Yes, and the TPS measures 1 volt after the car has been thoroughly warmed up.

 

I'll give it a shot tomorrow and post back with the results. Thanks.

 

Pressure sensor reading (car not running, ignition key on): 1.8-1.9v (same reading with and without the hose capped)

 

I didn't get to the TPS sensor yet...do you think it may be the pressure sensor gone bad?

 

Rtek released an optional cheap upgrade that was supposed to eliminate the secondary staging lean condition, did you know about this? I upgraded mine a while back and it seems to be better, though I still have some stumbling issues. However, since my motor is now blown I couldn't tinker with the tune if I wanted to.

 

latter poster's issue sounds like a failing airfow meter.

 

It would appear that yours is kaput. To make sure you might want to test two other wires at the sensor. W/key to on the Black/White wire measures 12 volts and the Brown/White measures 5 volts. If these are what you get then your Boost Sensor is out of spec.

 

Black/White: 9-10v
Brown/White: 2-3v


What does this mean?

 

?

 

At first glance, it would appear your battery is very weak. Measure the voltage of the battery itself. And you can measure the same two wires w/car idling to see if they are the same.

 

battery was at 12.8-13.3v

Gonna have to test again at idle tomorrow. Not in the mood to work outside when its 7 degrees plus crazy wind.

 

Was the battery reading w/the car running or not? Your reading is high for a car not running if that were the case. What you should do is find the four wire Green check connector near the leading coil and measure the Black/White wire w/key to on and it should read 12 volts. This wire eventually winds up at the ECU and powers it up. At pin 3I of the ECU is where the B/W wire is found. Find the smallest of the three ECU plugs and 3I is the top row far left position (B/W wire). W/key to on it should read 12 volts. You want the same reading at the check connector as you do at pin 3I. If it's 12 volts at the check connector but 9 volts or so at pin 3I then it would appear that the connector of two plugs ( FEM-02, front harness mates w/the emission harness) located above and to the right of the ECU is making a poor connection perhaps.

 

That battery reading was with the car off, key on. Voltage was jumping around a bit, but I didn't see anything less than 12.8v for sure.
I will have to check the voltage at the check connector and the pin tomorrow.
So after this info, are you now thinking that it's not the pressure sensor that's at fault?

P.S. - What I did find after grounding the pressure sensor black wire was that the electronics were working better..."Add Coolant" light was randomly coming on before and the A/C compressor clutch would intermittently engage and disengage, making an almost grinding noise...none of that happens now.

 

If the reading off of the B/W wire at the Pressure Sensor was representative of the required battery voltage that the sensors plus ECU requires, then it would probably lead to erratic behavior with respect to performance. The ground wire at the Pressure Sensor though should not have any affect on the Coolant light as the ground for the Pressure Sensor is for only a handful of engine sensors and it comes from the ECU via the main engine ground.

In the link below shows FEM-02 (nearest Orange connector). On top of the connector is the Front harness which is the B/W wire (two of them) that comes from the Main Relay that can also be found at the check connector near the leading coil. The bottom of the connector is the Emission harness that leads to the ECU (pin 3I would be the Main Relay). If you are truly getting very low voltage reading at the B/W wire found at the engine sensors then the Orange connector mentioned could be the cause of the low voltage.


Post #45. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/88-fc-cranking-but-wont-start-978170/page2/

 

2-3VDC for a ref voltage sounds.......................blaaaaaaah bad to me. If read correctly with the meter. Bad as bad ECU.

 

where is that orange connector located in the car?

 

Next to the passenger kick panel. If you got a proper reading on the B/W wire such as 12 volts w/key to on at the Green check connector, but a low reading at the Pressure sensor then you would want to check the Orange connector FEM-02 for a possible poor connection.

 

Yea, sorry....after posting here, I read up on the other thread and saw the post where you explained its location. I will have to check that as well.

 

Have you been able to check the B/W wire at the Green check connector?

 

usually they don't fail half assed, something is likely grounding out and soaking up the 5v ref signal. faulty load sensor somewhere, start unplugging sensors in the circuit to see when you get the full 5 volts back, could even be internal in the wiring harness.

 

Sounds like a good idea to me. Remove the plugs from..........TPS, AFM, ATP, VARIABLE RESISTOR (if equiped with one), boost or pressure sensor.

Then key ON and check the brown/white wire on each plug. Or heck, just check any ONE of those plugs and if the ref voltage is still in the low range you gave above...........tough. Bad ECU most likely IF there has been no harness swaps on the engine side of things.

I deliberatly bought one of these 2-3vdc ref voltage ECU's off someone on this forum out of curiosity. HE had put in another ECU and all was well after that for him.

The ECU I bought from him did not work in my working car. No good bum ECU with no ref voltage which means that sucker ain't a gonna ever produce spark EVER.

 

it should actually. i have proven with my injector test stand that you can get spark and injector pulse with just the CAS only attached to the harness, ground and 2 power feeds to B+ and main relay input.

 

Spark and fuel injector pulses come from the ECU. The ECU creates the ref voltage for it's internal electronic componets. I don't see how you could have spark without the ECU being attached to the harness. Can't happen. The ECU supplies the trigger signals to the coil assys via input from the CAS (CAS creates a voltage TO the ECU when spum).

I must have misunderstood what you wrote. You seem to be saying the ECU was not connected when you got spark.

IF the ECU was connected then you had 5vdc ref voltage.

Those sensors I mentioned above have NOTHING to do with spark or injector pulsing. I mentioned those items so IF he had a component outside of the ECU pulliing the voltage down, then with them disconnected there would be nothing pulling the 5vdc down ........meaning then he could easily look at the ref voltage on any of those plug to those devices and see if the ref voltage was now up to 4.5 to 5vdc. IF it is up then he needs to reconnect one item at a time till the ref voltage drops down again to the 2-3vdc he originally saw and THAT device is what is pulling the ref voltage down.

Never meant to imply that those devices I mentioned in the other post were what makes spark. Just an easy way to figure out if the ECU or one of the devices is what is kiilling the ref voltage.

I just know you had the ECU connected to the harness when you used your injector test device.

Again, NEVER meant to say those devices mentioned in my other post MADE the ref voltage or caused spark.

It's just that any of them if malfunctioning can kill the ref voltage and maybe the ECU while doing so (shorting out the device in the ECU that produces the ref voltage thereby making the ECU worth nothing).

 

i was just mentioning it as you said it needed the 5v ref(and inputs i suppose) to generate spark. yes just the ECU attached to the harness, powered up and CAS signal is all it needs for the baseline to generate spark and injector signal.

so in theory you can get an engine running(at least started it probably will stall once it gets out of priming stage) by removing literally everything from the engine except the CAS, it obviously won't run properly or be very drivable though.

but if the 5v ref is burned it could be causing other issues within the ECU which can cause phantom drivability issues if it even runs. my comment was based on a good tested ECU unit, just completely stripped down to run the injection tester.

 

Hey guys, we've had quite a few days of snowfall lately so I haven't been able to mess around with it. I will try the check connector and let you guys know as soon as I can get to it. Tomorrow should be right around 33-34 degrees with no snow so I can get out there and work on it a bit.
Thank you for all your help so far Hope I can get this figured out because I really like this car.