TBI code 13

[87scottsdale]

Have been getting code 13 on my 305 tbi. Just converted over to a 4 wire heated o2(I had a new one lying around)

My wiring is flawless from sensor to signal,ground power. Has any one truly fixed this issue and where do I need to start looking.

Thanks for input

[bd]

It has an open circuit 412, open ground or faulty sensor.  Refer to the 1987 LIGHT DUTY TRUCK
FUEL, DRIVABILITY AND EMISSIONS MANUAL, page 58 (3-30).

Did the code set before or after you retrofitted the 4-wire sensor.  I've been running the 4-wire sensor for years with no ill effects.  Verify ECM connections and grounds; make sure the oxygen sensor grounds to the engine along with the ECM at the same point on the back of the passenger cylinder head or equivalent location.  You may need to methodically reshape the ECM terminals to improve pin tension and connections.

[87scottsdale]

It had to be after I converted I believe. I had been getting an o2 code with the single wire o2. I can't remember if it was a code 13 or 44 (lean)

I will have to check some grounding points and pin locations.

[87scottsdale]

Ok. Haven't had much time to try and diagnose this. Since this is not my daily vehicle.

I am going back through my sensor wiring.

Being a 4 wire I have

Signal
Signal ground
Heater  -
Heater  +

I have been rethinking this.

I have signal paired with the factory Signal connection to the truck ecm
I have signal ground paired with the Heater ground
I have Heater + tied into wiper motor +12v (went this route since its was already a easy out of the way switched/fused 12v)

Effectively making this a 4 wire-3 wire connection.

My question is the ECM throws ground to o2 signal correct? So instead of having my Signal ground paired with my heater ground. Should my signal ground be paired with my Signal wire to the ecm?

Or am I thinking of this wrong?

[bd]

IMO - Because of the potential for subtle variances in ground connections, the O₂ sensor ground should be mated directly to the ECM ground connection at the back of the right cylinder head.  The heater ground should connect directly to its own dedicated engine ground.  The ECM grounds to back of right cylinder head and water outlet, the engine ground-to-battery, and cab ground-to-engine need to be cleaned and verified.

[87scottsdale]

The only ECM ground I can find is at the thermostat housing. The only ground on the rear of the passenger side head is the ground strap from cab to engine block.

I have not had a further chance to do any rewiring the signal ground up to the ecm ground,but did clean the ecm ground. If the ecm ground was faulty wouldn't the truck not run?

[bd]

Refer to pages 58 & 59 of the previously linked service manual.  The diagnostic chart for code 13 is published therein.  Circuit 413 (a light brown or tan wire) is the ECM ground for the O₂ sensor and attaches to the rear of the right cylinder head; alternately, it may connect to the intake manifold adjacent to the water outlet housing, along with other ground wires.  The 413 ground is a crucial circuit path in a 0-1-volt circuit.  There is no room for less than a perfect connection.  The O₂ sensor ground should connect directly to where the 413 ECM ground attaches to the engine.  Otherwise, you may introduce an error.

In general, all harness terminals should be crimped and soldered to their respective wires and housed in the proper connectors.  A system can experience partial grounds & connections and still run - just not perfectly. Symptoms can become intermittent. 

Incidentally, you should also check for a grounded O₂ signal wire.  Don't neglect the ECM board connections as previously mentioned.

As a reminder - don't connect any voltmeter to the ECM wiring unless it has 10 Megs or greater input impedance or you'll risk frying the ECM!

[87scottsdale]

My ALDL cable arrived today. Time to break the trusty laptop out and see what readouts on everything are.

I will post screen shots when I have a chance.

[87scottsdale]

Ok so after cleaning the ecm ground,and I also didn't like my current battery-engine ground I redid it. Negative terminal went from battery to alternator bracket. How it was when I bought the truck so I assumed it was a factory connection. Changed that from bracket to block. Seems like a much easier start and better idle. Let it run until almost operating temperature then drove it for a short ride at speed.

Code 13 did not show back up. I will continue testing and report back.