26 Apr 2014

Well that could have been fun…

Driving over to see mom, I briefly got on it in traffic and started smelling gasoline. That in itself isn’t terrible, since in open top cars, there are always all sorts of smells from other cars and the surrounding (I had smelled some pretty nice barbeques along the way). About that same time though, the car started running odd… uh oh, not good. The thought of 90 psi fuel spraying around meant finding a field to land in in a hurry, so with a couple of right turns I ended up in a quiet parking lot, perfect for field repairs. With a full set of tools always on board there wasn’t any concern about being stuck, though depending where the problem was located it might take a while to access it. Hit the battery kill just in case – no point in going up with a bang – then removed the engine cover and started looking around. Yup, the fuel smell was definitely coming from my car, and I could see it puddled at the bottom of the engine tray.

There just aren’t that many connections in the high pressure fuel circuit. The hose from the outlet of the high pressure pump to the filter, that one was dry. From the filter to the fuel rail… wet, huh. Then checked the hose at the other end of the fuel rail,connecting the engine to the fuel pressure regulator on the fire wall, also wet… huh, again. Both were slightly loose, and with the latter, I could understand it if I’d forgotten to tighten it after doing last weeks repairs. The former, at the outlet of the filter, was a bit more strange. Maybe I bumped it while installing the heat exchanger? Maybe, but why didn’t I smell gas earlier on then, from either of them, and why was it running oddly (idle speed fluctuating between 500 – 2000 rpm). Hmmm, vacuum leak?

Yes indeed. I’m using very high pressure “press and click” connectors here and there for several vacuum lines. The reason is that turbo and supercharged engines can have a fair bit of positive pressure in what are normally vacuum lines – in my case as much as 11 psi. Because of that, the hoses try to pop themselves off whatever they’re plugged onto, but this type of connector shouldn’t have been able to unplug. They are 3000 psi connectors used on paintball markers, where the hose is pushed into a collar which locks it in place, though this one didn’t seem to want to play any longer. Thinking it through, with the hose popping off, two things happen: the fuel pressure regulator loses its pressure reference, so fuel pressure goes to maximum – part of the reason for the leaks it seems. Also, with a vacuum leak, the idle was high, so the ECU was attempting to correct for it and making it worse. So the weeping hoses were tightened and the hose plugged back in, and I kept the car below boost during the rest of the trip so the hose wouldn’t pop off again.