1991 American Spec 500 Sl

[davesl]

I would appreciate any help on the above. The car has been running fine, but a few days ago I started up the car and it sounded like it was on 4 cylinders and had vibrations through the car. I drove it for about 4 km - it had no power and the only way I could make it change gear was to take my foot off the accelerator and a red light came on in the middle of the dashboard. After managing to get the car home the rear exhaust was extremely hot with hot exhaust fumes. Restarting the car, there was a notable smell of petrol which was only apparent on start up. Any ideas what could be wrong here? Thanks for suggestions.

 

[wscheffer]

I want to say it's the cat clogged up causing your trouble, but it's just a guess.

 

[davesl]

Many thanks for the suggestion. I thought it might be a problem with the cat, so I removed it from the car and cut it open. There were 4 separate pieces of wire mesh and honeycomb in the two boxes. All the pieces seem clear, unblocked and not broken. Do you happen to know if there are precats or is the 4 pieces all there are?

 

[television]

I do not think that there are any in the down pipes, is this your system

http://www.detali.ru/cat/oem_mb2.as...GA=722.353&CT=F&cat=515&SID=49&SGR=212&SGN=02

 

[wscheffer]

Possible bad (ICM) Ignition Control Modual, I be leave that their is two on the 500 SL one for each bank. This would explain the motor only running on 4 out of 8 cylinders.

Hope This Helps!

 

[davesl]

I do not think that there are any in the down pipes, is this your system

http://www.detali.ru/cat/oem_mb2.as...GA=722.353&CT=F&cat=515&SID=49&SGR=212&SGN=02

Thanks Malcolm. My exhaust is the bottom one in first drawing. Only difference is that mine has a sensor at front and rear of cat. I assume that there are no precats in that exhaust. Will be welding the empty cats back together tomorrow, but dont think this was the problem. Many thanks for your assistance.

 

[davesl]

Possible bad (ICM) Ignition Control Modual, I be leave that their is two on the 500 SL one for each bank. This would explain the motor only running on 4 out of 8 cylinders.

Hope This Helps!

Thanks William. I fitted two new ICM units 6 months ago. But thanks for suggestion.

 

[television]

Thanks Malcolm. My exhaust is the bottom one in first drawing. Only difference is that mine has a sensor at front and rear of cat. I assume that there are no precats in that exhaust. Will be welding the empty cats back together tomorrow, but dont think this was the problem. Many thanks for your assistance.

No there are no pre cats there, I think it is an ignition problem

 

[wscheffer]

No there are no pre cats there, I think it is an ignition problem

I also feel that this is an ignition problem!

Are you getting spark on all eight?

If so, what color is it?

A weak coil will still fire.

My suggestion is to go back to basics and start by pulling plugs, checking for spark and diagnose your way back.

 

[davesl]

I have replaced the exhaust minus the cat and it has made no difference at all. I have checked the ignition and found the car is running on 4 cylinders with the 2 outside plus on the left hand bank and the 2 middle plus on the right hand bank not working. (LH and RH when standing in front of the car). Could the ECU have gone to limp mode or is it something really simple like one of the two coils not functioning? When I take the HT leads out of the coils the one nearest the engine makes no difference at all to the running but the one on the outside on the inner flich makes the engine stop. I have reversed them and the engine will not start. Any ideas please?

 

[mattkh]

Hi
Try replacing the plugs

 

[ant500sl]

The ignition system on your car has a single ecu that controls two coils each of which fires 4 plugs through two distributors. Each circuit fires 2 plugs on each side, 2 inner plugs on one side and two outer plugs on the other.

Try saying that after a few!

As you have no spark on two inner and two outer plugs controlled by one of the coils I would suggest the first thing to check is the coil itself. If you have no test equipment you could just disconnect and swap the coils over (not just the ht leads) and see if the fault switches to the other set of plugs.

Also its not a good idea to disconnect ht leads while these engines are running as there is a possibility that you will get 20000 volts up your arm or worse still it might earth through one of the dozen or so ecu's fitted to the car designed for 5 or 12 volts!

Good luck.