rscruggs2

My check engine light is on and nothing seems wrong. Are there any self diagnostics I can do to find the fault?? It's a 99 SL500.

cliffyk

Your '99 has a full-fledged OBD2 interface, go to any FLAPS (Favourite Local Auto Parts Store) and they will read the code(s) for you--write down or remember the code(s) they are much more important than any description the auto store person will give you.

Or buy a code reader and read them yourself (and reset the MIL which the FLAPS may not be willing to do). They are not that expensive (Harbor Freight has models starting at $50).

The readers I had were all 10 to 20 years old, so last Fall I bought this very capable HF unit on sale for $90--with a $20 coupon = $70.

Once you have the codes post 'em here or "google" them for more info/suggestions...

rscruggs2

Our local Orielly's card tells everyone the same thing.....#4 sparkplug!

cliffyk

Someone should bring in a 1.0 litre Geo Metro and see what they say...

rscruggs2

LMAO! I'll take it to a friend who owns a shop.....He says he can get the code. Thanks for all the help.

rscruggs2

I just disconnected the neg battery connection for 4 hours and the check engine light went away. Simple fix. Regards, Rick.

lynns

Yes, and I think you have just applied a band aid and it will now take a couple of weeks for the DTC's to show up again and the CEL to come back on. If it does may I suggest that you pay your local Indy to print out the codes from a MB SDS since you also have a 32 PIN connector located on the passanger side back by the firewall that allows a Tech to read any/all DTC's that the car may throw. Cost is free or about $50-$75 pending your relationship..

rscruggs2

You guys are right.....I'll get it checked.

rscruggs2

Diagnostics complete. The connector on my car is on the drivers side by right calf and up. It said I had a loose gas cap and 3 plugs that had missed. That's easy to understand as they are the original plugs that came with the car. I ordered 16 plugs from AH and will get them installed when my mechanic (friend of mine) is free. The check engine light is out by the way. I checked my mileage today and it was 23.5MPG so things can't be too bad!

cliffyk

The misfire codes are not thrown only because of bad plugs, they can also be triggered by fuel injection or engine mechanical problems--though if you are still running the OEM plugs that would be a distinct possibility.

How many miles on them?

Here is the functional description of the misfire detection system...

rscruggs2

Thanks. 31,000 miles on the plugs, 31,000 miles on the car. Plugs are the ones that came with the car 16 years ago. My mech cleared the faults on Monday and the check engine light has stayed off. We are going to change the plugs next week. In the meantime I dumped in a can of Sea Foam and she is running much better.....my MPG was 23.5 last fill up. Probably a combination of old plugs and injection crud. I am optimistic on a successful and inexpensive repair. The doctor who was the original owner is a cardiologist and drove it from his house to his clinic 1.2 miles away for 12 years and sold it to me when the AC went bad. It had 19,000 miles on it when I purchased it 3 years ago.

cliffyk

At two 1.2 miles a day trips for 12 years that engine never got hot enough to boil off the crap byproducts of combustion, the plugs could be completely crapped up--once they are out post a photo of them if you can.

Seafoam is grade A snake oil, it consists of an emulsification of:

50% light hydrocarbon oil (pale oil);
30% petroleum naphtha;
10% isopropyl alcohol;
10% water

Here is the MSDS for it.

It originated in the 50s for use in marine engines that were run cold and/or improperly stored in winter--that's the "sea" part of the name; it is rarely if ever needed in a properly cared for engine as all gasolines and motor oils have additives that prevent anything seafoam would remove from building up in the first place. I have never used it in over 60 years of owning automobiles, bikes, boats, etc.--and would not use it in a lawnmower.

There is no automaker that recommends or even approves of it's use in gasoline engines, most specifically state that such products should not be used (diesels are a different story a they burn crap and run filthy to begin with).

If your engine is running better after pouring seafoam into it then it was seriously crapped up, probably from only being driven 1500 miles a year for 12 years at 1.2 miles a pop...

rscruggs2

I'm sure you are correct. I'm going to burn this up then use Lucas. I'll post some pics of the plugs when removed.

cliffyk

I take it you did not inject it through a vacuum line then, but put it in the fuel? That's good because it won't do much of anything there--put in through the intake manifold it can create all sorts ff problems. The Lucas stuff is not much different, a bit less pale oil and a bit more naptha, just more snake oil.

From the 1999 Owner's Manual:


In the US any name brand pump gasoline has all the additive needed to keep the fuel system, and valves and combustion chamber clean--buying and adding other stuff just lightens your wallet. Taking the car out and running it hard for 15-20 miles (bring it up to redline at WOT a few times) will do more than will any magic elixir added to the fuel...

rscruggs2

OK.....I'll scald her out tomorrow. Regards, Rick.

sutliffe

Have you recently changed the crankshaft sensor?

rscruggs2

No

rscruggs2

Plugs changed.....runs great....no lights.....all is good. The old plugs looked not all that bad but they ran at low RPM for many years. The engine now runs smooth and strong. I installed the double platinum on sale at AH. Thanks for all the help with this.