Intermittent Serial Data Problem

[Fless]

For a parasitic draw I would suggest NOT jumping to the "pull the fuse" method. The small fuses have test points on top of them and the voltage drop can be measured when there is current draw. Powerprobe's web site has conversion charts that will estimate the actual amp draw based on the fuse size and voltage drop. https://www.powerprobe.com/na/en/download-list

Pulling fuses, then reinserting them can wake modules that were previously asleep, making for a nightmare when testing. South Main Auto has a few, and others are available.

There are many good YouTube videos on efficient testing methods for parasitic draw.

 

[TJ Baker]

No, but I just borrowed a scanner that might be able to help. It's not bidirectional and I can't start working on the truck until next week, but from all the different ideas I've seen I'm feeling confident that I'll be able to track it down. The fact that there is a power draw might actually help.

Well, feel free to give a shout out if you need.

Here's a little look at the sort of stuff I do with a $15 OBD2 adapter..





This is what J1850VPW serial data actually looks like.
Ever heard of SOH (state of health) messages?
There's at least 10 or more of them here among the normal chatter in this screenshot.

Line 1: BCM sends bus wake up message
Line 2: BCM announces current Power Mode
Line 3: PCM announces the position of the transmission range selector.
Line 4: PCM announces engine is not running
Line 5: PCM sends SOH message
Line 6: IPC sends SOH message
Line 7: IPC acknowledges Transmission Range selection
Line 8: Onstar module sends SOH message
Line 9: RCC module requests current Power Mode
Line 10: BCM sends SOH message
Yada, Yada, Yada......

 

[BigDogYJ]

are you certain it’s a loss of data issue? Have you confirmed powers and grounds for ecm/pcm and bcm? Key grounding points are below driver headlight behind bumper is where ecm is grounded. And under dash cover at bottom of a pillar up against the windshield is where the bcm is grounded.

I only mention it because I started tracking what I thought was a class 2 issue years ago only to find I had an intermittent ground that solved the problem.

 

[axekick]

I was out of town over the weekend and got the flu so I've been man down all week, but you guys have given me so much to start with. Hopefully I can find some time to dig into this. The ECM is working fine. I have diagrams with all of the grounds and module locations. I'll start with the voltage drop across fuses and cleaning every ground I can find. I'll update when I get to work on it.

 

[axekick]

I have some updates as I get this thing working. Another problem I was having was not being able to put fuel in the tank. It would just click. It would take half an hour to fill it up. I went ahead and dropped the tank, took the whole cluster of evap lines off and just shook out all the carbon pieces, I replaced the charcoal canister and put it back together and took it to the gas station and filled it right up. So that's a success.

I also took the cluster to a local module/cluster rebuild guy. He called and said the cluster is corrupt and can't be rebuilt. He couldn't even pull the mileage info from it. So he sold me another cluster programmed to math my truck. I went ahead and paid to upgrade to one with a trans temp gauge. I have to go get it at lunch. I'll update how it goes. I do not think that's going to completely fix the class 2 problems but it definitely wasn't helping. I guess each thing I get solved will make it easier to find the remaining problems.

 

[axekick]

Another update, the new cluster seems to work perfectly! I think now if I can get all the check engine codes figured out I'll be able to get it inspected and registered.

As for that, I knew I had a weak cylinder. When disabling one injector at a time, the one that barely made a difference was cylinder 8 so I've assumed it was the problem. However, there was a code for a bad #1 coil and misfire codes. So before I drove to get the cluster I swapped the #1 and #3 coil. The code moved with the coil! So that's good news. I have some coils at my X wife's house and I have to go there tonight. I might actually have this thing running pretty good soon!

I still think there's a break in the class 2 data sometimes. I'll check the grounds BigDogYJ mentioned asap. but it doesn't really seem to be causing any problems with the gauges anymore and my scanner works most of the time and just loses connection occasionally. This project is coming along nicely, I think.