1990 560SEC Checking fuel pressures

[Mikesmerc]

Anyone know how to check the fuel pressure on the above? Whats 'control pressure' as I have seen this mentioned as the source of my hard starting/ backfiring and hessitant acceleration. Guydewney has mentioned the regulator may be leaking which I assume is leaking back into the fuel tank?? Would like to eliminate as much as I can before purchasing parts.
Would a compression tester work on fuel lines or is it only specific to gasses?
Thanks
Mike

 

[ant500sl]

You need a special tester specifically for KE Jetronic injection systems which means you will most likely have to splash out at least £100 or visit a fuel injection/Merc specialist. Some Mercedes dealers still seem to carry the necessary gear but whether they still know how to use it is a different matter.

 

[Mikesmerc]

Cheers Ant, would agree with the latter. Can get hold of an oil pressure test kit if this will do the job but will spend 100notes if it is specific. Would like to have a go myself.
Thanks
Mike

 

[ant500sl]

When I was looking for a pressure tester I was going to order from the US as even after shipping and tax it still worked out about half the price of anything available over here, if you can find one.

This is the place
http://www.etoolcart.com/index.asp?...might be worth a look. Good luck

 

[Mikesmerc]

Cheers Ant, just getting my head around how the system works. It seems that the fuel is constantly being injected. If so what about the exhaust stroke of the piston, is this exhausting unburned fuel as well?. Saw no mention of timing with the injectors. My old 350sl has electrically powered injectors which I assume only inject once during the four strokes of the piston.
Will have a look for the pressure testing kit.
Thanks again
Mike

 

[ant500sl]

Its easier if you think of the whole inlet manifold containing a mist of atomised fuel, when the inlet valve opens a quantity of fuel is drawn in dependent on the fuel pressure on a KE system or the duration of the injector opening on a more traditional system.

Fuel is only drawn in on the first stroke of the piston as the inlet valve remains closed for the following three strokes, the fuel injected during this time is used by other cylinders.

Only recently have engines started using sequential injection whereby the firing of the injector is timed to the opening of the inlet valve.

Good luck with your diagnosis.

 

[Mikesmerc]

Thanks Ant that clears that up. Going ordering that tester, very reasonable.
Regards
Mike

 

[Mikesmerc]

Ordered tester from the US. Saw another post on an american site which a chap had the same symptoms as my 560. He changed the fuel pump and it sorted it. My pump/s buzzes away merrily but every 10secs or so it gets louder for a sec or two, is this normal?
Where is a good source for pumps besides the main dealer and are there one or two pumps on a 1990 560 SEC.
Thanks in advance
Mike

 

[190]

Ordered tester from the US. Saw another post on an american site which a chap had the same symptoms as my 560. He changed the fuel pump and it sorted it. My pump/s buzzes away merrily but every 10secs or so it gets louder for a sec or two, is this normal?
Where is a good source for pumps besides the main dealer and are there one or two pumps on a 1990 560 SEC.
Thanks in advance
Mike

Euro car parts have the pump £75 here,s a link
http://www.eurocarparts.com/ecommerce/Search_Results.asp

 

[talbir]

Two pumps on a 1990 560SEC.

Stick with main dealer or get a good used one from the breakers.

 

[Mikesmerc]

Hi Talbir, so its a twin pump setup. Saw the pump on eurocarparts as 190 said for 75, so I assume I would need two. They are listed Bosch, are these not up to scratch?, would have thought the original ones are Bosch also.
If you have time you may be able to offer any ideas on my poor starting, have replaced dizzy, rotor,plugs,leads(cheap, have ordered new Bosch ones) checked fuel reg for petrol on vac side, replaced idle air valve(small bypass pipe is blanked on my one, normal?, unplugged ovp relay and revs increase and abs light comes on so I assume is ok, pressed down on meter plate after 20min and found a resonable resistance and returns to fully closed position, checked throttle sensor middle pin earthed, outer one earths at closed position and the other earths at open, disconnected 4 pin temp sensor when hot and revs increase, sprayed a can of WD around air pipes and no change in tune
Idles at about 650rpm but timing is 20deg BTDC at these revs, bit advanced?. Had a post on a while ago and would appreciate any advice. Here it is
http://forums.mercedesclub.org.uk/viewtopic.php?t=8465
Thanks again
Mike

 

[ant500sl]

You seemed determined to sort this one out yourself. May I make a few reccomendations based on my own experiences:

Get yourself a copy of the Haynes Diagnostic Fault Codes Manual. Although this contains a lot of data for other makes it has about thirty pages of very clearly written test procedures for just about every component on every vehicle. There is also a section on reading fault codes on late 80's to mid 90's Mercedes. The book is very easy to understand and with its help I rectified a fault on my SL for £50, the local dealer wanted to charge over £1000 without actually curing the problem.

Your car does actually have limited self diagnosis. On the left inner wing in the area of the ABS unit and ignition module is is screw off cap which covers a 9 pin connector. If you connect a multimeter capable of reading duty cycle (most digital ones do this) to pin number 3 and the negative probe to a good earth and runn the engine the meter should show 50%. If it shows a number greater than 60 or lower than 40 it indicates a fault, the number given indicates in wahat area the fault lies. It may well show 50 in which case you will still have to test everything, but is a good starting point and can save a lot of time if you are lucky.

Try it out and I will check the resulting code for you if it differs from 50%.

If it is fuel pump related I sadly breaking my 560 for spares so let me know if you need anything.

Good luck

 

[Mikesmerc]

Not giving up this time Ant, will certainly order that manual. The pressure test kit is on the way. Have a multimeter and will check that pin. I am determined to sort this out myself as I rang my local Mercedes main dealer last year and they basically told me that it would be a waste of time and money.
My brothers c180 was in there for two months fault finding and repairing, not going down that road.
You might PM me for a price for the fuel pumps off your old 560 if your interested(postage would be to Ireland Im afraid).
Thanks a lot
Mike