2G Electrical problem - 2 error codes

[zdrux]

Let me get right to the chase. Recently I've been getting a coolant temp sensor code which I shruged off as a bad connection to be looked at later. Few days ago, this code has stopped popping up at all (I have dsmlink).

Today on my way to work, the car drove fine. I parked, then came out an hour later to go to the store and the car dies when revved past 2k rpm. No codes at this point.. I can drive it if I keep the throttle at like no more than 5% open, otherwise it bogs out, and you can smell unburned fuel from the exhaust so I`m guessing it's getting flodded with fuel.

I limped it back, and then suddenly got 2 error codes - so I whipped out my dsmlink and it had "coolant sensor" and "airflow volume sensor" error codes... So I`m guessing that's why my car was bogging, it wasnt receiving an airflow signal and they may be related.

Some (a lot?) has been done on the car, and I've had electrical issues in the past (for example the ISC shorting out) - and I`m wondering if perhaps both of these sensors are on the same ground?! I`m assuming they are grounded at the ECU, does anybody know if this would make sense? If so, where would I check, at the ECU? Any chassis grounds I should also be looking at?

The sensors themselves are ofcourse plugged in and all the wires are there.

 

[Talonman86096]

Did you check the wires to make sure there were no breaks in them? I know that the tempeture sensor runs to ecu i think like pin 92 and there are a bunch of grounds that connect there so it wouldnt surprise me if the air sensor also goes there but im not positive on that. I would def. re-trace the wires from the temp. sensor though because i know my problem was a borken wire that was way up and like under the battery before it got through the firewall and to the computer. And I had problems of running really rich, high idle, and also my cooling fans wouldnt come on by themselves. Check that to see if they turn on when the engine gets hot. Also just could be a faulty sensor.

 

[zdrux]

Thanks for your reply.. from the general view and as far as I could see, the wires seem fine for both the coolant temp sensor and the airflow sensor, but further investigation may be needed. Perhaps tracing it by hand, removing the battery, etc.. see'ing if there's any frayed wires of any sort.

Also, does anybody know, or have a diagram of all the ECU grounds and where they are? I wouldn't mind inspecting and possibly replacing them if I find any trouble areas.

 

[Talonman86096]

Here is ECU pinout: http://www.vfaq.com/mods/ecu-harness-2G.html

 

[luv2rallye]

On a 2g (but not 1g) all of the engine sensors signal grounds MUST go to ECU pin 92 only. This is NOT the same as engine/chassis ground and must NOT be connected there. Some people (and even some mechanics) don't know/realize this and they mistakenly connect signal ground to the engine. A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine can cause misleading (and noisy) signals to the ECU and if it is still also connected to the original harness signal ground wire, now ALL of the engine sensors will have that problem.

 

[zdrux]

On a 2g (but not 1g) all of the engine sensors signal grounds MUST go to ECU pin 92 only. This is NOT the same as engine/chassis ground and must NOT be connected there. Some people (and even some mechanics) don't know/realize this and they mistakenly connect signal ground to the engine. A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine can cause misleading (and noisy) signals to the ECU and if it is still also connected to the original harness signal ground wire, now ALL of the engine sensors will have that problem.

Great info! Ok, so pin 92 is the magical one.. where does it lead? Are all the sensor gounrds spliced into this one pin somewhere in the engine bay? Where is it grounded? Anything else I should know?

p.s.: Sorry, I just looked at pin 92 on the diagram and its a "Ignition Switch - IG".. Is this a ground?! Are you positive of this?

 

[luv2rallye]

Great info! Ok, so pin 92 is the magical one.. where does it lead? Are all the sensor gounrds spliced into this one pin somewhere in the engine bay? Where is it grounded? Anything else I should know?

ECU pin 92 goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow, and fuel tank diff pressure. Pin 92 is grounded somewhere inside the ECU but all these sensors signal grounds must not be grounded anywhere but thru pin 92 (to avoid electrical noise and ground loops from affecting the sensors differential signals - ie. voltage between each of these sensors signal and signal ground). You can verify if there is an incorrect sensor signal ground connection somewhere to engine/chassis ground by unplugging ECU pin 92 and checking for continuity from harness pin 92 and engine/chassis ground. I'm not saying this is necessarily your problem but you asked about the sensor signal grounds.

p.s.: Sorry, I just looked at pin 92 on the diagram and its a "Ignition Switch - IG".. Is this a ground?! Are you positive of this?

Yes I'm positive. It's always been a misprint in that diagram. The real Mitsu manual (and Mitchells) show it correctly for a 2g DSM.