97 Cougar 4.6 barely runs P0340 code - TCCoA Forums
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post #1 of 8 (permalink) Old 02-22-2017, 11:06 PM Thread Starter
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97 Cougar 4.6 barely runs P0340 code

MY 1997 Mercury Cougar 4.6 L has 160,000 miles and had been running great. I pulled into traffic, put the petal to the floor, and it started stumbling and shaking. I pulled into the parking lot where I was going and expected it to die but it maintained idle but shaking real good. When I started it back up the SES light came on. I was able to coax it home but there was no acceleration, wouldn't go over 40 mph, and was still shaking bad. I used my code reader and got the code P0340, camshaft position sensor. I replaced the sensor but it is still doing the same thing and still showing the code. It will start if I push the gas while cranking but it won't rev over 2K. I am thinking it jumped timing but most of the threads I read say they have never seen this on these engines. But then I found ones on Explorers that show the plastic tensioners break and it can jump time. I want to get some opinions before I start removing the timing chain cover.
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post #2 of 8 (permalink) Old 02-23-2017, 04:50 AM
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I have no experience of this kind of problem, but it maybe worth resetting the ECU (battery off/on) and also checking the wiring to the sensor for bad connections/dirt etc, before dismantling anything.

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post #3 of 8 (permalink) Old 02-23-2017, 06:15 AM
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The cam sensor does nothing on these engines except help get the injector pulse on the right stroke when cranking. It's only used during startup, so it wouldn't affect the way the engine runs.

Recent maintenance history? When was the last tune-up?

Start and run it with the MAF sensor unplugged. If there's no improvement, move on. If there is, replace the sensor.

Check for vacuum leaks. Common leak points are in the lines leading to and equipment in the EVAP system; passenger side inner fender.

How's fuel pressure? Good spark on all cylinders? What happens if you disconnect then reconnect one fuel injector at a time (aka searching for a miss)?

Clogged cats aren't a complete impossibility either. Pop out the upstream O2 sensor on one side at a time then start it to see what happens.

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post #4 of 8 (permalink) Old 02-23-2017, 07:45 PM Thread Starter
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Thanks for the advice. I didn't really think the cam sensor could sense is the cam timing was off. I'll check it all out this weekend. I had an EVAP code when I first got the code so I figured out that system but it could have came apart. I try to clean and replace everything I can when I come to it. I just replaced the carpet and had the seats reupholstered so I want to keep driving it.

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post #5 of 8 (permalink) Old 02-24-2017, 07:43 AM
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On a 97, I would automatically suspect the PCM.


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post #6 of 8 (permalink) Old 02-24-2017, 08:55 AM
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post #7 of 8 (permalink) Old 02-24-2017, 06:26 PM
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The cam sensor simply informs the EEC which stroke the crank is on at startup. The crank sensor determines timing. In other words, with a dead cam sensor, every time you start the engine, it has a 50/50 chance of firing up and running normally.

It should be immediately obvious upon starting the engine whether it's running 180 out with regard to fueling (these cars have waste-spark, so ignition timing will be correct either way). Try shutting the engine off and restarting a few times until it fires up normally. Assuming it does, your cam timing is fine, the issue lies with the cam sensor signal to the EEC.

If you've replaced the cam sensor to no effect, the next most common cause of a faulty signal is a failing alternator, believe it or not. The alternator will likely still charge the battery without trouble, but will throw off the cam sensor due to AC voltage. Take a look at any of the main Mustang forums and you'll see a common theme: P0340 ends up being corrected via alternator replacement. Been there, done that myself.

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post #8 of 8 (permalink) Old 02-26-2017, 07:04 PM Thread Starter
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The PCM? Do they give problems especially after 20 years? This car is hard to start, has a rough idle, won't rev up much, and although it can move around, you wouldn't want to take it on the road. It was running fine until this happened and code P0340 comes up.

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