I'm going to tentatively say that we've got this problem resolved. I just finished a 45 minute and 60 minute test with no errors in calm air, no wind. I'll test more in the coming days to either build confidence or determine that the problem still exists. I'll be at 10k ft tomorrow, that will be a good test too.
The short answer, keep your fuel pump as far away as possible from any heat source.
The latest episode:
- Mike had asked me to sleeve the heater-side fuel line with larger rubber fuel line to insulate it from heat. No change.
- I added some reflective fiberglass heat shield material over the tubing for more insulation. No change.
Mike is in town doing training with a number of local upfitters & service centers this week and he arranged for me to meet at one of the upfitters (AVCRig
) and use my heater for training. This was doubly great since they are a Transit-only upfitter and are also a great group of guys.
Mike hooked up the EasyScan diagnostic tool and found no issue with the heater. His visual inspection raised no flags. He did the fuel quantity test both manually and with EasyScan and they came up within range.
When running the heater, Mike checked the temperature of the fuel pump and he thought it was warmer than it should be but not alarmingly so. It measured to 80°F. At this point, the training session was complete and I went home with directions to move the fuel pump. One of the AVCRig guys showed me how they tuck the fuel pumps right next to the fuel tank which allows for more airflow around the pump and not right under the van floor as I had done.
I got home and moved the fuel pump which also removed 15" of fuel line from the supply side and added it to the heater side. This got me a few additional minutes of runtime but still failed the same way.
Next, I shortened the exhaust to go straight down and out the side of the van, instead of going forward. This also removed 15" (about half) of exhaust pipe length. Now there is 21" of lateral distance between the fuel pump and the nearest bit of exhaust pipe where it had been as little as about 7".
With that, and minimal testing so far, I've gotten no errors on the last 2 tests. I'm wary but hopeful that this is the end of the saga.
Here is what the underside of the van looks like after these latest changes:
I plan to consolidate this whole saga with the helpful resources and post it to my blog within the next few weeks so no one else has to go through what I experienced over the past several months.
Thanks to all of you that had offered explanations, suggestions and moral support!