I didn't know where to put this but my port wasn't working either and I found out that if unplug my vcm it connects

 

Phil Manwarren:

Where are you disconnecting the VCM? But now you can’t read any data or codes right?


George

 

A couple of things. First we don't know the year of your engine but if it it a 2001 and if it has the original PCM configuration then the serial data bus connection in on pin 58 of connector C1 which is an 80 pin connector. It is a purple wire at the DLC but a dk grn wire at the PCM connector originally. Here is the pinout:



Next: There are multiple modules on the class 2 data bus in a normal Blazer configuration. This is a single wire data buss where all the relevant modules dump their digital data messages on that common single wire continuously in the J1850 communications protocol. The various modules are constantly sending and listening for their messages. Given your application some of the modules are probably not there BUT, the way they were all tied together originally is with a blade connector under the dash near the DLC. A single blade of metal is pushed into a slot and all of the class 2 data wires are now all in parallel. If that connector or blade is missing - no communication. If any module on that data buss is corrupt then all modules, the PCM and the DLC may not work. You need to look for the routing to see how that purple DLC data wire gets to the PCM but also is there anything else on that buss like a crappy hack where the blade connector used to be. IOW continuity from pin 2 on the DLC to pin 58 on C1 at the PCM is necessary but not sufficient. That connection cannot be corrupted.

Next, looking for a voltage on pin 2 of the DLC does not tell you much since there is an endless stream of pulses that look like square waves with variable duty cycle.

So now what? Look for the blade connector or any hacks where it used to be. Disconnect any other modules on that buss. Verify continuity from the DLC and the PCM. Verify quality ground and power at the DLC. Report back

George

 

I just figured out that you were showing a 24 pin connector from the VCM so my 80 pin connector pinout is wrong. Kyle may be right that this is a 2000 configuration and not 2001 as you guessed and I originally followed. Everything I said earlier is correct except pin 2 of the DLC needs to wind up on pin 11 of the 24 pin VCM connector. Unless there are older versions using a 24 pin connector with a different pinout.


George

 

Hunter Whiteside:

A few more thoughts. First, I checked all second gen 4.3l wiring diagrams and pin 11 of C4 is where the data line needs to land regardless of year assuming a 24 pin C4 plug which should be ‘96 - ‘00. That said, all of this assumes that when the engine was scavenged from a vehicle it was a Blazer or that all configuration of all 4.3l vortec are identical regarding the VCM and pinout. I don’t know how builders of your vehicle handle the stripped down remnants of a factory install. Is it a dedicated harness, VCM, etc or are they just deleting and terminating things from a full install? These pin outs are correct for a blazer but do they apply to you?

If you have or know someone with an oscilloscope a more elegant way to confirm the class 2 data pin on the VCM would be to probe and look for the waveform output. A less absolute method may be a DVM in AC voltage mode but there are sensors with pulsed waveforms like the MAF and O2 sensors that would confuse things.

George

 

correction my tccm

 

Phil Manwarren; correction my tccm

There are multiple modules on the class 2 data bus. This is a single wire data buss where all the relevant modules dump their digital data messages on that common single wire continuously in the J1850 communications protocol. The various modules are constantly sending and listening for their messages. they are all tied together with a blade connector under the dash near the DLC. A single blade of metal is pushed into a slot and all of the class 2 data wires are now all in parallel. Anytime you have a class 2 communication problem like at the DLC pin 2 you pull that blade to take everything off of the class 2 buss then add only the ECM back. If you’re communicating now then ECM is probably good. Then you add the modules one at a time until you find the one corrupting the database for every other module.

You should have started a new thread because now we have to ping pong Back and forth between you and the OP, a classic thread hijack.

George

 

I don't how to start a new thread!

 

Don't be jealous of my mad Photoshop skillz, lol.

 

Thats funny. Tom draw. I will join in.

I will add that if your looking at this thread first you have to go up to the sub forum index and then you can get to Tom’s thread starter button:




George