Engine cutout issue...or something...

[1badgmc]

I have this odd issue on my '98 Suburban that nobody can give me a definite answer on.

I cannot faithfully re-create the problem. Sometimes it'll do it, sometimes it won't. It happens when I've accelerated and am reaching my cruising speed and I'm backing out on the accelerator. When I'm backing off the pedal, the truck will lurch, almost like a really hard shift, which I know it's not. It seems like the engine cuts out for a split second. It's really annoying when I'm driving down the main freeway through town where there is a long series of overpasses, so there's a lot of up-and-down. Each time I reach the crest of one of the overpasses it will lurch like that.

I am getting a P0340: Camshaft Position Sensor Circuit Malfunction code. Nobody can tell me for sure if this might be the cause, but I keep thinking it is. My research tells me that this code is more often traced to a wiring or other issue rather than the sensor itself, but I honestly have no clue where the sensor is to start looking.

Any ideas?

[69c10stepside]

I think on the pre ls style vortec engines, the camshaft position sensor is on the distributor, under the cap. That is where it was on my 99 jimmy, vortec 4.3, and I know that the vortec 350 long block I had, only had the crankshaft position sensor in the timing chain cover..

[bwood]

I wonder if there is some excessive slop in the dist gear?

[Boog]

Have you unplugged the cps and cleaned the connections. They tend to get oil and dirt buildup there.

[ChevyTech]

I agree it could be poor connections, or that a wire harness rubbing through. Try wiggling the wiring with it running and see if it acts up.
Inspect the connectors.

CT

P0340 OBD-II Trouble Code

What does that mean?
This indicates that a problem was detected in the camshaft position sensor circuit. Since it says circuit, that means the problem could lie in any part of the circuit - the sensor itself, the wiring, or the PCM. Don't just replace the CPS (camshaft position sensor) and think that will definitely fix it.

Symptoms can include:
• Hard starting or no start
• Rough running / misfiring
• Loss of engine power

Causes
A code P0340 could mean one or more of the following has happened:
• a wire or connector in the circuit could be grounded/shorted/broken
• the camshaft position sensor may have failed
• the PCM may have failed
• there exists an open circuit
• the crankshaft position sensor may have failed

Possible Solutions
With a P0340 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:
• Visually inspect all the wiring and connectors in the circuit
• Check for continuity in the circuit wiring
• Check the operation (voltage) of the camshaft position sensor
• Replace the camshaft position sensor as required
• Check the crankshaft position circuit as well
• Replace circuit wiring and/or connectors as required
• Diagnose/replace the PCM as required

Source:
http://www.obd-codes.com/p0340

[1badgmc]

Originally Posted by Boog

Have you unplugged the cps and cleaned the connections. They tend to get oil and dirt buildup there.

...

Originally Posted by 1badgmc

...I honestly have no clue where the sensor is to start looking.

[bwood]

Under the rotor in the distributor.

[1badgmc]

Thank you.

[HarrisonTX]

I havn't visited this forum in about a year, and I came here with the EXACT same problem.

Mine is a '97 v6/5speed 1500. 230k miles. It happens when I reach the top of a hill, and back off the accelerator pedal. I will check that connection RIGHT NOW.

The frustrating this is it's impossible to re-create. I can't make it happen, it just randomly does it. Very unpredictable.

[1badgmc]

Originally Posted by HarrisonTX

The frustrating this is it's impossible to re-create. I can't make it happen, it just randomly does it. Very unpredictable.

EXACTLY! Sometimes I can go for a long drive and it won't do it at all. Sometimes I can take a short drive and it'll do it every time I back off the gas pedal. Other times it'll just do it randomly here and there on a drive. It's retarded. I know that if I ever took it to my mechanic and said, "here...drive it and tell me what's going on" that the thing wouldn't do it for him.

[HarrisonTX]

So weird to see this on the first page. Well, I just went and unplugged the CPS. It was super clean, but I wire brushed it off anyways. I took it for a 4 mile drive at highway speed, and hit two hills. It didnt do the chug thing, but then again, it does it occasionally. Since the connection was so clean, I doubt that is the problem. Time will tell though