wild guess on my part, I am by no means a certified MB mech just a common tinkerer. Has the car sat for any extended periods of time? I'm thinking a bit of varnish could be sticking the EHA up.

There are many things that could be essentially adding more fuel when I think about it, coolant temp sensor asks the ECU for more fuel when cold, WOT switch takes the o2 sensor out of the circuit and enriches the mixture when you floor the gas pedal. Check resistance readings on your coolant temp sensor and make sure your WOT switch located on the throttle body is functioning as a switch.

SAMM

Appatula, what is a WOT switch?

I bought a brand new Bosch EHA valve (fuel governor) and it has done absolutely nothing. No change, so I now have two perfectly fine EHA valves!

My car has an O2 sensor and a catalytic converter. I read somewhere that this means it is a CLOSED LOOP system. Does anyone know what this is? I am determined to find out what on earth is causing my ridiculous fuel consumption. So I will start with the basics of how it all works first. So anyone know this???

Always appreciated
SAM

SAMM

Also there is this round black rotary switch near the battery area. It has about 6 or 7 selection, one of which is S other is N other is the mercedes symbol and the others just have numbers like 4 5 6. Its green writing. Anyone know what this is supposed to be set to? I messed with this when I first bought the car and I think it may be related.

Furthermore, I bought generic Bosch O2 sensor which I connected up. However, I randomly connected the two balck/white wires up. I havent got a clue which way around it is supposed to go. Is one of these a negative and the other a positive? I may have put them opposite eachother!

Always appreciated
SAM

appatula

From what I have read, closed loop is when the ECU is compensating fuel mixture according to the O2 sensor reading (rich or lean). The only time a open loop exists is when the WOT (wide open throttle) switch is depressed (located on/near the throttle linkages). Therefore when this switch is depressed the O2 sensor is cut out of the mixture metering circuit and thus in a open loop situation. Sometimes this WOT switch fails and causes a permanent open loop scenario, in which the ECU opts for large amounts of fuel thinking that you are at wide open throttle.

Try looking at the throttle linkage with the air filter housing detached and you will see a small proximity switch, when the throttle is fully depressed it should be activating. Test it with an ohm-meter to assure it is not your culprit.

appatula

Not sure as to what this selector is, but I'll make a guess that it could be a selector switch to alter the ignition timing that was only available on euro spec models of the W124. The USA version only has the option to use various resistors to retard or advance ignition. As far as the wiring for your O2, USA spec sports a 3-wire sensor so thats out of my territory once again .

SAMM

Appatula,

some great info you have put up there. I havent got a clue what the Wide Open Throttle switch looks like. You say it is where the accelerator linkage/cable is located? Is the correct name for it Wide OpEn Throttle switch?

I am going to attempt attaching a photo here to show you and any one else who may have an idea the switch/selector

Always appreciated

Ron in SC

This is just a guess bit maybe the fan bearing bracket is shot and it's causing a lot of drag which makes the engine work a lot harder.

appatula

Good pictures SAMM, I now can give you a confident confirmation that the selector knob varies ignition timing as it is located directly on the EZL unit. I may be wrong but I am 95% sure on this. As for this WOT switch, I have tracked down some good information over at mercedesshop.com. The proper name for the WOT switch is the throttle valve switch or the TVS. The switch that I was referring you to is actually the throttle micro switch, this tells the engine when it should be at idle. The TVS is located on the throttle body on the opposite side of the throttle linkage, it is trailed by 3 wires that go into the same connector junction that the idle air control valve plugs into. Please read through this post and it should give you a good idea on where it is and how to test, http://www.mercedesshop.com/shopforu...ght=WOT+switch

I'll try to take some pictures tommorow after work

SAMM

Thanks once again for the info Appatula!
Im actually trying different settings every few days and seeing how the car responds. As in I turn the selector one notch and see what effect that has. I currecntly have it on 'N' I think, car feels sluggish when moving off, like theres too much unburnt fuel or something. I will change it tomorrow and leave it a couple days to see how it reacts!

Always appreciated!
SAM

appatula

SAM, not a problem. I was skimming through a few references on European model W124's and I found just what you need


It is for ignition timing, however, the manual should specify the correct settings via the octane fuel content you are using.

I also snapped a few shots of the Wide Open Throttle switch and electrical contacts in which you should be able to test it easily. The first picture shows me pointing at the connector for the WOT switch, test for continuity (I'm assuming the middle pin is a common point, so test for continuity btw pins 1&2 at wide open throttle and closed throttle and do the same for pins 2&3 and post what you get). The second photo is of the actual switch located on the side of the throttle body.

Peter Diseris

A new fuel distributor will set you back over a thousand pounds. German Spob off reconditioned parts for a fraction of the price. About 400 euros. I ordered one for today 300TE 24. Had the exact same symptoms you’re experiencing. Haven’t received it yet but i’ll let you know if it fixed my issue!