My friend Glen and I went hunting for the vacuum leak again today, and we found it!
We started by eliminating variables: cleaned the FI electrical contacts, tested the AFM for proper operation, verified fuel pump was running when key was turned to "start" position, still didn't start.
Next, we decided to check the fuel pressure. We popped off the gas cap to depressurize the fuel system, and put a fuel pressure gauge on the tap. Turned the key, and it started up! Ok, fine, we're not sure what happened, but at least the fuel pressure appears to be in spec.
At this point, the Giants/Marlins game was in B9, so we buttoned everything up, and went inside to watch the rest of the game.
After the game, we went back outside (with our heads hung low) and continued our work. Bus now doesn't start, even though it started just 30 minutes earlier.
So, we continue looking. We pull the oil breather off, and notice a lot of oil froth and moisture -- evidence of blow-by. I'll have Buslab do a leak-down test when it goes in for the oil cooler seals.
Put it all back together, and the Bus still doesn't start. The only difference we can think of is that the gas cap was still off when we did the fuel pressure test. So, we pull the cap and viola... the Bus starts up! We can even rev the engine, and it doesn't fall flat on its face.
So, while it is running, we put the gas cap back on, and try to rev it again. Sputter, sputter... It falls flat on its face again.
My thoughts turn immediately to the fuel pressure regulator. I pull the vacuum hose, plug it, and then turn the key. The Bus starts right up, and we can rev it just fine. Timing seems to advance properly, and I now have 17'' of vacuum!
So, I did have a vacuum leak (diaphragm of the regulator!), but the revving problem was a fuel starvation problem, not a timing advance problem!
I do have to replace the fuel pressure regulator; without it, it runs rich, and the excess pressure is not really good for the injectors or fuel system seals. I'll have that done when the oil cooler seals are replaced next week.
Posted by thorpej at October 4, 2003 05:30 PM