Diagnosing a no-start, no-spark on '97 TC

LTC1997

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I was heading out this morning in my '97 Town Car Sig, and then I wasn't.

Car had been parked two nights ago, ran fine.

Engine cranks vigorously, but no sign at all of fuel+spark.

I checked for fuel pressure at the valve, check.

PT scan tool reads "link error", then "no codes".

I checked for spark, found none, so I checked for 12v going into one of the coils at the R/LG wire, got 12v on RUN.

This is where I am now. Looking at my engine schematic in my un-trustworthy Chilton manual, I now can only think of checking the Camshaft Pos'n Sensor and Crankshaft Pos'n sensor.

I'm looking for any more possibilities, short-cuts or wisdom of experience.

Thanks in advance, and I'll follow up with wherever this goes.
 

LTC1997

Member
83
5
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Thanks for the data point there. I'll struggle to move the AC compressor out of the way I'm sure, looks like I have to go in from below. :-(

I checked for pulse at the injector, I am only getting a DC signal from the harness when the ign is ON.

What is weird though is that only my digital meter reads 25vAC on the injector plug with ign ON, dropping to 22vAC with the engine cranking. The Analog meter shows 0vAC, probably because there is some stray frequency going on that has no current behind it.

Too bad that my car has no tachometer to look at while I'm cranking the engine, that would let me know if the computer even knows that the engine is turning over. But no spark and no injector pulse delivered is telling me that the crank sensor is the #1 suspect here.
Can anyone confirm that a faulty CSP Camshaft position sensor will not keep a 4.6l in a '97 Town Car from sparking and injecting fuel? It's a whole lot easier to get to than the CKP Crankshaft Position Sensor, so I'm thinking that maybe I should run a test on that one just in case(?).

Not too much related to the topic here, but for anyone doing a round of diagnostics like this on their Town Car, put a trickle charger on it before even starting. Every time you open the door, turn key to start, and especially crank the starter, that's a lot of juice borrowed from the battery. Even after you close the door there is considerable drain going on for some minutes until the modules all go back to sleep!
 

LTC1997

Member
83
5
8
Well, I removed the shield below the engine and had a look-see, all looked normal but I curiously tried to remove the CKP sensor wire to see how difficult it was to push in the lock and get another hand in behind the tie rods and stabilizer to pull off the plug.
As I was doing this, I recalled a YouTube video by some young guy I had just watched, where he said that on his car the sensor began working again after he wiggled the connector!
So I removed the connector, then re-attached, removed and reattched it again, then went to start the car ...and it started!
So now I'm wondering if it is really just the connector, or if it's the sensor itself that might be faulty.
Thinking I will re-install the shield and keep my driving local for a while before chancing having to pay for an out-of-town tow back home.
Or maybe I should replace the sensor now since it's really not that hard and not expensive either(???).
I should note that the temperature has gone up a great deal since when it wouldn't start this morning, and thinking about what dave42 offered as real experience with this possibly-intermittent problem.


EDITING here to say that I went ahead and replaced the sensor while I had the big shield off, I figure that as lucky as I was that this one failed in my driveway, I should be quite happy to replace the suspect $30 sensor with a new Echlin part.

Easy fix, I'll add a tip I learned by accident that you can suspend the weight of the compressor with the loose belt by hooking the belt onto one of the three lugs on the front of the pulley, and the hoses might then be less likely to be stress-damaged by the weight of the compressor. You have to unhook the belt for a moment only when you actually pull the old sensor out and slide in the new one, using your other hand to support and manipulate the compressor an inch or so over. Other good techniques no doubt exist, but this one worked ok for me while I was fumbling for wrenches and stuff under the car. Oh, and I only had to raise the front end of the car by about 3-4".

Thanks for reading.
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