After Replacing DME Relay Troubles...

[ischmitz]

Looks fine to me.

[nene]

Hmm..

Other than that, I don't see any other anomalies within the boards.

[ischmitz]

Not all faults are visible when it comes to electronics and there is no definitive reason to believe the fault lies with the DME. If you need certainty the DME needs to be diagnosed properly and undergo functional testing.

As I said earlier your situation points towards the fuel pump as a likely candidate drawing too much current. It’s far less likely that two items went bad at the same time (DME relay and DME). Your observations say that swapping the damaged DME relay hasn’t rectified the poor ruining. That makes me think it’s a secondary failure and you still haven’t found the primary point of failure.

[GH85Carrera]

Originally Posted by ischmitz

Not all faults are visible when it comes to electronics and there is no definitive reason to believe the fault lies with the DME. If you need certainty the DME needs to be diagnosed properly and undergo functional testing.

As I said earlier your situation points towards the fuel pump as a likely candidate drawing too much current. It’s far less likely that two items went bad at the same time (DME relay and DME). Your observations say that swapping the damaged DME relay hasn’t rectified the poor ruining. That makes me think it’s a secondary failure and you still haven’t found the primary point of failure.

I would have to agree, and he knows lots more about electronics than I do. Something out of the normal range caused the relay to fry. Likely the fuel pump drawing too much power or a short or other issue. Find and repair that, then test.

[nene]

Well,

After waiting a week for a replacement fuel pump and then spending 3 hours installing it, the issue remains. Before starting up the engine, I checked to make sure that the cylinders were not flooded with fuel by using a stethoscope. Also cleaned up the spark-plugs and did notice that the drivers-side bank ones were a bit wet, in comparison to the passenger side, which leads me to believe that that side is NOT getting spark.

[john walker's workshop]

Check the injector harness plug on the shock crossmember for corrosion or poor connection. Reach in behind the heat blower motor to find it. Also check grounds on #1 intake. Carrera distributor caps are kind of funky with that black cover that tends to hide defects in the cap, like cracks and coil wire terminal burn throughs.

[nene]

Thank you for the response John,

I will take a peek later on tonight and report my findings.

[911pcars]

Let's try to isolate the cylinders that aren't "working".

Does it idle rough as well? If so, you can "short out" (disconnect) each cylinder in turn and determine which one(s) aren't contributing. If okay, the engine idle will drop and run rough. If not, there won't be any difference.

The old way of doing this was to disconnect the spark lead either from/to the distributor/spark plug. Do this with an insulated plier.

On fuel injected engines, disconnect the harness connector from each injector in turn and see if that cylinder is contributing, as above.

Could be a faulty spark plug, spark plug wire. Also, check the distributor rotor and the underside of the distributor cap for structural integrity. Rule out the more obvious, simpler stuff first before diving into more involved troubleshooting.

Sherwood

[nene]

Update:

Took a stab at all of John's recommendations and all appeared in good standing. Started the car and no change, as it still shakes and feels like it's running on a few cylinders.

I purchased a spark tester and had my wife help out with starting the car. All spark-plug cables were producing a good spark on all six cylinders.

Originally Posted by john walker's workshop

Check the injector harness plug on the shock crossmember for corrosion or poor connection. Reach in behind the heat blower motor to find it. Also check grounds on #1 intake. Carrera distributor caps are kind of funky with that black cover that tends to hide defects in the cap, like cracks and coil wire terminal burn throughs.

[nene]

Originally Posted by 911pcars

Let's try to isolate the cylinders that aren't "working".

Does it idle rough as well? If so, you can "short out" (disconnect) each cylinder in turn and determine which one(s) aren't contributing. If okay, the engine idle will drop and run rough. If not, there won't be any difference.

The old way of doing this was to disconnect the spark lead either from/to the distributor/spark plug. Do this with an insulated plier.

On fuel injected engines, disconnect the harness connector from each injector in turn and see if that cylinder is contributing, as above.

Could be a faulty spark plug, spark plug wire. Also, check the distributor rotor and the underside of the distributor cap for structural integrity. Rule out the more obvious, simpler stuff first before diving into more involved troubleshooting.

Sherwood

Sherwood,

I disconnected each fuel injector connection and didn't really notice any real change, due to the car running rough. I took a video of the engine running and will upload it.

I will check the fuel pressure and report my findings.

[acar24]

with the engine running spray small bursts of brake cleaner into the air intake. If it picks up and runs smothley it is a fuel problem if not it could be electrical.

[nene]

Originally Posted by acar24

with the engine running spray small bursts of brake cleaner into the air intake. If it picks up and runs smothley it is a fuel problem if not it could be electrical.

Thanks, I'll try that.

[nene]

Update:

After doing more digging, I again started the engine and this time I took off the the injector harness plugs from cylinder 4,5,6 and the only one that did not make a difference when unplugging was 4.

This time I took the time and checked the Ohms across all harness injector plugs and injectors, and this is what I found:

Harness plugs:

1. 11.56 ohms
2. 11.56 ohms
3. 11.57 ohms
4. 11.57 ohms
5 11.57 ohms
6. 11.57 ohms

Injectors:

1. 2.6 ohms
2. 2.5 ohms
3. 2.6 ohms
4. 61.1 ohms (that’s correct)
5. 2.6 ohms
6. 2.6 ohms

I guess a replacement injector is in order.

Serge

[ischmitz]

Good find and the replacement injector will certainly make a difference.

[nene]

Interesting how the engine always had a slight shake when it was running fine, and nothing I adjusted ever fixed it. I have a feeling this bad injector was always the culprit.

[nene]

Ok folks,

To close this thread and report a resolution, the culprit was indeed #4 injector. I purchased a remanufactured one from GB Remanufacturing, checked the Ohms (2.5), installed and VROOMMM!

I took it for a quick run and it all felt just dandy!!