Ignition Timing question - Benzworld.org

mjtray · 10-23-2003, 06:58 AM

Looking for some help please.

The car in question is a 1993 E280 M104 engine with 90,000 miles.

I have had an ongoing problem with the engine pinking/knocking due to pre-ignition.

I've run fuel injector cleaner through the system, had the induction system checked for air leaks, fitted cooler spark plugs, run it on high octane fuel (98 ron) and still the engine is pinking/knocking under load.

Head gasket is also fine and the car has had its emmissions checked and they are fine.

So why is my car still pinking/knocking???????

My mechanic mentioned that it may be carbon deposits that have built up in the engine and are glowing red hot, thus causing pre-ignition......is there any way to get rid of the carbon without having to lift the head for a de-coke???

I have also tried retarding the ignition by changing the settings on the rotating dial that sits up by the ECU...it has numbers 1-7 on it, however, none of the manuals I have read say how much it moves the timing by if you change the settings...any ideas?

All help much appreciated.

Cheers

Greg in Oz · 10-23-2003, 06:43 PM

Has it had the engine wiring harness replaced yet? Yours is one of the affected cars and is at the right age and mileage for the harness to be "bio-degrading". I'm not saying that this is definitely the cause of your problem, but it could be. Search this and other forums (eg. MercedesShop) using something like "M104 wiring harness".

mjtray · 10-24-2003, 06:50 AM

Greg,

Yeah, I must admit that the harness had gone through my mind due to the age of the car, however, my mechanic has checked it through and it appears to be OK, especially as there none of the other typical electrical glitches that normally seem to rear their heads when the harness is on the way out.

Grag/Anybody.......any other thoughts??

Cheers

Kiwi_bloke · 10-27-2003, 03:28 PM

Give it a hori tune up :P (Hori Aka Maori are the native ppl of new zealand)

take it out on the open road and give it a good flogging lol

I assure you if there is a buildup of carbon in you engine this will help, made mine run alot better :) The fact was a 50 year old man had mine and he drove lie a 70 year old lady, i mean, its always exciting to see a merc drop down a gear and blow out carbon deposits for half a mile on the open road.

I had the pleasure of looking like a diesel hehe

i take it the timeing on your car is controled by the computer? Im not familiar with the newer models, on the older mercs you could just turn the distribuor to retard the timeing.

BENZDOC · 10-28-2003, 07:31 PM

HERE IN THE STATES, WATER ALWAY'S DOES AN EXCELLENT JOB OF CLEANING. I ALWAYS DO THIS BEFORE TAKING OFF A CYL. HEAD FOR A VALVE JOB/ HEAD GASKET JOB. YOUR MECHANIC IS CORRECT IN STATING THAT THE CARBON IS IGNITING THE MIXTURE "BEFORE IT'S TIME", CAUSING THE PING. WITH THE MOTOR FULLY WARMED UP,TAKE A HOT 1/2 GALLON OR SO OF WATER AND A PIECE OF 1/8 INCH VACUUM HOSE. LOCATE A VACUUM HOSE ON THE INTAKE MANIFOLD AND REMOVE IT. HOLD THE IDLE AT A STEADY 2500 OR SO- AND LET THE ENGINE SLOWLY SUCK IN THE WATER USING YOUR HOSE. THIS PROCESS WILL STEAM CLEAN THE CARBON FROM THE HEAD, VALVES AND CYLINDERS. IT REALLY WORKS .

mjtray · 11-04-2003, 04:05 AM

Benzdoc,

Sorry for not responding........I've been away on vacation.

Just read your recommendation......sounds very scary...is there any danger that it will ruin my Cat or will steam get past the piston rings and into my oil etc etc.

Won't the engine just cut out if you do this????

Cheers

BENZDOC · 11-05-2003, 05:36 PM

I have never had any problems- I have been doing this 4 over 20 years- dont forget you are not pouring in water- its going in in a mist- very similar to water injection. as for the rings, if anything does get by, the heat of the engine will evaporate the moisture through the crankcase vent. do not be afraid..............

LondonThing · 11-07-2003, 04:04 AM

Quote:

I have also tried retarding the ignition by changing the settings on the rotating dial that sits up by the ECU...it has numbers 1-7 on it, however, none of the manuals I have read say how much it moves the timing by if you change the settings...any ideas?

If anyone has any data on what these rotating settings do, I'd love to have it too: my 300TE idles a tad low and a tad rough when waiting in traffic and I was wondering if it was a timing issue. At present the rotating plug/switch is on 'N'. Can anyone document the other settings?

LondonThing · 11-07-2003, 04:16 AM

You have to admit, the idea of a good thrashing has a lot of appeal, though!

I've done the thrash thing on a few cars; certainly, on the 300TE, it put out a BUNCH of smoke at 100mph on the further reaches of the M4, the first time I tried it. I thought I'd lost a piston or something, but after pulling over and going slow for a mile I went back up to speed and the car was fine. I may even try Benzdoc's water flush voodoo cure.

(the other two cars which responded well to the 'Maori strategy' were my C43, which runs brilliantly after 2,500 miles at serious autobahn speeds going down to Munich & back, and an old, old 3.0 v6 Alfa, which took a manic thrash down to the West Country in the pre speed camera days, before it really got better. I wonder whether we actually have the room in the UK to stretch these cars properly so they run right: the C43 went to Munich at 120mph plus, returned 25mpg, and the oil didn't even get dirty...)