560SEC bits replaced to date.

[Mikesmerc]

Still have a hard start/backfire and hesitant acceleration problem, hot and cold.
Today replaced the two fuel pumps and filter
previously replaced the following
New dizzy cap
New rotor
New leads
New plugs, twice.
Idle air valve.
Used a strobe light to check timing and appears to be advanced.
What should I replace next????
Thanks
Mike

 

[talbir]

Hi Mike,

I would have the balance of fuel delivery cheked on a machine, i.e. are all injectors delivering equal supply to the cylinders.

If your mileage is excess of 70k, then it may be that one or two injectors are blocked or even leaky. Which would cause starting problems hot and cold. Leaky injectors would cause loss of fuel pressure leading to hot start problems. Blocked injectors would mean you're not firing on all cylinders, hence a cold start problem.

I think it's a good idea to replace injectors that have seen more than 70k miles.

But have the fuel system components, i.e. distributor and injectors tested on a machine before replacnig anything.


Talbir

 

[piestore]

back fire

Hi

Ive just spent several days checking out a similar problem, it turned out to be that the timing chain had stretched and jumped a tooth on one cam shaft, it ran well considering that the timing was so far out. you would normally expect to hear a noisey timing chain but this engine was silent, the adjuster had burst and went far beyond its normal travel. could be worth checking ( this was on a 119 engine)

 

[Mikesmerc]

Hi Talbir, bought a pressure tester from the states to check fuel pressures but the fittings supplied were too small to fit the main fuel delivery/return pipework(supposed to fit all KE Jetronic systems). All that it would fit was the small fuel delivery pipe to the cold start injector, I think this is the control pressure test. Would this show up a leaky injector?
Finding any capable person for testing these systems over here is impossible, rang one German chap who specialises in german motors but he cant look at it for a couple of weeks. My main dealer told me not to waste my time or money bringing it in its too old he said. Have no faith in them anyway after my brothers C class merc was in there two months just to diagnose a faulty ecu.
Think there is an opening for an Andy Gayle over here.
One other thing I noticed is that when I changed the spark plugs the centre electrode was bright white in colour, does this indicate a lean fuel/air mix or advanced ignition?
Really dont believe its a mechanical timing fault Piestore as it is running reasonably well and this symptom appeared one morning when trying to start. All plugs on both banks are suspect looking.
Could it be the ignition control unit at fault (EZL???)
Thanks for the relplies. the search field is narrowing

 

[talbir]

Mike,

Yes, hooking that upto one of the injector feed lines will do the trick.

Another test for fuel pressure is to wait 20 minutes after turning off engine, then loosen one of the fuel lines on top of the injectors. Just one turn anticlockwise - you should get a small strong spray of fuel leakage as line is loosened due to the fuel pressure. Just like loosening a house water pipe connection whilst mains supply is still on....

(Of course, need to be careful with this test with fuel spray).

If you don't get that strong pressure release, then system is not holding fuel pressure. This could be due to fuel accumulator, fuel pressure regulator, any of the injectors (including cold start injector).

Cold start injector is easy to test - once engine is warm, remove fuell line to cold start injector, remove two 5mm allen bolts holding down injector and lif injector out of manifold. The tip of the injector should be bone dry, as the only time this injector is activated is on a bone cold start up. It's period of activation is also governed by the fuel relays depending on temperature, i.e. it sprays for 3 secs if temp is 5degC, 12 sec for -5degC etc.

If it's not dry on a warm engine, then it's likely leaking, which would also cause a rich running condition.

On the other hand, your plug tps should be black if running rich, but they are white. This does suggest either lean mixture, advanced ignition or incorrect heat range on plugs...which brings me onto the next question. What plugs do you have in there ? The 560's are very sensitive to plugs and plug gap. Only use Bosch W9 DC or W7 DC . No platinum.

 

[piestore]

back fire

Hi

As i said I was surpised how well this car ran with a timing problem(customer had car 3years with this problem and thought it normal) it is worth eliminating for the 1 hour it takes to check, But it could well be many other things DAS should tell you which cylinder is misfireing if this is NO 4 suspect timing swap items from one bank to the other to eliminate but you will need to know which cylinder or bank is giving the problem could be o2 sensor problem if only one bank affected

 

[Mikesmerc]

Excuse my ignorance but what is DAS?., all cylinders have the same plug condition , bright white, have changed a lot of plugs in my time but have never came across this appearance. Will check everything mentioned by everyone this weekend and am gratefull for the help.
Regards
Mike

 

[piestore]

das

Hi

DAS is MB "diagnostic assistance system" Its the software on our pc that allows us to get fault codes and actual value reading, most dealers will run a short test and supply a print out for no charge, when asking for the print ask for the "output protocal print" as this gives details of faults

 

[Mikesmerc]

That time of year again and I have pulled the old 560 out of hiding for the summer. Started last night checking fuel pressures and here is what I found.
With the guage connected to the union for the cold start injector.
At idle-650-700rpm.........95 psi
Endine turned off............49 psi
After 20min off...............46.5 psi
After 40min off...............43 psi
after 60min off...............42 psi.

Went for a drive with guage connected and stayed at 95 psi until I pressed the accelerator quickly, engine hesitated until she kicked down (4500rpm)and pulled like a train, then and only then did the pressure drop to 80 psi for a second. In other words there was no drop in pressure when she hesitated. Returned to 95psi.

Can anyone verify that these figures are healthy to I can eliminate a fuel pressure problem. Is it normal for the pressure to drop off by 7 psi after an hour?

Going removing rocker covers tonight to check engine timing as Piestore suggested.Will also check CS injector and type of plugs.

Thanks to everyone who has helped me so far.

Mike

 

[R129]

An old rule of thumb I've come across is that backfiring from the exhaust is usually caused by ignition problems whilst backfiring through the inlet manifold is usually caused by fuel pressure problems.

As you mentioned the apparently advanced timing and exhaust backfiring I would be inclined to think ignition. One thing worth checking is the ignition module as the 560 is a rare car and the modules run at £1000 to replace from a dealer. My point being that while experimenting with various modules I discovered that you can get a 560 to run reasinably well with a 420 or 500 module. These are much more common and I would'nt put it past some people in the trade to fit them instead of the genuine 560 item.

Just a thought as you seem to be having rather a lot of fun and games with your car.

 

[Mikesmerc]

Thanks R129, good to know about the ignition module. Still not sure if these pressures are healthy. I took off the cam covers tonight and turned the crankshaft with a ratchet and socket. Kept an eye on the timing marks on the camshafts until they aligned with the ones on the towers......err they didnt, looked down at the CS pulley and I had just gone past tdc. Right, went around again clockwise and kept an eye on the CS pulley until it reached TDC, the passenger bank camshaft ligned up perfectly but the drivers side didnt, about 4-5mm short of the mark on the tower. Not convinced that it had jumped a tooth I drew up the relevant diameters of the sprocket and the timing washer on a piece of paper, measured the distance between two of the teeth on the sprocket, marked this distance on the larged circle(sprocket) and drew two lines back to the centre of the circle passing through the timing washer circle and the measurment at the washer was about 4mm. So it seemed that she was after jumping a tooth on one bank.
One thing I noticed while turning the engine over was that the tensioner and associated guide fluctuated alot, seems very weak to what I expected> I understand that oil pressure stiffens this up alot when runnning but I could physically depress the guide/tensioner with just my fingers...normal?
While looking how to get the timing back to normal I caught the chain after the sprocket(nearest the centre of the engine) with two fingers and pulled the chain, the suspect cam flicked into the correct timing position leaving the chain between the two cam sprockets very loose indeed.The tensioner had slackened off.When I rotated the engine again the chain stiffened up.
I assume the tensioner should be fully extended when checking timing, if so my timing is out by one tooth, hense the backfire at start up. What caused it? faulty tensioner?.
If so I must give credit to Piestore, as I really didnt believe this could happen whithout some sort of odd sound or incident.
Sorry for stretching my nights efforts but I have to be sure about this before I go messing with it. If it is out I am getting a new chain and tensioner.
Very grateful for all the help from all and thanks for reading this longwinded post.
Mike

 

[R129]

Just had a look through the KE Jetronic manual and system pressure on this system should be between 6.2 and 6.4 bar which at 14.5 psi to a bar would suggest your fuel pressure is spot on.
After poking around in a number of m117 v8's it seems that quite often the plastic rails that guide the chains are very brittle. After years of use the plastic becomes prone to breakage which due to the multi pin fastening on these parts will go unnoticed on a basic inspection.
When they break it is possible for a piece of plastic to jam between the teeth and chain and cause a jump on the sprocket (if you're lucky).
Mercedes actually supplies specially offset keyways for realigning camshafts due to stretched chains so it would seem that this is considered normal wear for the engine. As far as I am aware they offer no instructions for maintenance on the chain guides although with other engines, the porsche 944 16 valve motor springs to mind there is a great deal of evidence to suggest that these plastic components only have a life of 100,000 to 200,000 miles depending on application. Admittedly 200,000 miles goes beyond the scope of most manufacturers service schedules so its most probably something that they have never looked into. Obviously with a merc v8 these mileages are not that high so I personally view the guides as a service part.
I have spent a reasonable amount of time looking into the problems with plastic guide rails mainly as a consequence of a 5k engine rebuild on a 6 year old porsche I once owned due to a plastic guide failure.
To date I still have'nt found a definitive opinion on when to replace the components as the majority of incidents are blamed on chain breakage which in reality is very rare, mercedes even state that half an inch of stretch or so in a chain is not a problem.
Alternatively it is possible that the person who last worked on the car before you was a pillock!
Good luck and if you need any tech details for the 117.968 motor give me a shout as I have a fair amount of info on them.

 

[Mikesmerc]

Thanks again R129 for your time and info.Have read about these offset keyways on a Haynes manual for my 72 350SL 116engine, wasnt aware it was to correct chain stretch.Half inch of stretch seems alot, about one tooth in fact. I have 145,000 on her now, is there a recommended mileage to change the chain? Will price a new chain and tensioner today. The guides that I can see dont look bad at all, no visible grooves but as you say they could be brittle.I had the car 1 year before this happened and was 100% mechanically until one morning she almost refused to start, backfiring etc. Thanks for the offer and will keep you in mind as I fear I will need a bit more help on this one.
Thanks again
Mike

 

[Myros]

research

when I was looking to buy my 500SL, all my research and the opinions of the chaps here who run V8s seemed to point to 75-100,000 as good time to change tensioners. It therefore became one of my stock questions of anyone whose car I was thinking of looking at. I'd rather have them done at 100k than hope they won't mess about, as it's odds on they will. Perhaps MB should think about redesigning the tensioner to make it a more long-lived part, but the cynic in me thinks that won't get off the ground.
Good luck with it Mike, and keep us informed.

 

[Mikesmerc]

Thanks Myros, going to change it now anyway. Bit the bullit an hour ago, while the tensioner was slack I lifted the chain to the right of the left bank sprocket and moved it a tooth. Wound the engine over by hand until TDC. Checked the suspect cam mark and looked as if it had gone slightly passed the mark. Stuck back on the covers and wound it with the starter motor with the coil ht disconneted in order to build up oil pressure in the tensioner. Reconnected the HT lead and..........same ****** thing if ever so slightly worse, blowing smoke out the metering place while the engine stumble rotating in reverse.Didnt try anymore to start it .
Took back off the covers and the tensioner had tightened up well, as I presume it should be. Rotated the engine by hand and both cam timing marks almost spot on..1mm at the most out.
Took off the dizzy cap to check the rotor position and there is a fine line at the tip of the rotor which appears to line up with another fine line on the distributer. All seems well, now somthing must be advancing the winding below the rotor, but what?
Will struggle on.
Thanks everybody, any ideas feel free to post.
Mike

 

[Myros]

out of my depth

Mike, I'm stil new to these V8s, but I remember my general bits and bobs. Did you say she fired up in reverse. That means you've got some wierd stuff going on in the electronics dept. My old beemer did the same about 15 years ago, and it took BMW all day and all their best heads to fix. It turned out a diode in the rev counter had failed, and instead of sampling the revs from the ignition, it was feeding current into it and buggering up the ignition electronics, causing non-starts, backfires, misfires and reverse fires. As the electronics on your 560 and my SL are about the same vintage as my old BMW, and it's Bosch K-type injection, something similar might be happening to yours. As you say, the oily bits are aligned and shouldn't be giving trouble now. Try all the connections you can see coming out of the ignition unit and dizzy, see if any have broken down. After that, it's multimeters at 20 paces.

Good luck

 

[R129]

Heres a simple little trick that I always start any diagnosis with on these engines.

If you look on the left hand innerwing where the ignition module is you will find a round socket with a screw cap and 9 pins in it. If you connect a multimeter set to duty cycle or dwell to pin 3 and the negative cable on the meter to a good earth you will access the rather basic onboard diagnosis system. This will only work with the engine running.

Basically if no faults are present you should get a reading of 50% or a variable number if the car has a cat. If the reading is anything else this may indicate a fault which can be cross referenced to the merc fault tables.

Only takes two minutes and can sometimes point you in the right direction.

 

[Mikesmerc]

Myros I believe that it is something freaky as you mention but leckys are not my favorite, I put it down to stupidity. Started it tonight with the same old symtoms, backfiring when trying to start and pinking/Knocking if too much gas is applied. R129 had alook at my old multimeter but I think its too old to read this but I can get hold of one pronto. I think I have been told before about this on one of my older posts perhaps by yourself but will check it out this time and report back.

Really appreciate the help
Thanks
Mike

 

[Mikesmerc]

Back again after a bit of an absense on this one. Purchased a multimeter with the funtion of duty cycle measured as a precentage. Started her up, unscrewed the diagnostic socket cap, placed the pos. in number 3 pin and the neg on the neg pole of the battery. Reads generally 1.7% but fluctuates from 1.6% to 1.8%. Obviously something wrong if it is suppose to read 50%, but what?

Any ideas?

Thanks for the help

Rgds

Mike

 

[Mikesmerc]

You will not believe this but my old dear has been forgotten about and garaged since my last post. I thought I might referesh it jus to see if anyone would have any other tests I could preform.
Thanks
Mike