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GRT/EIS Help

Scott Hersha

Well Known Member
I need some help with a couple problems I’m seeing in my RV4. I have a 15 year old GRT4000 EIS, and a new GRT Horizon 10.1 EFIS in my newly updated panel. Here’s my issues:

1. First one is with my Hall effect current transducer not indicating what it should. I have it connected properly according to the manual, where it senses alternator output, as recommended. My indications are: after engine start I see 7-8 amps positive alternator output until the battery replenishes (way too low). After engine start and in flight, I see anywhere from zero to +2 amps, and every once in a while -1 amp. It should not ever indicate negative in my installation, and with everything operating, I should be seeing +12 to +15 amps in flight. This is the third airplane I’ve had with this Hall effect transducer, and none of them has ever worked. So it must be something I’m doing wrong.

2. Second issue has to do with indicated fuel pressure. I have a carbureted O-360 in my RV4, using a 0-30 psi VDO pressure sensor. It seems to be fine after engine start and while taxiing with only the engine driven pump supplying pressure, anywhere from 3 to 4.5 psi. On takeoff I turn on the aux fuel pump. After leaving the pattern I turn off the aux pump, still climbing at wide open throttle. The fuel pressure then slowly drops to zero - over about 30 seconds - and I get vocal and indicated warnings. If I turn on my aux pump, pressure comes right back up to normal - 2.5 to 4.5 psi. Turning the aux pump off again, still climbing, pressure falls to zero again. During this time with fuel pressure at zero, all other engine indications remain normal - EGT’s, CHT’s, fuel flow, and smooth engine operation. When I level off, with the aux pump off and pressure still at zero, the fuel pressure gradually returns to normal. Yesterday I replaced the VDO sensor with another one I had on hand that had seen very little use in my first RV8, and then went flying. This one behaved exactly the same as the original, except after leveling at 8000’ it just stayed at zero. I flew around for about 30 minutes and it stayed at zero. All engine indications were normal. When I started my decent, the pressure gradually stared coming back up, and by the time I was in the traffic pattern, it was back to 4.5 psi. Aux pump stayed off. My engine driven fuel pump witness tube has never had anything come out of it. I don’t want to buy and install a new engine driven pump if there is nothing wrong with mine. For one thing, besides the cost, getting that pump replaced is very challenging due to very limited access in an RV4. This problem has been discussed before on this forum, but I don’t know of anything ever being resolved.

If you have experience in either of these two areas, or can make suggestions, please do so.

Thanks....
 
Scott,

2.5-4.5 PSI seems low to me. My engine driven pump shows north of 20 PSI with the boost pump it’s around 35 PSI. I have an IO -360, I don’t know if the engine driven pump is any different on an O-360.

I had similar issues with the fuel pressure when I installed my GRT EFIS about 4-5 years ago, and again when I replaced the 4000 unit with an R66. If I remember correctly the setting for the fuel pressure needs to be integer and I needed to change the aux offset as well, sorry but I am not at the hangar and can’t tell you the exact settings I used.

What does your fuel pressure read with the engine and boost pump off? It should read zero or very close to it, if not you will need to adjust the aux offset.

Hope that helps a bit.

Mark
 
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Thanks Skid. I have a carbureted O-360 Lycoming. Specified fuel pressure range for this engine is .5 to 8.0 psi, so my fuel pressure indications on the ground are completely normal. Your fuel injected engine has a different pump with much higher fuel pressures as specified. What’s not normal is 0.0 psi on my engine during climb, or any phase of flight with the aux pump turned off. I don’t know if this indication is telling me the truth. How can my engine run, flowing 15 gpm in a climb with zero fuel pressure? This isn’t a gravity flow fuel system.
 
Check to ensure your fuel pressure sensor is WELL grounded... that is always the first place to look. It should read a very low resistance between case of the sensor and the primary grounding point used by the EIS.

Also check that you've got the sensor well and properly connected to the sensor excitation voltage. Getting the correct resistor value between the 4.8V sensor excitation and the output/sense wire on the pressure sensor is critical, as are the settings.

If we reference GRT's "Use of VDO 0-30 psi Pressure Sender with EIS Auxiliary Input" document we see that for our carb'd engines we want to use a 200 ohm resistor, an Aux Scale Factor of 250, and Aux Offset of 47, and a (+) transfer function. This should yield 0.75 psi accuracy across the range of 0-10 psi.

Also note that if you did not previously have a fuel pressure indication before installation of the EIS, you may well have had fuel pressure dropping to a near-zero level on climb out and simply not known it. Your boost pump should be keeping the pressure up at some value around 5 psi at its output. Where you tap off fuel pressure to feed it to the pressure sensor could have a large influence on the accuracy of your pressure readings, too.

As for the Hall Effect ammeter, I'm not impressed with mine. I installed two of them, one in the alternator output lead and one in the lead between the battery and the main bus. I see them both fluctuating by as much as three counts while in steady-state cruise. I converted this aircraft from an AF2500 engine monitor to the EIS-66R; with the AF2500 I most certainly did not see this same kind of wandering ammeter indication so I'm reasonably certain the vague amps indication is a function of the GRT-supplied Hall Effect sensors.
 
Gauge sensitivity

I'm guessing that the engine driven pump is putting out, say 1.5 or 2 psi, which is enough for the engine to run normally, but not enough for the sensor and/or EIS sensitivity to pick up.

If this VDO sensor has a typical range of 10-180 ohms then 1 psi equates to 5.6 ohms. A fuel pressure of e.g. 2 psi should give just over 20 ohms, this is easily verified with a multimeter. You could test the old sensor by connecting it to a compressed air source and measure the resistance for various air pressures.
 
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VDO

Scott, I think these sensors are ****. I purchased a 6A with VDO 0-30 and for 200 hours no issue, then low pressure warning from eis4000. Replaced...all good for 6 months, 75 hrs and now high pressure alarm. Replaced again, no change , set high pressure alarm to 50!! Yesterday, long climb out from coast to 7500, @4000’ feet a low pressure alarm, boost on for shizz and grins, alarm stops, boost off, no other alarms. I’m sick of VDO sensors. I’ve committed myself to just keep flying and watch for any engine abnormalities. My numbers all good like yours. I gave you no help, but I’m not going to stay on the ground due to a **** sensor and a good running O320. My witness tube dry as well.

Question, engine off, boost on, what does the VDO show for pressure? I’m told should be around 8psi, mine is running a facet brand pump, don’t recall model number. Tony Bingelis built my 6A in 1992. Good logs show no pump change out. Same for the VDO until I changed a year or so ago. I did disconnect line from engine and put metered air line on sensor and found the current one installed to show 5psi more on the EIS than the airline gauge showed. I have two grounds on my sensor. I do not have it on a manifold... before her time :) Bracket on firewall with ground and one of the terminals grounded. Good luck.
 
With regard to the Hall effect current sensors: I like them, and feel they are a good trade off of reducing failure points (no resistive shunt) for accuracy. Seeing plus minus an amp (e.g., -1 instead of zero) is not surprising, given the low signal level from the Hall effect. Try not to have any other current carrying wires too close to the Hall detector. Make sure you use the regulated 5 volts for power, not 12 volts. Make sure you follow the set up instructions with regard to how many times the wire goes thru the toroid, and the calibration factors entered into the EIS. Finally, make certain the actual detector has not been pulled or vibrated loose from its slot in the toroid. IIRC I put a drop of epoxy on mine ‘just to be sure’.
 
Gents,
Thanks for the responses and suggestions. I will try all the suggestions made on this thread, and I will add an extra ground wire to my VDO sensor to see if that makes a difference. I have had this same issue in the past with other RV’s and never resolved it then, so I’m not hopefull. When I turn on the aux fuel pump in flight the fuel pressure quickly rises to a normal indication. When I turn on the aux fuel pump on the ground with the engine not running, the pressure will indicate 5.5 to 6 psi. I tend to agree with Butch on how to handle it, if this situation continues. Eliminate the low pressure warning because it’s a nuisance, use the aux pump for takeoff and landing, ignore the zero fuel pressure indication when that happens, and if the engine starts to get rough in cruise flight, turn on the aux pump.

As far as the current reading is concerned, I’ll check to make sure I haven’t pull the wires loose from the toroid. This is the third RV I’ve had with that green current transformer, and none of them have worked. The one I have now shows -1, 0, 1, 2 amps jumping rapidly between these four digits. In cruise I should be seeing a steady 10 to 15 amps. I’ve never seen anything close to that.

I’m even considering trying one of these:

https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01DDQM6Z4

Of course, it won’t warn me of an exceedance. I’ll have to be looking at it to notice.
 
Reversed

I recently installed the current transformer and it works as expected except in reverse. I am pretty sure I have it installed in the correct orientation... I may just flip it around.

Most of the time my fuel pressure reads in the 4 - 5 psi range but every so often, I will get an alarm when it drops below 2.5. I just turn on the boost pump for a bit and if appears to be fine after that. I haven't found any leaks. I'll also check my grounds next time.

Probably sending the EIS back to the factory to see why the warning light flashes constantly after engine start.

Just commiserating!

Cheers, Sean
 
contact support

...Probably sending the EIS back to the factory to see why the warning light flashes constantly after engine start...
Sean, I'd drop them an email and follow up with a call during their support hours to get some hints. My guess is that something is configured wrong, and they can identify it quickly. They've been really helpful for me when I stumble over things that are usually documented but I missed.
 
Done that

Hey Mickey - I have spoken to technical support and they have not been able to resolve it remotely...

Cheers, Sean
 
Possible cure

RV7A with carb 0-360 with nearly identical symptoms. Brief history: Replaced orig 2006 Lyc pump in 2017 with new Tempest when readings were higher than normal despite no other telltale signs of failure. Suspected sticking bypass valve. Problem solved. After 105 hours erratic readings like yours began & no telltale signs of failure. Turning on boost pump showed normal readings so replaced pump with new Lyc. A 15 min test flight indicated back to normal as did the next 1.3 hr flight. Erratic readings started immediately on next flight. Again boost gave normal readings & no telltale signs of pump failure. Discussed with tech at Advanced Flight Systems, maker of my AFS 2500 digital engine monitor who highly suspected a bad sensor despite the boost pump indicating normal pressure. Installed the new sensor & back to normal after a 30 min flight including a 5 min full power climb with boost off. I will update if anything changes.
 
Here’s a pic of the green current transducer. To the right in the photo is the load (main bus), and to the left is the source (alternator). The fat wire behind it in the pic goes from the starter solenoid to the starter, so no current when the engine is running. The other white wire in the pic looking like it goes straight down is a ground wire. So no current carrying wires near the transducer. After engine start, I see a max of 7 amps for a short time, then it bounces around between 0 and 2 amps with everything running, sometimes -1. I think I’ll try fooling around scale factor and offset. Right now it is set as recommended: Aux scale factor 164; Aux offset 313.

63C03BB3-D383-44E6-B798-74D746048791.jpg

Picture got flipped. Up is to the right.
 
Is that the hot side or cold side of the firewall? Sorry, I'm not seeing the picture well. I think it's the cold side. That starter cable shouldn't have any effect on the current sensor. Your path of adjusting offset is likely the best path to follow. I have to imagine that each sensor has some minor variations which would benefit from zeroing out via calibration.

BTW I have two sensors installed, one in the battery lead and one in the alternator lead. Both exhibit some offset from the absolute zero point and both exhibit some "bouncing" of their readings by a couple of counts. Generally they give a reliable indication of the state of current flow rather than an exact reading of current consumption. Turn on pitot heat, as an example, and I see a proportionally-accurate change in current flow so I'm ok with that.
 
I think these are more sensitive than shunts. If my strobes are off, the reading is stable. If the strobes (old Whelen) are on, there is oscillation which is reflective of an actual oscillating current (they draw around 5-7 amps for a short burst then draw nothing once the capacitor is charged then repeat after the flash). I suspect the EIS has no smooting and therefore shows the oscillations more than modern gear that has S/W smoothing. For example, my G3X smooths far more than I would like )reaction is slow to stabilize on a new reading)
 
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Scott, I see in the photo that the Hall sensor wire is cable tied to the fat high(er) current white wire. I don’t think I’d do that. In principle a twisted pair shouldn’t pick up any net voltage, but in practice? I note in the instructions a caution to use the 4.8 voltage source, that 12 volts can destroy the sensor. I wonder if on start up/alternator coming on line a voltage spike could have been induced into the sensor line? Just a thought.
 
Bob,
It’s worth a try. I can easily snip the cable ties and move the wires. I tried changing the scale factor to 157 (my EIS has software version 44). That made my indication go to -14 amps with the alternator off. I shouldn’t see anything with the alternator off. It’s on the inbound feed wire from the alternator on the cool side of the firewall. So I changed the scale factor back to 164, and the indication went back to 0 amps with the alternator off. In flight, or on the ground with the alternator on and most electrical components on I only see 0 to 3 amps. That can’t be right. Maybe I’ll play with offset next flight. I’m feeding the transducer 4.8 volt current off the EIS per instructions.
 
RE; GRT EIS Hall Effect Current Sensor

Scott,

From your picture and description of the installation it appears you are trying to measure the amp output from the alternator.

Take a closer look at the GRT "Hall Effect Current Sensor" installation data sheet. The connector on the sensor should be pointing in the direction of current flow (toward the load).

I think the reason you are measuring negative amps is that you have the Hall Effect sensor oriented incorrectly.
 
I am measuring the amp output from the alternator, as recommended by GRT in their install manual, and it is oriented toward the load. The arrow on the CT points toward the load, and the wire bundle is also pointed toward the load. It usually indicates 0 to +3 amps, occasionally -1 amp, and it jumps around rapidly. Should be +10-13 amps all the time. I’ve never seen anything close to this. It is configured on my Horizon EFIS on an ANL pin (analog), in accordance with what the GRT tech told me to do, since I don’t have any spare aux inputs on my EIS. Should work the same way. It is fed +4.8v from the EIS, also in accordance with the EIS install manual, and what the GRT tech said to do. It simply doesn’t work.
 
Hmmm... taking 4.8V excitation power from the EIS to power the sensor and feeding its output into an analog input on the EFIS. And you get weird readings. This sounds suspiciously like an issue with the EIS and the EFIS perhaps not using EXACTLY the same ground reference.

I'm curious... how did you end up not having sufficient AUX inputs on the EIS thus had to use one on the EFIS? I have two amp sensors feeding into the EIS-66R and still have spare AUX inputs. How many AUX inputs does your EIS have? (I'm just wondering if a signal intended for a dedicated sensor input on the EIS might have been installed in an AUX thus depleting your AUX input ports available.)
 
My EIS 4000 is an older one with only 4 aux inputs. I am using these for fuel quantity left, fuel quantity right, fuel pressure, and manifold pressure. My Horizon EFIS has 6 analog ports (+12 serial ports). I’m only using one analog port. Using an analog port was recommended by the GRT tech. Both units and the green CT are grounded at the brass ground bus (forest of tabs) on the firewall. Guess I’ll try GRT tech help again. Maybe I’m missing something.
 
My EIS 4000 is an older one with only 4 aux inputs. I am using these for fuel quantity left, fuel quantity right, fuel pressure, and manifold pressure. My Horizon EFIS has 6 analog ports (+12 serial ports). I’m only using one analog port. Using an analog port was recommended by the GRT tech. Both units and the green CT are grounded at the brass ground bus (forest of tabs) on the firewall. Guess I’ll try GRT tech help again. Maybe I’m missing something.

Are you sure that the EFIS analog port wants a sensor fed with 4.8 volts? It is possible that the EFIS wants a 12 volt supply to the sensor. I would not necessarilly assume it wants 4.8 volts. I wired up a flap sensor on my GRT EFIS, but just can't remember what I used as a source voltage. I remember a map of voltage to position and not offsets like the EIS.

Larry
 
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Just thought of something... if you are using an EFIS aux input, make sure the "internal pullup" setting is turned OFF otherwise your sensor reading from a powered sensor will never be right.
 
The amp sensor specifically says that a 12v feed power will damage it, hence the 4.8 v from the EIS. As far as the “internal pull-up setting” in the EFIS, where do I find that?
I spoke with GRT today and his only suggestion was to make sure the grounds are good. Maybe a bad crimp? Everything is grounded to the same point, so I’ll be checking those next. As far as my other issue, zero fuel pressure in a climb with the boost pump off, really had him puzzled, especially when I told him there are numerous posts on this site from other users of the same equipment exhibiting the same thing. Maybe that’s a ground issue too. I doubt it.

I did reset the offset on my amp sensor from 313 to 297, because I show -8 amps on the ground with the battery master on, engine not running - no alternator output. 297 got that indication to zero. I’ll find out if that makes a difference when I fly next. If it does, there must be a high resistance ground somewhere.
 
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