Mr. 8R6X7

iTrader: (4)

I just purchased an s5 tii and the boost gauge along with the rpm gauge are not working. All of the other gauges and lights work properly as they should. Where does the RPM gauge get its electrical signal? I couldn't find a wiring diagram. Where does the boost gauge get its signal from? I would think that the boost gauge gets a vacuum signal. Is the boost gauge signal vacuum or electrical? Thank you.

satch

iTrader: (1)

Boost Gauge gets its 'electrical' signal from the Boost Sensor from the Green/Yellow wire and it should read 2.2 to 2.5 volts w/key to on, plug connected to sensor. The tach gets its signal from the trailing coil via the Yellow/Blue wire.

rotary_bünta

iTrader: (3)

pm me your email, i tried uploading a 1 page pdf but this 100kb file size limit is terrible. i have fsm you need with wiring.

Mr. 8R6X7

iTrader: (4)

I was able to verify this yellow/blue wire coming from the trailing coil. It is one of a four wire connector. Now, on the harness side, the connector has another single (yellow/blue) connector which is just dangling there. I want to assume it is used for testing purposes because I couldn't find another wire to connect it to.

Is there a way of checking the signal or voltage coming out of the coil to the rpm wire? I would think the signal would be an on/off signal but is there any way to check if the coil is not sending the rpm signal or if the instrument cluster is just damaged? I am lead to this because the 4 wire connector is plugged in properly and the wires are all in good condition.

satch

iTrader: (1)

The bullet connector that connects to nothing by the trailing coil should read .76 volts DC while the engine idles at 750 rpm. If it does then either the problem is the wiring between the coil and tach or the tach itself is the problem. Also, there is a similar connector near the lead coil. Jumpering these two connectors together will cause the tach to use the lead coil for its signal. If this causes the tach to work then you know your issue is not the tachometer. So, if the jumper causes the tach to work and the voltage at the trailing coil bullet connector reads .76 volts DC while idling then the problem lies w/the wiring between the trailing coil and the tach. You also might want to check if the trailing coil sparks or not because if it did not then the tach could not work.

Mr. 8R6X7

iTrader: (4)

Great info! I will definitely try that. One thing though, if the trailing coil did not work, wouldn't the car have idling issues? It is idling fine with no kinds of hesitations.

satch

iTrader: (1)

The engine could idle fine using the lead coil alone. If the engine were running only on the trailing coil then it would run rather rough.

smikels

Take this for what it is worth. I had an issue with my RPM guage after I was adding a FMIC. The issue was the secondary coil was not grounded very well. I fixed the ground and it is now working fine. I just wanted to throw this out there. I am not an expert by no means and have not had this car that long and am still learning. So like the other guys have posted it is something with the secondary coil more then likely.

Mr. 8R6X7

iTrader: (4)

Just to give an update on my situation... I was testing the voltage on the trailing coil bullet connector and retrieved a .74 volt signal. So I take a look at the rpm gauge and it is working! What gives! I'm glad it started working but I am a little disappointed that I can't check to see what was wrong. I drove the car to auto zone to buy an air filter for it and I noticed that my boost gauge does in fact work. You can just barely notice it because it barely moves from the -20 to about -10 which leads me to believe that there is a vacuum leak somewhere. Does this mean that my turbo is not boosting to its maximum capability? Would you guys agree that I could have a vacuum leak and not a faulty sensor or gauge?

satch

iTrader: (1)

Did you test the G/Y wire at the Boost Sensor?

Mr. 8R6X7

iTrader: (4)

Yes and I retrieved a 2.25 volt signal with the key on engine off

satch

iTrader: (1)

Using the advanced search feature found this one thread. There are many other threads to help deal w/the possible causes of your problem.

https://www.rx7club.com/2nd-generati...-help-1049677/

Mr. 8R6X7

iTrader: (4)

Thanks Satch! You have been of great help with a lot of useful information!