Engine misfire, poor accel when raining - TCCoA Forums
 
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post #1 of 9 (permalink) Old 11-28-2004, 06:29 PM Thread Starter
 
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Engine misfire, poor accel when raining

Ocassionally when it is raining or very wet my '96 LX (3.8) will hesitate, misfire when trying to accelerate on the highway. Never had a code come on until last week the Check Engine light flashed several times then stayed on (and since then it runs great). I took it to Auto Zone to pull the code and they said it had some sort of multiple ignition misfire event but didn't show any particular sensors to be bad. They said to check the ignition wires. They all look okay to me, anything else I should check?

Thanks,
Bob
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post #2 of 9 (permalink) Old 11-28-2004, 09:55 PM
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sometimes if you have a bad or old ignition coil pack in a DIS system is can cause misfiring. But first, start your car at night time and look under the hood to see if you can find any arcing from the spark plug wires or plugs to the block or somewhere, that is pretty common. But most likely I'd say yopur coil pack (thing the spark plug wires plug into on a distributorless ignition system) is bad.
-Thomas

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post #3 of 9 (permalink) Old 11-29-2004, 05:28 PM Thread Starter
 
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Thanks! Ignition wires all look good. Let me ask you all this. If the DIS was bad wouldn't it cause misfires throughout the RPM range? This only happens when accelerating under a load. Does the DIS pack have it's own computer inside that controls ignition timing? Are there any other sensors that feed the ignition system information like a manifold pressure, crankshaft position or throttle position sensors that could be a culprit? Thanks again for the help!

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post #4 of 9 (permalink) Old 11-29-2004, 05:34 PM
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the crank sensor is what tells the coil pack to fire. The coil pack is like an ignition coil and distributor all in one. Except instead of the rotor telling it to fire, an electronic signal does. But the crank sensor is behind the timing cover, which is a sealed system, and shouldnt be exposed to any moisture.
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post #5 of 9 (permalink) Old 12-28-2004, 10:49 PM Thread Starter
 
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Thanks again! Finally tore into the motor today and replaced most all the sensors as they have over 159K miles racked up (engine rebuilt at 129K). When I took out the air filter it was soaked like a sponge! Upon further inspection the air silencer was full of water (about a quart). We did have a bit of a rainy (Monsoon) season here in the Houston area less than a month ago, but even then I am amazed how much water was in there. It's not like I drove the car through any flooded areas.

So anyway, after removing the air silencer, replacing the coil pack, the O2 sensors, TPS, fuel and air filters and cleaning the MAF, my 'bird runs like a champ! I'm curious to see what I get for highway MPG now. I was getting about 24 mpg which didn't seem too bad.

Still amazed at the amount of water ingestion...
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post #6 of 9 (permalink) Old 12-31-2004, 11:27 AM
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Just for the record, it's the cam sensor that controls the ignition timing. The crank sensor controls fuel injector timing.

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post #7 of 9 (permalink) Old 12-31-2004, 05:21 PM
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no, the cam sensors controls the fuel timing, and the crank sensor controls spark. But I was wrong in my previous post, the crank sensor is bolted to the exterior of the timing cover and can be replaced very easily. Just did one a few weeks ago on a local members car.

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post #8 of 9 (permalink) Old 12-31-2004, 07:10 PM
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I just checked sccoa.com and a service manual and the cam sensor controls ignition timing. Try adjusting it and see what happens to your ignition timing. Also note that if the cam sensor is damaged, your ignition timing goes out of whack. This is a useless argument, though, as it has nothing to do with his problem which he already resolved. The crank sensor has one vane that is not 120* offset to tell the computer where TDC is. That's how it runs with the cam sensor disconnected. The cam sensor is used to 'lock down' the ignition timing as it rotates half the speed of the crank and thus provides a more reliable signal.

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post #9 of 9 (permalink) Old 12-31-2004, 07:52 PM
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Quote:
Originally Posted by thebigslide
I just checked sccoa.com and a service manual and the cam sensor controls ignition timing.

NO, cam sensor controls FUEL. CRANK sensor controls IGNITION! Not only have I talked to many v6 experts about this, but here is a quote from a Ford Maintenance/Repair CD

Crankshaft Position Sensor

Note:
Initial engine ignition timing is set at 10 degrees ± 2 degrees before top dead center (BTDC) and is not adjustable.

The crankshaft position sensor (CKP sensor) (6C315) is a variable reluctance sensor which is mounted on the engine front cover (6019) and is triggered by a 36-minus-1 tooth trigger wheel located on the crankshaft pulley and damper.

The signal generated from the crankshaft position sensor is called the crankshaft position (CKP) signal, which provides:

l base timing

l crankshaft speed (rpm)

The powertrain control module (PCM) (12A650) will use this information to determine ignition coil (12029) turn ON and turn OFF time.


Ignition Components, Electronic

The electronic ignition (EI) system for the 3.8L engine consists of the following components:

l crankshaft position sensor (CKP sensor) (6C315)

l ignition coil (12029)

l misfire detection sensor

l related wiring


I know it seems odd, the cam sensor controling fuel, where the distributor, which goes in the same place as the cam sensor does on DIS cars, would control timing. But its the truth.

I've been searching sccoa for the past 45 minutes to find anything solid pertaining to your "facts" but there are a lot of mixed answers on sccoa, seeing as a lot of people there get the two mixed up as well. You cant always take what some guy on an open forum says to be an absolute truth.

-Thomas

1988 Notch Mustang: - 438W, direct port n2o, t56
2003 SVT Focus: - SCT X3 tuner

Last edited by Thomas; 12-31-2004 at 08:33 PM.
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