Dean Pichon
Well Known Member
I've been plagued with a rough idle on my -4 all summer long. I have a 180HP lycoming with AP fuel injection and dual P-Mags. Last week, I elected to abort a flight because the idle was too rough to inspire the necessary confidence to initiate a take-off. (The engine has, however, always performed flawlessly in the air.) After searching the achives for other's idle issues, and slowly eliminating all the "classic" causes, I traced my idle problem to air in the fuel system (Thanks to the troubleshooting guide supplied with the AP injection system).
Early in the summer, I had replaced and relocated the fuel filter to be before the boost pump to protect the pump from any debris in the gas or tanks. I pressure checked all the individual lines, but did not pressure check the filter itself. I wasn't too worried about it as it was on the suction side of the pump. Yesterday, I removed the filter with its AN hardware and pressure tested it. I found one of the pipe threaded AN fittings to be leaking at the joint. I had used fuel lube rather than Teflon tape or paste. I have little experience with Fuel Lube, but this was either not an appropriate application or a poor execution. I replaced the Lube with Teflon tape and re-assembled the system. Idle tests earlier today were beautiful.
Apparently, I had been sucking enough air into the fuel stream to produce rough idle conditions. For reasons not yet apparent to me, under high flow conditions, everything seemed to work fine.
I would expect this is an unusual cause to a common problem, but hope this experience may be of use to others.
Dean Pichon
RV-4
Bolton, MA
Early in the summer, I had replaced and relocated the fuel filter to be before the boost pump to protect the pump from any debris in the gas or tanks. I pressure checked all the individual lines, but did not pressure check the filter itself. I wasn't too worried about it as it was on the suction side of the pump. Yesterday, I removed the filter with its AN hardware and pressure tested it. I found one of the pipe threaded AN fittings to be leaking at the joint. I had used fuel lube rather than Teflon tape or paste. I have little experience with Fuel Lube, but this was either not an appropriate application or a poor execution. I replaced the Lube with Teflon tape and re-assembled the system. Idle tests earlier today were beautiful.
Apparently, I had been sucking enough air into the fuel stream to produce rough idle conditions. For reasons not yet apparent to me, under high flow conditions, everything seemed to work fine.
I would expect this is an unusual cause to a common problem, but hope this experience may be of use to others.
Dean Pichon
RV-4
Bolton, MA