Intermittently Blows 20 amp ECM 2 Fuse - 2001 Suburban
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."
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'll post some followup scope patterns of the replacement pump when they become available.
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…
Thanks for the input Martin, it's greatly appreciated!
Excellent case study. A great example of current probe use.
Great diag and write-up! I have a question though: how close was the truck to blowing up? One EVAP leak away?
Provided with the right circumstances (Proper AF and ignition) there could have been a big problem.
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....... ;)
Nice find, thank you for sharing :)
GREAT Sherlock Holmes Diagnostics and usage of the equipment.
It was actually Watson who came up on scene and provided direction...