c-dawg

Hello,
I have a 1996 SL 600 with 55k that has been giving me some minor problems lately. I'll try and list them below and any assistance would be greatly appreciated.

1. I almost stall (and have stalled a few times) when the RPMs drop to around 500 after I rev the engine. The lights get dimmer and there is a little stutter. There is also hesitation after I brake to turn and want to accelerate again. I thought it may be the battery since it is still an OEM one and I've only owned the car for 1 year. I had the battery checked at Les Schwab and they said the battery was fine but the alternator had a low output. Should I replace the alternator? Any suggestions on which kind?

2. I get a hesitation and sometimes a backfire when I drive the car for the 1st 10 or so minutes when it is cold. it feels like it is struggling for air or something and then the rpm's kick in. I ordered a couple of K&N filters which I'll put in this week. I'm also thinking of replacing the spark plugs since I don't know the service history of the car. any suggestions on what may be causing the hesitation and how to resolve it?

3. Has anyone tried the IAT sensor modifications that claim to add horsepower? Just wondering if they work or not.

Thanks for any help and I look forward to your responses!

blueSL

I wouldn't plan on doing any modifications to the car until the car is working properly and probably not even then. The SL600 has plenty enough power for the chassis to handle. Your car is not working properly and needs fixing.

If there's no service history (not good news), you need, at a minimum to:

- change the oil and oil filter
- change the spark plugs, does sound like your car is mis-firing
- check the brake discs (rotors) and pads, these cars are heavy on brakes

Don't know who or what Les Schwab are but if they say the alternator is bad and you trust them, you should get it replaced. Personally, I would only fit an MB original part, there's far too much electronics in this car to mess around putting in what is supposedly an equivalent part.

c-dawg

thanks for the response. I've already had the oil and filter changed and they also replaced a cylinder coil(?) due to a misfire. this was several months ago though.

Les Schwab is a national chain of stores in the USA mostly specializing in tires, but sell wheels and batteries too. The one I went to is pretty reputable and I was ready to spend big $$$ on a battery that they said I didn't need. I forgot this was an international forum...

as for spark plugs, I've heard good and bad reviews about the Bosch platinum +4 ones. what are people's views on these? http://www.boschusa.com/AutoParts/SparkPlugs/

thanks again!

RUCKDR

c-dawg,
As blueSL said, NO mods until the car is running properly, including using the original Bosch plugs intended for the car( I believe the single electrode ones), they are just fine. MANY more things to check; plug wires, O2 sensors, fuel filter, plugged injectors, catalytic converter (may be partially, eventually totally, plugged), etc., etc. Take it to a shop and have a scope analysis done. I don't think Les, at least here, does a complete scope analysis,
Later,

c-dawg

Thanks for the info. I had the alternator tested again and this time it tested fine. I'll go for a 3rd test somewhere else to see if it is an issue. I've also replaced the filters with 2 K&N filters.(the old MB paper ones almost crumbled in my hands...) This has helped a little bit. It runs smoother when cold. I've also run a couple of tanks with fuel system and injector cleaner.

I'll probably start with changing the plugs and the fuel filter. I've been reading other posts about changing the dist. cap and rotor and wires. Looked at my engine and there aren't any caps or rotors. The harness plugs directly to the CPU.

1. Should I look into replacing the entire harness?

2. Where is the fuel flter?

thanks,
cg

blueSL

The SL600 uses direct ignition which means each spark plug has it's own coil, all driven from the engine management unit. Those who are advising replacing distributor caps, rotor arms and HT cables are way behind the times. Your next priority should be to replace the spark plugs, the harness will be very expensive.

The fuel filter is, I believe at the fuel tank end, not the engine end of the fuel feed.

c-dawg

so here's the update on my issue... The alternator is working fine. putting out 14.2 amps, battery is fully charged with 800 CCA's. I've been misfiring cylinders like crazy. last year the #8 one errored out and they replaced the ignition coil. the same code came up recently and the fix was still under warranty so I dropped the car off to have them look at it.

WELL.....I apparently had 2 cracked air intake boots. these are the parts that are in between the air mass sensor and the intake manifold on the engine. the parts were $96x2. guess it isn't a common part to find on the internet. I looked at my old boots and they were shot! there were cracks in a few of the folds. on one of them there was even old crusty glue where someone tried to fix it before I owned it. I don't think the shop I went to would sub out the bad parts for me to look at so this was the issue.

the tech guy said that the air mass sensor determines the fuel mixture and I was getting too much external dirty air in my engine after the sensor. they were surprised that the thing even started let alone ran! I just got it back from the shop an hour ago. it doesn't idle rough, I get the horsepower (389 ) that I bought it for, and it is just flat out fast now.

I'll still change the plugs and the fuel filter soon since they said that it is what they'd do at 60k miles. needless to say, I don't know why I'm in front of this computer rather than driving... I'll update you if anything goes wrong!

c-dawg

blueSL

Good you got it sorted, enjoy the car!

sl3204me

It would be nice to think that all you have to do to cure the stalling problem is to change out the rubber boots.Like another person said,there can be other sleeping problems waiting to rear their ugly heads.At the minimum,change the plugs,the ignition wires,and have each coil checked.Pray that the engine control unit is ok.Check all wiring harnesses including the alternator wiring power harness,the main engine wiring harness(goes to each coil),and the air flow meter harness(called an engine body mounted harness).Specifically look for deteriorating insulation on any of the wires inside the casing.I started getting stalling problems on my 1995 SL320 and have replaced 3 harnesses now and the alternator.I am also praying that the main engine computer is ok.It runs $1800 at the MB dealer.Much more on the AL600.