Lesson about grounds learned today

[jpwalt1987]

Hey guys, I learned something important today and I figured I would share. I am running an SD chip from with the 3 bar map sensor along with an alkycontrol kit. I had been noticing that my fuel corrections were doing really stupid things. One day it would all be perfect like it was when I first set it up then the next time I would have all kinds of fuel being pulled. It only happened at idle, low throttle fuel and highway fuel. WOT was always spot on. I came to realize that the strange reading would come when I either had the headlights on or the heater or a/c. I checked voltage at the map sensor and compared it to the powerlogger reading everything matched. I would turn off the a/c and notice that the fuel correction would straighten out. Today I back probed the map sensor connector and cycled the high load devices on the car. Sure enough the map voltage out would change drastically and the correction would go crazy. Checking the resistance on the ground wire in the map to the battery showed about 100 ohms. So I spliced a wire into the ground and ran it to the negative terminal on the battery. I retested with the high load devices( a/c , hi beam lights). BOOM!!!!!!! Rock solid!!!! I had already had to buy a new battery and also changed the negative battery cable with no difference. I also picked up almost a half of a volt at the fuel pump by running a large ground cable from the fuel pump ground location to where the bumper shock meets the frame. Next is to run a cable from the engine to the frame. Just an FYI. Thanks for reading. Jeremy

 

[Blazer406]

Excellent!

Thanks for sharing.

I agree the grounds are often overlooked...IMHO..... me included. They are just as important as the hot wire.

 

[jayp57]

And remember it is easy to check voltage drop on your ground circuits with a voltmeter. I used to do it in my shop first thing when someone had a "weird" problem.

 

[jpwalt1987]

And remember it is easy to check voltage drop on your ground circuits with a voltmeter. I used to do it in my shop first thing when someone had a "weird" problem.

Refresh my memory on the proper way to do this if you don't mind.

 

[GNVenom]

The MAP sensor feed connector in the GN should NOT be used for anything other than powering the Tach/Boost module on the analog-dash cars. The 5 volts is inconsistent, and the ground (as evidenced by the OP findings) is also inconsistent.

***Read Carefully: DO NOT USE THE TACH/BOOST CONNECTIONS TO FEED YOUR ALCHY MAP SENSOR***
This refers to the connector that is plugged into your MAP sensor from the factory. And, it's only found on the cars with the standard analog dash - not on digital-dash-equipped cars.

The best - and ONLY reliable way to feed a secondary (3-bar) MAP is to tap off of the TPS for both the 5 volt source and the "sensor ground" which is consistent with the ECM.

Another factor to consider is the age of the wiring on our turbo cars. I am seeing many instances where there is excessive resistance within the grounds and also within the positive feeds. This leads to all kinds of voltage drops and sensor inconsistencies. It's becoming a real problem, even with un-modded cars.

 

[jpwalt1987]

The MAP sensor feed connector in the GN should NOT be used for anything other than powering the Tach/Boost module on the analog-dash cars. The 5 volts is inconsistent, and the ground (as evidenced by the OP findings) is also inconsistent.

***Read Carefully: DO NOT USE THE TACH/BOOST CONNECTIONS TO FEED YOUR ALCHY MAP SENSOR***
This refers to the connector that is plugged into your MAP sensor from the factory. And, it's only found on the cars with the standard analog dash - not on digital-dash-equipped cars.

The best - and ONLY reliable way to feed a secondary (3-bar) MAP is to tap off of the TPS for both the 5 volt source and the "sensor ground" which is consistent with the ECM.

John, I followed the instructions in the SD chip and Alkycontrol manuals where it required tapping into the tps 5 volt reference by the main ECM connectors. It required cutting one wire and running a jumper to the map feed from the the tps feed. I would have to find my instructions to be more specific. Thanks for the input. I think that wiring issues are one if the main problems with these cars and they creep up on you.

 

[bison]

The MAP sensor feed connector in the GN should NOT be used for anything other than powering the Tach/Boost module on the analog-dash cars. The 5 volts is inconsistent, and the ground (as evidenced by the OP findings) is also inconsistent.

***Read Carefully: DO NOT USE THE TACH/BOOST CONNECTIONS TO FEED YOUR ALCHY MAP SENSOR***
This refers to the connector that is plugged into your MAP sensor from the factory. And, it's only found on the cars with the standard analog dash - not on digital-dash-equipped cars.

The best - and ONLY reliable way to feed a secondary (3-bar) MAP is to tap off of the TPS for both the 5 volt source and the "sensor ground" which is consistent with the ECM.

Another factor to consider is the age of the wiring on our turbo cars. I am seeing many instances where there is excessive resistance within the grounds and also within the positive feeds. This leads to all kinds of voltage drops and sensor inconsistencies. It's becoming a real problem, even with un-modded cars.

I've seen damaged engines because of failure to do this. This is so easy to overcome. All that's needed is the de-pinning tool and the extra wire/loom to route it cleanly toward the firewall and zip tie it to the factory wire harness at the heater box. Then it's easily connected to the map sensor by pinning the other end after cutting it to the correct length.

 

[TireFryer]

I've seen damaged engines because of failure to do this. This is so easy to overcome. All that's needed is the de-pinning tool and the extra wire/loom to route it cleanly toward the firewall and zip tie it to the factory wire harness at the heater box. Then it's easily connected to the map sensor by pinning the other end after cutting it to the correct length.

Reviving an old thread...
I'm a visual learner, as are others on here I'm sure... Any chance you can post a pic or sequence of pics demonstrating your solution?
TIA