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After reading all the threads, one possible cause for no spark is the ground to the coil is not being pulsed by the DME. First verify at the DME plug connection pin that the wire to the coil on the negative side has continuity from the plug to the coil and also that the wire is not shorted. The DME generates the pulse ground, on and off, for the coil voltage on the primary side that produces the hi voltsge spark.
Did you verify 12 volts to the positive on the spark coil? Maybe there is no tech bounce because there is an open or shorted wire in the circuit?
After reading all the threads, one possible cause for no spark is the ground to the coil is not being pulsed by the DME. First verify at the DME plug connection pin that the wire to the coil on the negative side has continuity from the plug to the coil and also that the wire is not shorted. The DME generates the pulse ground, on and off, for the coil voltage on the primary side that produces the hi voltsge spark.
Did you verify 12 volts to the positive on the spark coil? Maybe there is no tech bounce because there is an open or shorted wire in the circuit?
In a turbo car, the signal that drives the tach is separate from the one that drives the coil (I'm not sure how it is in an NA car). The signal goes from the DME to the tach and KLR in parallel, then from the KLR back to the DME, then from the DME to the coil. So I wouldn't expect problem with the coil to affect the tachometer. Still, it's entirely possible that the tachometer just isn't working for some other reason.
Did you verify 12 volts to the positive side off the spark coil?Maybe there is no tech bounce because there is an open or shorted wire in the circuit?[/QUOTE]
Correcting it because it caused confusion.
1. Did you verify 12 volts to the positive side off the spark coil?
2. Separate issue for no tech bounce. Maybe there is no tech bounce because there is an open or shorted wire/connection in the circuit for the tech.
I will check the voltage to the coil in my next round of diagnosis this weekend. The tach was working well up until the point that the car crapped out, and was still working as the car was losing power as this problem developed.
I was focusing on getting the car off the track (and not getting run over) with very little power as the issue occurred, and it would not hold revs above 3k or so if I recall.
You mention a "nick" on a sensor. The car also ran quite well before suddenly having a problem leading to a no-start. I would bet the two are related, or at least something happened to a component to cause damage, short, etc. Short of the flywheel moving lifting a sensor stud up (imagine that!), could something have fallen into the bellhousing?
One of the studs (reference I believe) is easy to check and measure through the TDC hole with a $1 plastic rule:
The only time a car has died on me while running has been fuel pump. I'm very curious what else can suddenly die or break....
FYI stud beats reference sensor..., which begs the question: if a stud is damaged, what could do it? A rock? Broken flywheel tooth? Your stud in earlier pic IS awfully shiny. How does that happen?
PS: for a new sensor, the shield shouldn't show continuity with ANY of the pins, not just the centre one
Post photo of reference sensor with the nick and specify which one. When I was chasing the no start, an "expert" said that the clutch disc was failing causing damage to the flywheel set screw and the sensor that determines top dead center. Maybe in your case, but chased that tail for 2 days and it was not the problem.
Can you borrow a fiber optic probe to examine the reference sensor for top dead center. You can see the condition of the set screw. In my situation, the head of the set screw was polished, no rush, so I thought the gap was to great. I did not determine what polished the top of set screw, but the solution to my situation was random clogging of the fuel injectors leading to fouled spark plugs.
Had the fuel injectors cleaned and tested and replaced the spark plugs, engine has started every time
I picked up an Amazon mini osilliscope and was able to get a strong signal at the DME plug from the speed sensor:
I tried the same for the reference sensor and no signal. So next I tried to check the signal at the reference sensor itself, so as to eliminate the harness, and no signal. I tried using a different sensor and same thing - flatline...
So it seems that perhaps that reference flywheel pin may be the issue, although I am perplexed as to how that would suddenly fail. Here is a pic of the reference sensor that was in the car when it died and the nick that I mentioned. The other crap on the sensor is glue as I glued a .8mm washer onto it to use as a tool to set the speed sensor clearance after this mess cropped up.
So the next thing I am going to do is remove the reference sensor bracket and maybe the starter to see if I can get a better look and feel for the reference sensor stud.
If that is the cause of my woes, I am wondering whether it is feasible to address that without having to remove the flywheel (and transaxle, crossover, torque tube, bellhousing, etc.).
I just don't see how it would be possible to get that little stud out from up top if its damaged. I'm not sure if that would be possible even if the stud were pristine.
From the picture posted earlier, it looks like that stud is wiped out. The only time-saver I can offer is that once the TT is slid way back, it is possible to wiggle the bellhousing out without taking the crossover off. (saves a ton of time not having to entirely remove it) To gain a bit of clearance, separate the header from the crossover. This will give you just enough clearance to get the BH off and then take care of that stud.
if your stud ->to-> sensor gap is correct and you are not getting signal and you are confident in your measurement, and confident in the parts then clearly there is not enough difference in height from the outside of the flywheel to the stud t in order to trigger the magnet. Might be a good time to freshen the clutch while you're at it...
You did try to swap the good-reading speed sensor into the reference position, right? If it's the stud you can see in the TDC hole, you *might* be able to get an allen in there somehow. Yikes!
From the picture posted earlier, it looks like that stud is wiped out. The only time-saver I can offer is that once the TT is slid way back, it is possible to wiggle the bellhousing out without taking the crossover off. (saves a ton of time not having to entirely remove it) To gain a bit of clearance, separate the header from the crossover. This will give you just enough clearance to get the BH off and then take care of that stud.
if your stud ->to-> sensor gap is correct and you are not getting signal and you are confident in your measurement, and confident in the parts then clearly there is not enough difference in height from the outside of the flywheel to the stud t in order to trigger the magnet. Might be a good time to freshen the clutch while you're at it...
In my testing of the reference sensor, I discovered the top of the allen set screw was polished but there was a depression in the top for an allen head wrench. I did not attempt to remove the set screw.
The gap is set by the speed sensor and the top of the "teeth" on the flywheel is about 5 mm, the same height as new set screw.
Turn the crankshaft until the set screw is visible and centered in the hole for the reference sensor. Attach a 2 mm solid shim to the failed sensor. Insert the sensor and tap in down gently until it stops. Determine if the sensor with shim is seated on top of the set screw or on the clamp down.
If on the clamp down, repeat with 3mm shim, if same outcome, try 4mm shim. If same outcome, then something significant broke loose within the bell housing and IMO, best to inspect the clutch
Update - I pulled the reference sensor bracket and that stud is not very studly. A mere nub at best. Full Bobbit, but I'm not sure how the heck that happened.
I tried to drill and remove the nub with an EZ out (and some heat) but no go. I broke the EZ out and that little piece of hardened steel is now stuck so I am pulling the flywheel. Tranny is out and torque tube is back, but I ran out of time this weekend so I still need to remove the bellhousing/clutch/flywheel.
My guess is that the $8 stud is likely to turn into a clutch job and RMS (why not). Wondering if I should consider a lightened flywheel while I'm in there and emptying my wallet. I don't want something that is hard to live with, but it's not a daily driver (if it were I'd be walking a lot of late); more of a weekend toy and 3x/yr track car.
What are folks thoughts on either the Fidanza aluminum unit ($350 or so) or a lightened steel one? This is not something that I thought I needed, but since its coming off I may as well consider a possible "upgrade".
Thanks!
Last edited by Porvair; 11-12-2018 at 06:49 PM.
Reason: typo
You may as well consider solving how that stud broke! Wow; that's crazy.
Could something have possibly gotten into the bellhousing? From top maybe? Did you leave the washer you used to gap on and somehow it jammed? This mystery needs an answer or you might be removing whatever flywheel you go for!
10-30-2018, 07:51 AM
