13 Oct 2013

Here are the findings of last week’s fuel pressure failure – educational, and very humbling:
1. Installed new Bosch 044 pump, which is much larger than the Walbro – still zero fuel pressure!
2. Kinked the fuel pressure regulator return line to see if fuel pressure would increase – still zero.
3. Attempted to empty tank by rerouting fuel hose to regulator into a fuel can instead – still no flow.
4. Assumed FOD plugging up tank outlet – wrong, full flow at outlet of tank.
5. Assumed FOD plugging up 40-micro inlet-side fuel filter – wrong, full flow out of inlet filter.
6. Connected outlet of pump directly to fuel can – full flow.
7. Disassembled 10-micro outlet-side fuel filter to examine filter element. Filter element was in good condition, but noticed that flow direction arrow on filter housing was opposite how I had it connected (so what, right?).
8. Examined filter element for signs of deformation – nothing. The only notable difference was that the spare had a flat end (second picture) and my filter had a rounded end (third picture).
9. Installed new filter element, reversed filter plumbing, turned on the pump – full pressure, engine started.
10. Couldn’t figure out how the filter element could prevent the car from starting, since it was neither clogged nor collapsed.
11. Then, it hit me. Running the filter as I had it, fuel entered the filter on the inside of the element (see fourth picture), flowed through it, then down to the other end of the housing, and out. Apparently, the filter element finally developed enough pressure drop for it to be pushed off the end of the inlet housing, hitting the other end of the housing, where fuel pressure deformed the filter element end cap into a perfect plug – and presto, zero fuel flow!

It could have happened anytime, anywhere, and it was a bitter pill that it happened on lap four of a race weekend. My guess is that it was due to the higher than normal fuel flow giving it that extra push; a bitter lesson, that. I don’t know how I managed to install the filter backwards; it must have been during final assembly that I either forgot (or never noticed in the first place) that it was direction-sensitive. So I have to take back all the bad things I said about Walbro pumps; there was apparently nothing wrong with mine.

In other news, I’m pretty sure where the banging noise is coming from. The front engine mount is very close to the chassis, close enough that it is likely hitting it when getting on or off the gas hard.

During assembly of the new fuel lines I experienced something that I’d only read about. After the hose was assembled I blew through it and it seemed to have poor flow. Looked into the end of it and, sure enough, there it was, the infamous “flap.” Very good to catch it now because it could have caused all sorts of odd problems if it closed only under high fuel usage, very likely causing the engine to stumble or run lean.

There’s a local radar trap which hadn’t been active lately, but it was today as I was returning from checking out the new fuel system. I think the only reason I didn’t get “rewarded” was because the cop had just taken a reading on the guy in front of me, and he seemed so surprised to see such an unusual car that he momentarily lowered his radar gun, giving me time to slow down. Close call.

Lastly, progress on the book manuscript is moving right along. The final editing is about half way done, so another couple weeks for that. Then there’ll be one more pass through to check on physical layout of the pages, such as figure placement, dangling paragraphs, and mis-sized pictures. After that, several draft copies will be printed, with a final “fan through” to check for anything really bad, and then it’s time to go live. So for now everything is still on track for a late November release.