RustX7

On and on goes my quest. Checked the voltage at the stock boost gauge on my 87 TII today.

FIRST of all, the FSM is a little hazy on which pin is D. It looks like this in the FSM:

--
---------
| C A |
| D B |
---------

And the voltage at D should be 2-2.5 V at 3.9 in Hg of vacuum. Now, I'm assuming that diagram is situated such that the boost gauge would be in front of you and the wires would be coming out toward you, yes? (those two --'s at the top indicate the clip on the connector)

If so, my voltage at about 5 in Hg is something like 1.6 V. As I apply more vacuum, it decreases. It starts at no vacuum at about 2.3V. Does that mean my boost gauge is junk?

What happens when your boost gauge is junk?

NZConvertible

You want the brown wire with a red stripe.

RustX7

Ok I'll check and see which one I was looking at.. the gauge also doesn't go up to 0 when I start the car, which makes me wonder more. It's like it's dead.. I'll see if it says anything when I spool up the turbo soon.

HAILERS

Mine reads 2.20 at idle with the vac hose off and plugged. With the hose on the sensor, and at idle, I see approx 1.15 to 1.20. When at idle, and vac hose plugged, if you read lower than expected, rev the engine up to about 1100-1500 rpm. The alt output seems to effect the output just a touch. Like it'll go from 1.15 to a steady 1.20 on my car(hose plugged).

And while your idling with the sensor hose plugged...gradually raise the rpms from a idle of 750 to just above 1100 rpm. You'll notice as you reach approx 1100 rpm,,,,the idle will jump all by itself to approx 1500 rpm. That's a result of the ECU advancing the timing a touch. Not unusual.

Brown wire with a red stripe.

HAILERS

You might consider accessing the brown/red wire AT the ECU, pin 2B. See if there is an output there. Rev the engine with the vac hose on the sensor. The voltage should go down during deceleration. Down to as low as .24volts. Then go boost the car on the hwy. If its a turbo you should see the voltage go up to about 3.5 plus volts at stock boost levels.

All the plug diagrams should show the wires looking from the wire side of the electrical plug as looking into where the wires are inserted in the plug.

HAILERS

A lot of boost gauges will not go to the zero. They will move when the key is turned on...but not all the way to the zero.

Try this. Plug the vac hose that goes to the sensor. Now start the engine. Did the needle come a lot closer to zero than before???? Most likely it did. Go figure. Maybe the alt is effecting the voltage??? Bad connections to/from the sensor/gauge????????

And by the way. I looked at pin 2B at the ECU for my tps reading. OOOOps. .75 volts. Reset the same to one volt. Never noticed a thing irregular with the car in the last couple of weeks/hell months since I last looked at it.

RustX7

OK I'll plug the hose and see what it says but I kind of doubt it will change.. really "feels" electrical to me.. Going to have to re-read your instructions tomorrow, a little buzzed right now.

HAILERS

The boost gauge needle is supposed to go to the Zero hash mark when the key is turnec to on. Mine does not. It comes close but is still about three needle widths from reaching the zero.,

What I found is.....if I take the vacuum line off the boost sensor and plug it (to keep from having a vac leak only) and then start the car and idle it, the needle will indeed go right to the Zero hash mark. I think it has something to do with the alternator putting out to the battery/ECU. Got me. The vac hose being plugged was to keep the vacuum from the engine from influencing the sensor.

Yes, it's electrical. I did not mean to imply anything else.

RustX7

Hrmph. Haven't had a chance to mess with it yet, but when I start the car, the needle doesn't budge. It just sits at the bottom of the gauge. Looks totally dead. However, when I rev her up kind of quick (not too too quick) the needle will temporarily jump, though not very high... I'm trying to picture what the gauge looks like.. is it a 20 at the dead bottom of the gauge, then some space, then a zero and normal guage marks up to 20 at the top of the gauge? I think thats what I remember. If that's the way it is, when my needle does it's sad little jump, it doesn't make it to the zero.

I haven't taken the car out yet to get on it at all. Still getting plates and such.

HAILERS

Turn the key to ON. The needle should go to ZERO.

START the car. The needle will be at the bottom becauses you are pulling a vacuum at idle.

Quickly rev the engine. The needle will bounce up about three or so needle widths and fall back down. Thats normal.

For you to see boost pressue.....the car has to be driven and have a load on it. Ain't a gonna happen til you get the licence plates etc and go for a drive.

I'm getting the feeling that there is no real problem with the car. Won't know til you drive it and floor it in some gear.

IF you drive it and say floor it in third and see NO boost pressure at all, then you have a serious problem.

And by the way, when I turn my key to ON (not start), the needle does not reach the zero. It comes about three needle widths short of zero. The only way I can make it reach zero is to pull the vac hose off the boost sensor, plug the hose to not screw up my idle, then start the car. It will sit right on zero then. It has something to do with the alternator output to the ECU. I think.

Yeah, if everything is connected up, I can sit at idle and blip the throttle and the needle will momentarily rise up a few needle widths.

RustX7

Oh good. Gotta get on her then and see.

Hey do you think electrical tape on the TID at the junction with the turbo will melt? Sort of half serious question, actually..

HAILERS

It might last for a while. The adheisive will probably get gummy and give out eventually. It should be good for a while whatever that means. You just have to be sure that whatever you do....don't let anythingget sucked in that hose. Not good for compressor blades. Should be good for a few weeks though. Maybe duct tape with a coating of high temp rtv(RED?) over the top of it?? would be better and longer lasting??? Truly clean non oily surfaces for it to attach to? Yeah! I like that for a temp fix. Duct tape with red rtv covering it. Duct tape could fix world hunger if given the chance.

RustX7

Ok so duct tape wrapped around the whole outside of where the crack is, then completely covered with red RTV? What's the red version's specialty? Sounds messy, but then I've never really used RTV for much..yet

Just hypothetically, if you started boosting with an intake leak, what happens... unmetered air makes you go lean and possibly ping because the car thinks it has less air than it really does, thus causing it to not supply enough fuel?

Can a TID be safely made from home depot supplies? I can totally picture how to make the tube but I'm not sure how I'd get the holes in it for that bypass valve and that other vacuum line that attaches below it..

HAILERS

I had a crack there......so I bought a new duct. Just thought about the duct tape and RTV. It's just rtv at the local autozone. Red for hot applications I think. Hot/warm places. Maybe a wrap around the duct, and make sure the rtv overlaps the sides on a clean dry surface to give extra support. Like I said, I bought a new one. Others on this site have made ones.

Yes. Unmetered air the afm won't see.

RustX7

Well I don't exactly run the monster garage so I think I'll order a new one too.. funk dat!

RustX7

I think the boost gauge is working. I took it for a drive and that needle definitely goes all over the place. Usually sits at zero when I'm just cruising. Then when I get on it it'll easily get to about 2/3 of the way up the scale. Haven't totally beat the living **** out of her just yet but...

The 40 on the gauge is kilo pascals I'm guessing?

HAILERS

https://www.rx7club.com/forum/showth...threadid=16779

HAILERS

By the way, I think your the one that asked about a breakout box for the ECU. I finally started making a home made one from an bad ECU. Desoldered the jack from it. Cut the three plugs for the ECU from the a wreck in the wrecking yard about a foot from the ECU.

Soldered wires from the ECU jack to the plugs with a splice in wire in the middle of each section. I put a female part of a snap connector on each spliced wire to pick the signal off with a meter.

So I plug the cars ECU plugs into the jack out of the use d ECU, then plug the three plugs out of the wreck car into the running cars ECU and pick off the signal with the female connector on each splice.

Time consumming. Actually it's not finished. I need ten more of those female connector and RadioShack does not open for another three hours. I've no idea why I'm making it. I could have used it a lot a couple of years ago, but not now. Oh well. Beats trying to put a meter lead in the back of a ECU plug.

RustX7

Thanks for the thread up there.

And yeah, I opened up a junky N/A ecu (I think the plugs are the same anyway?) and thought about all that crap... it looked like a serious PIA to connect those solid metal, flat-shaped conectors.. did you get the solder to hold OK?

Then I thought that simply wire-tapping each wire on my existing harness (I know, I don't really like the idea of cutting into those wires either, but whatever) and running a couple of feet of each of those wires into a bundle and hanging it somewhere easily accessible WITHOUT REMOVING THE CARPETING would not only be easier to do but also make testing even easier in the future. No solder, no screwing around with the carpeting and no unplugging the harness even. Sound good or sound stupid?

HAILERS

I used wire taps for several years with a Molex plug on the end to insert the meter leads into. Never had any trouble. There's only about six to eight things worth looking at anyway. TPS voltage, boost sensor voltage, four injectors voltage, bac, and I threw in the IAT and afm. Oh, watched 02 voltage til I got a wideband. Secondary fuel injector voltage was fun to watch for a while. I'm easily entertained.

RustX7

I was thinking it would be sweet to hook them all up to a digital voltmeter with a dial switch on in with enough nodes to switch to all the pins. Throw that sucker below the radio or something...or in the glove box...

NZConvertible

No, it's 400mmHg like it says on the gauge.

RustX7

DOH