04 Taurus/Sable 3.0 DOHC Misfire only when warm.

563 Views 14 Replies 5 Participants Last post by rjacket, 4 d ago

Tom G

Discussion Starter · 27 d ago

Can't find a solution despite a lot of posts on this topic. Does anyone know something new besides what I've checked/replaced; plugs, vacume lines under hood (because it only happens afer heat soak, I'm sure it's not vacume behind firewall), EGR gaskets, broken ignition coil connectors, one bad coil. Smoke test reveled only very tiny smoke leak when both hot and cold. NO OBDII codes currently present. This model does not have the vacume line that rots which runs under the intake. No visual cracks on any plastic parts. Misfire does NOT happen when cold or on short first drive of the day. When it sits for 10 or so minutes after that short drive, it begins misfiring and generally clears when acceleration is increased dramatically. (that would seem to indicated a vacume leak, but again, I've replaced many lines and checked all others. Thanks

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rjacket

· #2 · 27 d ago

You need to run the mode 6 test in Forscan to identify which cylinder(s) are misfiring. There is other data that it can report that will help you diagnose this in a structured way.

chartmaker

· #3 · 27 d ago

Tom G said:
Can't find a solution despite a lot of posts on this topic. Does anyone know something new besides what I've checked/replaced; plugs, vacume lines under hood (because it only happens afer heat soak, I'm sure it's not vacume behind firewall), EGR gaskets, broken ignition coil connectors, one bad coil. Smoke test reveled only very tiny smoke leak when both hot and cold. NO OBDII codes currently present. This model does not have the vacume line that rots which runs under the intake. No visual cracks on any plastic parts. Misfire does NOT happen when cold or on short first drive of the day. When it sits for 10 or so minutes after that short drive, it begins misfiring and generally clears when acceleration is increased dramatically. (that would seem to indicated a vacume leak, but again, I've replaced many lines and checked all others. Thanks

I bought '05 DOHC with a warm only misfire. Dealer cut $200 off I took it with the misfire. I drove it 180 miles home with the misfire which was worse when sitting in traffic but no so bad at road speed but still did it a few times. Used the code reader that I had as in the picture and used the "pending code" feature and it was #3. I switched #3 and #6 and the misfire followed the COP. I put a JY coil on it and no more misfire.
I was surprised that that bad a misfire would not set a code. That Pending Feature is really important.
-chart-

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snosaint

· #4 · 22 d ago

As the coils heat up they reveal their weakness...

rjacket

· #5 · 20 d ago

snosaint said:
As the coils heat up they reveal their weakness...

There's a video on youtube about the lower intake manifold gaskets causing misfires only when warm. Spray carb cleaner while running to test.

chartmaker

· #6 · 20 d ago

rjacket said:
There's a video on youtube about the lower intake manifold gaskets causing misfires only when warm. Spray carb cleaner while running to test.

Fuel trims would be a eliminate that issue, for any vacuum leak.
-chart-

Reactions: 1

The White Falcon

· #7 · 19 d ago

rjacket said:
There's a video on youtube about the lower intake manifold gaskets causing misfires only when warm. Spray carb cleaner while running to test.

Those are phantom misfires rather than actual ones, plus that tends to happen more when the car is idling. OP didn't specify either way though.

rjacket

· #8 · 19 d ago

chartmaker said:
Fuel trims would be a eliminate that issue, for any vacuum leak.
-chart-

You're right. I misremembered and the symptom from leaky lower intake manifold was rough idle when cold, not misfire when warm. The same guy did a video with the same car where they had misfire when warm due to coil on plug issue.

chartmaker

· #9 · 19 d ago

The White Falcon said:
Those are phantom misfires rather than actual ones, plus that tends to happen more when the car is idling. OP didn't specify either way though.

Pic of what feels like misfire, no code, no pending code. Ford Tech told me this is common.
-chart-

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Tom G

Discussion Starter · #10 · 16 d ago

Thanks to all the suggestions. I've had it all apart, (manifold off, COP's off, etc) and checked for leaks, cracks in hoses and all the visual stuff I could. I'm going to do some extensive driving and looking at fuel trims next. I don't have Forscan so I can't do mode 6 tests with my scanner. Also tested resistance on all the COP's and they're consistent. I had replaced a bad one some time back and the new Bosch one reads a bit higher.

chartmaker

· #11 · 16 d ago

Tom G said:
Thanks to all the suggestions. I've had it all apart, (manifold off, COP's off, etc) and checked for leaks, cracks in hoses and all the visual stuff I could. I'm going to do some extensive driving and looking at fuel trims next. I don't have Forscan so I can't do mode 6 tests with my scanner. Also tested resistance on all the COP's and they're consistent. I had replaced a bad one some time back and the new Bosch one reads a bit higher.

Most readers will read fuel trims. At idle +/-10% is fine. PIc my '04 Sable wagon after fixing leak at the EGR to intake. Was ~+20% before and only issue is bad cold idle. No codes.
Unlikely vacuum leak would cause misfire.
I consider checking fuel trims on all my 4 vehicles. For sure on new buy. Easy and routine.
-chart-

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rjacket

· #12 · 16 d ago

Tom G said:
I don't have Forscan so I can't do mode 6 tests with my scanner.

An ELM327 is $20 or less and Forscan is free or ~$5.

Get them, run the mode 6 test, and you'll see which cylinder is misfiring.

No need to do extensive driving etc. An ELM327 + Forscan pays for itself after a few minutes.

Reactions: 1

Tom G

Discussion Starter · #13 · 15 d ago

Thanks again. I was thinking of a more complicated tablet type reader when Forscan was mentioned. I'll try that next.

Tom G

Discussion Starter · #14 · 5 d ago

Solved, finally. Thanks to all for suggestions. And rjacket I will try the Forscan.

I couldn't see anything unusual in fuel trims on scanner. It seemed so much like bad coils I've replaced in the past, and one on this engine. So I made the decision to order a cheap set of 6 online for about $36. I figured that would be a quick way to part-shoot the issue even if they don't last long, then I could narrow it down to the actual bad coils(s) later. I did the full 6 coil swap in 45 minutes last night, (I've honed my skills at intake and related parts removal for access after about 5 times doing this). Drove it about 65 -70 miles today with 5 stops and at least one long heat soak. Not a SINGLE misfire. So now I'll do swap in and outs on the front facing bank with the factory coils to determine the bad ones. And we'll see how long a cheap set goes before breaking down.

Thanks again to ALL of you.

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rjacket

· #15 · 4 d ago

Congrats and thanks for the update. It's good that the cheap coils are all working.

The reviews I saw on highly rated cheap coils suggested a life of a year or two. Be sure to update us!

Btw, in some instances, only boots, not entire coils are at fault so you may want to consider that when testing.

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