AO

Thanks for the clarification, John. Very interesting stuff.

Tony

Ok..where is this vac feed line to the engine taken from?
is this a particular to the pre 87 cars? Is there a vac line to an elctronic box or unit somewhere? its an 86.5

I think it is definitley load related as things occur just as peak TQ occurs.
Belt slip would leave dust and there is not a trace it would also be a smoother line i think.
As far as an air leak, boy, i dont think so, we were pretty happy the way it all went together. Boost hits and stays..doesnt drop off...car idles better than most other 928s.

As far as ignition, i think coils could be a good possibility as thats the only thing he hasnt changed on the car..cap rotors..plugs...MAF..injectors...all new. He runs a tight car .... and F22

BrianG

The EZK vacuum signal line follows the fire wall from near center (off the spider in the engine valley), toward the passenger side, where it turns downward and then penetrates the firewall to run to the EZK beside the LH module.

Shane

The 85-86 32valves had the vacuum signal to the brain, in 87 they upgraded to the knock sensors.

Here is a pic.


It plugs into the back of the ezk.

Tony

Hey Darien, i think we may have found our problem

We saw that line and had no idea what it was. I thought it was a line to the tank venting or somehting..
I think we need to see if its hooked up...or if its getting toooooo much vacuum.

may be onto somehting here.

John Speake

Hi Shane,
On the MY87 and later, there is an electronic load signal fed from the LH ECU to the EZK.

This controls the advance mapping. The knock sensor system is a seperate "fail safe" system. Quite serperate.

Tony

Ok.

what are the consequence of
1) too much vaccum on this signal line
2) or the line capped and no signal


so instead of Kock sensors this EZK takes a signal from vacuum and adjust the timing?
In a nut shell then the there is timing control on the 86.5 cars but its done via this vac signal?

Thanks guys!

MarkRobinson

I have on my car an aquarium check-valve to prevent boost from entering the MAP sensor inside the EZK computer. I'm unsure if others are doing this as well, but since I'm assuming there are no maps for boost for either the EZK or LH (which gets its timing signal electronically from the EZK's MAP sensor), I'd rather not let either computer know there's boost. Here's my first dyno with the turbo, with a leak at the throttle housing @ 4500rpm: a very steady drop in power, just like yours, that's why I suggested it. If your belt is lightly slipping, your boost may not fall off as mine barely did when this happened, until a certain CFM is reached. Just a thought.

Tony

Thanks Mark. I thik this vac line is good candidate for a closer look.
I had no idea that a line is fed to the EZK.

Rennlist...Price of membership....priceless

mark kibort

you have to talk to your dyno operator to see if the graphs were showing the slip adjustments. if you slip, the dyno 99% of the time, takes the spark signal and upgrades the HP curve to where the rpms at the drums "should" be. this tends to inflate the HP numbers too.

I bet its what Mark R. was talking about. his graphs are pretty telling!

Mk

Darien

SWEET I have a few things to check

Darien

Checked the vacuum line to the EZK, it's good. But where should it drawl vacuum from? It's currently tied into the brake boost vacuum.

MarkRobinson

it should pull vacuum from the central tree (off the main port on the throttle body that also serves the fuel pressure reg, dampers)

Darien

Mark, I have two ports on the throttle body, is there a difference? Which one is the "main port"?

MarkRobinson

I the one that tree's about 6 other lines. I think it's the higher-one. The incorrect one has a single feed to the EGR valve on the passenger's side. Anyone have "the" diagram handy? Mine's in my car, can't remember where i found it....lemme look again.

Mark