High Fuel Pressure Transients - Normal (GRT/EIS)?

Hi,

RV-8A, Aerosport IO-360-M1B, emag/pmag, EIS/GRT Sport (I forget which fuel injection system, but it was whatever is standard at Aerosport). Have the GRT high fuel pressure warning set a 45, and we're getting ~5 second spikes up to 58 psi. According to the EIS logger, pressure appears to average ~29, and after each spike the reading returns to that level. Experienced several transients in a 30 minute up and around hop.

*update - these occur with the boost pump off, our tech adviser says it can't physically go this high, so we'll check the wiring and contact GRT. But curious if anyone else has seen this with the GRT sensor*

Thanks,
Steve

Fuel Pressure

srv said:

Hi,

RV-8A, Aerosport IO-360-M1B, emag/pmag, EIS/GRT Sport (I forget which fuel injection system, but it was whatever is standard at Aerosport). Have the GRT high fuel pressure warning set a 45, and we're getting ~5 second spikes up to 58 psi. According to the EIS logger, pressure appears to average ~29, and after each spike the reading returns to that level. Experienced several transients in a 30 minute up and around hop.

*update - these occur with the boost pump off, our tech adviser says it can't physically go this high, so we'll check the wiring and contact GRT. But curious if anyone else has seen this with the GRT sensor*

Thanks,
Steve

Click to expand...

I've had the opposite lately. My FP has been dropping to 15-18 psi for 3-4 seconds occasionally and setting off the alarm. It usually runs 24-25 psi. I have 255hrs on a new mechanical pump.

I have seen exactly the same thing. GRT now sells a different fuel pressure sender (stainless) for fuel injected engines than what they used to provide in the earlier kits. I don't know if this is in response to this problem or not. I've since sold my Rocket and am building another and I noticed the difference in the senders. You might call GRT and see. I'm betting the change is related to the problem.

I had the low pressure blips too, but never been able to trace the problem. A friend who had the spikes

I had the low pressure blips too, but never been able to trace the problem.

A friend who experienced the spikes had an APRS antenna cable (just experimenting with different locations) near the pressure transducer wire. Whenever the APRS transmitted, the pressure spiked. So perhaps check the transducer wire run for proximity to antenna/coax cables.

EIS blips

Are you seeing these blips on the EIS screen or in the EIS serial data output stream?

The EIS serial data does have a problem with the 16 bit binary words. The MSB and LSB do not correspond t the same time sample so when the LS data byte rolls through 255 to 0 the MSB may not be correct for one data sample. This results a blip in the data.

A GRT rep made a comment to this effect on their EFIS yahoo group some time ago.

Doug Gray

Hummm

The problem could be one or more of three. It's either the sender, wiring or the efis. If the sender has been replaced and the wiring checks out then the effis is suspect. In the past I have found that the "smoothing software" was at fault on another product.

srv said:

RV-8A, Aerosport IO-360-M1B, emag/pmag, EIS/GRT Sport (I forget which fuel injection system, but it was whatever is standard at Aerosport). Have the GRT high fuel pressure warning set a 45, and we're getting ~5 second spikes up to 58 psi. According to the EIS logger, pressure appears to average ~29, and after each spike the reading returns to that level. Experienced several transients in a 30 minute up and around hop.

*update - these occur with the boost pump off, our tech adviser says it can't physically go this high, so we'll check the wiring and contact GRT. But curious if anyone else has seen this with the GRT sensor*

Click to expand...

I have the same exact issue (IO-360-B1B, dual p-mags, AFP fuel injection, GRT EIS/EFIS). GRT replaced fuel pressure sender, but no change. My high pressure excursions most frequently happen at two times (1) shortly after run-up, before take-off (2) after reduction in power, as I enter the pattern.

Given the times of occurrence, it makes me think that it is heat related (relatively high heat prodcution with reduced air cooling), but I have never seen any associated change in engine performance. Could it be that the fuel is momentarily boiling somewhere, producing the pressure peak?
I recently installed a heat shroud on my fuel pump, but have not as yet connected a blast tube to it, so dont know if this is the "solution" yet - wouldnt help during run up anyway.

Sure would like to get to the bottom of this - tired of seeing the red warning light flash, even if it is only momentarily. Please advise if you learn anything new


erich

Re: EIS blips

The EIS data is logged off the sport display USB port. We haven't caught the EIS 4000 display itself showing higher data, but then it's probably not being looked at within the same 5 second interval. I suppose we could program in a warning on the 4000 to verify it hits the same values as it is writing out to the sport.

No APRS in this a/c. Ran some ground tests and jiggled the wires yesterday, not able to recreate.

Last flight, this was logged around the time we entered the pattern, so a datapoint to erich. It's happened other times, but can't say if they're all connected to power changes.

Emailed GRT, don't expect a reply until next week.

In my case, the EIS is sending the info to a GRT EFIS. Both the EIS and the EFIS report the high fuel pressures simultaneously, as one would expect. Given this and the other circumstances, it seems likely that the data are "real".

Heck, Im happy to have company on this issue (but not as happy as if I found the answer...). Better than fuel pressure precipitously dropping I guess. I have 35 hours on the plane now - the transient high fuel pressure issue happens on every flight, but things are good otherwise.

erich

Fuel Pressure Transients

mannanj said:

I've had the opposite lately. My FP has been dropping to 15-18 psi for 3-4 seconds occasionally and setting off the alarm. It usually runs 24-25 psi. I have 255hrs on a new mechanical pump.

Click to expand...

My problem doesn't happen on short local flights. It usually happens at least once or twice on a 2-2 1/2hr leg on a cross country flight. I am always in cruise mode at 75-8500ft. VFR, no radio transmissions, just listening to my tunes on the 396 XM Radio.

I have no idea of lowering of the pressure mode as I'm usually watching for traffic until the BEEEP-BEEEP-BEEEP BEEEP goes off. When I look down both the EIS-4000 and the GRT Sport are showing 15-18psi. It always clears up, slowly creeping back up to normal. Guaranteed to get your attention though.

It was happening before my installed APRS system, so that has nothing to do with my situation.

I guess I need to talk to GRT about a new pressure transducer.

transient high fuel pressure resolved!

After living with transient high fuel pressure readings since first flight 1.5 years ago, I have finally figured it out and thought I would update this thread for future viewers - its some sort of fadio frequecy interference issue between my SL40 com and the fuel pressure sensor/EIS from GRT.

My high fuel pressure readings were almost always shortly before takeoff and then several times shortly before landing. I always thought it had something to do with high heat/low cooling air flow around the engine. After a flight last weekend with the typical occurrences, I asked myself "how the heck does this keep occurring right before takeoff - how could it KNOW that I am going to take off? It finally dawned on me that it knew because before every takeoff I got on the radio and announced my intentions! Sure enough next flight - 1 to 1 correspondence between radio calls and high pressure readings. Its been staring me in the face the whole time - just didnt click before. Ok, now to fix this and get rid of the flashing red light on my EFIS once and for all....

erich

I've had the same problem since I started flying my plane It only happens during transmission also. If anyone can help solve it I would appriciate it.

Interesting thread. I have had similar problems. I'm using the Vans FP sender going to a Dynon. Transient spikes up to 40 psi from a normal background around 22-24. When the boost pump is on, I get a rock solid 21-32 psi with no spikes. I haven't thought about the radio issue and will check to see if there is a correspondence there. I, too, would like to get rid of the red warning boxes.

greg

fuel pressure readings

We have noticed a fuel pressure issue with our GRT EIS engine monitor also.

Our problem is that our Fuel Pressure (we have a carb) sometimes floats listlessly between 6 or 7 PSI on the high side to 1 PSI on the low side.

Our engine does not seem to have anything wrong with the engine driven mechanical fuel pump or the electric fuel pump concerning wandering fuel pressure.

Any ideas out there?