Saturday, March 17, 2018

Fuel Gauge..Malfunction!!!


"What do you want me to do Mix?"  "Push freak! Push!" -Sir MixaLot


I Think I've Got Enough...Hopefully.

This is something I said a few times while driving "Trogdor" to get tagged and titled last year. 

The Fuel Gauge had never worked since I got the car back in early 2017.  My buddy said it worked for him, when he had it, but the car had sat for a few years, so who knew what was going on with it?

Bad wiring?  Faulty Sending Unit? Bad Gauge?  Who knew?  I know I didn't have any idea.

 I DESPISE troubleshooting Electrical Problems, especially ones that could involve tracing wiring down.  So, I let it slide for the most part.  Eventually, I made a half assed attempt at fixing the problem, by taking the old "Troubleshooting Shotgun" and threw some parts at it.

Round 1....Fight!

The car had left me stranded on the way back from the registration trip due to Bad Gas in the tank and a thoroughly grungy, and nasty looking Walbro Fuel Pump and Filter Sock.

So in typical DSM Fashion, Trogdor was brought home on a flatbed trailer from it's maiden voyage under my ownership.  Not a good way to start things.
Just Chilling For Two Hours, Waiting For A Tow


To ensure this didn't happen again.  I drained the tank, and added some Marvel Mystery Oil to the tank along with fresh fuel.  The car ran great and made it to Cars And Coffee the next morning without a hitch.  No one paid any attention to it, but I was stoked. 
I Made It!!

Nobody Cares!
In order to avoid another encounter with a Flatbed, I decided to replace the existing Fuel Pump and Fuel Filter.  I had already bought a used Fuel Level Sending Unit, because like I said, throwing parts at something without actually troubleshooting the issue ALWAYS works.  

60% of the time.

Swapped out the pump with another Walbro 255 lph HP from Auto Performance Engineering in Texas.  I've bought pumps from him for years and he only sells Genuine Walbro Pumps and Install Kits. Go see him for your Fuel Pump needs.  A great guy to deal with.

The Fuel Level Sending Unit was swapped out at that time with one that checked good with a multimeter.  The one that was in the car when I bought it, didn't read correctly on the meter. 

Per the FSM: Full-Approx 1-5 Ohms, Empty- 103-117 Ohms.

Put everything back in, and started the car to check for leaks.  No leaks...and no change in the Fuel Level Gauge.

*FML*  The Troubleshooting Shotgun has failed me. Again.

I decided to try and fix it later, when I had time.

A Funny Thing Happened On The Way Home...

"Later" never really happened, because of a slight accident back in September of last year.  I  had other things on my mind, besides my cars and I was pretty busy just trying to get back on my feet.

I eventually did get back on my feet, and I resolved to finally try and really figure this issue with the car out.  It wasn't a life or death type issue, it just made my OCD flare up because the stupid gauge continued to defy me by displaying "E" all the time.

It was mocking me, and I wasn't going to stand...or sit for it.

It's Go Time..

Stop Mocking Me!

 I cracked open the Factory Service Manual and started troubleshooting with the easy stuff first.

Continuity-  I checked to see if the circuit from the Fuel Pump Connector to the Connector in the Dash for the Gauge Cluster was complete.   

Using some wire, jumper leads and my multimeter I checked the path from Connector E-30 (Fuel Pump Connector) to C-65 (Under Dash/Body Harness).  This checked good.

From C-65 to D-05 (R/H Side Dash/Gauge Cluster) showed good as well.  I also checked continuity from the Gauge itself to the Ribbon Connector on the back of the Gauge Assembly.  It was good as well.

The resistance in the path from E-30 to D-05 was approximately 3.3 Ohms.  I was told that anything over 1 Ohm was suspect.  I had a mishmash of wires, leads and probes to check the circuit, so I couldn't get a clean resistance reading.  

My main concern was that a path existed from the Fuel Pump Connector to the Dash, which I had confirmed.  

Time to move on to the next step.

Resistance- I checked the resistance reading from the Fuel Level Sending Unit again.  It read approximately 10 Ohms, and I knew that the tank was still fairly full from before the accident.  This seemed to indicate that the Sending Unit was still good, since it should read around 10 Ohms with a mostly full tank.  

I checked the resistance on the Fuel Level Gauge in the cluster as well using info from the FSM.  It passed all checks, except for a reading between the A-B Terminals.   It read approximately 20 Ohms lower than what it should.  

Per the FSM, the next step was to replace the gauge with a new one.  I had one spare Gauge Cluster and I installed it in the car to test the Gauge.  It didn't work, and I was worried about the Fuel Level Sending Unit being bad after all.

Let's Try This Again

I put an ad out on a local Facebook group, and someone in town said they had a spare 91+ DSM Gauge Cluster For Sale.  I swung by and picked it up from the guy and hoped for the best.

I Hope This Works

Plugged the new Gauge Cluster in and.....
SUCCESS!

The used Gauge Cluster worked as it should.  No mockery present.

  I swapped the Fuel Level Gauge from that cluster to the one that came in my car and checked it again.  

No issues, works like a charm.  

Mock me, will you? Hah!!

Did I Learn Anything?

Yes.  I still hate troubleshooting Electrical Issues.

But, if properly applied, using logical steps to troubleshoot issues with the proper information and tools, you can eventually diagnose and rectify a number of issues without "throwing parts at it."

And it probably won't take you almost a year to fix something either.


Alpha, Mike, Foxtrot...

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