Contour Enthusiasts Group Archives Forums General Troubleshooting Periodic violent misfires and stalls

I have a 1998 Mercury Mystique, 2.0L Zetec Automatic. The car runs perfectly most of the time. Periodically, say once or twice per week the car will start bucking violently, (as if I were towing someone and they kept slamming on the brakes). At lights and stop signs the engine will sputter and occassionally stall. Usually if I horse it a bit, the problem will go away but not always. I have tried to look for arcing at night but see no signs of any. I do have a check engine light that reports a faulty cam sensor. I have replaced the sensor but the light comes back. After a few days of not happening the light turns off. A few days later it will start bucking again. There does not seem to be a pattern to this behavior, be it rain or cold or heat. The only thing that "sometimes" helps is letting the engine warm up for 15 minutes before leaving with it, (but this usually makes the check engine light come on faster).

Any ideas?

Welcome to CEG!

What was the code?

Perhaps this is a VCT problem.

If it is the CPS be sure to check the electrical plug and wiring.

Thanks for the quick reply.

The actual code was (is):
P0340 - Camshaft Position Sensor circuit fault.

I have taken it to 2 different Ford dealers and got 2 completely different diagnosis.

The first thinks it is interference in the engine compartment that is causing the sensor to read as faulty, which in turn is making the computer go into a diagnostic mode which causes the timing to go out of whack. They are willing to "try" to track it down but it will cost me 4-5 hours of labor and there are no guarantees... I am therefore not convinced that this is much of a possibility.

The second says they "think" it is a cam solenoid. This is apparently the actual actuator that the sensor reads. This is a $600CDN part and they say 6 hours of labour. Again no guarantees so I am hesitant.

VCT I assume is the Variable Cam Timing? Is the Cam Solenoid the only player in the variable timing? Is there a way to bypass the variable part and simply fix it to a specific timing? (maybe less performance and ecomomy but if it fixes the problem...)

CPS I also assume is the Cam Positioning Sensor? I want to try changing the plugs and wires next weekend, is there a possibility that this is the problem? (I checked at a local parts place and the spark plugs were $18 each! Is this normal for this car or are there cheaper ones out there?) I don't want to sound cheap but if it isn't the problem I will be out $80 just for the plugs, plus the wires etc. Is there any other component "spark" related to be changed? ( no cap or rotor, but an equivalent? )

Thanks again.

A Variable Cam Timing problem will return a code of P1380 or P1381.




P0340 Camshaft Position Sensor circuit fault


If the sensor has been replaced, the problem has to be in the wiring from the CPS to the DIS module (Distributorless Ignition System), or in the DIS itself (although this would be extremely unlikely). The Camshaft Position Sensor sends a signal called the CID (Cylinder IDentification)To the DIS and EEC at startup. This signal establishes firing order. The crankshaft position sensor (VRS) sends the DIS the PIP (Profile Ignition Pickup) signal to establish base crankshaft timing (usually 10 degrees).The DIS module should be in the case with the ECU (engine control unit)inside the car.

You really need to inspect the connector on the cam sensor for corrosion on the contacts and the wiring for abrasion, cracked insulation, and shorts to ground.

The cam sensor output is monitored but not really needed once the engine is running. When the engine is acting up you can try unplugging it and see if the bucking stops.

Any Dealership worth a plug nickle should have the equipment to scope the CID, PIP, and SAW signals and tell if that were the problem. Perhaps if you need to you can find an independent garage capable of doing such from someone in the Canadian forums.

Tell us where your at or if your on the east coast - where your to.
If you are near me - I found a great place for diagnostics....

I'm in Montreal. If you know of anyone good around here I am all ears.

I will have a look at the wiring, connectors and harness tonight.

Is there a list of all sensors and their locations anywhere? I have purchased the Haynes manual for the car but it does not seem to show all locations with accuracy. It was Ford that changed the CPS so I would like to make sure I am looking at the right cabling.

Thanks again!

EBay
You are looking for the FORD 'Electrical and Vacuum Troubleshooting Manual'. These books cover everything, every plug , wire , connector..........

I was thinking a bad coil or plug wire? Do you smell eggs?

Check the wireing harness by an engine hook that is placed on the cylinder bank next to the firewall. It may have been damaged if the cheap rubber guard slips off and exposes the sharp edge to the harness that presses against it.

horseydugModerator- "Code is indicating a wiring problem, not sensor problem. The two sensor wires go directly to PCM although they pass through a 12 pin connector, rear of ps pump. Wires have a grounded shield. Best to do physical inspection and ensure connector is properly snapped in place as a starting point."

A p0340 on this vehicle doesn't necessarily mean a circuit failure (wiring, sensor or pcm). The strategy that sets this code looks for a signal at the appropriate time, and if it is not seen within about 25 degrees of crank rotation, the pcm will log this code. If it happens on two consecutive drive cycles, the check engine light will turn on. A timing belt or pulley issue will cause this same code, however, your symptoms aren't quite what you'd see with a timing belt problem. Based on that, wiring is the first place i'd go. Second, scoping the appropriate lines at the pcm while the engine is running will tell you if the signals from the cam and crank sensors will let you know if they are the cause of the problem. RFI is a very real problem on todays cars - but it is usually generated from the old aluminum DPFE sensors (which your's doesn't have) or coil-on-plug ignition coils. On your car, the alternator, coil pack and cooling fans all can generate rfi that would interfere with low voltage signals like the cam sensor signal. Find you a good shop with knowledgable people to work our problem.