MB968

The ABS sensor on my Mazda was a VR sensor, just like the one on our crank. As I mentioned, and maybe I didn't state it clearly, but both the frequency and the voltage changed with wheel speed as you mention above. At very low rpm of the wheel, the voltage as read with the AC setting on a VOM was barely more than zero volts. With changes to the speed of the wheel, the frequency and also the AC voltage changed. As fast as I could spin the wheel I had something less than 5 volts (thus my 0-5 volt notation in the post above). And as stated above, using an older style analog VOM, I could see the voltage change, as well as the frequency change as I changed the speed of the wheel. So though I'd agree a scope would be better as you can see the actual waveform, even I who used a scope professionally, don't have one anymore. And, for virtually all cases, using an old style analog VOM with a meter should be good enough to see how smooth a signal is, and if it changes with speed as it should. What I don't know is if you just jog the starter, just exactly what you will see. I think it will be enough to confirm the condition of the sensor. But, I've never tried it.

Dan Shea

First off, thank you for all of the responses. I will try to answer all of the questions...

Car is an 86, that had the 8v retired due to a rod bearing #2 failure. It had a 3.0l S2 swap about 6 years ago.

The ICM was replaced late last year so I suspected/hoped that was still OK.

Anyway since my first post I've done the following:

New speed/ref sensor. (16v only has one)
New ICM

Still no spark.

But, I also grabbed an $89 oscilloscope off amazon, and while I don't wish its design on anyone, I did determine dme signal at the ICM. So I've ruled out the ICM and now I'm leaning towards coil/distributor cap/rotor.

The only reason I hesitate is the catastrophic nature of the failure. Literally drove the car home, turned it off, moved it ten feet, then DOA.

MB968

Haven't played with coil based cars for a long time, but I seem to recall they were also easy to check with a VOM. Could probably find it on the net as there are still a lot of muscle cars running a coil/distributor setup.

william_b_noble

see if you are getting spark from coil secondary. If yes, then it's rotor or cap or wires or plugs. If no, look at primary with the scope

Dan Shea

What's the best way to test spark at the coil? I don't want to electrocute myself or fry a good coil.

Dan Shea

Nevermind, found the procedure on clark's garage. I'll do some more tinkering when I get home and let ya'll know what I find.

I'm supposed to take a road trip up through the Adirondacks next weekend so I'm REALLY hoping to get this sorted out.

Dan Shea

630 Friday update: I pulled the distributor cap, both rotor and cap are showing heavy carbon buildup so I'm going to order new ones. I don't think this is the true cause but it definitely isn't helping.

I also did a test on the coil. I have 12.2v at the positive side. 6k ohms resistance between (-) and output and .4 between (-) and (+) terminals. So I tried testing the spark at the coil per Clark's garage.

I put a sparkplug in the output wire and grounded it via the threads. Then disconnected the (-) green wire at the coil and connected a ground lead wire to the (-) terminal. With the ignition in the on position I tapped the ground lead off the coil to a ground which should cause spark at the plug. Here's where I had questions.

The spark between the lead and the ground far surpassed the spark at the plug. I had almost an unseeable amount of spark at the plug. It was a hairline of spark, no lighting bolts.

Second test was to hook Up the coil properly but run a lead off the output wire that hovered over a ground to see what happened when I cranked it. I got no visible spark except when going from start to run with the ignition that gave me the giant stream of electricity I was expecting...

Ideas?

Olli Snellman

Speed & reference sensors are very expensive if you but them as oem parts. Same sensor can be found for example Volvo 740 2.3 engine. Even as a Bosch part Volvo unit is much cheaper. Same sensor can be found as aftermarket part as well, Facet unit 9.0212 works great, cost about 45€-55€

Dan Shea

Photos...

Signal from Speed Sensor:

https://www.dropbox.com/s/df4pydzwedutbip/IMG_001.BMP

Rotor:
https://www.dropbox.com/s/gbh7lx24fm...2017.29.17.jpg
Cap:
https://www.dropbox.com/s/zqt7fwxc62...2017.28.52.jpg

MB968

Not an expert, but by looks of the speed sensor signal, I'd guess it is OK.

To me the rotor and cap, although they don't look great, don't look so bad as to not allow the car to start and run.

Tampa 928s

Get a noid lamp from your local auto supplier hook to an injector see if it flashes. I have found injector harness can short internally and take al the injectors down. Get a timing lamp and see if you are getting spark you will quickly isolate you problem.

Dan Shea

I'm 99.9% sure that I do have fuel, just not spark. I have a pressure gauge on the rail that reads within spec and when I pull a plug I they're wet with gas. I'll leave the .1% just incase I'm an idiot.

Will a timing light tell me if I'm getting good signal out of the ICM?

I'm at a point now where I'm trying to determine if I'm losing the ignition signal before or after the ignition coil. I tried using the oscilliscope to grab a signal from the signal wire off the ICM to 12v power (switched ground) but it was either too high voltage or too fast because my scope goes off the charts.

The other thing that really confuses me (and I could see this with the scope) is that the only time i get a definable signal/spark out of the coil is when the ignition switch rotates back from start to run.. Could the ignition switch be faulty in that it will signal the starter to spin but not tell the dme to create spark?

So many questions, and it will probably be something small and/stupid.

turbodave

Yes, and has been the cause of many misdiagnosed problems. The DME must see a CONSTANT 12V for it to operate properly. Since you are getting spark between key positions in your test, this would indicate that your ignition switch is suspect. I would advise anyone who is having intermittent no-start, fuel or ignition problems to check the switch first. Age, normal wear and having extra keys on the key ring contribute to this. I would replace it anyway if it's the original switch. This would atleast take that part of the power supply problem out of the equation. GL

Dan Shea

Ok, I'm keeping this thread alive for any other poor soul that runs into a similar issue.

While I wait for my parts to arrive in the mail I went through and inspected all of the connections I had to rig up in order for the S2 motor to work. I also replaced all of the butt connectors I had with waterproof ones and wrapped in another layer of heat shrink tubing.

Tonight I brought the battery to the store to have it tested... It tested with ~900 cca, so battery is crossed off the list of possible suspects.

When I got home I ran a 12v test light from the (-) terminal of the coil to the (-) terminal of the battery which should flicker when the ICM breaks the ground signal. This didn't flicker, but rather dimmed when the starter was working. In conclusion I don't think it was a successful test as it didn't rule out the coil or ICM.

Second test was to retry sticking a sparkplug into the coil output wire and run a really good ground to the spark plug threads. This gave me similar results as before, no spark when cranking, spark when switching to run... So I tried jiggling the key as I held it to start hoping to get contact inside the ignition switch. BINGO! I was able to create a few repetitive orangish/blue sparks from the plug while massaging the ignition switch.

So I’ve ordered a new ignition switch, and I think I’m going to replace the coil because the spark wasn’t full blown blue but weak and orange hued.

I’ll let yah know what happens next..

StoogeMoe

Well, if you have an oscilliscope, you could test the (-) terminal on the coil. It should be a very short pulse. You won't see it with a light.

Also, the ignition switch provides 12V to the (+) side of the coil. If this is worn, you won't get a strong voltage to the coil and can result in the weak spark you were getting. You can jumper right from the (+) battery to the (+) coil. This will bypass the ignition switch.