Today was a real head-scratcher.

A couple of months ago, Steve and I installed the SLK32 AMG gauges into the car. Rudy did a phenomenal job coding the '32 gauges to accept my VIN, and everything crossed over seamlessly. Everything worked great -- RPMs, speedometer, temp gauge -- except the fuel gauge.

At first, we thought it was the sending unit... Surely with the AMG motor and the base M112's differences in fuel needs, there was a funky unplanned difference in the sending unit, right? Nope.

After much discussion, it was determined that the '32 and the Crossfire have the same sending unit part number. As pretty as the gauges were, they simply would not read the fuel level, and the gauge was constantly pinned to zero.

So, today, I admitted defeat, and brought my OEM gauge cluster (the one that came from MY car) back down to Steve's garage. I had carefully swapped the white face gauges from a regular SLK 320 (160 mph speedo, so my OEM gauge calibration would work) and replaced the needles as carefully as possible.

Remove the steering wheel, rip the car's interior apart, remove the AMG gauges, transfer the Crossfire plastic shroud back onto the OEM gauges, connect to the harnesses, reinstall, get everything back together, and ---- still no fuel.

Fuel gauge #2, this time my OEM gauge (which read perfectly fine before the AMG cluster install) is now flat-lined like the '32 gauges were.



Adding insult to injury, the needles weren't as "lined up" as I thought they were, b/c once I reconnected the negative cable, the temp gauge pegs 1/4" below the cold line, speedo 1/8" below 0mph and the tach needle is 3/8" below 0 RPM.

Those are easy fixes, basically I have to take the cluster back out and rotate the needles counter-clockwise until they zero-out, thus resetting the servo position.

But the fuel has me stumped.

Is there a fuse I should check? Can a sending unit just mysteriously "fail" with a cluster removal?

Odd that two totally different gauges would have the exact same problem. Either the sending unit is not communicating, the harness from the left side of the cluster is compromised, or... I don't know.

If it's the sending unit, I'm throwing the AMG gauges back in. Just seems odd to me that, the least complicated function of both gauges is the very portion that isn't working.

One side note -- seatbelt warning was silent with the AMG gauges installed - not even the dummy light. After installing the OEM gauges back in, the alarm is still silent, still no light.

I did, however, get the FSS indicator back.

Pointers/assumptions/educated guesses appreciated.

 

John, does the fuel gauge get its signal directly from the sender, or does the fuel gauge get its signal from the ECM?

 

Here's an uneducated guess....is it possible that the coding/programming has somehow rendered both fuel gauges as inoperable?

 

James, that's a Rudy question... or perhaps someone else with a history of Star-DAS.

Sparkie -- the coding was ONLY on the AMG gauges... the VIN was zeroed to allow the use in my car. When you plug it in, VIN syncs and you should be good to go.

The fact that the OEM gauges (which had nothing done to them) do not work is beyond me.

 

On my MG and Sunbeam I use a potentiometer to check sender and gauge. Stone age but it works. My bikes have a reserve valve. Gary

 

My first fear was that the left side is simply not getting power, but the temp gauge (LCD) and the t-stat gauge (analog) both function. All lights work. Speedo and RPM function normally. Mileage is perfect, everything.

Highly unlikely that two different cluster assemblies with zero affiliation with each other, would both fail to read fuel. It makes about as much sense as a hair dryer working, then you unplug it, then you plug it back in and it's a dud.

Rudy suggested checking the voltage on the sending unit. Dumb question, but isn't that in the tank?

 

After some research, seems there are more MB fuel gauge problems than you can count.

Some interesting responses in this thread...

Faulty gas gauge - MBWorld.org Forums

Tomorrow, I am going to try resetting the fuse... quick process and it just might work. There was also a mention that the dealer could "flash" the gauge cluster and correct it.

But at what cost?

 

dealers...look out, my local dealer gets a fin to just hook it up...luckily, the owner's son was willing to reset my airbag system for lunch....lol...

 

Well, we can eliminate that step.

Pulled both fuses related to the instrument cluster, plugged them back in, no dice.

It appears after reading the service manual that a "no fuel gauge" malfunction is fixed by one of two ways... new sending unit (NOT a fun repair) or by replacing the instrument cluster. Shocking that TWO DIFFERENT instrument clusters can't read the fuel, but can read everything else perfectly fine. Even more shocking that the fuel sending unit would magically go kapütt when installing something at the other end of the vehicle.

At this point, the AMG gauges are going back in, since I originally blamed them for the fuel needle but now it appears it is NOT gauge-cluster-specific.

As to what the heck will make the gauge spring back to life, is anyone's guess.

 

John, there are a couple things you can check next time you have the cluster out. With the plug disconnected, see you have any resistance between 5L & 4L. If you have any amount of fuel in the tank, and the circuit is open or "0", then you have a problem with the wiring or a bad sender. If it is an open circuit or "0", try the same test at the sender itself.

Also you can test for continuity for the two wires running from the PCM to the cluster. Disconnect the plugs at both ends and use an ohm meter to be sure the wires are good. I would expect you should have "0" ohms on both of those wires.

 

Looking at the Repair Manual the two wires from the sending unit go to the instrument panel directly. I would check the socket that plugs into the panel to see if there is a reading on a multimeter of the resistance and if it is within the prescribed amount. Removal of the sending unit should not be too hard as long as there is not too much fuel in the tank and you are not smoking a cigar.
The rear of the instrument pane is a printed circuit I believe have you damaged it anywhere or at the gauge or socket connection?

 

Thank you for the tips, I saw that page but I'm no electrician

I think Steve has one of those meters, not sure though. They're inexpensive either way.

 

I'm beginning to think it's either some super-simple "GOTCHA" step or it's an issue away from the gauges. Just really strange that two different clusters would both function perfectly fine except for fuel.

I plan on buying a multimeter, that appears to be the only way to diagnose it.

 

I have never been in the instrument cluster with my SDS system, but most everything that you can get into has a quick test which may hep you if you can get it the car hooked up.

 

I'm thinking it's a programming/diagnostic issue. The sending unit worked perfectly prior to the gauge swap. I simply can't bring myself to believe that it died that instant.

I'm convinced that if I could get a friend at MB to plug into the car, with everything hooked up, he could go in and "activate" something or clear something and set the car straight again.

The problem is, I have no friends at MB, and MB is no friend to the Crossfire. If they even accepted the challenge (they won't) it would be $$$.

Palantine, IL is a long drive to get to Speedriven.

So, I'm reduced to chasing wires.

 

You probably need to follow Rudy's advice and check voltage. You don't have to go in the tank to do this. Just find the wires from the sending unit.

 

If old Steve doesn't have a digital multimeter I would be SHOCKED

Good luck with the fix, sorry it has to be an issue with the coolest gauges around...

 

Gotta pay to play. Nothing is painless with this car...

 

Not when you want to make them as unique as we strive for...

 

I've got one

Steve has one too.