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Old 08-07-2014, 08:21 PM   #1
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Default Car won't start, intermittent spark

Hi everyone,

My car stopped running a couple weeks ago at the track and I'm looking for some help in troubleshooting. The engine stopped running after a downshift before I got back on the power in a corner. I was able to coast into the pits, but ever since then the car refuses to start. The engine turns over and I've checked many things with no results. When the engine cranks it occasionally sputters lightly as if it's trying to fire, but never makes much progress. I'm a bit of a useless noob when it comes to my megasquirt, but I did run a few ignition logs and got inconsistent info. The latest ignition log after all the troubleshooting described below seems to imply that the ECU is getting a good CAS signal.

Background info: My car is a 1995 with a Flyin Miata turbo kit and Reverant Enhanced MS2 ECU. The car has been turbo'd for over a year with over 15 track days and was running strong right until it died.

To date I have done the following to try and fix the problem:
- Checked fuel pump, it runs as expected and fuel can be smelled in garage after cranking
- Listened to injectors with stethoscope and can hear them firing
- Checked throttle body and throttle cable, they are not stuck
- Checked spark with timing light (on all spark wires), spark is intermittent and inconsistent
- Checked spark by pulling plugs out and cranking engine with plug resting on engine: spark is intermittent and inconsistent
- Changed plugs (to recommended NGK plugs that were properly gapped)
- Changed ignition coil
- Changed Main relay
- Changed Camshaft Angle Sensor
- Checked CAS wiring (has ground continuity, 12 volt, +4V, -4V when in run)
- Visually inspected grounds and ensured they were tight (strap near dipstick, grounds under master cylinder, ground at back of intake, ground at front of intake)
- Wiggled the CAS/Ignition coil wiring during cranking, no effect
- Checked that it has oil
- Verified oil pressure during cranking
- Verified timing belt is in one piece (through hole left during coolant reroute, I did NOT remove belt cover to verify timing, however timing belt was changed 2 years ago prior to turbo, and was re-verified when engine was out to fix oil pan leak and do coolant re-route 1.5 years ago)
- Verified cams turn when cranking (through oil filler port)

Right now I'm thinking there is a shorted or broken wire somewhere (in the engine bay or at the ECU), that I have a bad ground, or something has gone wrong with the ECU. Does anyone have any tips on where to look for said items? Or if there are other possibilities for why my car won't start?

The wiring diagram implies that there is a ground on the top of the engine, but i'm not sure where that is. Does anyone know? Also, is there a good method for getting good grounds beyond cleaning off the terminal and tightening the bolt well?

Also, I have a data log and ignition log that I took today while cranking the engine. I attached them so that you could look at those and let me know if I'm missing some key info that's in there.

Thanks in advance for any help,
Attached Files
File Type: msl 2014-08-07_12.04.06.msl (234.2 KB, 42 views)
File Type: csv 2014-08-07_12.04.25.csv (21.6 KB, 43 views)
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Old 08-07-2014, 10:23 PM   #2
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One other thing I forgot to mention. I'm not sure if it's relevant, but it could be. When I put my motor back in the car after fixing the oil pan leak last year I noticed some odd behavior with the Tachometer. Here in Washington we have bumps in the lane lines on the highway. Ever since I reinstalled the engine I noticed that the tach needle would drop significantly every time I changed lanes and hit the bumps. The engine never stumbled and there was no loss of power, just the tach dropping for a split second as I went over the bumps. In the week or so leading up to my car dying I noticed that that had stopped happening. However now when I crank the motor I get no movement on the Tach. I don't recall if it moved during cranking or not before dying though. And the ECU has a Tach signal...

If I recall the tach and ignition system share some common wiring. Perhaps that common wiring was partially broken and would lose contact when I hit the bumps, but now has completely failed? Or is this just a red herring?
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Old 08-08-2014, 05:19 PM   #3
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Anyone got any ideas??
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Old 08-10-2014, 06:36 PM   #4
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In case anyone cares, I seem to have found the problem.

After much head scratching I found that the timing light I was using was faulty. I checked spark again by putting all four plugs on top of the valve cover and cranking. Spark was definitely good. It would seem I was fooled into thinking it was bad spark by the failing timing light. BUT, the car still didn't fire.

So I did a compression test and found I had compression, and all the cylinders had fuel in them. So I had spark, fuel, and air. But no running engine. The only conclusion was that the timing was off. I bought a new timing light and found that the timing was probably 30-45 degrees retarded. Pulled the valve cover and sure enough, timing is way off. After scratching my head trying to figure put how that happened, my buddy looked down by the crank pulley and saw debris. It turns out that one of the rubber seals on the timing belt cover fell into the timing belt. It must have gotten between the belt and the pulley and allowed the pulley to skip many teeth.

How did the rubber seal get in there you ask? Well when I did the coolant reroute I removed the thermostat housing completely. I didn't pull off the rubber seals that interface with the t-stat housing on the belt cover. Simple oversight cost me a lot of money, aggravation, blood, sweat, and a non-running car for the past month... Stupid.

So as a warning, don't trust timing lights implicitly and pull out any useless rubber seals if you remove the t-stat housing!!!
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