Stock boost gauge not reading any pressure

[zer0faith]

So I looked at the tsrm and it said that it means the turbo pressure sensor is failing but when I turn the key the gauge goes to zero, then when I start the car it drops all the way back... So the questions are:

Could it be a vacuum leak also or should I just go ahead and replace it or maybe just go to an aftermarket one and bypass it?

And if I do go aftermarket and completely remove the stock one if the ECU would throw codes or throw the car into limp mode?

-V

 

[Dirgle]

The factory boost gauge should go to zero when the ignition is turned on. Then when the engine is started and idling it should go all the way down. I see no issues as far as that goes

Concerning positive pressure readings, the factory gauge has a very slow response time. Have you stayed in boost long enough to see pressure on the gauge?

The pressure sending unit for the factory boost gauge is not tied into the ECU, and there for will not cause codes or issues if it is not functioning properly.

Due to the slow and limited nature of the factory boost gauge, almost everyone goes aftermarket.

 

[jetjock]

What he said. You could always pressurize the thing to see what happens. Simply disconnect the far end of the hose and roll it up.

 

[zer0faith]

Awesome thanks, I appreciate the help. I just got home and my fiance bought me this car as a present while I was in Afghanistan and now I get to fix everything that is wrong with it! haha

 

[80083r]

Awesome thanks, I appreciate the help. I just got home and my fiance bought me this car as a present while I was in Afghanistan and now I get to fix everything that is wrong with it! haha

nice fiancée, be sure and let us know if it doesn't work out...

with the CAR, I meant the car!

 

[Dan_Gyoba]

Heh. Thanks to this thread, I just checked my own factory boost gauge. It reads about -1 (x100mmHg) when I turn on the ignition before it starts up. I've never seen it read at the top of the meter. It used to top out at about +2 (x100mmHg) but has been going to about +3 (x100mmHg) since I swapped on the 3" exhaust. I suspect that the +2 should have read about +3.5 or so, and that now it should be past the top of the gauge. It'll be nice once I have an accurate boost gauge installed.

 

[3p141592654]

Its also quite easy to make the gauge respond faster by changing out a few component in the white box the gauge plugs into.

 

[zer0faith]

Thanks again for the info, I'm picking up an auto meter boost gauge and just going to pull the stock one out and put the auto meter one in its place

nice fiancée, be sure and let us know if it doesn't work out...

with the CAR, I meant the car!

Thank you she is pretty awesome, even hands me tools and is wanting to learn how to turn wrenches on it!

Its also quite easy to make the gauge respond faster by changing out a few component in the white box the gauge plugs into.

how so?

 

[3p141592654]

link to word file:

www.freewebs.com/supraboost/files/1bar boost gauge.doc

 

[Dirgle]

Broken link Pi.

http://home.swipnet.se/pelleman/supra/boost_eng.html

 

[3p141592654]

Whoops. It's a link to word file that apparently doesn't play well with the forum. I think I fixed it now but your link is better.

 

[mkiii222]

link to word file:

www.freewebs.com/supraboost/files/1bar boost gauge.doc

Broken link Pi.

http://home.swipnet.se/pelleman/supra/boost_eng.html

:: dothewave ::

Yet another thing to do to the stupid car this summer. Thanks.

 

[zer0faith]

:: dothewave ::

Yet another thing to do to the stupid car this summer. Thanks.

Haha one of many things... I have a list with about 30 things that need to be checked off.

 

[Dan_Gyoba]

Okay, so if I'm reading this document correctly...

The stock boost sensor is essentially a 2 bar sensor, with the zero point at almost 1/2 bar, therefore it's capability is to read between 1/2 and 2.25 bar absolute. Its resolution doesn't go all the way to zero, so it doesn't really work as a vacuum gauge.

But it can.

So if I were to tap the signal into (for example) the 3.5bar MAP sensor for my Zeitronix wideband/datalogger, then replace the gauge face with appropriate measurements and zero point, the stock gauge could become a full range vac/boost gauge?

Given the response graph, the stock sensor maxes out at about half the sensor's range (About 2.8V) With the 3.5bar Zeitronix sensor, that 2.8V equates to about 14-15 PSI positive manifold pressure.

The zero point would be -20.95PSI, which would never happen. If I were then to use the laser printer trick to make a new gauge face... I'd get the gauge to read ~+/- 1 bar, with no modicifations to the electronics of the gauge at all. This gets you the top range as suggested by the modification, but includes manifold vacuum, which the stock sensor cannot do.

If I did want to (Say to change the range a little) I personally wouldn't use a trimpot, instead I'd trace the circuit and choose a fixed value resistor. Doing this could increase the range of the gauge a little, though I'd be happy enough with it at that. Most likely, I'd just change out the capacitor in order to make it more responsive.

 

[3p141592654]

Yes, that is all correct. I made a board to replace the toyota one with adjustable gain and y-intercept. Has sat on my shelf for 4 years never tested. One of these days.....

 

[Dan_Gyoba]

Wish I had access to your PCB setup... Or did you send it out to one of those places that does it for a fee per square inch? (The best I have is photoresist PCBS, a UV lamp and a big jug of etch solution.)

 

[grimreaper]

Guessing by his initials in the corner of the board, he had a run of boards printed. Any extra boards jon? Time to get a few of those parts hanging around your garage into the car!
Run the 5v signal into a I/O pin on the ecu and boost pressure can be logged.. to much to tinker with, never enough time.

Dan have you taken V readings from the sensor with the car at idle? The formula in question shows 44kpa as a zero point on the stock sender. 30-35kpa would be an expected stock idle vac. Ill check mine out this weekend and see. The author did mention absolutes were not promised.
You have all you need for surface mount setups! Do you use a drill press for the through holes? The inability to apply silk screen has kept me away from etching my own.

 

[3p141592654]

That board has an adc on it that can drive a 3.5 digital display. I got bogged down on the custom gauge face since the display houses all want adobe illustrator files and I don't have that app, which is pretty expensive. You are looking ta $200+ to get some custom faces made, although there are sites that show how to make your own with a laser printer and multiple films.

These days you can get 2 layer and 4 layer boards made at dorkbots for so little money that it is not worth it to make your own.

 

[Dan_Gyoba]

@grimreaper: I haven't taken those readings. I've just tried with the ignition on, but not started. It comes to about -100mmHg with atmospheric pressure in the manifold. Might be the gauge that's wrong, or it might be something electrical. I have other fish to fry when it comes to sorting this stuff out for the time being, so I just haven't got to putting a meter on things yet. I'm also giving serious consideration to leaving the electronics alone, and just using the 3.5bar sensor, then doing the laser printer trick to make a gauge face. It's not like I'm going to use the gauge for tuning, or anything important, just for a sort of "at-a-glance" gauge for manifold pressure. (Though really, between the AVC-R and Zeitronix datalogger, I'll have a more than accurate enough gauge.)

I have a drill press, so the holes aren't a problem. I also have jigs made up for 0.1" hole centers in nice straight lines. I don't do much with SMD, as it's a pain to solder by hand, but I have done it. I prefer to get DIP packages for ICs if I can, as I'm usually not that pressed for space/size with the majority of my projects. Still particularly for small capacitor values, SMD makes some board design much easier.

@pi: I can convert stuff to Illustrator, and can usually do a pretty good job of converting raster images to vector as well.

 

[3p141592654]

The faces I have are in paint shop pro 9. Can you do anything with them?