Full Boost at 1100rpm?

[Robbbyg]

We Previously spoke about too much Boost too soon...
some even were saying that the more boost at lower revs the better...

I don't know for sure what the turbo is doing,
Now in hindsight i have to concede that my 1.5 avg daily boosting when going to the shops was possibly an electrical Gremlin??

(see pic) on start up the guage goes to that spot, sometimes it moves a bit when idling sometimes it doesnt... sometimes when driving its spiking pretty high, (off the gauge) and i drive to the sound it makes..
Recent things i did to car (possible i inadverdantly changed something?)
were

Advanced Timing about 4-5%
Idling high see pic at 1100 because of timing advance, ill drop the idle when i can,
i also
Unplugged wiring from engine bay and cleaned Engine
Checked and tightened Earth wires,
Checked wiring in and around rear fuse panel
Lowered WG to .8 bar (was 1.1) (i went back and checked the diapharagm was in place and all bits secure)

I also reseated, checked fuses, leads, all the bits i could see physically,
unplugged wire from Boost Sender
checked again and re plugged boost sender wire

Otherwise car is showing no problem in driving, charging, starting or cruising everything is fine.

But the boost sensor wire is this a symptom of electrical gremlin?
anyone with similar prob?

[T77911S]

never trust that boost gauge.

[RarlyL8]

Mine boosts at 1bar when the engine is not running. I have the best turbo on the planet!!

Seriously, that is not a joke. The gage sits at 1bar when I shut the car off. Never trust it, they are junk.

[WERK I]

In most cases, bad ground between boost sender on IC and chassis ground. Securely ground IC to engine and see if symptoms change.

[mark houghton]

Originally Posted by WERK I

In most cases, bad ground between boost sender on IC and chassis ground. Securely ground IC to engine and see if symptoms change.

Yep, first place I would look. If you were to unplug the wire from the sending unit, your gauge would peg. It has to have a good ground for the gauge to sit at zero. Somewhere I've got the resistance values for the sender at various boost levels, if you need to trouble shoot the sender itself.

[Robbbyg]

Thanks for the replies,
In answer,

I agree i cant trust the gauge and i do generally listen to whine of turbo ..but if there is a mechanical fault,
ie ;say a prob with wg and the electrical side of it is malfunctioning.. how do we know if car is over its safe limit of boosting..?

does happen pretty quick and i do err on the side of caution when driving but i dont want to i want to really give it to her sometimes but i don't because his forum i hear about engines detonating when too much boost..?? and its starting to get me worried,
But then why do the factory boost guages go to 1.5?? if 0.7 or 0.8 is the safe limit? as 1.5 is Double the factory spring? that doesn't make sense

Anyway
Re; the Bad ground where is the ground on non IC cars??
i did change to a new ground strap that was next to the CDI box and im sure it is secure, i sanded under where it seats to bare metal and sanded to bare the strap connection then bolted it to the body nice and tight.. i cant see any other grounds in the rear..

I Took wire off sender and grounded it, it doesnt drop all the way to zero , about 0.2 on the guage so we can assume it is definately an earth problem..?

The Sender it self, the wire seems to disaappear into the abyss behind the pipes..that i think can be culprit but im stuffed if i can find where it comes from..
So i can assume that i need to follow the wire somehow find where it starts from??

I just want to drive without being apprehensive at all, its a pain to hold back when the valves need a good blast

I Appreciate the help




Relay area, has been double checked the only doubt i have is when i replaced the ground instead of behind the plate holding the cdi, it is between the plate and the CDI now, it is secure, but is in new location im assuming that this is fine?

[Robbbyg]

Rarly8 before you put another 930 on Ebay let me know
Especially if rhd !

[Tippy]

You just need an aftermarket boost gauge. Then you'll know what's really going on.

[WERK I]

Robbbyg,
The boost sensor can be checked for bad ground by running a wire, with alligator clips on each end, clipping one end the metal "can" of the sensor itself ( the nut that allows the sensor to screw into its mount works well ) and the other end to anywhere on the engine. I used one of the small bolt heads that secure the engine shroud to the cooling fan shroud.

[mark houghton]

Originally Posted by Robbbyg

I Took wire off sender and grounded it, it doesnt drop all the way to zero , about 0.2 on the guage so we can assume it is definately an earth problem..?

Sounds like a faulty gauge then. Did it peg to the max when you removed the wire, but only settled to .2 when you next grounded the wire? Could also be a problem with the sender itself. It's a simple pressure sensitive rheostat with very little resistance initially (thus almost mimicking a direct grounding of the wire), and as boost rises so does the resistance. Could be it's shorting out inside the sender, seeing huge resistance too soon (basically mimicking a disconnected wire then - and causing a very high gauge reading when it shouldn't be).

[Robbbyg]

Yes it did max out when disconnected.
Will check it out with alligator clips tomorrow, i did notice today that it did settle when driving so im also thinking the wire itself could be a bit worn or not holding a good current after wiggling it

[WERK I]

I seem to recall when I rebuilt my engine, the sensor has a calibration set-screw underneath the rubber boot, but then maybe I was dreamin'.
I'll confirm this when I drop the engine this coming Winter season.

[mark houghton]

More data, to help with your diagnosis:

Here are the normal resistance values for the sender:

0.0 Bar: 5 - 13 Ohms
0.9 Bar: 117 - 129 Ohms (mine reads 112 at .8 bar)

[Les Paul]

Like everyone has hinted at just get the boost gauge that goes in the clock hole. Works very well.

[guru944]

Les Paul;

Recommend a aftermarket Boost Gauge (VDO, Stewart Warner) stick with analog

Prefer VDO or SW for the look and they are pretty accurate for years (+5 or more)

see my other response to 930 stalling with electrical ground issues. This may also help you.

Later...

[Robbbyg]

FIXED !


CAUSE

The wire that joins to the Boost sender was frayed at female spade connector

Repaired by cutting 1cm off wire and recrimping spade connector to it

Another Easy fix that didn't cost anything ,
cant complain about that

Have a nice week

[Uncle]

Good work.

[930cabman]

The factory boost gauge on our 1987 930 works just fine, I see no need to make any changes.