91 TR won't start. Help please!

I would check to see if your fuel pumps are working... Steve (he is an ace with troubleshooting) will chime in.. Does not sound like the starter solonoid because she is cranking.. I would bet that you are not getting enough power to the fuel pumps or a possible loose connection. Wait for Steve.. he will guide you thru.

R

 

Dear Ferraristi,

When you crank and crank and it sounds like it's going to start but dies one second later, this is a classic tachometric relay issue or related issue.

Do a search on Tachometric relay. Read up and you will be able to go over with Steve M on a diagnostic procedure with a good sense of understanding.


Shamile

Freeze...Miami Vice!

 

That is a very long list

Please confirm/deny if it is a US version TR (engine family F113A040).

Seriously, you need to do some simple tests to first decide whether it is ignition or fuel related. The first thing to do is check if ignition spark is occuring, or not, during the starter motor cranking period -- easiest (and safest) way to do that is with a clamp-on timing light and just see if it flashes, or not, during engine cranking. If no spark, we'll look at the ignition system; if spark is OK, we'll go into the fuel side of things.

Although 1 no-brainer thing for the ignition that you can easily do is just unplug/reseat/make sure that it is plugged in the small round 4-pin connector under the coolant expansion tank (this connects the flywheel sensors to the ignition ECU). You can also unplug/reseat the connector for each flywheel sensor (one is black and the other white) on the LH side of the clutch housing.

Since you report that it cranks over, but never fires nor coughs at all (is that right?) -- this can only occur if the ignition system for both banks or the fuel system for both banks is totally dead.

 

No trouble -- glad to help one of the TR brethren if I can -- and thanks for the clarifications.

There are more things that will take out just one bank of ignition or just one bank of fuel, but there are a few things in each system that can take out both banks at the same time (so those are the things that we'll look into once you can confirm deny whether it's an ignition problem or not).

Of course -- I'm not working to a fixed time deadline

 

Had the exact same symptoms about 5-6 years ago.. It was the crank sensor or TDC pickup, can't remember which.

 

Does your TR have an alarm/anti-theft system that may have become active?

 

Checking/cleaning the connections is good, but it doesn't prove the flywheel sensors themselves are actually working or not. The next thing to do is measure the resistance of each (unplugged) sensor (which is easy) and the AC voltage coming from each sensor when it is plugged in and you are cranking the starter motor (which is not so easy because the connectors are waterproof so you need to make some sort of jumper wire arrangement to keep the sensor connected while also being able to measure the AC voltage between the two pins) -- see post #2 in this thread for the details for making the measurements with a DMM:

http://ferrarichat.com/forum/showthread.php?t=190856

If either of those two flywheel sensors is bad, it will give the symptom you have (no spark on either bank). If you have the luxury of an oscilloscope display, the waveforms would look something like these:

For the (white) RPM flywheel Sensor:
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For the (black) TDC flywheel Sensor:
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Glad to hear that you got it sorted -- but I'm going to remain a little skeptical about the "fix"...

 

I'm suspicious that it may have been something else because these are very simple sensors inside that are essentially just a coil of wire (probably wound around an iron core) that detects the presence/absence of another ferrous part passing nearby (i.e., they work on the principle of variable reluctance rather than being a more sophisticated Hall effect sensor that detects a changing magnetic field). Maybe the magnetic state of the iron core can make a difference (and this is what bringing a strong permanent magnet up to the sensor might influence), but it hasn't been widely reported as a common "fix" for these sensors. One problem always is, that whenever you work on these things, you wind up flexing things so, sometimes, just that rooting around process can fix a connection. If it fails again, you might try measuring the resistance of the sensor (by unplugging it as gently as possible) to see if it is an open resistance when bad -- but as long as it stays working, I wouldn't worry about it one iota

 

Steve, can you help clarify these 'scope traces a little for some troubleshooting I'm trying to do on another issue? Does the solid central horizontal line represent 0V, meaning that the 5V pk-pk is a -2.5V to 2.5V square wave centered around 0V across the sensor? Is one of the leads going to each sensor a ground, meaning I could use a ground-referenced measurement, or would I need to always be in differential mode for the measurement? I've used a frequency counter to look at the RPM, but I have yet to actually put it on a 'scope.

Also, do you have the same info for what the RPM sensor output looks like AFTER it's left the ignition module on the way to the dashboard on the MN brown with black stripe wire on pin 24? Except for one magic ride home from work where everything worked perfectly, I'm always seeing exactly 1/2 the correct revs on the tach and am trying to see if it's something related to the waveform being odd or a missing ground reference or something that's causing the tach to only see half of the transitions by the time the signal makes it all the way there.

Thanks yet again!

 

Unfortunately, I can't answer this question as I have only made the measurement connected across each sensor. The schematic does not show either line going to either sensor being directly connected to ground, but they don't show what goes on inside the ignition ecu.

No -- since my tach hasn't given me any grief (knock-on-wood ), I haven't had a need to investigate the processed tach signal coming from pin 24 of the ignition ECU.