Disassembly: Manifold Pressure Differential Sensor

[awdonly]

Expecially if you are trouble shooting wierd issues.
In fact try this exactly...

Check the wire from the purge solenoid has continuity to pin 16 of the 98/99 ECU plug.
Check that wire doesn't have continuity to ground.
Flash the completely stock 99 rom peripheries to your car.
Unplug your EVOX MAP. If your pin 92 is hooked up in parallel to your LCDBC then unhook it.
Make sure your lights and all accessories are off.
Start your car from a overnight cool down (so its room temp) while hooked to EVO scan.
Note the coolant temp, air temp, baro, airflow, idle rpm speeds and approx time if/when the purge solenoid starts to do its clicking.
Report back with coolant temp, air temp, baro, airflow and time when it started.

Completed following all instuctions to the letter (except I couldn't wait for room temp - it was 95 degrees today and may garage is still HOT! I prob won't have time tomorrow so I proceeded after 7 hour cooldown) - clicking started about 3 minutes in to test. RPM=843.75;CoolantTemp=154.4;CoolantTempScaled=147 .2;AirTemp=86;MAFAirTempScaled=89.6;Baro=83.79;Air Flow=56.25

If it helps - complete log from Evoscan 2.9 (wasn't sure if I should use scaled temps or not so I took both scaled and unscaled) is here. Clicking started about 10 seconds from end of log.

[99 vr4]

If I was using ECU boost control, I would go that way, but I'm using the LCD boost control so I'm sourcing the sensor with that.

Just a quick question, does the LCD Boost Controller have a +5v DC output?

In order for the MAP sensor to operate properly with the ECU, you MUST tie the MAP to the sensor POWER and sensor GROUND at the ECU. Pin 81 is +5v DC for the sensors and pin 92 is the sensor ground. You can also reference this from the TPS for testing purposes. If you have a different power supply source, there will be a delta introduced into the system and the ECU might act wonky.

Also, can you please measure the resistance of the purge solenoid and measure the voltage at the purge solenoid plug. I just want to be sure that your purge solenoid is not bad and that you have stable voltage at the solenoid.

In the mean time Greg has asked me to disconnect a bunch of stuff on my 99 to see if I can duplicate this issue. I will be disconnecting my vent solenoid (which you don't have) and my fuel tank pressure diff sensor (which you don't have) to see if I can trigger the same conditions that your ECU is seeing and see if I can duplicate this.

Also, can you confirm that you DON'T have anything in the following pins on your ECU harness? Pins 35 (Purge VENT) and 93 (Fuel Tank pressure diff sensor).

Also, the following should be empty as they are various pins NOT used on the VR4: Pins 5, 7, 8, 30, 31, 32, 33, 34, 53, 56, 63, 64, 76, 81, 82, 86, 87, 88, 89, 90, 94, 95, 96, 97, 98

@Greg, the 99 has a different purge solenoid and it is bigger, so can you measure the resistance of yours to be sure there is not a big difference between the two solenoids?

[Jesters Deadd]

Do you have a montero MAf by any chance?
Ok, did you get any CELs?
Now turn on the lights and defrost. While at idle does the clicking stop?
With lights still on turn on AC. Does clicking stop?
With the lights still on rev the engine quickly several times. Does clicking stop while reving?

[Jesters Deadd]

Your solenoid should measure 35-44 ohms. PLease finish the testing above to confirm it is working corretly or not.

[awdonly]

Just a quick question, does the LCD Boost Controller have a +5v DC output?

In order for the MAP sensor to operate properly with the ECU, you MUST tie the MAP to the sensor POWER and sensor GROUND at the ECU. Pin 81 is +5v DC for the sensors and pin 92 is the sensor ground. You can also reference this from the TPS for testing purposes. If you have a different power supply source, there will be a delta introduced into the system and the ECU might act wonky.

Also, can you please measure the resistance of the purge solenoid and measure the voltage at the purge solenoid plug. I just want to be sure that your purge solenoid is not bad and that you have stable voltage at the solenoid.

In the mean time Greg has asked me to disconnect a bunch of stuff on my 99 to see if I can duplicate this issue. I will be disconnecting my vent solenoid (which you don't have) and my fuel tank pressure diff sensor (which you don't have) to see if I can trigger the same conditions that your ECU is seeing and see if I can duplicate this.

Also, can you confirm that you DON'T have anything in the following pins on your ECU harness? Pins 35 (Purge VENT) and 93 (Fuel Tank pressure diff sensor).

Also, the following should be empty as they are various pins NOT used on the VR4: Pins 5, 7, 8, 30, 31, 32, 33, 34, 53, 56, 63, 64, 76, 81, 82, 86, 87, 88, 89, 90, 94, 95, 96, 97, 98

@Greg, the 99 has a different purge solenoid and it is bigger, so can you measure the resistance of yours to be sure there is not a big difference between the two solenoids?

Yes the LCDBC has a 3 pin connector for external MAP sensor (+5/sensor output/sensor ground). The sensor output is wired into the MAP input on the ECU in addition to the MAP input on the LCDBC- only delta would be bad read on MAP level by ECU and I've now correlated those (OEM boost gauge on Chrome 1.1) with the boost level output on the LCDBC and they are very close (they were off because I was using OMNI 4 settings on LCDBC - my bad).

ECU conversion harness was purchased from BlackStealth on 3si who has been making these for awhile. I have no reason to believe it was made incorrectly, but will ask him to verify the pins in question are not used.

Solenoid measures 43.6 ohms.

[Jesters Deadd]

Yes the LCDBC has a 3 pin connector for external MAP sensor (+5/sensor output/sensor ground). The sensor output is wired into the MAP input on the ECU in addition to the MAP input on the LCDBC- only delta would be bad read on MAP level by ECU and I've now correlated those (OEM boost gauge on Chrome 1.1) with the boost level output on the LCDBC and they are very close (they were off because I was using OMNI 4 settings on LCDBC - my bad).

ECU conversion harness was purchased from BlackStealth on 3si who has been making these for awhile. I have no reason to believe it was made incorrectly, but will ask him to verify the pins in question are not used.

Solenoid measures 43.6 ohms.

I doubt it is the conversion harness.
What power circuit is your LCD boost controller hooked to?

[awdonly]

Switched Fuse 12 (15A) - chose this circuit because low loading - it no longer powers fuel pump.

[awdonly]

Do you have a montero MAf by any chance?
Ok, did you get any CELs?
Now turn on the lights and defrost. While at idle does the clicking stop?
With lights still on turn on AC. Does clicking stop?
With the lights still on rev the engine quickly several times. Does clicking stop while reving?

Stock MAF (evo MAF ready to install but limiting variables). Yes I've constantly had CELs since testing included keeping all peripheries as stock - and stock '99 code is also the same. I can double-check what is stored after dinner and should be able to run test you requested tonight. Unfortunately that will be the last input from me on this for 10 days. Anything else you want me to squeeze in tonight?

[Greg E]

What power circuit is your LCD boost controller hooked to?

BINGO! 150 points to Adam.

Turned on my headlights, fog lights, AC, rear defrost, stereo and 4 ways. Engine warmed up, purge solenoid started clicking! Now to figure out which address is the load switch and I'll have something for you to test again awdonly! Thank you Adam!

Few other notes:

*The purge solenoid on my car shows a resistance of 38.9ohms. Lower than what awdonly is showing HOWEVER the manual shows a spec standard value of 36-44ohms for ALL year cars (91-99). So even though they may be different part numbers, they have the same specs.

*On the 98/99 cars the purge is mounted onto the intake plenum instead of on the firewall. So when it's active on my car, I can't hear it. Had to touch it with my hand in order to notice it was active.

*The EGR solenoid on the 98/99s was moved down into the position of the purge solenoid on the 91-97 cars. That tricked me earlier....

*The vent system even though it functions with the purge system, it's a completely and totally separate system. The purge does NOT use the fuel tank sensor for operation. Only a few condition bits activate the purge which I'm currently testing. The only thing the two systems share is periphery 2 bit 13 and NONE of the peripheries disable the system. Only the OBD checks for them. The purpose of the vent solenoid is just to check the operation of the fuel tank sensor. Since this isn't present on the 91-97 cars, periphery 2 bit 13 needs to be switched off to keep the CE light off. This will NOT effect the purge system in anyway.

Going back into my little hole for a bit but I hope to have something for you to try later awdonly. BTW, what's your real name? I appreciate your help with this too!

[BlackStealth]

I just checked the list of empty pins, and they match to what I have as empty pin also. The very early conversion harnesses did have pin 75 (Muffler mode changeover) connected, but I have left that out, as I'm sure it's useless for a 99 ECU.

One thing I want to point out is that signal ground on the ECU is not the same signal ground used on the LCD BC. How much of an impact this has, I don't know. Sharing the sensor could potentially cause a problem. Does Evoscan show correct readings for the MAP sensor?