Z28ELECTRICIAN

Every time I try to interface with my vehicle with a scan tool or even a generic code scanner I get "communication error". I have the LT1 scan master turned off so lets out that theory to bed. Ever since I have had the vehicle I have never been able to do this.
This winter I removed the engine to do just to dress up the under hood area. I didn't touch the rotating assembly, but I did have the heads reworked(cleaned, seals, and new guides as a few were badly worn). When I started the engine for the first time it ran great and idled normal. After the first initial start the vehicle has developed a dead miss, will not idle, and all the plugs are black like they are fowled. The only this I have found during my inspections was the VSS and the reverse solenoid connectors were swapped. I'm sure your thinking how is this possible but the vehicle was previously an auto and whoever did the install made it possible. I obviously swapped the connectors back and now the vehicle will go into reverse but still wont idles and runs rough.
My fear is since I had the connectors reversed I may have fried a driver in the PCM but without being able to communicate with the PCM I am shooting in the dark.
The vehicle has an Ed Wright PCM which was installed by the previous owner. I'm not sure if that is why I have the comm issue but I'm sure there are several people on here with a similar setup that may be able to shed some light on this.
Just a little background on me. I am an ex GM mechanic with an ASE master cert so have a little vehicle knowledge, but I left turning wrenches 12 years ago to become a union electrician.

Injuneer

Original OBD-2 PCM? Power to the ALDL connector, i.e. cig lighter fuse good? If you turn the Scanmaster on, does it read the PCM?

Z28ELECTRICIAN

Injuneer,
First off thank you for the reply.
Yes the ALDL has good power and ground. Not sure if the PCM is original as I have only owned the vehicle 6 months, but i did find a receipt from Ed Wright programming. I have also checked the resistance on wire on pin 9 to PCM connector C4 terminal 30 and its OK.
Yes when I turn the scan master on i can read all inputs from PCM to scan master. I have seen on previous posts that Ed Wright PCM cant be over written by LT1 edit or any other software buy I would like to think that you could atleast read PCM data and DTCs but I got nothing.
BTW i do own a copy of the GM service manual.

Injuneer

Sometimes people swap to a 94/95 OBD-1 PCM because it can be tuned with cheaper software. If that was the case, the Scanmaster would be reading any OBD-1 DTC's. Apparently it isn't. And I'm sure you are aware it will not read the Pxxxx format OBD-2 codes.

If the PCM is sending the data stream to the Scanmaster, no reason the correct OBD scanner shouldn't be able to read it. Damaged pins? Would be too obvious.

16-pin ALDL connector?

Do you have a copy of my Scanmaster guide?

Z28ELECTRICIAN

Yes a 16 pin ALDL. I performed a pin drag test on all used pins on the ALDL and all felt ok. I even did the same at the PCM connections. I agree if the scan master can read the data why cant my scan tool. i just disconnected the scan master during half time and still no data on scan tool.

Injuneer

How do you disconnect? I have single pole mini switch on the Scanmaster data wire. The tail from the switch is spliced directly into the tan data wire in back of my 12-pin ALDL connector. I get 12v power and ground from other sources (no 12v pin in the OBD-1 connector).

Z28ELECTRICIAN

I just removed the wire that is T tapped on the tan wire at the back of the ALDL. Basically I was making sure that the T tap wasn't causing an open in between the ALDL and the PCM. Knew it wouldn't be that easy but I'm grasping at strings here.

GaryDoug

An OBD1 pcm (93-95) will be communicating using pin 9. An OBD2 pcm (96 up ) will be communicating using pin 2. What specific scan tool are you trying to use?

Z28ELECTRICIAN

Thank you GaryDoug.
I am using a Mac Task master scan tool. I have entered a 96 Z28 Camaro into the scan tool. I can try to enter a 95 when I get home this evening and see if someone has converted my car to an OBD1.

Injuneer

Does your Scanmaster report DTC's? Which pin is it attached to? That will tell you.

Z28ELECTRICIAN

I told my scan tool that i was working on a 95 OBD1 and boom i know have communications and can read DTCs.
The DTC is DTC36, the dreaded opti high resolution code. I am hoping that this is just a faulty opti causing my drivability issues but I need to do some checks to be sure since I just had the motor out. To be honest I hope I find a wiring issue because not only is an opti expensive, I have to remove the water pump and supercharger to replace the darn thing.
Thanks guys for all of your help. I will keep you posted with my findings.

Hey Injuneer, I have read your paper on the LT1 scan master and i have a stupid question. How do you pull DTCs with it. I am sure its simple but not sure how to do it.

Injuneer

OBD-1 PCM swap. See post #4.

Actually, DTC 16 is the bad one.... can't run without the low resolution cam position signal. DTC 36 for the loss of high resolution signal should still allow the engine to run, with a minor loss of timing accuracy. Where you seem to get in trouble is when the high res signal becomes erratic. Then you seem to get some rough running, RPM surges, etc.

Clear the code and see how soon it comes back. Check the harness connectors for corrosion, bent pins or a broken connector lock. Original Opti had a short harness that ran from the gray connector on the bracket on the passenger side of the intake manifold to the Opti. Some aftermarket replacements, including the MSD have an integrated harness already attached to the Opti (no connector), and plug directly into the gray connector.

On the Scanmaster, there's a small button that cycles the display through the various sensors and PCM parameters. One of the screens is DTC (may be labeled "MAL" - can't remember). If you have any codes they will appear on the right side of the display, one at a time.

Z28ELECTRICIAN

Injuneer,
I saw post #4. That's what led me to run the vehicle as a 95, and it worked. Thanks.
As far as the DTC36 I checked all the terminals and decided to order a new Opti from MSD. I removed the opti today and found it full of rust, big shocker.
The vehicle ran, but it ran terrible. See Post 1. Hopefully this clears up all my issues. Thanks for your help again. What's crazy is the car ran fine before I removed the engine so my first instinct is to think I screwed somthing up.

Injuneer

An AC Delco or Delphi would have been a better choice. The MSD costs more, has a few problems of it's own, and the somewhat useless "timing" screw has no true 0 reference setting.... they tell you to count turns of the screw. For some reason, as good as their ignition systems are, their attempt at the Opti is just so-so.

GaryDoug

If there was really a lot of rust, make sure the Opti ventilation hoses were ok and connected at both ends.