In Brief= Newly rebuilt 3.4L KFG headers, Borla exhaust and 4T60 trans. I recently dropped the cradle and replace the exhaust manifold gaskets as I had installed the 3.4 gaskets originally. Prior to that, the only code that was present was a code 32 which I was going to resolve as soon as i got the exhaust leak fixed. After reinstalling the motor everything was normal for about 3 or 4 days then I was having an issue with the motor cutting out randomly. It seems that I have that rectified (fingers crossed) and now I am getting a code 13. Today I went to AutoZone and got a new O2 sensor and installed it. I took it for a drive and as soon as the temp came up it set the code 13 again. What could be causing this?

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86GT 3.4LProject

[This message has been edited by BAM-BAM (edited 09-17-2011).]

Missing ground? The only way to know for sure is to check the O2 signal at the ECM.

I never had the problem before. I didn't have to remove any grounds to remove the engine cradle. And how would I be able to read the O2 inputs at the ECM?

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im having the same issue. engine light will pop up. checked codes and i get code 13. replaaced sensor. all good for 2 months. then it came back. engine light would come on. turn the car off. start it back up and its gone for afew weeks and then pops back on.

Not sure which ECM you're using, but on the Fiero ECM there are two wires that need to be intact for the ECM to be able to read the O2 sensor. If the purple wire leading to ECM pin D7 is frayed and grounding out along the way, or broken, you'll get code 13. To test for continuity along the wire, use a multimeter set on ohms and place one lead on the ECM connector pin (after you've unplugged it), and the other lead on the pigtail connector from the O2 sensor. You should get 0 ohms. If not, then the purple wire is broken somewhere. If good, then next you have to switch one of the leads to a known good ground and should get infinite ohms. If not, then your purple wire is frayed and grounding out on the frame along the way somewhere.

To test the continuity of the sensor ground circuit, place one lead on ECM pin D6 and the other to a known good ground. You should get 0 ohms. If you don't, then your ground wire is broken.

Thanks Blooz, I do a little work on that today.

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OK Blooz, here is what I did. I used my meter and performed the afore mentioned continuity checks and all were satisfactory. The only one I couldn't prove was the the harness connector to D7. I could verify that it wasn't grounded as indicated by the infinite ohms. I just didn't have enought hands to perform the full length continuity check. However, that being said; I did remove, resurface and reconnect the G503 and G504 grounds that attach to the engine head on the firewall/driver side. I am positive that the previous connection was not satisfactory. I am still getting the code 13. I also checked my TPS for S&G's and it moved through the range from .49 vdc to 5.03 vdc. I checked it several times with identical results. I am using the Bosch O2 sensor from AutoZone. Is there and issue with this one? It didn't look like the one I removed but I figured that wasn't important.

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**BUMP**

On the ECM - take out the terminal position assurance (light green colored) piece from the ECM connectors. Use long pins to back probe the contacts. With the engine warm and running measure the voltage at D7 (Purple) using D6 (Tan) as your ground. You should be getting +.4 to +.6. If that voltage is missing the ECM reports a code 13. So if the voltage is there, and the pins on the connector seem reasonably tight, the only conclusion left is the ECM is bad.

If the voltage isn't there then you need to see why it is not.

You really must test the continuity of the purple wire to know for sure. Use a length of spare wire to extend your reach if needed.

If the purple wire turns out OK, then there are a few other potential causes. Code 13 trips when the ECM doesn't sense a voltage increase above .550 volts after 20 seconds or so of running. If the wires are OK then that leaves the O2 sensor not working properly or it isn't the right part number for your engine, or a faulty ECM. Given that you bought a generic O2 sensor, I'd bet that's the cause.

Blooz, not too long ago my O2 sensor blew out of the exhaust. I replaced it with a Bosch unit. I have had no problems, or trouble codes, since.

[This message has been edited by n7vrz (edited 09-20-2011).]

No doubt... but Bosch makes many different O2 sensors. They may not all be calibrated identically. What part number did you use?

(Bear in mind also that I would suspect the O2 sensor is faulty only after double checking the integrity of the wiring.)

Blooz, PD, I will perform the check as PD suggested, that should prove or disprove the integrity of the wire. I will also, just to be sure, enlist a helper to assist me in the continuity check. THis should definitively prove the wire. THe O2 sensor I bought have a warranty so maybe I'll take it back and try the Denzo OE sensor.

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OK, I used a piece of wire to extend the reach of my meter leads so that I could check the integrity of the purple wire from the connector to the ECM. I had solid continuity. I even shook the connector around to ensure that the wire going into the connector was solid. So that checked out. I have no shorts or grounds in the wire from the connector to the ECM.

Next, I did as you had mentioned PD. As I was driving, with the ECM lying on the center console skeleton. I drove around until I felt she was warmed up. The temp guage was at about 180-90, where it usually sits during normal driving. At a stop light, I put the car in park and took the readings between D6 and D7. The reading fluctuated wildly between .7-.2 and all points in between. nerver a constant voltage. Is this normal? Also, just to note, the SES never came on. It seems to happen when I am traveling at about 50-55 and the RPMs are around 15-1700. I normally cruise at 65 MPH with the tach at 2k. Guess I need to take her for a drive and see if maybe all of the disconnecting, reconnecting and probing fixed something?

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Yes, the reading from the O2 sensor is supposed fluctuate quite wildly. At this point, the only potential causes I can see are:

1. the connections weren't tight and as you suggested are now better; or

2. the O2 sensor is calibrated slightly differently than an OEM one.

Thanks Blooz, I am taking a small road trip this morning and I will let you know how it turns out. BTW, with the SES light on and a code 13 I would be running in open loop correct? And that could cause the noticible decrease in my economy?

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quote Originally posted by BAM-BAM: BTW, with the SES light on and a code 13 I would be running in open loop correct?

Yes. Here's what the service manual says:

The ECM supplies a voltage of about 0.45 volts between terminals D6 and D7. The O2 varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if the exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below 360*C (600*F). An open circuit or cold sensor causes open loop operation. {Added: Under closed loop operation normal voltage should vary continuously between 0.1V and 0.999V.}

If the conditions for a code 13 are present, the voltage will be fixed between 0.35 and 0.55 volts and the system will stay in open loop.

Blooz, PD, I made it to the halfway point on my little road trip. Actually I had to drive into work (35 miles) and no code 13. I will make one more post on this topic (unless it reappears) when I get home. If I still have no code 13 popping up, I will consider this matter closed. Now it's on to the code 32, which I believe to be a bad solenoid since everything else is new including the SS vac lines.

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That's good news. As for your code 32, be sure to check your grounds G503 and G504. They are the two pairs of ECM sensor grounding wires that attach to the transmission-end of the forward cylinder head. Sometimes they're bolted to the bellhousing bolts too. One pair has a black and a green wire, and the other has a tan and a black wire. Both pairs are prone to breaking because of the heat from the exhaust crossover, which also makes them hard to access.

quote However, that being said; I did remove, resurface and reconnect the G503 and G504 grounds that attach to the engine head on the firewall/driver side. I am positive that the previous connection was not satisfactory.

Yeah, I took care of those a few days back. They were not tied under the bolt head but rather between the bolt head and PCV tube bracket. I rectified that and sanded the block surface to ensure good contact. I also performed continuity checks.

BTW, still no code 13. So I guess I should cosider the O2 matter closed and move on to the EGR issue. I really want to thank both Blooz and PD for all the assistance and good advice.

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Peace!!

B2 OUT!!
86GT 3.4LProject