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camshaft position sensor question
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trekvana
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Sep 11, 2012, 7:39 PM
Post #1 of 5
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camshaft position sensor question
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alright so i got a question regarding the camshaft position sensor and how it relates to fuel injection.
i got a 1998 2.2l chevy s10 (162K miles) which is just sucking gas like a vacuum. i can always smell excessive gas fumes by the tailpipe. once every few months i get error code p0342-camshaft position sensor low input.
so this has got me thinking my injectors are running on batch mode / limp home mode. the only thing i can think of is that the ecm is firing off all the injectors at the same time in hopes of catching the right cylinder. this would explain the poor gas mileage.
i dont have an oscilloscope to check the cam sensor square wave signal. i can check the injector pulse widths with my scanner. they are all firing within 0.1ms of each other.
anyone here know anyway i can check my theory? can i use injector pulse widths to diagnose?
more info: fuel pressure checks out. no leaky injectors. fuel pressure regulator is not leaking. whenever car is warmed up i have a hard start problem. like if i run into the store to get something, when i come back out after 20 minutes then i have to keep cranking to get her to start up. however when the car is cold, like in the morning, she starts right up. im thinking this is from flooded cylinders or overheating cam sensor???
(This post was edited by trekvana on Sep 11, 2012, 7:42 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 11, 2012, 7:58 PM
Post #2 of 5
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Re: camshaft position sensor question
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What is the fuel trim long and short at idle in closed loop? If the engine was running rich, you would think it would be setting a P0172.
Have you checked for a leaking fuel pressure regulator (FPR)? You may have to run the engine with the vacuum line disconnected from the FPR for several minutes to see if fuel comes out the nipple.
Have you inspected the wiring at the cam position sensor. Did you unplug the cam position sensor connector and inspect for oil intrusion or improper terminal tension?
You can check for power and ground at the cam sensor plug to be sure it is there. Not sure if the cam sensor is a pull up or pull down signal type. You can tell by unplugging the cam sensor connector with a meter on the signal wire. You really need a DSO or maybe a graphing multimeter to look at the cam sensor signal at the PCM connector to see what is going on with it. DSO is preferable.
Can't really use injector pulse width to determine if the cam sensor signal is missing. Some scan tools that can get into the factory side of the PCM can look at the cam sync PID to see if it counting up while the engine is running. You can also watch the cam sync PID will doing a cam sensor bypass test to make sure the signal wiring and PCM is good.
If that code sets, the PCM will revert to Alternating Synchronous Double Fire mode with the injectors which may end up wasting more fuel than if it was firing sequentially.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 11, 2012, 8:05 PM)
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trekvana
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Sep 11, 2012, 8:20 PM
Post #3 of 5
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Re: camshaft position sensor question
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Long fuel trim is +5 with short bouncing around zero. Im idling at 900 rpm so i think the +5 is there to counteract some vacuum leak.
One of the first things i did was to replace the fpr.
The cam sensor is a pull down design. Cam count pid is always incrementing. Cam resync count stays ar zero.
How do i perform a bypass test?
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Discretesignals
Ultimate Carjunky
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Sep 11, 2012, 8:37 PM
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Re: camshaft position sensor question
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+ 5 long term isn't bad. When it gets past +10/-10 is when you really should start to looking for problems.
If the cam count is incrementing, that means the computer is getting the cam signal. I believe I had it wrong. The cam resync counts up and cam count stops if the signal is intermittently lost. Have someone watch the cam resync while you wiggle the harness and wiring around. Look at the freeze frame data for the P0342 code and see if you can duplicate the condition when the cam code set.
I would imagine if the computer isn't getting the cam sensor signal for some reason, that might cause a delayed start. The computer has to revert to asynchronous firing after seeing a whole bunch of resyncs and has to guess when to start the sequence. Some vehicles won't even start without the cam signal. Nice of GM to have a back up mode.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 11, 2012, 8:51 PM)
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trekvana
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Sep 11, 2012, 8:54 PM
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Re: camshaft position sensor question
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Right, luckily the spark timing is only dependent on the crank signal for this car. Uses a 7x cranking signal. The cam signal is there only for injection timing. When it loses the cam signal i believe it goes into batch fire mode. It would explain the excessive gas smell
(This post was edited by trekvana on Sep 11, 2012, 8:58 PM)
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