'Backfire' issue, any help gratefully received!

[w124fan]

Hi everyone,

I'm coming to you cap in hand for any advice, and help, you could give me, regarding an ongoing issue I have with my '94 S124 E280.

I recently inherited this car from my father, who had owned it for over 10 years.

When it came to me, it had a hideous misfire, which it had been suffering from for months, to my knowledge...

A compression test suggested an issue with the head. I have recently been laid off, and with what the cars current (lack of) worth, I elected to do the work myself (not realising the can of worms I was opening!).

With the head removed, the issue was obvious, a big chunk out of one of the exhaust valves. I had this changed, and the head machined, and stem seals renewed.

With the engine back together, it wouldn't start at all...I think you know what's coming...the loom was a tangle of bare wire, and dust...

I took this off, and using new wire, and Merc's repair kits for the coil leads, spliced in repair sections, put it back, and all seemed good...

However, I seem to have some legacy issues of a very heavy thirst, and a slight hesitation, and backfire, or splutter, on partial throttle, below about 2000 rpm....but fine above that figure. Oh, and gearchanges are a bit too 'jolty'.

I got the codes from the ECU, indicating MAF, coolant sensor, and fuel mix too rich. I changed the MAF, and coolant sensor, but no change...

Could the loom still be behind any of this? Or could it (hopefully) be something that won't cost a grand to replace (I think Mercedes are out of order for not putting their hands up to the fault with these looms, mine was damn right dangerous, I'm surprised it hadn't caused an underbonnet fire!) You guys seem to know about everything that can go wrong with these cars, so I'm hoping you can help, as I want to keep the car on the road, but can't really afford to keep changing parts on spec, which don't fix the issue...(nor can I really go on with 12-20 to the gallon...)

Many thanks

Simon

 

[BlackC55]

I'd have a look at the loom again, check the cam timing and do a compression check just to be sure.

The whole looms are no longer available from MB. You may have to get one made.

 

[BlackC55]

I would check your work back with the loom repair too.

 

[grober]

Exhaust backfire is usually caused by unburnt fuel igniting outside the combustion chamber perhaps indicating one or more of your cylinders isn't firing or as BlackC55 has indicated the cam timing is slightly off. Have a shufty at the plugs to see if you can find the cylinder that's not firing. The M104 engine uses a lost spark system with 3 coils on cylinders 2,4,6 igniting two plugs at a time. 1+6, 2+5, 3+4

 

[johnsco]

These cars don't win any prizes for their fuel efficiency.
You may get some improvement if you can sort your other issues.
I ran an E230 Estate some years ago (W124) and I was always in the petrol station.

 

[aghajaved]

off the topic but i need a little help. i have e220 with m111.960. the compression pressure range according to mercedes is 7.5 to 10 for fuel optimised m111.960 and 10.5 to 14 for m111.960. now i am a little confused which one applies as i could not find any information regarding fuel optimised m111.960 engine. my compression test results show 8.5 bars in all four cylinders

 

[grober]

My "guess" would be that the "fuel optimised" 111.960 engine runs a lower compression ratio to run on lower grade fuel. If that is the case your engine compression test is within the specified value. As a general rule its more important to see equal pressures across the cylinders than the absolute value itself.

 

[aghajaved]

first thank you grober for your reply.
thats the confussion. the compression ratio mentioned is 9.8:1 and there is only one compression ratio for this engine i have seen mentioned everywhere. if there were two ratios then there would be no confussion.