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P-Mag Tach Signal to GRT EIS?

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
Hi folks - I am hooking up a new P-Mag to my GRT EIS, and am sure someone has this answer ready - for the tach signal, Sandy sent me a drawing to modify the EIS board (removing a capacitor and resistor) that is labelled "Lightspeed Mod". I sent her an email asking if this is truly intended for P-mags as well (I'd hate to mod the board if I don't have to), but thought I'd check if anyone has done it.

I removed the resistor that was installed in the tach signal that was required with Slicks...just wonderign if you did the mod as weel (the mod only applies to newer EIS's - mine is from 2004).

Paul
 
Hi Paul,

Yes, I am driving an EIS-4000 from a P-mag and had to snip a couple of components to make it work. I received a Word doc called 'GRT EIS LS Tach Modification' with a photo pointing to 2 components on the board - I think a capacitor and resistor. Works just fine, although I admit I was a little nervous weilding the sidecutters!

Pete

PS Is there a 'files' area where I can up-load the doc?
 
On the Bendix to Pmag conversion I did, I only had to remove the resistors that were attached in line with the P-lead wires. Once that was done I simply set the EIS for the correct pulse output and it worked like a charm.
 
Toobuilder said:
On the Bendix to Pmag conversion I did, I only had to remove the resistors that were attached in line with the P-lead wires. Once that was done I simply set the EIS for the correct pulse output and it worked like a charm.
Click to expand...

Thanks - Do you know the vintage of the EIS Michael? I don't know when they switched to a leter design (that Sandy said needed no modificaiton, but mine was definitley the old model (2004-ish).

Sandy did get back to me to confirm that the mod (to the older units) is applicable to ALL electronic ignitions.

Paul
 
Paul, I have Slick LASAR ignition, and it would not drive the GRT EIS either.

As I fully expect the LASAR to fail sometime in the future, I decided to take the ignition unit out of the equation, and went with the Vans tach drive generator. Now, no mater what ignition system I have, the tach is set, and just simply wont care.

Hopefully the transducer will last longer than some folks have been reporting recently.
 
Paul,

Be aware GRT has upgraded both hardware and software for the EIS unit. Both look and feel are identical, except at boot time. The later mod displays the software version for about 3 seconds at start up.

One of the changes was the tach input circuit, with additional configuration parameter.

I am not familiar with the p-mag interface but I would guess the newer version does not require the hardware fixes.

GRT are good folk, they will upgrade an old unit for a very reasonable price. In my opinion well worth the cost and includes transfer of your old configuration into the upgraded version.

Doug Gray

Doh... It seems you knew this already - reminder to self "must read entire thread before posting".
 
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Paul,

FYI, I also had an E-mag driving an unmodified 2003 or early 2004 vintage EIS-4000, for a while the tach signal worked fine, but then stopped. I didn't investigate too thoroughly and swapped the tach drive to the mag.

Pete
 
My EIS was purchased in October 2005 and required the modification be performed to enable accurate rpm readings from p-mags.

Erich
 
Closing out the story - I did the mod to the EIS (it took about ten minutes - and five of those were removing and replacing the unit in the airplane), and now everything works great! First test flight just as the sun was setting yesterday, and I have NEVER flown such a smooth engine (and this one was smooth with Slicks!).

Summary - P-Mag driving the (field) modified EIS with NO resistor, and a P/R setting of "2" is working perfectly.
 
PMAG tach drive

Paul I'm wondering if the PMAG feeds tach info even when switched off during the mag test? I'm currently feeding it from the Slick and lose tach signal when I switch the mag off. My EIS is not able to read two signals as it has not had the modification, and I'm considering feeding it from a tach signal generator instead.
Thanks, Tim
 
tim2542 said:
Paul I'm wondering if the PMAG feeds tach info even when switched off during the mag test? I'm currently feeding it from the Slick and lose tach signal when I switch the mag off. My EIS is not able to read two signals as it has not had the modification, and I'm considering feeding it from a tach signal generator instead.
Thanks, Tim
Click to expand...

I'm pretty sure it does Tim, but can't go test it becasue the airplane is down right now for some cylinder work. I'm almost certain that the Tach signal persists as long as there is power on the P-Mag (not the same as having the ignition hot).
 
tim2542 said:
Paul I'm wondering if the PMAG feeds tach info even when switched off during the mag test? I'm currently feeding it from the Slick and lose tach signal when I switch the mag off. My EIS is not able to read two signals as it has not had the modification, and I'm considering feeding it from a tach signal generator instead.
Thanks, Tim
Click to expand...

Tim,

Yes it does - switching the mag switch off says 'no sparks please' to the P-mag, the electronics still operate.

Pete
 
Does any one have the document that describes the changes that need to be made to the EIS in order to read the signal from PMAG? My EIS was purchased around 2008 but not sure if it is the newer model or not.

Thanks in advance
 
For some reason I have not been able to start a new thread (perhaps a glich in the system) so I am using this thread with the hopes of getting some info from our members.



I have been contemplating installing a Pmag and have some questions for those who have installed and used it. I currently have dual Slick Mag which has been running trouble free since the beginning so I am not trying to fix any issue but hoping to improve it hence these questions. I am thinking of keeping one Slick and installing one Pmag.

- What improvements have you seen since moving from Slick to PMag
- Any rise in CHT, if any (my CHTs run in the mid 300 while cruising during summer and lower 300 in cooler days but can climb to 400 during extended take off)
- Any appreciable saving in fuel economy
- Do you have it on top cylinder or bottom
- On startup , do you start with Pmag or Slick
- Finally for those with GRT EIS, what modification did you have to make to be able to get accurate RPM

Thanks in advance
 
Just did this.
I had both slicks. Then I replaced the right mag with a p-mag. Now I am running both p-mags.

Here is my answers/opinions to your questions
- What improvements have you seen since moving from Slick to PMag?
Lower idle rpm let's you slow down faster. Better fuel economy. And very slight increase in top end RPM's.

- Any rise in CHT, if any (my CHTs run in the mid 300 while cruising during summer and lower 300 in cooler days but can climb to 400 during extended take off)
Slight rise in CHT. About 10-30 deg depending on the phase of flight and how lean I go

- Any appreciable saving in fuel economy
Yes and no. I could choose to save the fuel or go faster. At the same RPM, I would save about 0.75gph over the slicks. O-320 150hp

- Do you have it on top cylinder or bottom
Both. I installed as instructions. So for one p-mag, 2 cylinders were on top and 2 were on the bottom

- On startup , do you start with Pmag or Slick
I did it wrong. I changed the non-impulse with the p-mag first because it was easier. But this had me starting on the slick. It should start easier on the p-mag

- Finally for those with GRT EIS, what modification did you have to make to be able to get accurate RPM
Just took out the restor and set the EIS to count 2 sparks per revolution. I did not need to alter the EIS in any way.

Hope this helps.
One p-mag is good but two are better. With one, I could not lean out without getting some roughness/backfire sound. With two p-mags the only issue is making sure I don't lean so far that the engine stops. It never gets rough, so I have to watch the EGT's when leaning.
 
Thanks for the feedback and sharing your experince.

I am wondering since I am going to replace only one (at least at this point) should I replace the left or the right side. Only the left side has impulse coupler.
 
The instructions say to replace the left if only using one. One of the advantages to a P-mag is the easy starts.

But as I mentioned I replaced the right first. This also worked. But i did this because I knew I would quickly replace the left one, and did not have an extra non-impulse gear around.
 
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