Trying to think of anything that might be causing this JDM S5 TII to not idle right, and I have noticed that the boost gauge on the dash doesn't register anything at all. When you start the car it flickers ever so slightly but never moves. Have checked the vacuum line going to it and that's fine, so I want to check the actual sensor itself.

The FSM talks about applying vacuum to it but I don't really have the tools to be able to do that at home. Was wondering if there are any stock readings that I can check out, like the S4 voltages mentioned here:

https://www.rx7club.com/showpost.php...58&postcount=3

At the moment I have the following voltages. All were taken with the engine off, the key to ON, and the pressure sensor harness connected.
Brown wire with blue stripes around (top right): 0.03V
Brown wire with white stripe (bottom right): 5V
Yellow wire with green stripe(bottom left): 2.38V

Any ideas would be greatly appreciated

 

It's a 2 bar MAP sensor. atmospheric pressure is going to be around 2.50 volts depending on ambient conditions (on the signal wire, presumably yellow/green wire) and very high vacuum is almost 0 volts. At the sensor's max range (nominally 14.5 psi boost but could be higher than that) the sensor will read almost 5 volts.

your other two wires are your ground and your 5 volt reference. It works like any other linear 5 volt sensor (temp sensor, TPS, etc).

 

Thanks for that. Will have to look a little further then to find out why my gauge is not showing any boost or vacuum.

 

Like the series five FSM says, the output voltage of the boost/pressure sensor should be approx 3.4 to 3.6 vdc with the key ON, engine OFF. Turbo car.

Your sensors output is kaputski.

And it's a green wire with yellow stripe.

 

But doesn't it say in the service manual you've got to apply some vacuum to the sensor in order to check that 3.4-3.6V?

If the sensor is dead, could it cause problems with an unsteady/misfiring idle?

 

No. You don't have to pull a vacuum on it to prove it bad. See the attached jpg. It gives two tests of the pressure sensor. Yours fails the first one. It's bad. Get a good one.

Frankly you don't even have to plug the hose as called for in the jpg. Just key ON and measure the voltage on the G/Y wire (with it still connected to the sensor of course). If you plug the vacuum line and actually start the engine, the voltage of the G/Y might be a hair more but no more than a hair more in voltage. Not worth mentioning.

As for your gauge, just connect a source of pressure to your sensor and watch the gauge as you apply pressure to the sensor. Gauge should go up. Just proves one way or the other that the signal is getting to the gauge. Not much more than that. But your sensor is bad. So get a good one.

 

Cheers for that. Believe me when I tell you I did read that, but I must have just read it wrong last night.

So what effects could a dead boost pressure sensor cause?

 

And could I use an N377 boost pressure sensor in there? Currently I have an N370 but from SonicRaT thinks it should be ok according to one of his posts.

 

What car does the N377 come off??????

Aarron Cake says it's for a series five turbo. So since your car is series five turbo, that's what you want.

EDIT: I notice on series five cars, both non turbo and Turbo read the same according to the Control Unit pages. NOT like that on series four.

 

that's what I get for being too lazy to look at the FSM

 

Well this is strange. I've tested 3 pressure sensors now and all 3 are giving me the same 2.34-2.35V on that wire with the ignition on and the engine off. Are all 3 sensors bad or does it look like my problem is elsewhere?

Still can't work out why my boost gauge is not showing anything.

 

Even with the car running and moving, the boost gauge is still not showing anything. My aftermarket gauge is recording the correct readings though.

Any thoughts on what more I can check out here. I've been checking voltages at the sensor. Am doubting it will be any different at the ECU though. I could live with it if it was just for the gauge, but am sure it must have other effects in the ECU, and if the right boost pressure isn't being sent there then I'm not gonna get the best out of the car.

 

Where are you checking the voltage (how far from the sensor)? Perhaps there is a broken/damaged wire somewhere between the sensor and the test site or ECU?

Where is the aftermarket boost gauge connected to the motor? try running the Pressure sensor hose to where the boost gauge is getting its vac source.

 

Aftermarket boost gauge is T'd to the the pressure sensor hose so it's not that.

I was checking the voltage at the sensor itself. May have to try checking it at the ECU instead.

 

Didn't get round to checking the ECU connections before I drove it to my garage to get inspected and registered to be road legal. But I did notice something when driving. When I put my foot down a little (only slightly into boost), the stock boost gauge needle moved up a little, but only 1/8-1/4" or so. Might be a stuck boost gauge needle but there is a little movement there I think.

 

 

So today I received my new boost pressure sensor in the mail. this was after I did the test voltage (load test) on my old sensor. It only had 2 volts going to it. So I installed my new sensor and I reset my ECU by taking off the both the positive and negative leads to my battery and then held both the leads together for 15 seconds to drain all voltage in the whole system. I then put my leads back onto my battery. I started her up and now the code disappear on she is running fine with the new boost pressure sensor.