car problem (real head scratcher)

[Battis]

My 2005 Lincoln Towncar (104,000 miles) bucks at approx. 40 MPH when I give it the gas. No codes show up. If I turn off the overdrive it doesn't happen.
Trusted mechanic said it's probably the transmission (he described what he thought was the problem).
Transmission guy said it sounds like a misfire.
Any ideas?

[35isit]

Have someone with the proper scan tool figure which coil is dropping out.

[Battis]

That's the problem - no codes are showing up.

[colt38sp]

Sounds like the Torque Converter. I had this happen once on a F-150 and all it needed was a fluid/filter change and problem went away. I am no mechanic though.

[Plate plinker]

Your halfway there. By turning off the overdrive you have in my non mechanic mind proved it is the transmission. Seems it could be the torque converter lock up get flaky. Find a better transmission guy.

[35isit]

That's the problem - no codes are showing up.

It doesn't have a bad enough miss to turn on check engine light. A scan tool that shows what each cylinder is doing will show which one or (ones) are dropping out under stress. When you turn off overdrive there is not as much stress on engine.

[nvbirdman]

I think maybe the reason you're not getting an engine code is because the problem is not in the engine. Check the transmission.

[popper]

Could be either. Torque converter is 'locked' when in overdrive - had that happen on a couple autos. Solenoid in trans. controls it. Over-run clutch in converter will cause it to buck when slowing down to stop - won't unlock usually due to crud in the clutch. Could be low engine torque 'lugging' in OD or computer not dropping OD when lugged. Yup, need scan tool while driving (loaded).

[s mac]

I'm a Ford tech, and agree that it's probably a misfiring coil, in overdrive, 50-60 mph especially on an upgrade is often when the miss shows up. Need a scan tool to test drive running power balance. Those often won't set a dtc.

[Battis]

The mechanic took it out with the scan tool and it didn't show anything when it happened. He thought it might be the solenoid in the transmission, especially at that speed (40 mph), and especially when I turned the OD off. The transmission guy said (on the phone) it could be, but it might be a misfire, too. The car does have a history of bad coils but they usually show up on the scan.
So...am I doing any harm by driving with the OD shut off? Other than bad gas mileage.

[skrapyard628]

Just from what you stated I would really be led to believe the torque converter clutch is not unlocking properly. Could be the solenoid for it, could be the clutch itself is sticking, or even possibly the wiring.

Most generic scan tools wont allow you to monitor the TCC solenoid for on/off function while driving or at all. They usually will only post a code if the solenoid is completely burned out (open circuit) or there is a break in the wiring harness for it (once again, open circuit) And Im unsure if the system on that vehicle even allows you to monitor the TCC with the proper Ford scan tool (maybe someone here knows Ford scanners better and can say).

I had the same issue on an '02 Nissan Frontier. I replaced the torque converter clutch solenoid and checked all the wiring for it while I was down there. Problem fixed.

If you end up replacing the TCC solenoid you usually have to remove the drain pan for the trans. Obviously if the pan is off you might as well put a new filter in and give it some fresh trans fluid while youre in there.

[Battis]

I'm heading to the transmission place now. The guy is good - he replaced a clutch in a Jeep Eagle Summit for me many years ago when no one else could, or would, do it.
Thanks for the tips. Now I know what questions to ask.

[Handloader109]

Lincoln.... Ford product. Does it have individual Coils on each sparkplug? If so, then one or more is going bad. Won't throw code unless they fail entirely.
I've a 2005 Ford truck that I thought was the tranny, but it was bad coils.

[Finster101]

Do a complete exchange of the trans fluid. The "washboard" effect should clear up. It's a very common Ford issue, if your trans guy didn't know about it find someone new.

[35isit]

I'm a Ford tech, and agree that it's probably a misfiring coil, in overdrive, 50-60 mph especially on an upgrade is often when the miss shows up. Need a scan tool to test drive running power balance. Those often won't set a dtc.

Ford parts department for 25 years. Probably sold 500 coils for that problem on Lincolns, Crown Vics and pickups. That's why I posted what I did. Worked with a technician once who always priced the job to replace the "bad ones" and all of them. He said it will be back sooner or later for the rest. By putting in all of them you were just heading off future repairs.

[Battis]

I never made it to the transmission place. I got on the highway and it started bucking even with the OD off. I went back to the trusted mechanic (I really do trust him) and he said we're back to the bad coil that's not bad enough to set the code light off (as 35isit and smac said). I asked if it's worth it to change all 8 coils and he smiled and said it was worth it to him. It's happened in the past - the engine light won't come on until the coil is completely gone. Luckily I only need the car for around town driving.

[brass410]

I'm with starmac, you probably have, A-bad coil or B the boot that covers the coil to plug area is starting to breakdown, sometimes there's only one, others it can be all 8. I see this a lot here in the shop, when it gets real bad, it will show as a random misfire, when you remove the coil take a real close look at the coil on plug boot sometimes you can see carbon tracking on them.

[Brassduck]

103000 miles, I'd put a set of plugs in it first.

[osteodoc08]

Get a scan tool. See which cylinder is misfiring. It’s not frequent enough to throw a code. You can use one for free at autozone or similar. This is typical symptoms of fords COP when they’re going bad. You’re due for plugs. Those 4.6L and tranny combos in the town car are pretty solid

[6bg6ga]

I hate to disagree but I would have a Ford technician with a Ford diagnostic tool or a really good mechanic with a Mac diagnostic tool check it. The cheap diagnostic tools at the parts stores are gunk for the most part. Misfiring? The "Good" scan tool should have shown misfires a count of the misfires for example on cylinder #1 XXX misfires at least good scan tools do. My experience ....Ford is notorious for torque converter problems and they will manifest themselves as kind like a miss. I went thru (4) torque converters on (4) different Ford F250 vans.

It was mentioned 103,000 miles a set of plugs. I went 180,000 miles on a set no misfires.

My GMC Envoy had a slight miss that didn't set a code but the Mac scan tools showed how many times it missed on the affected cylinder. So, it doesn't always set a code. Narrowed my problem down to a intermittent coil pack which I changed and problem was gone. I'm a firm believer in not throwing parts at something. The problem needs to be found and then replace the part. As for throwing all new coil packs on it ...... I wouldn't because your probably looking at $80 ea on up.