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Old 10-29-2005, 06:39 PM
Registered User
Join Date: Oct 2005
Posts: 40
1990 500 SL trouble

I'm new to Mercedes and hoping you can give me some guidance. I picked up a 1990 500 SL that's been sitting for quite some time (at least 3 months, probably more).

Engine runs fairly smooth when idling, or gradually pressing the accelerator, but if you stomp on it the engine stumbles and dies. Also, the dashboard goes squirrelly at the same time - all the lights flicker, the gauge needles bounce around, and the tach starts showing slower than it should - tach shows about 400 rpm but is engine is turning about 900 rpm. When you speed up to about 3500 rpm, it only shows 1500 rpm. The tach can also act up a few minutes into idle, and then correct itself a few minutes later.

Could the dashboard issue be related to the engine stumbling?

Thanks for any insights.

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Old 10-29-2005, 07:05 PM
t walgamuth's Avatar
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 36,078
it sure

sounds like it.

i dont know a lot about those newer models but when electrical acts really goofy i would check your ground first. engine to chassis and battery to chassis.

tom w
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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Old 10-30-2005, 08:22 AM
Registered User
Join Date: Dec 2002
Location: Grand Rapids, MI
Posts: 766
Wiring harnesses can be a problem for those years--check yours; if the insulation shows significant deterioration you've probably got your problem.
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)

SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)
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Old 10-30-2005, 04:15 PM
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Join Date: Oct 2005
Posts: 40
Thanks for the tips....and the super fast response!
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Old 10-16-2006, 09:50 PM
Registered User
Join Date: Oct 2005
Posts: 40
FIXED at last

Well after 13 months we've finally figured it out - everything was a result of an incorrect ignition coil.

New coil, voila - runs beautiful and no wacky gauges.
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Old 10-17-2006, 09:35 PM
Registered User
Join Date: Jul 2003
Posts: 545
thats one to remember

Thanks, Juan
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