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post #1 of 9 (permalink) Old 07-26-2016, 10:09 PM Thread Starter
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Lean codes and engine misfires. Need help

Hi everyone,

I just purchased a 97 tbird V8. The car has 78k miles and it's in good shape. However I'm currently having some issues. The car is giving four codes:

P0174 - Bank 2 System too lean

P0171 - Bank 1 System too lean

P0430 - Catalyst system efficiency below threshold Bank 2

P0141 - Oxygen Sensor heater circuit Bank 1 Sensor 2

The car idles smooth, but immediately misses once you quickly accelerate, seems like its firing on 6 cylinders not 8, struggles getting up to speed. It feels like it loses half the power it should have. Now if you ease into it, its not bad. It does have an exhaust leak, I hear it when I accelerate.

Now I have checked the MAF, looks new, not dirty, hooked up the vacuum gauge, thats perfect. Fuel pressure is where its supposed to be as well.

The one thing I did notice was when I used my timing light. I checked all the spark plug cables with it. Some throw multiple sparks fast at idle, others throw a normal spark at idle and some don't throw any spark when I accelerate. Has anyone had that issue before? Could this mean bad coil packs or a bad ecm?

Here is what I wrote down for the coil signals:

1/2/4 regular pattern

3 regular pattern, but quits when I accelerate

6 is ok somewhat

5 fast pattern/intermittent slow pattern

7/8 fast pattern

This tells me that too much spark is leaning out the system and the ones with slow to no spark is giving the miss.

Any input would be appreciated, thank you.

1997 Thunderbird LX V8 - Sport Package
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post #2 of 9 (permalink) Old 07-27-2016, 06:12 AM
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You mentioned an exhaust leak, I'd fix it.

How old are the spark plugs and wires? Check for vacuum leaks too.

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post #3 of 9 (permalink) Old 07-27-2016, 07:49 PM Thread Starter
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Thank you Joe, I went ahead and ordered motorcraft coils and there is no vacuum leak.

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post #4 of 9 (permalink) Old 07-28-2016, 04:20 AM
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Definitely look into changing the coil packs. I've had similar problems in the past and nearly everything was resolved with the coil packs.
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post #5 of 9 (permalink) Old 07-28-2016, 09:45 PM Thread Starter
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The new packs should be delivered tomorrow. Hopefully that solves he the problem. Then I'll move on to the exhaust.

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post #6 of 9 (permalink) Old 07-30-2016, 01:05 PM Thread Starter
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Just installed new Motorcraft Coil pack, platinum spark plugs and plug wires. Still has the same miss and irregular spark pattern. Did a compression check and its about 180 on all cylinders. It did start quicker and does idle smooth.

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post #7 of 9 (permalink) Old 07-30-2016, 08:08 PM Thread Starter
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Fixed, checked MAF again and cleaned it. Runs perfect now.

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post #8 of 9 (permalink) Old 12-25-2016, 09:32 PM
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So the MAF had a direct effect on the ignition timing irregularities?
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post #9 of 9 (permalink) Old 12-28-2016, 11:31 AM
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No but the PCM references values from the MAF and the front o2 sensors to achieve target AF ratio. If the MAF is not working right, you will get lean codes in both banks like you're seeing. When you unplug the MAF the idle should be noticeably rougher, if it's working correctly. If there is no change in idle, the MAF is bad.

Also check the o2 sensor heater fuse.
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