OBD gremlins ... need assistance please

[HSRACER]

So I bought a 67 with a 5.3 in it already and the PO had the OBD port laying under the hood.

While it was in that location I had my tuner come give the engine a once over and cleaned up some parameters in the computer. At the time I didn’t have ac in the truck or a working speedometer.

I have since added Dakota Digital gauges and old auto air to the truck. While doing some work to it I also thought I should have the obd port under the dash as they were from the factory.

Here is where the problems start. I extended the data wire (purple) and the power is hooked to a constant hot. The two grounds were attached together and screwed into the kick panel on the side under the dash.

My buddy has done this setup many times in his LS swaps without a problem.

I need to get into the computer again to turn on my fan trigger for the new electric fans I have now installed and the computer is not recognizing my hp tuner hook up or a small scanner code clearer that I have.

I have pinned out the data line and ensured continuity from the connector to the obd tab. My friend butt connected them and heat shrinked as well.

Another friend told me you can’t butt connect the data line as it is to sensitive to resistance so I then removed the connectors and soldered the wires.

Still no luck on the ability to get the computer to talk with either of my scanning devices.

I have read that some people have had to extend the two ground wires back from the actual harness vs just grounding them together on the body.

I will be unwrapping the main harness tomorrow and looking for those two ground wires he cut and seeing if extending them to the obd does anything different.

Also the Dakota Digital Gauges aren’t seeing a speedometer output. Wonder if the issues are related?

Any additional thoughts or advice is greatly appreciated!

[LockDoc]

-
I am going to move your thread to the LSx Swaps forum.

LockDoc

[HSRACER]

Originally Posted by LockDoc

-
I am going to move your thread to the LSx Swaps forum.

LockDoc

Ok thanks. I accidentally put the first one in the suburban category so I guess it can be eliminated

[LockDoc]

-
Read through this thread and see if it helps.....

http://67-72chevytrucks.com/vboard/s...d.php?t=579001

LockDoc

[HSRACER]

Originally Posted by LockDoc

-
Read through this thread and see if it helps.....

http://67-72chevytrucks.com/vboard/s...d.php?t=579001

LockDoc

I read that one already. Thank you. It was what I used to verify my pin out and correct colors. Still waiting to see if the grounds need extended to the same wires in the harness.

[ls1nova71]

Have you verified that the ground is actually a good ground? Is your engine grounded to the cab and frame?

[HSRACER]

Originally Posted by ls1nova71

Have you verified that the ground is actually a good ground? Is your engine grounded to the cab and frame?

Yes I have tested the power and grounds through the obd circuit.

The engine has a large mesh ground strap between the engine and the frame.

The battery is grounded to the engine and has a leg going to the front fender.

[nsb29]

I don’t see were you saying anything about a ground strap to the cab You need to try running a grounde from your engine to the cab

[HSRACER]

Originally Posted by nsb29

I don’t see were you saying anything about a ground strap to the cab You need to try running a grounde from your engine to the cab

So the battery ground strap has two wires on it. The main heavy wire is attached to the engine block and at that connection the smaller wire is part of that ring loop connector and goes up to the front fender from the engine ground.

Is that not the same as going to the cab?

[BR3W CITY]

Soldering can increase the resistance on connections if the mass of solder is too large. This is the most sensitive on the low voltage (1.5, 5, 10v) signal lines. If the wire being used was a different type/gauge, the resistance can be altered as well.

The way I'm reading it; things worked, the lines got extended/relocated, and now it doesn't work. I'd see if you can bypass the splice and get it to read. Worst case scenario would be replacing the wire end-to-end with a new wire.

[HSRACER]

Quick update.

I have unwrapped the harness and found what looks to be a red or orange wire that was clearly cut where the old obd was located on the harness. Also right next to it is a black only wire that was also cut.

The red wire in the harness is keyed power and the black is what I believe to be ground.

I have extended the red and black wires to the obd connector wires. No changes at all, the scanner keep saying no link when it times out.

Also added a braded jumper wire from the valve cover to one bolt on the brake booster mount to ensure a good ground at the cab.

Nothing has changed the situation

[HSRACER]

Originally Posted by BR3W CITY

Soldering can increase the resistance on connections if the mass of solder is too large. This is the most sensitive on the low voltage (1.5, 5, 10v) signal lines. If the wire being used was a different type/gauge, the resistance can be altered as well.

The way I'm reading it; things worked, the lines got extended/relocated, and now it doesn't work. I'd see if you can bypass the splice and get it to read. Worst case scenario would be replacing the wire end-to-end with a new wire.

I will move the obd back to the harness and see what happens then.

[kipps]

Keep in mind that obd2 pinouts appear to be quite different between gen III and gen IV engines. Most of the info I'm finding is for gen III.

[87chevy.com]

Maybe the ecu is locked??

[HSRACER]

Originally Posted by 87chevy.com

Maybe the ecu is locked??

My tuner says he never ever locks the computer.

Bottom line is it isn’t sending any data down the line and I can’t read any engine related data on my buddies scan tool.

What can cause a computer to run fine and take an initial tune then still run perfect but not allow any downstream data flow..??

[HSRACER]

All I wanted to do was turn on the fans so the computer will run them but I am about to give up and wire them key on or get an independent fan control.

My speedometer isn’t working either and I have ordered a Dakota Digital GPS to work around that.

This crap costs a fortune and still frustrating the heck out of me

[HSRACER]

And some more info to consider, after the time was put in we never tried to use the obd again until after we moved it inside. So I can’t realy say it was working properly after the tune.

We had to adjust the throttle position vs pedal travel when we were in there and the HP tuner warned us to do so at our own pearl. The truck runs, drives, shifts, and starts perfect even though I can’t get back into the computer.

Knowing I can’t get back to the tune is just killing me but I am looking at the above work around so I will learn to get over it I guess.

[HSRACER]

Originally Posted by kipps

Keep in mind that obd2 pinouts appear to be quite different between gen III and gen IV engines. Most of the info I'm finding is for gen III.

My Comp is an 04 with the TAC module for the throttle pedal. What gen would that be? Also it worked good enough and properly when we tuned it in December

[BR3W CITY]

Any chance you have a blown fuse somewhere? I recall F-bodies losing com after an AUX fuse would blow.

I might also be wrong on this but; isn' the second ground on the port actually an ECM switched ground, and not a raw chassis ground? One is black/white, the other just black.
The ECM ground would be using the internal grounding to the harness..I'm going out on a limb but if its designed for ECM ground, then it may have a different expected resistance vs a chassis ground, and going straight to ground would change that value.

[HSRACER]

I have now taken the computer out of the truck and I put it in a friend of mine truck and it reads just fine and runs as it should. That verifies the computer itself is working properly.

[HSRACER]

While it was in my friends truck I was able to pull these codes out of it.

None of them actually set off my check engine light but I am not sure if they should have?

I don’t really know where to go or what to try next. I suppose a full pin out is in order.

[HSRACER]

Originally Posted by BR3W CITY

Any chance you have a blown fuse somewhere? I recall F-bodies losing com after an AUX fuse would blow.

I might also be wrong on this but; isn' the second ground on the port actually an ECM switched ground, and not a raw chassis ground? One is black/white, the other just black.
The ECM ground would be using the internal grounding to the harness..I'm going out on a limb but if its designed for ECM ground, then it may have a different expected resistance vs a chassis ground, and going straight to ground would change that value.

I am trying to find a pin out diagram of my computer. It is the blue and greeen connector version.

Do you have any idea which color wire is the ground and which is a triggered ground? I would guess the solid one is ground and the white and black one is triggered.

[sprint_9]

Originally Posted by HSRACER

So the battery ground strap has two wires on it. The main heavy wire is attached to the engine block and at that connection the smaller wire is part of that ring loop connector and goes up to the front fender from the engine ground.

Is that not the same as going to the cab?

No its not the same. If that is all the grounding that the cab has that is classified as a bad ground. It might work but its not right.

Stock, the cab had 2 grounds to the back of the engine from the firewall, and 1 to frame.

You mentioned that you ran a ground from the booster bracket to the valve cover? Run it to the block or head. No paint under the connections, use a star washer for good contact.

This might not solve your problem but should be addressed anyhow.

[BR3W CITY]

Originally Posted by HSRACER

I am trying to find a pin out diagram of my computer. It is the blue and greeen connector version.

Do you have any idea which color wire is the ground and which is a triggered ground? I would guess the solid one is ground and the white and black one is triggered.

Pin 4 is chassis ground, 5 is "signal ground"
It may not be the problem, but GM does differentiate them.

The codes you posted would mostly be set to not report, so they exist on the log but don't trigger the MIL.

The "U" code is the one we're having the issues with. Thats the one actually indicating the failure on the OBD circuit. If your actually getting low voltage on the data port it means you have wires crossed somewhere. Put a meter on the data line and see if it reads anything less than 2.5v, as that's what should trigger the DTC.

[HSRACER]

Originally Posted by sprint_9

No its not the same. If that is all the grounding that the cab has that is classified as a bad ground. It might work but its not right.

Stock, the cab had 2 grounds to the back of the engine from the firewall, and 1 to frame.

You mentioned that you ran a ground from the booster bracket to the valve cover? Run it to the block or head. No paint under the connections, use a star washer for good contact.

This might not solve your problem but should be addressed anyhow.

I did use star washers and cleaned all paint off of the connectors. I will move it to the iron block tomorrow. Thanks.