17 replies to this topic

[Colorado Mark]

OBD1 on a GM when jumped A-B will flash "12"  one blink then 2 blinks.  That is normal and tells you that it is diagnostic mode.

 

Any other codes will be displayed between the three sets of code 12 blinks.

 

32 would be an EGR circuit fault.

 

What is the 8th digit of you VIN so we know what engine you have?

[DavidGraves]

The 8th digit is K ...

 

350 with auto trans in K2500

 

You folks from Colorado are Awesome !

 

DG

Edited by DavidGraves, 02 April 2021 - 12:24 AM.

[Jon R]

Hi David,

 

I have a 1993 K2500 5.7L Silverado, and have owned it since new, fixing it as things have gone.  It's easy to work on, except for replacing the tank fuel pump - I haven't had to do it yet, but I'm dreading it.  Mine has about 150,000 miles on it.  It has been an extremely reliable truck with only a few things that have failed over the years beyond normal wearouts. 

 

It's important to remember that OBD I was never intended to be a general diagnostic tool.  It was intended to detect and annunciate problems with the emissions equipment.  There are many part failures that won't trigger an OBD 1 code or CEL, but will affect the running of the engine.  You need to use old-school troubleshooting skills rather than expecting OBD 1 to tell you what to replace.  The ignition and injection systems are relatively simple. 

 

Here are the things that I have had to do to fix misses, rough running, or stalling.  The first few are obvious normal maintenance ones.

1) Distributor cap and rotor - probably replaced 4 times total

2) Plug wires - replaced at about the 20 year 120k point

3) Spark plugs either once or twice - can't remember for sure

 

Here's the tricky one that had me stumped for a long time until a local GM injection system expert clued me in:

The engine would die at stop lights at low idle when it was warmed up.  (This started out the as an occasional miss at stop lights but then it began dying.)  This turned out to be due to the reluctor magnet in the distributor (the donut shaped magnet below the eight pointed star shaped piece that rotates in the distributor and triggers the ignition module) aging under the high temperature condition to the point where its magnetic field was so week it would not trigger the ignition module at very low engine speed.  The failure of the ignition also kills the fuel delivery, confusing my troubleshooting, which was why I ended up meeting the fuel injection expert.  He patiently listened to my story of everything I had investigated.  He then told me he would be happy to take my money and service my injection system, but said there was one thing I hadn't eliminated yet.  He explained the above magnet deterioration and sure enough he was right.  Very cool guy.  So ...

 

4) Replaced the distributor at about 23 years 135k point.  It's run like a top ever since.  It was surprisingly easy, and an OEM part is reasonably priced.  No check engine light with this issue ever, though.  If you haven't had to do this yet, be expecting it. 

 

The ONLY thing that has ever turned on the check engine light for me was a failed EGR valve. 

 

These trucks used to be everywhere, but you don't see them much anymore where I live.  I get a lot of compliments on mine because it is in really good shape.  I finally, after 28 years, ordered a new GMC 3500HD that should arrive this month. 

[DavidGraves]

Hi Jon

 

Maybe we should buy your truck !!

 

I echo many of your comments about this vintage Silverado.

 

I mostly mothball this one with the Hawk...use it only for the longer trips we (used) to take to the SW or Baja etc.

 

Thanks for the insights....I need to start doing more of my own repairs as the very few local mechanics seem to consider this ninties vintage vehicle an antique.

 

One question I do have.....

 

There is  a second 12-16 plug terminal fully visible at about the drivers' right knee under the dash....what is that connection for ?

The OBD 1 terminal is off to the left of steering column and not fully visible.

 

David Graves

 

Nehalem 

[Jon R]

I looked under the dash in the driver’s right leg area and did not see any large open connector. My obd1 connector is all the way to the left side.

Edited by Jon R, 02 April 2021 - 11:59 PM.

[DavidGraves]

I will try to get an image...may need to email it to you...Will PM if so.

[Jon R]

Here is a picture of the right side of the steering column area on my truck.  For some reason the attachment process turned it upside down as it appears here, but when you click on it, it is back as I attached it.  The bottom of the ash tray is next to the black aftermarket brake controller.   

Edited by Jon R, 03 April 2021 - 02:27 AM.

[DavidGraves]

PM sent

Edited by DavidGraves, 03 April 2021 - 05:26 PM.