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Ground issues with G4 Storm PnP @ MR2 Turbo

Felix Kreysig

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Recently I discovered an interesting issue with my Link G4 PnP, fitted to a 2nd Gen 3SGTE.

The setup:

I am running two wideband Lambda sensors, an LC-1 LSU 4.2 for the gauge and a Techedge WBO2 SC0B 4.9 Sensor for data acquisition and tuning.

The prologue:

After I installed the Techedge sensor I noticed that the Techedge AFR readings around 14.7:1 where always about 0.5 points richer than the LC-1 (at stoich the LC-1 displayed 14.2:1). First I accounted this to a badly calibrated 4.2 sensor but a repeated free air calibration didn't change anything. Since both sensors are mounted in close proximity to each other I then just accepted the difference as an inaccurate LC-1. The reason for my quick resignation: the Techedge is advertised as being extremely accurate thanks to its so called "differential input". This feature means the controller has a separate "voltage correction input" which is to be connected to the ECUs or dataloggers ground and picks up differential voltage which is added or substracted to the actual WBO controller output to reduce noise or offset voltage. So I connected that input to the ground point where my ECU is grounded.

The issue:

On a recent test drive after installing a water injection I noticed the LC-1 was telling me I would be starting to lean out progressively, starting at 3500. Of course I ignored it once again blaming my LC-1. But at 4500 @ 0.8bar and 13:1 my knock phones came alive... I took a look at the logs and: the Techedge read 12:1 as supposed. The with increased load the LC-1 did obviously no longer display richer AFRs than the Techedge but increasingly leaner. Now I started to doubt whether the LC-1 was really faulty. So I decided to rewire the Techedges differential input from the ECU ground point to the ground wire approx. 5cm (2inch) after the ground connector of the ECU... and voilà: both LC-1 and Techedge read the same! So I measured differential voltage between ECU ground input and ground point and got a whopping 0.5V difference increasing with injector pulse width (which makes perfect sense when assuming that injector current is being sent through the ground wire...).

I have to admit: my engine wiring loom is in a.... pitiful condition to say the least. He has seen many different ECUs and piggybacks, is about 23 years old and so on. So replacing the loom is mandatory BUT: while rebuilding the ECU plugs I noticed that the PnP ECU only uses ONE single ground connector. The OEM ECU uses at least 4 different ground connectors for actors and one separate ground for sensors. Additionally the ground connector of the OEM loom used by the PnP ECU is the dedicated sensor ground so the ground wire is the smallest of all available. Even if my loom would be in perfect condition I would deem the ground wire to be much to small. The wire-in G4 Storm ECUs also have at least two separate ground connectors... so is there any way to improve the PnP units grounding?

P.S.:  after being aware of that issue and revising some of my logs I noticed that occasionally the TPS input voltage to the ECU seemed to drop with increased load without the TPS Sensor being moved. The TPS Sensor ground is placed at the intake manifold (since there is no separate sensor ground aside from the expansion connector which is not used when just plugging the G4 to the OEM loom). That seems to be connected to the ground offset voltage.

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Hi Felix,

you where experiencing what we refer to as ground looping.

All wideband meters that do not have a sensor ground output accompanying the Analogue volt output of the wideband must use the ECU earth as the negative power ground for the unit.

If the wideband has a dedicated wideband analogue output sensor ground then this must go to ecu sensor ground.

Having the TPS grounded to the manifold is also not wise due to earth looping.

The TPS sensor ground needs to go to ecu sensor ground, parallel it with the IAT or ECT sensor ground,or purchase an expansion loom.

Good find anyway Felix, well done.

Thanks for sharing.



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Having the TPS grounded to the manifold is also not wise due to earth looping.

The TPS sensor ground needs to go to ecu sensor ground, parallel it with the IAT or ECT sensor ground,or purchase an expansion loom.

Thats obviously the major issue with the 3S-GTE PnP ECU setup as it uses the OEM sensor setup while discarding almost all OEM ECU ground points. The OEM loom grounds the sensors to the intake manifold and the actors somewhere at the chassis or block I believe (would have to look up ground locations though...). So I'll try to replace the remaining ground wire at the ECU with a larger diameter and hook all sensor grounds to ECU sensor ground at the expansion connector...

Edited by Felix Kreysig
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  • 2 months later...

The ECU (E01) and its sensor input (E02) is grounded at the intake manifold yes same place same bolt same ring, the other 2 grounds on the ECU are outputs (E1 diagnostic plug ground output) and (E2 sensor ground output which your TPS uses).   There is no way for any of these to be disregarded because nothing would work at all, I am yet to put in my engine and loom etc so I will update again later, but I think the main thing is understanding how it actually worked stock 1st of all


EDIT: E1 output may actually be disregarded, since there was nothing on it other than the diagnostic plug, and since  TE1 is gone, there would be no need for an E1 as Toyota's fault finding and timing setting method is completely obsolete with new ECU

Edited by mikegt4dude
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