Hard stop under boost

Rich76_911s · Rich76_911s's Garage

Hey guys,

I'm running into an issue on my recently rebuilt engine.

It's running well off of boost and builds boost slightly up to about .5 bar, but once I hit 0.5 bar the engine just suddenly hard stops.

I noticed on one occurrence that the AFR meter hit 20 when this happened.

I did replace and test the new overboost sensor which seems to be functioning as expected.

However, I'm wondering if I may have caused this issue by using a silicone elbow to connect the intake air pipe to the turbo. Some idiot (yeah me) cut the intake pipe and I used this elbow to "repair" the hack job cut I made.

Do you think this elbow is collapsing (See photo with arrow) when boost builds up and is causing a major lack of airflow through the engine? Or am I on the wrong path in thinking this could be the culprit and should be looking into the yellow overboost relay?

Really want to be out on the road putting some miles on it this fall!!

* *Sorry photo isn't loading at this moment will try again later**

greglepore · 10-04-2021, 09:05 AM

Try running it on a brief run without the elbow and see? But I suspect its something else.

Rich76_911s · Rich76_911s's Garage

Here is the photo:

Rich76_911s · Rich76_911s's Garage

Quote:

Originally Posted by greglepore

Try running it on a brief run without the elbow and see? But I suspect its something else.

Greg - I am running CIS and I don't think I could run it without that elbow, otherwise the metering plate wouldn't see any airflow and would be closed at all times. Resulting in no fuel.

But maybe I am misunderstanding your suggestion.

greglepore · 10-04-2021, 10:08 AM

Ok. Didn't realize you were on cis and that the metering occurs upstream of the elbow. But I find it hard to believe that you could create enough of a vacuum there to suck the hose shut.
If its leaking elsewhere that would also account for a crazy high afr, as the metering unit would see giant airflow but none would actually be reaching the intake...

speednme1 · 10-04-2021, 10:20 AM

Rich I had a similar issue. Turned out to be a bad fuel pump relay(although it was new). I replaced it with the old relay and the issue went away.

Rich76_911s · Rich76_911s's Garage

Quote:

Originally Posted by greglepore

Ok. Didn't realize you were on cis and that the metering occurs upstream of the elbow. But I find it hard to believe that you could create enough of a vacuum there to suck the hose shut.
If its leaking elsewhere that would also account for a crazy high afr, as the metering unit would see giant airflow but none would actually be reaching the intake...

Thanks Greg - I wish I was running EFI

Quote:

Originally Posted by speednme1

Rich I had a similar issue. Turned out to be a bad fuel pump relay(although it was new). I replaced it with the old relay and the issue went away.

Thanks, Ray that is an easy fix if that is all it is. I have a couple of those lying around from various cars I've taken apart over the years.

krasuskyp · 10-04-2021, 11:25 AM

DOOD! YUUUUUGE CONGRATS on getting back on the road brohammage!

WELL DONE!

Hope this fix is something simple for ya...

Rich76_911s · Rich76_911s's Garage

Quote:

Originally Posted by krasuskyp

DOOD! YUUUUUGE CONGRATS on getting back on the road brohammage!

WELL DONE!

Hope this fix is something simple for ya...

Thanks, amigo. If you want to make some money buy whoever sells Zanax cause I'm going to need an IV of that stuff in constant supply

Gonna take me a while to get comfortable with this build even though I've been about as anal as I can get.

mark houghton · 10-05-2021, 06:15 AM

Me, I would at least try grounding out the wire to the overboost switch....even though you have installed a new switch, it could be defective. At least take that possibility out of the equation.

RarlyL8 · RarlyL8's Garage

^^^
This is classic overboost switch malfunction. New part means nothing today, cheap crap everywhere.

Rich76_911s · Rich76_911s's Garage

Thanks, Mark and Brian. I'll give that a shot and report back. Might not be until the weekend that I can tackle these things.

smurfbus · 10-05-2021, 09:42 PM

could also be the first elbow on the metering plate. Mine did that.

Rich76_911s · Rich76_911s's Garage

All ya all that guessed overboost sensor win the prize. Grounded it out and the car built 0.7 bar without a problem. Thanks for all the suggestions. Good news is it’s a relatively easy fix.

Only issue left is that I’m getting some smoke out of the turbo / oil line connection.

mark houghton · 10-08-2021, 08:25 AM

Great news! It's usually the simplest things.

gsxrken · gsxrken's Garage

Quote:

Originally Posted by Rich76_911s

Only issue left is that I’m getting some smoke out of the turbo / oil line connection.

Hope it’s not the line from the breather area to the turbo. That one would be a beeyotch to get at with the intake and etc on the engine. Is it new?

Rich76_911s · Rich76_911s's Garage

Hey Ken. Yeah that’s the line. Fortunately I got one from Turbokraft that is a flexible line.

I’m pretty sure it’s just not tight enough. I added a GT-35r turbo and there is an oil restrictor at that junction. I imagine the oil pressure is quite high behind that restrictor and that’s where I’m leaking. I just have to tighten it down some more, I hope.

Going to make a better ground for that overboost switch and take it for a longer test drive today. Also need to wash 3 years of dust off the car.