D-jet FI Part, Unknown to me Options

[Rhodes71/914]

Off my '75 2L. Not very far from the ECU. What is it, what does it do?

There isn't one on my 1.7

(IMG:http://homepage.mac.com/seanrh1/.Pictures/914%20Pics/FI%20ECU.jpg)

Sean

[John]

Part of EGR electrics????? Just my GUESS as I don't really know either.

I know these cars had an "EGR" light on the dash though. Something must have turned it on.

That looks like a lot of wires going to that thing.

[scotty914]

i thought the egr light was turned on by a counter in the pass side foot well by the speedo cable

but i have never owned a djet so i could/maybe/probably am wrong

[Allan]

I think it's the rev limiter.

[eric914]

The part description for the part shown:




- E 039 905 351 RELAY FOR SPEED DISCONNECTION 1 914-2,0(CAL)


Not shure what it does. Only present on CA cars. Possible part of Cat system?

[Root_Werks]

I thought that was what took the place of the mechanical rev limitor on the dist rotor? It was on the 75-76' models. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[ClayPerrine]

It's a rev limiter. The rev limiting rotor that came in most 914s created a delibrate misfire at high RPMs. This would cause unburned fuel to dump into the exhaust. That increases Hydrocarbon output at the tailpipe. Thats a big NO-NO for a catalytic converter engine. The cat will overheat and melt the catalyst if a lot of raw fuel is dumped into it.

So they added a rev limiter to the injection. This cuts injector pulses when the engine speed reaches the preset RPM level. Same effect as the rev limiting rotor, but it doesn't dump the HC into the cat.

[Allan]

I posted the same pic and asked the same question when I tore my motor out and that is what I was told. Now you got me wondering.

[Allan]

Okay, I'm clear.

[Rhodes71/914]

OK thanks for the info. Wonder what RPMs it cuts out at?

Can I eliminate it?

[Cap'n Krusty]

Shuts off the fuel on decel. The Cap'n

[mattillac]

if that things a rev limiter, then i don't think mine works. but my dizzy doesnt have the rev limiting rotor that my haynes manual shows.
if i remove that thing, will i gain HP? (IMG:http://www.914world.com/bbs2/html/emoticons/slap.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/alfred.gif)

[nebreitling]

i have NEVER gotten a satisfactory answer on this...

i have been told that it's a rev limiter by many knowledgable 914ers.

but mine sure as hell never worked as a rev limiter (ask me how i know! (IMG:http://www.914world.com/bbs2/html/emoticons/unsure.gif) )

one familiar mechanic at a very well-known independent porsche shop told me it was to compensate for barometric pressure/altitude (or something like that). he told me that he had seen it be the fault of a few poor running cars in states like colorado.

car ran just the same with it plugged in as it did no plugged in, regardless of altitude. no you won't gain any power. but you'll remove like 3 oz., which will make your car that much faster!


honestly, i think it's just there for show.

[Mueller]

if'n the Cap'n is correct, it wouldn't be too hard to test depending on if it didn't allow the allow the injectors to fire or not under deceleration....the very early 1.7's had that feature built into the ECU from what I have read....

[McMark]

Where's Mr. Anders when you need him? He's supposed to know all this stuff.

[nebreitling]

QUOTE (Cap'n Krusty @ Jan 18 2005, 04:08 PM)

Shuts off the fuel on decel. The Cap'n

if i had to choose one, i'd probably put my money down on this -- although isn't that what the decel valve is for?

[Rhodes71/914]

Well I thought I would get a simple answer but obviously that's not the case.

I like eric914's post

QUOTE

E 039 905 351 RELAY FOR SPEED DISCONNECTION 1 914-2,0(CAL)

That really tells us a lot "speed disconnection" I guess that could be decel.

I think I will just leave it plugged in and call it good.

[John]

Well, my "guess" was wrong...... (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

I checked the 75 wiring diagram when I got home from work and sure enough it is a "speed switch".

It ties into the trigger points in the distributor and potentially disrupts the pulses from them....

You can remove this without ill effect. From the wiring diagram it is difficult to determine the function.

[JeffBowlsby]

Believe the Capn gents...say it ten times...all together now...

Its a rev limiter
Its a rev limiter
Its a rev limiter
...

It was only an option on some of the 1975-76 cars. Some of the 1975 cars in particular do not have them. So there are actually 2 FI harnesses for the 1975-76 2.0L cars, one with and one without the connector for this gizmo. I make them both, but most people want the one with the connector.

It is not an atmospheric control...all D-Jet cars have that built in as a feature of the MPS. Atmospheric pressure modifies the action of the diapragm within the MPS as appropriate, which is one of the reasons its a great device...

You can disconnect the rev limiter and the only thing that will happen is that your cars revs (speed) wont be controlled under those conditions under which it is supposed to work. Check out the wiring digram for it in the manuals and maybe you will understand it better.

The Decel valve is not a rev limiter, it serves a different purpose entirely.

[ClayPerrine]

QUOTE (nebreitling @ Jan 18 2005, 08:17 PM)

one familiar mechanic at a very well-known independent porsche shop told me it was to compensate for barometric pressure/altitude (or something like that). he told me that he had seen it be the fault of a few poor running cars in states like colorado.

The altitude compensator was on some the 1.8 L-jet equipped cars. It's not needed on a D-Jet car. The L-jet harness in my wife's 1.8 has the connector for the altitude compensator, but the box is not there. I think it's NLA.


It's a rev limiter. Both the part number and the wiring diagram back this up. If yours didn't limit the rpm range, then it's broken. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Someone who has one needs to do a dissection on it just out of curiosity,