Tuned lly duramax no added power between tunes

[shakenfake]

Sounds like a classic GMT800 issue. I've never come across it but 03-05 trucks I am always hearing stories on how they don't like to take tunes and require the PCM/ECM pulled and benched.

 

[JoshH]

There is a com wire connector under the dash near the I/P fuse box above and behind the park brake release called SP205. All the data wires for all the modules are tied together in that block with a jumper cap. It is, IIRC, a 2x6 connector with a white cap. If you pop that cap off and jump wires B and D, you basically just made a bench harness and isolated the ECM to the OBD2 port. I do this to every LLY and LB7 I flash now because almost all of them have some sort of aftermarket electronics gizmo that causes hell with flashing.

 

[Chevy1925]

^^^ 100% this. We have a bench harness to do it but that’s a hell of a lot easier the way Josh is saying.

 

[Tactical Camel]

There is a com wire connector under the dash near the I/P fuse box above and behind the park brake release called SP205. All the data wires for all the modules are tied together in that block with a jumper cap. It is, IIRC, a 2x6 connector with a white cap. If you pop that cap off and jump wires B and D, you basically just made a bench harness and isolated the ECM to the OBD2 port. I do this to every LLY and LB7 I flash now because almost all of them have some sort of aftermarket electronics gizmo that causes hell with flashing.

Thanks boss, I will give it a go today.


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[1FastBrick]

Sounds like a classic GMT800 issue. I've never come across it but 03-05 trucks I am always hearing stories on how they don't like to take tunes and require the PCM/ECM pulled and benched.

That only Applies to the Diesels.

The gassers never had that problem. You might have to pull a radio fuse with and aftermarket radio But Otherwise unless someone has done some major Electrical work It's usually a non issue. More often than not the 10 Amp Cigarette lighter fuse is blown and it won't communicate with the PCM. That's because the OBD2 port pulls it power off the Cigarette lighter circuit in these trucks.

 

[1FastBrick]

There is a com wire connector under the dash near the I/P fuse box above and behind the park brake release called SP205. All the data wires for all the modules are tied together in that block with a jumper cap. It is, IIRC, a 2x6 connector with a white cap. If you pop that cap off and jump wires B and D, you basically just made a bench harness and isolated the ECM to the OBD2 port. I do this to every LLY and LB7 I flash now because almost all of them have some sort of aftermarket electronics gizmo that causes hell with flashing.

That's a handy peace of info!!! Thank you!!!

 

[shakenfake]

That only Applies to the Diesels.

The gassers never had that problem. You might have to pull a radio fuse with and aftermarket radio But Otherwise unless someone has done some major Electrical work It's usually a non issue. More often than not the 10 Amp Cigarette lighter fuse is blown and it won't communicate with the PCM. That's because the OBD2 port pulls it power off the Cigarette lighter circuit in these trucks.

Interesting, because I hear it all the time from gasser tuners lol
RDF1 on PT.net talks about it a lot. I had never even heard of it until the past couple years and now it seems like everyone knew this but me

 

[1FastBrick]

I have never had the issue on a Gas truck With EFI Live. Usually an aftermarket radio will cause noise on the buss but once you pull the fuse its a non issue.

The only issue I ever had was on my 2000 it would reset the clock radio to 12:00 when the Flash was complete, and that truck was 100% stock.

 

[Tactical Camel]

There is a com wire connector under the dash near the I/P fuse box above and behind the park brake release called SP205. All the data wires for all the modules are tied together in that block with a jumper cap. It is, IIRC, a 2x6 connector with a white cap. If you pop that cap off and jump wires B and D, you basically just made a bench harness and isolated the ECM to the OBD2 port. I do this to every LLY and LB7 I flash now because almost all of them have some sort of aftermarket electronics gizmo that causes hell with flashing.

Update: I done just like you said, it acted like it took the tune but again no change with the dsp5 switch, now i also have the anti theft light on, battery light on, oil pressure gauge doesn’t work and fuel gauge doesn’t work, also can’t read the pcm now. It all worked fine at first start up but after about a minute it done all that. I think I’m going to try to get another tune sent.


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[2004LB7]

Update: I done just like you said, it acted like it took the tune but again no change with the dsp5 switch, now i also have the anti theft light on, battery light on, oil pressure gauge doesn’t work and fuel gauge doesn’t work, also can’t read the pcm now. It all worked fine at first start up but after about a minute it done all that. I think I’m going to try to get another tune sent.


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Can you read back the tune and see what it is?

Those errors will likely go away when you drive the truck as they were a result of being disconnected from the network