Jerry Cochran

Jerry Cochran

Well Known Member
Normally my fuel pressure with the mech pump runs 30-35 psi and with the boost on goes to 40-ish. Suddenly the other day I got a warning on my GRT EFIS when the pressure went to 190 psi and that has continued since, so am very reluctant to fly until this is sorted out. No engine stumbles or anything otherwise abnormal. Fuel flow is fine.

This is an injected Bendix system on an IO-360 with 160 trouble free hours since new.

I've never heard of this before, so if anyone here has ideas, advice, answers, please respond.
 
fuel pressure sensor failure

Sometimes they read very weird before they quit completely.
 
Hmmm, upon reflection I don't think it's the sensor because it reads perfectly normal until the boost pump goes on... Then goes right up to 190-195 psi. If I got screwy readings all the time then I'd think it was the sensor.

Anyone?
 
Can't Happen

First off there is no way possible for a diaphragm engine driven fuel pump to make more than 26 PSI. This is because the spring in the fuel pump is what sets the pressure. The spring in the pump pushes on the diaphragm so the pressure that is generated is the result of the diaphragm area times the spring force. An actuating rod is attached to the lever arm. The lever is actuated by the cam that moves the lever and pulls the rod to collapse the spring. The spring then pushes on the diaphragm and fuel is discharged through the outlet check valve in the pump. So it?s pretty much impossible to make more than the 26-PSI due to the spring force generated by the spring. To do what your saying the spring in the pump would suddenly have to generate about 8 times more force; not likely. There?s also no way the electric boost pump can generate 190 PSI as the dead headed pressure of the pump (Airflow pump) with no relief valve is 125 PSI.

Personally I would suspect the pressure transducer. It?s easy to verify the pressure reading by putting a known MECHANICAL gauge teed into the pump outlet hose.

Normal operating pressure for a high-pressure diaphragm fuel pump (LW-15473) is 22-26 PSI. Airflow boost pumps run 26-32 PSI. Pressures over 100 PSI will cause the fuel injection fuel control to turn into a sprinkler.


Don
 
operational question

I'm glad this is coming up. I have a vertical induction Precision Airflow FI, the standard mechanical fuel pump, Van's boost pump, Grand Rapids pressure transducer and Grand Rapids EIS and EFIS.

Normal indications are in the 27-32psi range. I originally set the alarm at 34psi. I have had now a number of occaisions where I get a high fuel pressure alarm. Originally I taxied back and tried different solutions, including simply setting the alarm higher. I still get high fuel pressure alarms occaisionally.

Here's the question: is a high fuel pressure alarm of any use? Does it ALWAYS mean a transducer/sensor/indicator failure and not an actual high pressure situation? Is the only useful alarm LOW fuel pressure? Does a flakey high fuel pressure indication mean that your much more important low fuel pressure indication will be equally useless?

I'm trying to figure out what goes into a sensible go/no go decision.
Thanks

Jeremy Constant
 
I see occasional high fuel pressure readings on my GRT EIS/EFIS system with AFP injection set up as well. Am I seeing a trend here?

For me, I finally figured out that I was always seeing the elevated fuel pressure warning just after transmitting on my SL-40 com, which quickly returns to normal. Apparently some kind of RF interference problem, which can be tricky to track down and fix. Now that I understand it, I ignore the momentary warning light. Dont want to disable it, just in case the real thing happens.

erich
 
Thanks Don and others...

I never get the high readings with the mechanical pump, just goes real high with the boost on. Guess I'll swap out the transducer and see what happens..
 
Verify with a normal pressure gauge. If that reads fine then you know it is between the pressure sensor and the indicator inclusive.

Replacing the pressure sensor is another option.
 
Which boost pump do you have? Airflow performance has a relief valve that could be stuck. I had an accessional high fuel pressure at the beginning and replaced the O-ring in the relief valve and solved the problem. It is an easy thing to check or replace. Let me know if you need more info about it or can not locate it.
 
Double check the ground...

Jerry Cochran said:
Normally my fuel pressure with the mech pump runs 30-35 psi and with the boost on goes to 40-ish. Suddenly the other day I got a warning on my GRT EFIS when the pressure went to 190 psi and that has continued since, so am very reluctant to fly until this is sorted out. No engine stumbles or anything otherwise abnormal. Fuel flow is fine.

This is an injected Bendix system on an IO-360 with 160 trouble free hours since new.

I've never heard of this before, so if anyone here has ideas, advice, answers, please respond.
Click to expand...
I also had high fuel pressure indications, but totally normal engine (Subaru in my case) operation. That lead me to suspect the indication, not the pump. I removed, cleaned, and reinstalled the connections and it went away.
As a test, pull the ground, or the lead wire if no separate ground, off the pressure sensor and see what pressure is reported. If it goes to 190 or thereabouts, it's a connection problem, not the pump.
 
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