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914World.com _ 914World Garage _ D-jet FI Part
Posted by: Rhodes71/914 Jan 18 2005, 11:20 AM
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
Sean
Posted by: JOHNMAN Jan 18 2005, 11:32 AM
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.
Posted by: scott thacher Jan 18 2005, 11:35 AM
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
Posted by: Headrage Jan 18 2005, 11:36 AM
I think it's the rev limiter.
Posted by: eric914 Jan 18 2005, 11:38 AM
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?
Posted by: Root_Werks Jan 18 2005, 11:43 AM
I thought that was what took the place of the mechanical rev limitor on the dist rotor? It was on the 75-76' models. 
Posted by: ClayPerrine Jan 18 2005, 11:48 AM
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.
Posted by: Headrage Jan 18 2005, 11:48 AM
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.
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Posted by: Headrage Jan 18 2005, 11:49 AM
Okay, I'm clear.
Posted by: Rhodes71/914 Jan 18 2005, 05:49 PM
OK thanks for the info. Wonder what RPMs it cuts out at?
Can I eliminate it?
Posted by: Cap'n Krusty Jan 18 2005, 06:08 PM
Shuts off the fuel on decel. The Cap'n
Posted by: mattillac Jan 18 2005, 07:34 PM
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? 
Posted by: nebreitling Jan 18 2005, 08:17 PM
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! 
)
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.
Posted by: Mueller Jan 18 2005, 08:35 PM
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....
Posted by: McMark Jan 18 2005, 08:39 PM
Where's Mr. Anders when you need him? He's supposed to know all this stuff.
Posted by: nebreitling Jan 18 2005, 08:54 PM
| 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?
Posted by: Rhodes71/914 Jan 18 2005, 09:43 PM
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.
Posted by: JOHNMAN Jan 19 2005, 12:54 AM
Well, my "guess" was wrong...... 
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.
Posted by: Jeff Bowlsby Jan 19 2005, 09:18 AM
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.
Posted by: ClayPerrine Jan 19 2005, 09:53 AM
| 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.
Someone who has one needs to do a dissection on it just out of curiosity,
Posted by: Rhodes71/914 Jan 19 2005, 11:23 AM
OK Jeff I'll repeat after you...
it's a rev limiter
it's a rev limiter
it's a rev limiter
Thanks for clearing that up.
Posted by: RustyWa Jan 19 2005, 01:51 PM
I've got one, but have a questions on them. Are they dependant on certain ECU's? Can you have say, a '74 ECU and then get this device and the harness with the SL wiring...will it still work?
Just curious.
Posted by: bondo Jan 19 2005, 02:04 PM
| QUOTE (nebreitling @ Jan 18 2005, 07:54 PM) | ||
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? |
The decel valve doesn't do a thing to the mixture. All it does is add a controlled vacuum leak (kinda like the AAR does) when you let off the gas. It brings the RPMs down slower than would happen without it. Most people don't like this and remove it. It can calso cause funny things if it fails.
Posted by: Jeff Bowlsby Jan 19 2005, 02:04 PM
| QUOTE |
| Can you have say, a '74 ECU and then get this device and the harness with the SL wiring...will it still work? |
I wouldnt frankenstein these parts Rusty...its not that easy.
So in a word, No. Not only are the harnesses wired a little differently, you would also need the 75-76 fuel injectors and TTS...and I bet that the 75-76 ECU is internally different to accomodate this SL.
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