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Discussion Starter #1
'97 bird w/135K on the odo.

My car developed a bad miss lately that I can't even come close to figuring out. So I took it to a shop for diagnostics and while they didn't finish the diags, at least they eliminated quite a few things for me.

The car just feels like it locks up, very severely sometimes. Whether I am sitting in park, driving down the street, cold engine or hot, the "miss" is the worst of any car that I have ever owned. Also the car is starting to have a hard time starting on occasion. I will not drive this car unless it is to a repair shop. It feels like it could just seize up. It also shudders bad at times. And the problem is getting worse.

Here is what the shop did and eliminated.

No codes
Cleaned & checked the MAF sensor
Checked the TPS
Checked the DPFE sensor (whatever that is)
Checked and passed the ignition system & secondary ignition system (whatever that is)
Emissions are good
No problem with the catalytic converters or O2 sensors
Hooked up the car to some type of fuel machine they have so that they can run my car off their machine instead of my gas tank/fuel pump/fuel filter - no change
Fuel pressure checked out fine.
Swapped out my coil for one they had on the shelf - problem is still there.

They were able to determine that all six cylinders are dropping off at the same time.

In other words they did a bunch of diagnostics and were unable to determine the actual problem. However they only charged me for one hour of labor - nice of them. I have the car at home because they were closing the shop for the weekend.

Here is what they think the problem may be - cam sensor or the car's computer. Or possible bad or loose connectors.

When the problem first appeared I took the car to a tranny shop, because to me it felt like the tranny was locking up. Tranny shop said the tranny is in good shape.

So what do you think? Could it be a cam sensor or computer? NAPA sells three cam sensors for the car in prices ranging from $28 to $62 (if think). I don't like throwing parts at a problem, but if the consensus is that there is a high probability the cam sensor has gone bad, I will buy a new one.

Any other thoughts what may be going on?

I would really appreciate your input.

Thanks,

Scott
 

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Discussion Starter #3
Well since they said that the ignition system and fuel pressure were both good, I'm not sure how to answer your first question. I would think if the problem was with with fuel delivery there may not be such an immediate lock-up type of feel to the engine. Only guessing, but I would think there would be fuel igniting in at least one cylinder and enough centrifugal force in the other cylinders to keep the engine turning over and running, although very roughly. Making myself clear as mud?

Yes, the tach does drop when the lock-up/stumble/miss occurs.

I have been reading my Chiltons (I know, should have bought a FSM CD instead) and they call it a Camshaft Position (CMP) Sensor. Looks like it can be tested and installing a new one could be a little tricky. I am too much of a dummy to test it and installing a new one appears to require a special synchro positioning tool as well.

Btw, where is it located on the engine? Is it located right behind the water pump and below the coil pack?
 

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If the tach drops, that means the computer is losing RPM input from the engine, which comes directly from the crank position sensor. The cam position sensor is used to synchronize the fuel delivery to the stroke during startup, or in other words it lets the PCM determine if the #1 cylinder is on the intake or exhaust stroke so it knows whether to fire the injector or not, but once the engine starts the cam position sensor is largely irrelevant. The crank position sensor should be your suspect here, so inspect the wiring to it to make sure the wires aren't exposed and intermittently touching.
 

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Discussion Starter #5
Dang, Chris. A clear explanation of what does what. I'll direct my attention on the crankshaft sensor and see what I come up with. Thank you very much.

Just another thought, though. Since the car is getting harder and harder to start, is that still a symptom relating to the crankshaft sensor?
 

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It's very possible, but as I said in the starting situation the cam sensor plays a big role. The biggest indication will be to see with a scanner if the PCM is getting a signal from the crank position sensor during cranking. You could also look at the tach to see if it bounces a little while cranking, but datalogging would be the most accurate.
 

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Discussion Starter #7
Well here is an update. I replaced the crank sensor to no avail. The car is back at the repair shop and they even swapped out the cam shaft sensor, also to no avail. The car will not start at all now. The repair shop is helping me out financially by only working on it when they have a lull in their business - which means they did not touch it this week. I appreciate what they are doing for me, but I need to get this car back on the road.

So I asked a counter man at Advanced Auto Parts and he said that it could be the ignition control module. Something about the module needing a good ground and that they have a type of dilectric grease built in to them. Heat build up can ruin the grease and cause intermittent problems that eventually gets worse. Since the repair shop supposedly checked out the ignition system, maybe they checked it out when it was running fine and now the ignition module has totally given up the ghost. The owner of the shop is the mechanic working on my car and he was not in today when I stopped by, so I couldn't run my guess past him.

Advanced Auto did say that they can bench test the ignition module but they did not have one in stock that I could look at for comparison purposes. I popped the hood on the 'bird and didn't really see anything that resembled the pic on the Advanced computer.

So my next question is this - Where is the ignition control module located on a late production year 1997 Thunderbird 3.8?

Thanks again,

Scott
 

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There is no ignition control module. Not separately anyway, it's built-in with the PCM. Has this shop actually determined what is missing? By that I mean is the signal from the crank or cam sensor not getting to the PCM? Are there bad grounds? Is the PCM not providing good reference voltage? These things and more should have all been checked before a single part was replaced.
 

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Discussion Starter #9
Chris, I don't know specifically how they went about their diagnostics. I think that I will print out this thread and take it back to them next Monday. This is a good shop and all the wrenches are ASE certified as far as I know. I would think they know a lot about a lot of things, but not everything about 1997 Thunderbirds.

Hate to think that I would have to pay another towing fee and take it to the Ford dealership. Nothing against the dealership, but they have higher rates and would want/need to start the diagnostics over again. But if it comes down to it, that's probably what I will have to do.

Btw, is the PCM the car's computer?
 
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