SL 500 Fuel or Electrics?

[justinb]

Hi,

Ive got a 1992 sl 500 (r129) with 85k on the clock. Its been stood up for about 3 months but started regulary. Its was serviced about 4k ago...Recently its started missfiring after about 5 mins idling. When you floor the throttle it just splutters and cuts cuts out and revs high in idle. Its not realy feasible to drive as when you select D it cuts out..

It only seems to happen when its warm as when its started from cold its fine. Anybody any suggestions? Im thinking maybe crap in the injectors? As there's no distributor theres nothing obviously electrical I can check?

Kind of like to get it on the road for the summer!!!

 

[R129]

It may well be that the problem you have has been caused by letting the engine idle for extended periods. You really should take it out for a run regularly.
My first thoughts would be to clean up and check the ignition system on the car. Regular idling can foul the plugs while over winter there is plenty of chance for moisture to make its way into the distributor caps and cause a number of problems. This in itself may not cause the stalling you experience but its always better to check the simple things before thinking the worst.

 

[peterchurch]

It may well be that the problem you have has been caused by letting the engine idle for extended periods. You really should take it out for a run regularly.
My first thoughts would be to clean up and check the ignition system on the car. Regular idling can foul the plugs while over winter there is plenty of chance for moisture to make its way into the distributor caps and cause a number of problems. This in itself may not cause the stalling you experience but its always better to check the simple things before thinking the worst.

If it was damp I would doubt the car would start at all It might be worth checking the MAF if you have one on the car

 

[turnipsock]

You could always change the plugs and distributor bits. Is there a suppresor? cos that would be my guess.

If you change these bits you could always use the old bits later if they prove to be OK.

 

[justinb]

Thanks for the advice...

Took the plugs out and cleaned them, reset the gaps ( they were way out!) then ran some redex through it and took it for a spin..so far, so good.

The engine idle seems to be higher now than it used to be as it settles at about 950, as opposed to 750rpm. But now it runs and revs no problem. How easy is it to reset the idle speed?

During the winter I have had the battery disconected, is it possible that reconecting the battery may have affected some sort of memory which is why it has been playing up? Or am I talking complete crap!!

As always, help and advice greatly received!!!

 

[R129]

Glad to hear things are working again.

The increased idle may be down to the idle valve which is a little electric motor that allows a variable amount of air through into the engine which in turn affects the idle. With the regular idling and warm ups you described it may be possible that the valve is clogged with gunk in much the same way that you probably found your plugs to be.

Its situated on top of the engine in the middle of th "V" and is a cylinder about 3 inches long with a two terminal connector at one end and two rubber hoses at the other end. If you disconnect it and give the hose end a good rinse with degreaser or car cleaner it will clean up nicely.

Same advice again, it may be something completely different but always best to start with the easy/obvious/cheap things first. Too much emphasis these days on replacing and testing the expensive bits which are generally very reliable and overlooking the bits that have been going wrong on cars for the last 100 years or so.

Regarding the plug gaps, they will open up in use over thousands of miles and the differing gaps you mention may be an indicator that they have not been checked or replaced as often as they should. Might be a good idea to get a service done before summer.

Finally I cannot over emphasise how bad for a car allowing it to warm up at idle from cold is. Best to get it out on a run and get things warmed up properly, it also gives you a chance to fiddle with all the electrics, aircon and switches which helps prevent them seizing over the winter.

 

[justinb]

Smiles all round, well mostly!! Have been using the car regularly now and done about 1000miles. Engine is absolutely sweet, as I guess most of the crap has been blasted through, engine idle was slightly up but have adjusted it and it has stayed where it should be.

I guess I wont be leaving it to idle now as I think all the condensation has built up in the exhaust making it sound slightly more raspy than it used to. i.e it now had a hole!!! Im not into gun gum so its a trip to MB specialist... :-(

 

[pascal]

Great Justin.

Now with the summer coming up, and all that.
That V8 engine (R119) is considered by most to be the best ever V8.

Peter should be back later, as he is very well up in R129 exhausts & cats.

Pascal

 

[peterchurch]

Hi,
When you say raspy do you mean a "trying to clear ones throat" sort of rasp? I had some real probs with my drivers side 2nd cat, and ended up replacing the whole set with some OE ones from Camberley autospares MB wanted £560 plus vat per pipe for MB stock (oh and fitting on top!) I got both sides for £330 plus vat each... However mine are not quite right and are going back in next week to be looked at

Before you touch the cats make sure the MAF is working or you could be back here in a few months I am safe as I have dynos showing the car was running perfectly when the cats were replaced and the car is still running A1

While the car has been mis-firing un-burned fuel can get down into the cats. This in turn melts them! Your poor plugs or a buggered MAF will do this for you

I am told that OE parts should be perfect and make no more noise that the original kit... if you need a back box I am told that remus make a good one for £350 +vat Its nice and quiet too...

 

[justinb]

Right, where do I start!! Got under the car this morning to take a look.
Whole system looks pretty rusty as you would expect but in a couple of places, particularly where the sytem from each bank of cylinders joins into one looks pretty rotten with the outer piece of metal (stainless?) pealing back to reveal the exhaust.

Ive put my hand all around it with the motor running and cant feel anything leaking, so I'll check all the flange nuts are done up tight.

Dont want to dig too deep in me pocket for this!!! But then who does?

Had a Rover V8 once and this sounded the same, somehow remember the MB sounding a little more refined!!

 

[peterchurch]

The trouble is that very few SLs end up in breakers so finding second hand kit is hard as I said the front sections are £560 + vat + fitting each side...

My ones were £330 per side fitted including vat

I would start by ringing round a few specialists to get an idea of what is available for your car... then go and see MB and see what they think ...