ECU says I need a camshaft sensor

[salewit]

I've got a 92 Legacy 2.2 Non-Turbo that continually fails smog (fuel mixture too rich they say). My "check engine" code is 13 camshaft sensor. Car otherwise runs great. I checked connections on the sensor and even checked it with a multimeter (static test) and it seemed ok.

 

I have two problems. 1) These buggers are expensive. Over $100 for something I'm not certain is bad. 2) I have 6 hours left on my temporary registration! I see these sensors online for less than $50, but I don't have the luxury of time.

 

 

Is there a better way to test these, or do I just bite the bullet and replace it? My local Autozone has it in stock at $130. How likely is it that this is what is causing the engine to run rich? The plugs are sooty black.

 

Thx

[lmdew]

You might want to clear the code and see if it comes back. The junk yard will have one for you I'm sure. They don't go bad to often so its worth a shot.

 

You may also want to just pull it out and clean of the end of the sensor. I've seen them full of metal and junk. Takes about 5 minutes.

[salewit]

Thanks. I did clear the code and it almost immediately came back. Just curious... what is it that the sensor is picking up? Is there a magnet embedded in the camshaft sprocket?

[OB99W]

[...]what is it that the sensor is picking up? Is there a magnet embedded in the camshaft sprocket?

The magnet is in the sensor; reluctors are built into the camshaft sprocket. See: http://endwrench.com/images/pdfs/DirectIgnition.pdf

[salewit]

I have a question about the trouble codes thing at http://www.surrealmirage.com/subaru/subaru.html I have a 92 Legacy non-turbo.

 

Next, connect the test mode connectors (green T-shape). Turn ignition to ON position without turning on engine. At this point if the check engine light does not come on, it is faulty and must be fixed before continuing. Depress accelerator pedal to floor, return to half throttle and hold for two seconds, then release. Start the engine. Now the light can blink in two different ways. If everything checks out so far, it will blink to indicate a number 01, 02, 03, 04, 05, 06, 07, or 08. If a problem is already detected, it will blink according to the chart below. Either way, your next step will be to drive the car with the test mode connectors connected. You must drive over 7 mph for at least one minute, and shift up to 4th gear if you have a manual tranny. Now, either you will discover any trouble codes, or if you have none it will blink at a steady rate.

With both green and black disconnected, in normal driving mode, I'm getting code 13.

 

With the green connected and black disconnected, I get the check engine light with ignition on, but when started, I get NO check light. What does this mean?

 

And also, I'm thrown off by the text "your next step will be to drive the car with the test mode connectors connected". Are we talking the black pair and the green pair, or just the green pair?

[porcupine73]

You need to check the sensor output with a scope. Just checking resistance tells you only a small part of the story.

[nipper]

You need to check the sensor output with a scope. Just checking resistance tells you only a small part of the story.

 

A analog meter will do. You are looking for a very low but consistant AC pulse that is at the proper intervals.

 

The cam sensor gives the ECU input to manage the fuel injectors. Without it it goes into a pre programmed fuel map, hence why its bad for emissions.

 

 

nipper

[OB99W]

I have a question about the trouble codes thing at http://www.surrealmirage.com/subaru/subaru.html I have a 92 Legacy non-turbo.

 

With both green and black disconnected, in normal driving mode, I'm getting code 13.

 

With the green connected and black disconnected, I get the check engine light with ignition on, but when started, I get NO check light. What does this mean?[...]

Follow the directions you found at the site; the green connectors are for "test mode", the black ones are for "read memory mode".

 

As already suggested, make sure the sensor tip is clean of foreign material, and that the mounting area is clean; a fraction of an inch of extra clearance between the tip and reluctors can cause the output to be low. Sometimes the coil goes bad, sometimes the magnet weakens; either can result in low (or sometimes no) output from the sensor. Unless you know what the correct amplitude is, a meter test will only tell you if there is output, not if it's strong enough. Also, seeing output at the sensor doesn't mean it's getting to the ECU, so look over wiring/connections. If that all appears okay, consider getting a used sensor, which should be quite a bit less than $130.

 

I seem to remember that this car had a problem with previous work on the timing belt. Did the emissions ever improve after the timing was resolved? If not, is there any possibility that the camshaft sprocket is somehow wrong, mismounted, or has damaged reluctors?

[salewit]

Yeah, good memory! Ever since the valve timing adjustment it's been purring like a kitten and running really nicely. When I took it into smog, the hydrocarbons went from 5 times over the limit to well below, but the CO2 at idle went from 1.87 to 2.92 (1.00 is the limit).

 

Anyway, never mind all that stuff about camshaft sensor. I *did* go out and spend the $130 and put it in. Nothing changed, and then I did some more investigating and noticed what I *thought* was the black test connector was actually the seat belt light and buzzer. I was wondering why the light stayed on even though I was buckled up.

 

Anyway, I reset the code before I discovered this screwup. I drove it around a little and no new codes.

 

Since I take it there is no fuel mixture adjustment, and I now have no codes, what would be my next step?

[OB99W]

[...]CO2 at idle went from 1.87 to 2.92 (1.00 is the limit).

[...]

Since I take it there is no fuel mixture adjustment, and I now have no codes, what would be my next step?

Your '92 has OBD-I, which unfortunately isn't nearly as sophisticated as OBD-II. There can easily be sensor problems that won't generate trouble codes. For example, a rich mixture may be due to the ECU running open-loop all the time, caused by a bad coolant temperature sensor (CTS). It's normal for the mixture to be rich during engine warmup, but if the CTS doesn't "inform" the ECU that the engine is warm, the mixture will remain rich. An OBD-II system typically "knows" that it doesn't take forever for an engine to warm up, and generates a code, but the earlier OBD apparently just believes the sensor.

 

Bottom line is I'd start by checking the CTS.

[salewit]

Is there the ability bring it in to service and have them connect to the ECU to see what's going on? And if so, would that be a dealer thing, or any garage?

[Cougar]

There isn't anything the ECU will tell you about the problem other than if it senses something wrong with the sensor circuits. It takes good trouble shooting skills to determine the real causes of a problem. Some error codes can help point you in the right direction of where to look for a problem.

 

I am not a good emissions tech but the high CO2 readings may be due to a intake air leak. This would prompt me to check the manifold gaskets for a leak.

[OB99W]

A decent technician should be able to resolve things; it shouldn't matter whether that's at an independent shop or the dealer, but having Subaru experience may help get the job done faster.

 

I'm assuming that we're talking about high readings of CO (carbon monoxide), not CO2 (carbon dioxide). High CO is typical with an overly-rich mixture. On the other hand, high CO2 is usually found when the exhaust stream is diluted with air (as from an exhaust system leak), and the car will fail I/M (or won't be further tested) under that circumstance.

 

Although the ECU can compensate to some degree, a badly obstructed intake can cause the mixture to be rich by limiting airflow, so a simple thing to look at if you haven't already is the air filter (and make sure there aren't any mouse nests ).

[OB99W]

Another simple thing to check is the PCV operation. Make sure the valve is working freely, and the hoses aren't "gunked" up. If the engine oil gets sufficiently fuel-loaded, it will affect emissions.

[salewit]

Thanks for all the help. I changed my camshaft sensor, and coolant temperature sensor, and brough her in again, and it failed again.

 

The thing is running smooth as silk. I did connect a vacuum gauge to it recently and the needle is rock stead at about 22 inches, and I've already checked for vac leaks, so I don't think it's that. The PVC was replaced a month ago and the engine oil I changed on that last smog check. The air filter was changed about a year ago, and "looks" clean on both sides.

 

I didn't look for exhaust leaks. Not sure what to look for there. I'm fairly certain the thing is running real rich. The plugs are sooty black, and you can actually smell this thing when it's running.

 

There hasn't been any new "check engine" codes since I changed the cam sensor a few weeks ago. About the only thing I can think of is the oxygen sensor. It was change about 3 years ago and the car has passed last time with that sensor.

 

Any other ideas?

[avk]

If does fail on CO2 at idle, I don't understand what can be done, unless the idle speed is too high. The carbon in the fuel has to go somewhere. It's either CO2 or CO, right?

[Cougar]

I recommend you check the voltages of the CTS for the ECU and the MAF sensor to verify they are where they should be at normal operating temperature and engine speed.

 

You should check the O2 sensor also using a scope to see how it is functioning.

[nipper]

Thanks for all the help. I changed my camshaft sensor, and coolant temperature sensor, and brough her in again, and it failed again.

 

The thing is running smooth as silk. I did connect a vacuum gauge to it recently and the needle is rock stead at about 22 inches, and I've already checked for vac leaks, so I don't think it's that. The PVC was replaced a month ago and the engine oil I changed on that last smog check. The air filter was changed about a year ago, and "looks" clean on both sides.

 

I didn't look for exhaust leaks. Not sure what to look for there. I'm fairly certain the thing is running real rich. The plugs are sooty black, and you can actually smell this thing when it's running.

 

There hasn't been any new "check engine" codes since I changed the cam sensor a few weeks ago. About the only thing I can think of is the oxygen sensor. It was change about 3 years ago and the car has passed last time with that sensor.

 

Any other ideas?

 

What were your counts exactly?

 

nipper

[salewit]

Ok, 1st time. No modifications: Max limits= 120 HC, 1.0 CO

 

Idle 575 HC, 1.87 CO, 12.5 CO2

2500 RPM 49 HC, 1.62 CO, 13.6 CO2

 

----------------

 

Replaced PVC valve, and fixed valve timing (off by 2 teeth), changed oil and filter.

 

2nd time

 

Idle 117 HC, 2.90 CO, 14.3 CO2

2500 RPM 29 HC, 1.35 CO, 15.7 CO2

------------------

 

Changed camshaft position sensor and coolant temperature sensor.

 

3rd time

 

Idle 260 HC, 3.78 CO, 12.4 CO2

2500 RPM 77 HC, 1.59 CO, 14.1 CO2

 

 

Now I just changed the oxygen sensor.

[nipper]

Ok, 1st time. No modifications: Max limits= 120 HC, 1.0 CO

 

Idle 575 HC, 1.87 CO, 12.5 CO2

2500 RPM 49 HC, 1.62 CO, 13.6 CO2

 

----------------

 

Replaced PVC valve, and fixed valve timing (off by 2 teeth), changed oil and filter.

 

2nd time

 

Idle 117 HC, 2.90 CO, 14.3 CO2

2500 RPM 29 HC, 1.35 CO, 15.7 CO2

------------------

 

Changed camshaft position sensor and coolant temperature sensor.

 

3rd time

 

Idle 260 HC, 3.78 CO, 12.4 CO2

2500 RPM 77 HC, 1.59 CO, 14.1 CO2

 

 

Now I just changed the oxygen sensor.

 

Changed it after the third test or before it?

 

nipper

[salewit]

Changed the oxygen sensor AFTER the last test. These tests are like $30 a pop, so I thought I'd wait a bit and see if anyone had any other suggestions before I go in again. I'm gonna check the MAF voltages (although I'm 90% sure I did that early on in the process).

 

Here's the thing that leads me to believe it is something ON the engine. This car always passed smog. Then we replaced the engine, and ever since it would not pass. So things like the MAF and oxygen sensor weren't touched as opposed to anything attached to the newer engine. But I just don't know where else to check.

[nipper]

o2 sensors dont last for ever, they wear out in time. That would have been the first thing i changed, along with a tune up.

 

But thats just me :-p

 

 

Another possability is leaking fuel injectors or worn fuel injectors. Also dump a can of that fuel additive that guarentees passing. I dont like them, but after three tries its time.

 

nipper

[salewit]

Also dump a can of that fuel additive that guarentees passing. I dont like them, but after three tries its time.

 

nipper

 

You mean like Toluene? Tried already on #2.

[nipper]

You mean like Toluene? Tried already on #2.

 

but that was before the bad o2 sensor

 

 

nipper

[salewit]

Ok.. changed the O2 sensor, went in for a smog again and she failed again.

 

Idle HC 233 (120 Max), CO 3.36 (1.0 Max)

2500 HC 66 (140 Max), CO 1.84 (1.0 Max)

 

I'm lost now. I don't know what to do or where to turn. I've replaced the PVC, Cam sensor, Coolant sensor, Oxygen sensor. The oil has been changed, there are no vacuum leaks. The car runs smooth as silk.

 

Any further suggestions? Tried the "magic potion" on this last round as well. I'm convinced it is something ON the engine (since my last engine always passed smog).