R129 fuel problems

[johnandcrew]

I have just purchased a 1990 300SL auto, and have been told by the dealer to just fuel up with normal unleaded, the EZL ECE is set to S, is what he has told me correct? as the owners manual is slightly confussing, the 300SL I have does not have a cat fitted.

 

[renault12ts]

You're welcome!!

 

[stats007]

AFAIK S is for 98 RON - you should be able to judge yourself as to whether the car benefits from super unleaded.

It's a 300SL, not an SL300 by the way .

 

[johnandcrew]

The car has stood for over a year prior to me purchasing it, it is running poorly, I have been told that this is down to the exhaust being partially blocked and am going today to have this rectified, as I have only just got the vehicle I have nothing to compare it to as I have only driven it when it is running roughly, with what you have said am I correct in thinking that S setting is for super unleaded 98 RON and normal unleaded at 95 RON should be avoided?
The reason I am asking is I do not want to get a new exhaust only to find it is not running correctly due to either the wrong fuel or EZL ECE setting.

 

[Number_Cruncher]

The EZL setting would not cause rough running, it might cause some pinking under load.

I would be checking the plugs aren't fouled, and making sure the HT ignition system is in good order.

 

[johnandcrew]

I have just had a service, new plugs did not solve the problem, HT leads appear fine, vehicle appears held back when excelerating as though it is being restricted more noticable at lower speeds.

 

[Number_Cruncher]

>>HT leads appear fine

Checked how?

The leads can break down internally, and you won't see anything from the outside. Checking the firing voltages and burn times on an oscilloscope is the best way to see what's going on, although there are some DIY checks which will find many problems.

 

[johnandcrew]

The leads were checked by a good friend who works as a mechanic, he could not find a solution to the problem but did say he had checked the HT leads and they were ok, the reason I am looking at the exhaust is a auto transmission specialist looked at the car and said he has 30 years in the trade and he is 95% sure that is where the problem is, I was just ensuring that the type of fuel and EZL setting were not cotributing to the problem.

 

[BTB 500]

What would partially block a non-cat exhaust system??

 

[stats007]

Have you had a diagnostics check? Lambda control, egr, O2 sensor & MAS could all be causes.

 

[johnandcrew]

It was suggested that as the car had stood for 12 months then the exhaust could have become partially blocked, I have not had any diagnostic checks done as yet as the 2 places I have taken the vehicle do not have the correct connecters, I have just got back from removing the exhaust and it did not cure the problem.

 

[BTB 500]

I have just got back from removing the exhaust and it did not cure the problem.

I'm not surprised, the 'blockage' story sounded extremely unlikely to me!

Good luck with getting it sorted.

 

[Druk]

Distributor caps on these M103 engines are notorious for getting (and retaining) damp.

 

[johnandcrew]

Thanks for the info will check it out

 

[stats007]

My diagnostics DVD is from the US and as such doesn't cover 129060 with the M103 .

 

[Mark300SL]

I do have a 129060 and the only time I have ever had running issues with it in more than 8 years it was cured with a new Dizzy cap, Rotor, leads and plugs
I knew they were "due" and from ECP the total wasnt even remotely expensive. Add to that the whole ignition system can be changed in 1/3rd the time it takes to do the exhaust.

They really are very simple engines and not hard to diagnose, even the modern star systems wont tell you a lot about the engine

Mark

 

[Will]

Check the distributor cap and rotor arm (easy and potentially free ) Probably one of the more common problematic areas on M103 engines.

Other than that, could it be a gummed up fuel distributor or faulty potentiometer on the airflow meter?

I take it the vehicle was running fine prior to being parked up?

Will

 

[stevesey]

What would partially block a non-cat exhaust system??

Mice perhaps - if standing for 2 years.

Better description of "running roughly" might help (diificult I know) - will it rev? Does it misfire under load or at partial throttle? etc

 

[johnandcrew]

I have no idea how it was running prior to me purchasing it, the problem now is it appears to be restricted it struggles to pull off, this is more noticable at low speeds when you try to use the kick down the engine revs increase slightly but the car struggles to pick up speed, the kick down button appears to be working but the power is lacking, once up to around 60 mph the car picks up speed much better, I hope this helps, I will check the distributor cap and leads, thanks for all your suggestions

 

[Ian B Walker]

A liter of atf in the fuel tank (full tank) would clean out the the fuel system. As your car has no cat it would not damage anything. Being stood for some extended period of time some fouling should be expected.