Intermittently Blows 20 amp ECM 2 Fuse - 2001 Suburban

Scott Owner/Technician Claremont, California Posted   Latest  
Case Study
Driveability
Electrical
2001 Chevrolet Suburban 2500 LS 8.1L (G) 4-spd (4L80-E)—3GNGK26G01G135069
Blown Fuse

Verbatim from the work order:

"Customer purchased the vehicle earlier this year. The seller informed him that it had an electrical issue where the concern was corrected. For the last three weeks the vehicle will stall while driving. When it stalls, the engine will not crank. The vehicle still has electrical power when the stalling condition occurs. The customer then replaces a blown fuse in the fuse box and the engine will start. He is able to continue driving, but this issue continues to happen. He has replaced the same fuse multiple times.

The vehicle has also been at several other shops to correct this issue, however they weren't able to correct the concern. Check and advise."

ECM B

Initial inspection revealed that there was all sorts of extra (substandard) wiring all over the place to support just about every external off-road light array available. So our initial assumption was that this was likely a man made problem. 

After our visual inspection came up dry, we decided to connect a fuse loop in Fuse B and connect a current probe to monitor while we start and run the vehicle. We lucked out at one point where we shut down the vehicle and on key-up, the fuse blew. Looking back at the scope, we can see where this happened. Zooming in a bit we can see it happened right on key-up.

After looking over the wiring diagrams we were convinced that the issue was isolated in the tank, but wanted to try and gather a little more evidence. We then removed the tank skid plate and used a mallet to tap on the tank while monitoring current. Yes, Houston, we have a problem!

We gained authorization to remove the tank for inspection and this is what we found:

Pump power wire melted into one of the fuel tank sender wires. 

We peeled the wires apart for a closer look here and here:

The cause, poor connections = high resistance = increased heat!

We'll post some followup scope patterns of the replacement pump when they become available.

+16
Martin Instructor
Burnaby, British Columbia
Martin Default
 

Nice write-up Scott. When approaching vehicles with a "rat's nest" of wiring or aftermarket add-ons, it is a natural mindset to blame the current fault on what is readily apparent, as in your photos and become rather resistive to investigating the concern. That factor can severely inhibit a successful diagnosis, as may have been the case during previous diagnostic attempts. Without the…

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Scott Owner/Technician
Claremont, California
Scott Default
 

Thanks for the input Martin, it's greatly appreciated!

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Todd Mobile Technician
Morinville, Alberta
Todd Default
 

Excellent case study. A great example of current probe use.

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Great diag and write-up! I have a question though: how close was the truck to blowing up? One EVAP leak away?

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Scott Owner/Technician
Claremont, California
Scott Default
 

Provided with the right circumstances (Proper AF and ignition) there could have been a big problem.

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

When asked this question in regard to tank wiring or fuel pumped into the ECM I have always answered this way. There was no ignition because it was flooded....... ;)

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Noah Technician
Methuen, Massachusetts
Noah Default
 

Nice find, thank you for sharing :)

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Jim Mobile Technician
Southampton, Pennsylvania
Jim Default
 

GREAT Sherlock Holmes Diagnostics and usage of the equipment.

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Scott Owner/Technician
Claremont, California
Scott Default
 

It was actually Watson who came up on scene and provided direction...

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Ray Diagnostician
North York, Ontario
Ray Default
 

Excellent work and presentation!

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Scott Owner/Technician
Claremont, California
Scott Default
 

Thank you!

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Scott Owner/Technician
Claremont, California
Scott Default
 

Here are a few comparison files after the installation of a new pump. Old pump pattern measuring speed New pump speed New pump cycle Note: this pump has 10 commutator bars

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