Stock "pressure gauge"

[skelly]

`Allo. This is kind of a difficult thing to search the site for because of the prolific use of words like "boost", "vacuum", "stock" and "gauge", and unfortunately the Haynes repair manual doesn't seem to get into it. So here's the deal: my stock boost/vac gauge doesn't seem to be getting a signal. it's pegged at the bottom and doesn't budge other than a slight twitch when first starting the engine. My questions are:

1) Is it an electric gauge with a remote sensor mounted somewhere on the engine, or is it a purely mechanical gauge?

2) Where is the vacuum source for this gauge in the engine bay?

The Haynes manual shows the gauge on the elecrical diagram with a wire coming from it to "MFI Control Unit" but doesn't mention MFI control Unit anywhere else in the manual that can be referenced, so I have no idea what and where that is. But it does lead me to believe that the gauge is electronic and that there is a sender somewhere under the hood that I am unaware of and that is probably unplugged in the wake of my recent round of maintenance.

Thanks for any insight you may be able to spare.

- SK

 

[Quasimondo]

`Allo. This is kind of a difficult thing to search the site for because of the prolific use of words like "boost", "vacuum", "stock" and "gauge", and unfortunately the Haynes repair manual doesn't seem to get into it. So here's the deal: my stock boost/vac gauge doesn't seem to be getting a signal. it's pegged at the bottom and doesn't budge other than a slighty twitch when first starting the engine. My questions are:

1) Is it an electric gauge iwth a remote sensor mounted somewhere on the engine, or is it a purely mechanical gauge?

2) Where is the vacuum source for this gauge in the engine bay?

The Haynes manual shows the gauge on the elecrical diagram with a wire coming from it to "MFI Control Unit" but doesn't ever mention MFI control Unit anywhere else in the manual that can be referenced, so I have no idea what and where that is. But it does lead me to believe that it is electronic and that there is a sender somewhere under the hood that I am unaware of and that is probably unplugged in the wake of my recent round of maintenance.

Thanks for any insight you may be able to spare.

- SK

1. It's neither. It's just a moving needle that tells you what the ECU thinks the turbo is pushing based on the MAF sensor. I trust that guage to give me an accurate boost reading as much as I trust a used car salesman.

2. There is no vacum source for this gauge. Get a mechanical gauge, and use that to keep an eye on boost.

 

[boostedinaz]

`Allo. This is kind of a difficult thing to search the site for because of the prolific use of words like "boost", "vacuum", "stock" and "gauge", and unfortunately the Haynes repair manual doesn't seem to get into it. So here's the deal: my stock boost/vac gauge doesn't seem to be getting a signal. it's pegged at the bottom and doesn't budge other than a slighty twitch when first starting the engine. My questions are:

1) Is it an electric gauge iwth a remote sensor mounted somewhere on the engine, or is it a purely mechanical gauge?

2) Where is the vacuum source for this gauge in the engine bay?

The Haynes manual shows the gauge on the elecrical diagram with a wire coming from it to "MFI Control Unit" but doesn't ever mention MFI control Unit anywhere else in the manual that can be referenced, so I have no idea what and where that is. But it does lead me to believe that it is electronic and that there is a sender somewhere under the hood that I am unaware of and that is probably unplugged in the wake of my recent round of maintenance.

Thanks for any insight you may be able to spare.

- SK

The gauge is pointless and once you get a good mechanical gauge you wont even need it not look at it again.

 

[99gst_racer]

Yup, Quasimondo is correct. The readings of the factory boost gauge are merely ECU estimations. There are no sensors whatsoever.

Is your ECU stock or has it been chipped (TMO, Keydriver, etc....)?

 

[skelly]

Interesting - I wonder why the gauge wouldn't display any output then. I do have a mechanical autometer boost/vac gauge which I use under the hood to verify the vacuum, but I'm not ready to install it yet. My ECU is stock and I just replaced the capacitors in it. Thanks for the replies.

- SK

 

[steve]

My ECU is stock and I just replaced the capacitors in it.

Did the gauge stop working about the same time?

Steve

 

[skelly]

Did the gauge stop working about the same time?

I do believe so. I'll try giving the harnesses a wiggle to see if one of the connections is loose.

It's also possible that the thing has lost power. The short version of a long story is that the dash is a jungle of garbage, amateur wiring because some kid who owned the car before me adapted this gnarley alarm system with built-in cellular/pager notification and all this crap. So I gutted the thing and it turned out that it was tied to the power windows and such things which now don't work because I removed those electronics. In time I will revert the wiring under there to the way it was shipped from DSM, but it is entirely possible that one of the several spliced power lines under there was part of the instrument cluster as well.

- SK

 

[steve]

I just spent the past two days ripping out the loose harness from an old aftermarket alarm in the Stealth. Next is the aftermarket remote starter. Between the two they have totally hosed the ignition harness so I know what it's like. I hate being upside down in the front seat trying to reach stuff.

The "Boost" gauge output is pin 3 on the ECU. It's a PWM signal. I don't think I've seen one go bad on the ECU but if your caps leaked anything is possable. It's close enough to where things normally get damaged.

Steve

 

[skelly]

...I hate being upside down in the front seat trying to reach stuff...

Ugh - as if us old men don't have enough back problems already, right? If only there was a flip-up dash with a prop like the hood has ::

So I found & fixed the problem: operator error. There were a couple extra harness plugs in the way of reaching the ones from the ECU and I'd missed plugging one that was below and to the left of the ECU. Once that was reconnected the gauge worked fine again, for what it's worth. Heh.

Thanks for the input.

- SK