Intermittent Temporary Rich Engine Start-Up Condition?

Paul462 · #1 08-24-10, 08:25 PM

Thanks for the input, Herb! Yes, the rear engine drips fuel when the airplane sits. We overhauled the fuel divider three times to no avail, and replaced the primer O-rings (also no avail). Nowadays I turn the rear engine fuel selector off, which minimizes the fuel drippage.

hharney · #2 08-25-10, 04:08 AM

Sounds just like my issue with the front engine. We have to come up with something to solve this issue. The company in Texas (don't remember their name) says that the fuel pump could be the issue. The fuel is leaking past the diaphragm or valve or something but it's like $800 to rebuild the fuel pump. Have you looked at this?

Paul462 · #3 09-07-10, 10:43 PM

The rear engine drip we're getting can only come through the fuel divider or the primer. The fuel divider is upstream from the fuel pump(s), so if the fuel divider were doing its job, it would cut off the fuel flow, and stop the drip.

rmorris · #4 09-09-10, 11:14 PM

Remember that there is another portion of the fuel system that you might consider....I overlooked it orginally when getting my system overhauled on the front engine. I was having issues with the high/low fuel flow settings, and they tried a bunch. I then overhauled the spider, fuel pump, cleaned injectors, adjusted fuel flow to book specs....then finally someone said - hey, what about the throttle body. Tried one from another Skymaster, and problem went away. I sent mine out for overhaul, and all has been good on that issue since (over a year now).

On a related note -- I mentioned all the issues to another a&p about a month later, without telling him the fix. he said, just replace the throttle body with an overhauled one. Says he keeps an extra one lying around for troubleshooting. Go figure, never know which mechanic will have which little jewel of information. Guess that's why we all try to share info on this website, eh?
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hharney · #5 10-06-10, 01:13 PM

I have a new exchange fuel pump and throttle body on the front engine. In earlier post I had the fuel divider overhauled and still had the draining issue but worse than before it was overhauled. Sent it back to the repair station and they bench tested it and said all was fine. So that's when I sent everything, pump, throttle body and divider valve (injection lines and injectors) to ACI in Texas. They said that the throttle body was old and obsolete, had the wrong adjuster set screw in the servo, fuel pump was also obsolete (all these were original) and they charged me a bunch of money for new exchange units off their shelf. Well we got it all back together and low and behold the drains still leak. Post flight or engine operation, fuel will leak out of the cylinder drains. ACI did not mess with the divider valve because it was under warranty and they said their bench test was good.

The divider valve will hold 4 PSI under operation and 2 PSI while static. We put a gauge on the line from the servo and it reads just barley 1 PSI. We also left the line off the servo overnight with the fuel selector on to see if the fuel could be coming from somewhere else but there was not fuel leaking in that procedure. So after spending well into $2500 it still leaks. Yes I have a new pump, throttle body, divider valve, etc. but this whole issue started with the fuel leak that is still there. Next step is to send the divider back to the repair station and bench test again. It has to be passing through the divider.

On a second note, we did some fuel pressure adjustments too. It was suggested by the Texas shop to just verify their factory settings. The fuel pressures were low so we did some ground testing and adjustment. The one thing that is concerning is that you can't get full RPM on the ground. There is an correction table that provides multipliers for compensating but it only indicates to -120 RPMS max and I could only get 2550 RPMS. The procedure calls out 2800. Well that's -250 RPMS. We did some calculating and came up with the multiplier and set it. When we flew the aircraft it achieves the 2800 on take off but the fuel flow was pegged on the engine we adjusted. We turned it back down a little and I need to fly it again to see where it's at. Next month we are installing the JPI 760 with fuel flow that I purchased at Oshkosh this year. I really don't trust the fuel flow gauge in the panel for accuracy.

Anyone else ever have fun with fuel pressure adjustments?

And to end it all, I can't get my G5 power mac to start up, really weird thing going on there too.

Stay tuned.

edasmus · #6 04-01-11, 12:58 PM

Herb:

After a flight last weekend, I have noticed a very very slight drip of fuel coming from the cylinder drain tube from my rear engine. I have never noticed this before. I sat and watched the tube for about 10 minutes and witnessed maybe one drip per 90 to 120 seconds on average. I was reading this thread and was wondering if you ever resolved all this with a high confidence level as to the cause?

Thanks, Ed

hharney · #7 04-04-11, 12:13 PM

After having the fuel divider rebuilt 3x, replaced the throttle body and fuel mixture control, beat my head against the wall, replaced the check valves, checked fuel head pressure on divider valve, adjusted fuel pressure and beat my head against another wall, IT IS STILL DRIPPING!!!!!!

Granted not as bad and only out the port side, front engine. At one time after the first divider rebuild it started dripping out both sides.

I'm into this thing at least $3K. Granted the throttle body and mixture control really had nothing to do with the drip but it was all tied in together.

Frustrating. Last time I talked to Paul he said his just quit for no reason.