[Corky]

As my topic says I am having issues with reading codes and engine idling smooth, then rough, then stalling!

First let me tell you the story behind this, it is a 94 base model 3.4 L with 160,000 kilometers and before all this happened the car ran without issues.

So,while driving I got major hesitation from the engine, check engine light came on and I could smell burning from under the hood, pulled over and shut down the engine. Popped the hood and there was smoke coming from around the EGR Valve and I could smell rubber burning. Let this all cool down and started the engine, the EGR Valve gasket (the metal one between the solenoids and base let go, it melted spark plug wire #3 and I could see arching, the heat also melted the wire loom around the wires to the EGR Valve. I suspect it has been like this for a while!

Here is where the repairs begin.

1. I bought a new OEM EGR Valve and installed with new flange gasket.

2. Installed new wires and plugs, it was so hard to remove the wires that I cut 1,3 and 5 and the spark plugs were so badly rusted, although I have had the car for 8 years I only put on 20,000 kilometers so plugs and wires were not a thought.

3. Cut away all the damaged wire loom and all looked good, nothing burnt.

4. Now for the test, removed the negative post from the battery to clear codes and started the car, it started right away,ran great for about 3 minutes then went into a idle that sounded like I have a loppy cam, check engine light came on and it ran better, how can this be! Restarted and same scenario.

5. So now for the code checking, the usual paper clip to ground does not work on this car as I have read in these forums so I bought a Innova 3130C with adapters for OBD-1 and it would not connect to pull codes, I have read a lot in these forums about how these Innova work and don't work so i found locally two early GM code readers, a Equus 3008 and an Innova 3123, both of these would not connect.

6. I have checked all fuses, power to the OBD-1 connector and all is good!

Now I need some help, is this a bad ECM? I mean would the engine even run if it was corrupt?

Do I need to take the car for a drive to restore some parameters in the ECM?

Why I can't pull codes bewilders me, can all three readers I have be unable to read codes for some reason.

I am leaning toward taking the car to a local shop where they he can attach there Snap-On reader and see what they get.

Any suggestions would be greatly appreciated.

Thanks,

Corky

 

[GaryDoug]

None of those scanners will work for a 94. There were/are only a few that will. The best known one is the Actron CP9185 or CP9190 (full kit)

http://www.amazon.com/Actron-CP9185-AutoScanner-Diagnostic-Scanner/dp/B000T8UG52

You would also need the CP9127 adapter for OBD1 connection with the CP9185. The CP9190 already has it.

If you want more data and have a laptop pc or one you can put close to the car (within USB extension cable length, 32ft+), you can buy a cable for about $60 and use my free scanning app, Scan9495-V6. Lot of data and datalogging. See the topic about that in the pcm section here.

"check engine light came on and it ran better, how can this be!"

For many sensors, when it becomes defective, the pcm recognizes that and stops using it at the same time that a new code appears. Then the pcm uses a "guess" value or another sensor(s) to take it's place.

 

[Corky]

Thanks Gary for this information, I have a PC in the garage and will download your app, the cable you are talking about is this the one from OBD Diagnostics Inc. shown below!

Took the car out for a ride today and as mentioned when service engine light is on it runs good however when it clears it sputters and runs poor, as you were saying the PCM is using a guess value to make the engine run, makes sense.

Also when engine is idling and sputtering the exhaust is black, enough to coat the rear bumper, comes off easily nothing burnt and no stains!

Corky

ALDL (GM OBD1) Cable with 12 pin Connector

OBD Diagnostics, Inc., PO Box 2002, Redondo Beach, CA 90278

Item#

Weight

Price

Qty

ALDL (GM OBD1) Cable with 12 pin Connector, USB

aldlobd1u

0.37 lbs

$59.95 ea

 

[GaryDoug]

That's the cable.

Sounds like the engine is running very rich on fuel. Could be engine coolant temp sensor or O2 sensors. If the ECT sensor code sets, the pcm will default to 194F temperature. If the O2 sensor code sets, the pcm will revert to open loop fuel mode.

 

[Corky]

I am wondering now if the leaking EGR Valve I had may have overheated the wire to the 02 sensor. Will the coolant temperature sensor also provide the same signal to the dashboard gauges, reason I ask is that my temperature gauge since I have owned the car always stays in the low end of the range.

Looked up your info on making a USB to 12 pin cable and I have both so I will save the money make my own and maybe get to the bottom of this.

Thanks

 

[GaryDoug]

The coolant temp sensor for the pcm is separate from the one for the instrument cluster gauge.

It's very unusual to have a USB-to-TTL converter like the one I specified. Make sure you are not confusing that with an ordinary USB cable. That cheaper cable to make is several posts down in the topic. But if you actually have the USB-to-RS232 converter, you can make that one instead.

 

[Corky]

I may have the USB to RS232 in my collection of cables, if not I will source the one you recommend.

Thanks,