E-man930

I finally got around to making a stainless steel braided wastegate pressure line to replace the soft rubber one that was on my car...
Noticed my max boost now dropped to .9 Bar from 1.0 Bar... I have not decided if this is a bad thing yet since the car almost feels like it is pulling the same. Now the really interesting part is that when I let off of the gas pedal from WOT and full boost I no longer get a boost spike! The boost gauge just drops to zero where as before it would spike up about an extra .2 bar...
I can also now audibly hear the wastegate pop open under full boost to vent and dump the excess. (I mean I can hear the valve kind of "pop" open... not the noise coming from the engine's exhaust with a vent to atmosphere dump tube...)

I'm thinking the old spongey line would flex and not open the wastegate as far as the stainless braided line currently is... I just can't place my finger on why my boost dropped to .9 Bar...

Any ideas?

E-man930

special tool

You probably were bleeding control pressure before.
It feel the same because you did not have the proper fuel to match the excess air, especially if it was spiking.
You are most likely VERY lucky that you decided to change the line.

E-man930

I did a few more runs last night and this time I moved the tell-tale needle out of the way of the boost needle and the car is hiting 1 Bar... Looks like the tell-tale was hindering the boost needle from showing correctly. I 'm going to test the old line and look for holes/tears/rips...
Will post findings tonight.

Here's a few pics of the new line.

E-man930

Yen

I bought a '77 930 with a dead boost gauge which constantly points at 1. Car drives fine but produces one/sometimes a string of pop sounds whenever I lift off the accelerator pedal. Is this problem from the boost that i cannot read or just misfires/backfires from the engine which could be fine tuned?

sand_man

I think the backfires are some what normal on decel. My car (an '87) came equiped with a decel valve (part of the smog system) that assisted with keeping the revs up slightly once the throttle pedal was lifted. I have since disconnected the valve as it began to interfere with my normal idle. I've noticed that there's more of a backfire/gurgling sound now on decel...I kind of like it though.

One thing to watch, however, is that excessive backfires can be indicitive of a lean mixture. At least that's what I once read in another thread.

Geoffrey

It does not matter how lean the engine is when the throttle is lifted. Lean misfires on decel are normal and are more pronounced on a car with a good exhaust.

sand_man

I found the thread I got the info from:
https://rennlist.com/forums/showthre...light=backfire

Yen

Thanks guys! Exactly what the mechanic told me and in fact, he has the same phenonmenon on his '86 carrera too, does'nt bother him.

Sameer

Yen,
Backfires are normal on decel and especially more with after market mufflers/exhaust

BrianKeithSmith

Dang, there's an echo in this thread!

A930Rocket

LOL

Sameer

Very Funny guys