Turbo Gauge Behavior

[Fourdoorcat]

First of all: the car runs great. If there was no Turbo gauge, I likely would not be writing this at all.

Lately, instead of going to zero bar, the needle seems to be normally at 0.25 bar. Under load, it at times goes to 1.0 bar. No lights come on; no hesitation, stumbling, desire to idle poorly. Nothing. At times, it does behave in the "normal" manner: zero without boost and max of 0.6 or so bar. It seems to desire the 0.25 to 1.0 bar mode more and more.

I did do the "wiggle" by disconnecting the wastegate vacuum line and cycling the rod about a dozen times. This didn't change anything.

Is this something I should know about, but didn't do an adequate search of the forum to find?

Thanks in advance,

Ken

[superbad]

Check the ground on the boost gauge transducer. It's the orange rubber thing mounted to the left of the engine on the inner fender, it will have a vacuum line running to one end of it.

[Fourdoorcat]

Hey thanks, Superbad. The ground wire from the frame going into the grommet next to the green wire with the slip-on lug both appear to be tight and uncorroded. I did reset the slip on, but there was no change. Then I ran a clip lead from the frame of the transducer to a metal point on the intake plenum. That seems to do the trick! Wire on while idling; gauge resets to zero. Wire off; goes to 0.25bar. Wire back on; same as before.

I had the wheel liner off when I did the timing belt and am willing to bet I did something to affect that ground. Not a big priority, but something that goes onto the fix list. I attached a picture showing where the jumper went. I had to hunt around for a "real" ground. This is not so obvious with our plastic cars!

Your help was really appreciated!

Ken

[Fourdoorcat]

A follow up:

I thought this over today and decided that I had missed something. I measured the resistance from the ground lug at the bracket to the engine block (not from the bracket to the engine block). The resistance was a couple of ohms, i.e. a direct connection. Even though the ground lug looked OK, it wasn't from an electrical perspective.

Here's why: The screws that hold the bracket for the boost sensor thread into some sort of captive, plastic nut. This isn't the mechanical configuration that would yield sufficient clamping force to produce what is called a "gas tight bond" for a lasting electrical connection. The consequence of tightening it too much is to strip out what are probably relatively fragile threads and reduce the force exerted between the lug and bracket even more.

So I burnished the mating surfaces with steel wool and remade the connection. A resistance check and quick run of the motor shows the same result as the jumper wire from last night. The problem is solved, for now.

A lasting solution would be to drill and tap another hole in the bracket and attach the ground wire lug to it. Then sufficient torque could be applied. That task will go on the fix list.

Ken

[GeoffSmith]

Not the best earthing point IMHO and the usual cause of gauges reading higher than normal.

[Kragof]

I think mine has a similar issue, thanks for this.

I was wondering what the turbo was doing and didnt take me long to find this thread

[TOWATL]

Hi guys!

The turbo gauge on my car shows much less pressure than it should. The car seems to have enough power, so I am wondering if the issue described here could also have the affect I am seeing.

Thanks!

Cheers

[jello]

I'm having a similar issue. Interesting thing to me is this - the reddish/orange thingy on the passenger side (USA) of the engine compartment is a factor. I think that's the pressure gauge transducer, right?? I have an alligator clip ground to one pole, and the turbo gauge reads very steady. My concern is that I never get overboost anymore. I have boost, but it is 0.5 bar max. If I take off the alligator clip ground, the gauge is totally erratic. Could read 1 bar when I'm decelerating, etc. but it seems like I have more boost. Maybe it's in my head. Anyone know if the gauge transducer effects the computer and the overboost????

Phil Bates

[JPope]

Thanks guys i have had my elan for 2 months and my boost gauge used to be erratic and is now always on 1 bar. this will defiantly help me get that resolved. its the little things that drive me crazy.

[djwazza68]

I have possible earth problem, but can't figure it out. The gauge returns a negative .25 boost under load, and sits at zero normally. What is going on? The earth from the bracket on the transducer appears to be good.

[Fredjohn]

I have possible earth problem, but can't figure it out. The gauge returns a negative .25 boost under load, and sits at zero normally. What is going on? The earth from the bracket on the transducer appears to be good.

Check the other end of that earth lead. If you have a multimeter, do a continuity check of the transducer earth lead.
I assume the vacuum pipe is correctly attached at both ends?

[djwazza68]

I've got a good earth and the tube is fine, it's seems that the gauge is reversing the input in some fashion. I get a reverse boost indicated as the turbo kicks in. Is there an easy electrical fix? My auto electrics are pretty sketchy at the best of times....