woods83709
Member
I need the forums help with this one. I have recently confirmed that that my RV-9A, O-320 E2A (Carbureted, FP Prop) is suffering from bouts of Vapor Lock. Early in the week after a prolonged taxi and hold I was cleared to depart the main runway. Elevation 2880, air temp 85 degrees F. All checks normal so I departed with the boost pump ON. About 10 feet off the ground the engine coughed and just about died. Luckily with lots of runway I was able to land with no issues. Taxied back to run-up area and engine seemed to be running rough and when power was applied about every 2nd or 3rd time the engine would cough and just about die. Something was wrong so I taxied back to the hanger.
Day 2 84 F I took the cowl off and looked for anything obvious, nothing. With the cowl off I ran the engine, hard, to try and duplicate the problem. No luck. Limited by CHT?s I must have run it for an hour ranging from static max rpm to quick idle to max. Limited by CHT?s I would have to back off after a while to prevent damage.
Day 3 85 F Replaced the cowl and repeated the ground runs. However, this time after the engine was heat soaked from prolonged running it began to cough again. Interesting note that with the boost pump on it seemed to make it worse, not better! From idle to around 2000 rpm it would sputter and want to die almost 100% of the time with the boost pump on, and only 50% of the time with it off. The fuel pressure would hover around 3-4 psi at idle. When the engine is cold it would stay there until full power, however, when hot, once power is applied it would drop to near 0 psi with the boost pump off, around 2 with the boost pump on.
Day 4 83 F Wild Card (Auto Fuel 91) I have been using 91 oct (Ethanol free, check every batch) auto fuel exclusively for the past three years with no issues, even in very hot 90-100 degree days. However after some VAF forum research I thought this might be the culprit. I drained one tank and filled it with 100LL. Went back out and did my ground runs. When operating on autofuel I could get the engine to cough and sputter like the day before. Once purged, the 100LL would not do it! Fuel pressure stayed around 3 psi at all times with no fluctuations. With the boost pump on it would go up to near 5 psi with no fluctuations and/or sputters. This is what I believe to be classic vapor lock. I also think that I probably have some of the last ?winter? blend 91 octane as I fill up a 40 gallon tank, which was done around April. Winter blend has a higher vapor pressure thus more likely to vaporize.
Gascalotor mounted on firewall copilot?s side. Fuel lines fire sleeved, fuel pump NOT shrouded.
Thought about running a blast tube to the gascalator and the fuel pump, however I am not sure there is enough airflow on the ground to make a difference. This is when my vapor lock issues are likely to occur so it probably wouldn?t do much good. Has anyone had this issue and were they able to solve it? I realize that 100LL ?fixed? the problem but I would like a better solution. Anyone have any thoughts?
If you can help it please reserve your autogas vs 100ll arguments. I have access to 91 oct and I have made the decision to use it so I would like helpful suggestions on how to solve this vapor lock issue, outside of exclusive 100ll use.
Brett in Boise
Day 2 84 F I took the cowl off and looked for anything obvious, nothing. With the cowl off I ran the engine, hard, to try and duplicate the problem. No luck. Limited by CHT?s I must have run it for an hour ranging from static max rpm to quick idle to max. Limited by CHT?s I would have to back off after a while to prevent damage.
Day 3 85 F Replaced the cowl and repeated the ground runs. However, this time after the engine was heat soaked from prolonged running it began to cough again. Interesting note that with the boost pump on it seemed to make it worse, not better! From idle to around 2000 rpm it would sputter and want to die almost 100% of the time with the boost pump on, and only 50% of the time with it off. The fuel pressure would hover around 3-4 psi at idle. When the engine is cold it would stay there until full power, however, when hot, once power is applied it would drop to near 0 psi with the boost pump off, around 2 with the boost pump on.
Day 4 83 F Wild Card (Auto Fuel 91) I have been using 91 oct (Ethanol free, check every batch) auto fuel exclusively for the past three years with no issues, even in very hot 90-100 degree days. However after some VAF forum research I thought this might be the culprit. I drained one tank and filled it with 100LL. Went back out and did my ground runs. When operating on autofuel I could get the engine to cough and sputter like the day before. Once purged, the 100LL would not do it! Fuel pressure stayed around 3 psi at all times with no fluctuations. With the boost pump on it would go up to near 5 psi with no fluctuations and/or sputters. This is what I believe to be classic vapor lock. I also think that I probably have some of the last ?winter? blend 91 octane as I fill up a 40 gallon tank, which was done around April. Winter blend has a higher vapor pressure thus more likely to vaporize.
Gascalotor mounted on firewall copilot?s side. Fuel lines fire sleeved, fuel pump NOT shrouded.
Thought about running a blast tube to the gascalator and the fuel pump, however I am not sure there is enough airflow on the ground to make a difference. This is when my vapor lock issues are likely to occur so it probably wouldn?t do much good. Has anyone had this issue and were they able to solve it? I realize that 100LL ?fixed? the problem but I would like a better solution. Anyone have any thoughts?
If you can help it please reserve your autogas vs 100ll arguments. I have access to 91 oct and I have made the decision to use it so I would like helpful suggestions on how to solve this vapor lock issue, outside of exclusive 100ll use.
Brett in Boise