Hey guys, first post here. Ive had a 92 6 speed for about a month now, and so far its been one issue after another unfortunately. It was seldom driven for the last 2 years or so according to PO. When I purchased it, I had an intermittent H64 code that would come on after about 20-30 minutes of driving, normally at idle. This has been the only code. Sometimes it would stay on, sometimes not. No noticeable change in drivability either on or off. The car seems to be running well, but it does seem to be running pretty rich. Soot on the back bumper after driving it around, smells like gas, poor fuel economy (11 mpg!). I assumed it was the computer compensating for a nonexistent condition, so I started with the o2. I put a Bosch in this morning on the drivers side, previous one definitely had some age on it, and harness seems a little oily from some leak above it. I cleaned the harness off, put the Bosch in, cleared the codes and went for a drive. First it threw a H63 (o2 sensor circuit open), I pulled over and cleared it, and then no codes for about 30 minutes. Then my h64 came back by itself. Im assuming its not my new sensor, but im not sure what to jump on next. Car seems to be running fine with the exception of the rich condition. Any thoughts? Most other threads involve drivability issues as well in this situation. I haven't seen any quite like mine.

 

A couple things come to mind. One is a new Bosch sensor may not be good, sadly. I've been advised by legit know-it-all mechanics that NGK/NTK are the best replacement O2 sensors. Another factor would be if there is something wrong (like an intermittent short) in the wiring harness between the sensor and ECM. You might try probing the pins on the ECM while the car runs to see what kinds of voltages are being sent. If you want to isolate the sensor itself as the problem (or not the problem), you could try swapping the left and right bank sensors.

Of course, the other possibility is that something really is making it run lean. The best way I know to detect this would be a wide-band in the exhaust on the problematic bank, and to log actual measure AFR. That is a massive PITA, though. One thing that would differentiate a true lean condition from a problem with the sensor system is what kind of AFR you have right after a cold start, before the coolant temps warm up. During that time, the ECM won't reference the O2 sensors at all (it's in open-loop mode), so if it's lean during that time then you have a legit lean condition and need to start looking at things like intake leaks or a bad injector. If it runs fines during open-loop and then has issues after warm-up (closed-loop), then you probably have an issue with the sensor or harness.

The best thing you can do is to locate the Factory Service Manual and run through the trouble-shooting diagnostics for this code.

 

Thanks for the info MatthewMiller! I don't have the equipment to do that kind of diagnostic right now unfortunately. The code never come up until after the car has warmed up. Just drove it for about 20 minutes and had a code come up again. I assumed it was 64/right bank lean again, but I checked and it was h44/left bank lean! I have not replaced that side o2, so im guessing this might change my approach. Probably would not be an intermittent short on both sides? Because im getting codes on a new sensor and an old one, im thinking it may truly be a fuel condition? You think injectors are the next thing to look into? Would plugs be a waste of time with my current scenario? Not sure when they were changed last.

 

I agree.

I seriously doubt it's plugs. The only way I know to diagnose injectors is to take them all out and have them tested and cleaned. That's not super cheap, so maybe someone else has an idea? The other big issue that causes lean conditions seems to be intake vacuum leaks. I'm no expert on this, but there are good tutorials on how to check for that if you google for it.

 

I'd be looking for intake vacuum leaks.

 

Ok. Im still getting lean codes on both sides, and H63 (Right o2 circuit open). That H63 code is making me wonder about that new o2 though, I don't remember seeing that one before. All the codes are still intermittent though. Running 93 octane conservatively around town im averaging 10.5mpg hand calculated. I will check on intake vacuum leaks next, thanks for the suggestions guys!

 

I haven't been able to find any vacuum leaks with a simple aerosol test. I do have one vacuum line under the plastic top injector cover passenger side that's a little cracked, but idle was not changing when I sprayed it. I took the intake assembly off the car and ran it open and then blocked off the throttle body to test for leaks. This promptly killed the engine. Not sure if this is a very comprehensive test, but I watched a guy on YouTube try it and it never killed his engine. Any other common vac leak locations to check? Kind of in the dark about the next steps.