Drewster67

I was tending to my Shark and in the Fuse/Relay compartment I found this "device" spliced into the wiring. The only markings on the board state Helitrim Model 91. Searching the Web I found that this device is potientometer(?). I'm not an engineer and the application notes are PHD reading. Does anyone know what board is for?.

HELITRIM 91
TRIM POT 1K ST TA 9MM...

<a href="http://www.bitechnologies.com/pdfs/2appnotes.pdf" target="_blank">http://www.bitechnologies.com/pdfs/2appnotes.pdf</a>

Thanks Everyone

Greg86andahalf

Sounds like a trim pot. I wonder what circuit it's in. Can you trace either what harness connector feeds it, or where it goes form the trimmer?

Greg

John Speake

Hi Drewster

Almost "certainly" this is a remote version of the idle mixture pot. used with your Euro LH system. The MAF has a built in pot, as you know. but it is difficult to get to. A remote pot, on a proper bracket is available from Porsche. It was fitted to pre cat. euro cars, like early GT's.

Looks like someone has fitted a homemade version of this to your car. It is a 1k pot (i.e. 1000 ohms) the recommended starting value is 382 ohms to ground.

Drewster67

<a href="http://boards.rennlist.com/upload/Hel91" target="_blank">http://boards.rennlist.com/upload/Hel91</a>
<a href="http://boards.rennlist.com/upload/heli92" target="_blank">http://boards.rennlist.com/upload/heli92</a>

Here are a couple shots of the chip. Notice on heli92, the two green wires that go to the "brain" (I think) are disconnected. Also, there is one exta white wire that doesn't seem go anywhere?.

When I first opened it up, the frayed wires were taped up and the wires leading to the brain were connected to the device?.

If there are no real advantages of having this chip in place, I'm just going to wire it back up as OEM. Any thoughts as what would be best?.

Thanks Again -

Randy V

Talk about a living archive of esoteric Porsche information!

Very impressive Mr. Speake.

John Speake

Hi Randy,

Not really ! (thanks) I've been looking at LH brains, but mostly MAF's recently.

I have just completed a test rig for MAF's It can test a MAF with 12 preset levels of airflow, from below idle flow to something near full throttle (big fan !!)

I'm hoping to be able to offer a repair and recalibration service for 928's.

John Speake

Drew,

Before you disconnect this pot, make sure the one in the MAF is OK. There might have been a good reason for someone going to the trouble of fitting the remote one.

Disconnect the 6 pin plug to the MAF, measure the resistance from pin 6 to the body of the MAF.
It should vary from 0 to 1000 ohms Full clockwise is max. It should move smoothly and continiously. Another problem is that sometimes the spindle of the pot get corroded solid inthe casting.

John

Drewster67

John - Too late - I already wired it back up as oem. In all honesty I can't tell the difference, then again, my shark was down for about a month.

Later on tonight I'll wire it back in and see if there are any differences. What should I be looking for I.E. Better Acceleration, Better Gas Milaege, Higher top End, Smoother/More Responsive shifts. In other words and pardon my ignorance - I still have no idea what this device does?. Even after my research!

Thanks again for the feedback and the link for the ROW manuals - (BTW - the link is under construction) -

Off topic Question - Do they celebrate Halloween in England?. Just curious?.

D67 <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

John Speake

Hi Drew,

OK, the pot only affects the idle C02 levels. You should set the pot with a CO meter on the exhaust, and the air pump feed hose disconnected.

If you want me to mail the pages from the manual, let me know.

Yes, British children do the Halloween thing. But only in the last 10 years or so. It seems to have been imported from USA !

(Same with Fathers Day)

Richard S

Drew, the picture you posted of the mystery box looks kind of like the one I have on my 84 Euro. Mine is a box made by Neutronics (in San Diego I think) which allows Euro cars without O2 sensors to be federalized. This box splices in an O2 sensor, along with splicing of other wires, and then allows you to adjust for rich or lean fuel mixture. Just adjust it correctly once, then forget about it.
Regarding the other pic, the 2 green wires from the brain are usually disconnected, and are to be connected if you have to use lower octane gas, or get a tank of bad gas. The white wire may be for an O2 sensor, at least mine is white.
Hope this helps.
Rich
79 A/T
80 5 spd, 84 Euro S motor

Drewster67

Thanks everyone for the feedback. I tried to wire it back in but, for the lack of functioning brain cells, I couldn't remember the configuration. (My cheat sheet mysteriously vanished) So I left the original wiring in place.

John, I appreciate the offer for the notes but at this time, I don't think I'll need them. I just registered my shark and she's not due for an emmisions test for another two years. (Lucky Me)

Richard, thanks for the heads up regarding the green wires leading to the ECU. I have them unplugged.

Thanks again everyone - mystery solved!