SL/R230: 04 SL 500 Backfires on Hard accel.
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Newbie
Joined: May 2018
Posts: 2
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2004 SL500
04 SL 500 Backfires on Hard accel.
Hi all, Been lurking for a while and love the forum. I have a 2004 SL500 with a strange issue that I have not seen covered anywhere on the net (that I can find) Car has 89k on her and purrs like a kitten. It has the resonator/muffler delete done and gets so many compliments on the sound. I actually had some guy follow me until I stopped somewhere to find out what exhaust system I have on it. I love the car and attention it gets but it has an embarrassing issue when you accelerate hard. The car will backfire violently then go into what I assume is limp mode (engine runs but does not respond to gas pedal) until you pull off the side of the road and get below a couple MPH then it dies and looses steering power. If I shut off the key then try and restart it starts right up normally but the CEL is on. The car runs and drives normally unless you get past maybe 1/2 pedal on acceleration. Once the car is rolling it has no issues at high speeds just getting there from a stop. The CEL stays on until the second subsequent start then goes out. It used to pop once in a while a couple years ago when I bought it but not often. Now it is pretty predictable and I can no longer take my sons mustang without him pulling up beside me asking if I need tow back to the garage. When it used to do it before it would not go into limp mode just pop and kept on going and did not throw the CEL on. So what ever it is has progressed but as long as I drive it like an old man it is fine. Anybody ever heard of this? I have code reader that I bought and will hook it up today and see if anything shows up.
Member
Joined: Feb 2016
Posts: 84
Likes: 19
C300 and SL500
04 SL 500 Backfires on Hard accel.
My 04 had a similar problem last year. My indie finally figured out one of the catalytic converters needed replacing.
It was throwing generic misfire codes, so we went through the usual suspects - plugs, wires and coil. At this point it was running beautifully, but would still misfire under hard acceleration when hot, then the CEL would come on and the suspect cylinder would shut down. The misfire wasn't always on the same cylinder, but it was always on the same side of the V.
My indie was getting desperate and kept the car for a week while trying various swaps, scratching his head and reaching out to various experts and tech's. Finally someone suggested checking the cat and sure enough when tapped it rattled like a can of loose change. Replacing it solved the problem.
I think the mileage at the time was <60K which I'm told is low for a cat to fail so it wasn't obvious and the codes didn't help much.
Good Luck
Gary
It was throwing generic misfire codes, so we went through the usual suspects - plugs, wires and coil. At this point it was running beautifully, but would still misfire under hard acceleration when hot, then the CEL would come on and the suspect cylinder would shut down. The misfire wasn't always on the same cylinder, but it was always on the same side of the V.
My indie was getting desperate and kept the car for a week while trying various swaps, scratching his head and reaching out to various experts and tech's. Finally someone suggested checking the cat and sure enough when tapped it rattled like a can of loose change. Replacing it solved the problem.
I think the mileage at the time was <60K which I'm told is low for a cat to fail so it wasn't obvious and the codes didn't help much.
Good Luck
Gary
Thread Starter
Newbie
Joined: May 2018
Posts: 2
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2004 SL500
I plugged in the OBDII (Foseal and Dash Commander) It had 1 code stored P0335 Crankshaft Position Sensor "A" Circuit. Took the car for a 30 mile drive (in old man mode) with Dash commander running and it did not throw any additional codes. I stopped at the beach and called my local Autoparts store and they had a crank sensor for it so I swung by and picked it up. Now just got to figure out where the sensor is located on that car lol. Oh and while I was coming back my AC quit working and the AC light flashes then shuts off...........Back to the parts store for some R134A fingers crossed that takes care of it. I was wondering about a plugged cat causing the backfire problem. I guess if it is the crank sensor that would make sense if the computer wasn't compensating for the timing. Hopefully this is it!
Senior Member
Joined: Jul 2015
Posts: 355
Likes: 41
From: amarillo texas
2003 sl 500
backfire
For several years of the SL's there was a problem with excessive wear on the timing chain idler sprocket. Your VIN is the key to that. Other members may respond on this thought. Hopefully not your problem.
moretech
moretech
