1992 B2600i, yet another no start question!

Hi there, I'm looking for some help diagnosing a no-start condition. I also posted this over on the mazdaworld forums, so apologies for those who frequent both boards. I've done a lot of searching but can't seem to find any references to this exact problem.

Vehicle: 1992 B2600i 4X4 extra cab.

The truck was previously running like a top, with zero symptoms, no missing, stumbling, or rough idle, or anything. I was driving slowly on an old logging road (rough, but not bad by any means) and the truck sputtered a couple of times, recovered, then sputtered again and quit, within a few seconds. Kind of felt a bit similar to having water under the distributor cap. I re-started the truck with a bit of difficulty, and had to keep it revved up to keep it running. It ran poorly for about 20-30 seconds, long enough for me to get it turned around so someone could tow me out. Then it died again and I couldn't re-start it. It cranked strongly but would not start. Got it towed home and proceeded to try to figure it out.

Stuff I've tried:

Checked for malfunction code and got nothing.

I disconnected the fuel line from the fuel filter and verified that there is lots of fuel volume flowing when the engine is cranked. Did not test actual fuel pressure since I don't have a fuel pressure gauge. Also jumped the yellow two-pin connector to
make the fuel pump run continuously (I could hear it running) but still, no start. I didn't test the circuit opening relay (under the kick plate by the driver's door) since I was getting good fuel flow, obvioulsy the fuel pump is working. But, I will pick up a fuel pressure gauge to test pressure and rule that out.

I tested the voltage at the positive terminal of the ignition coil, and got 11.8 volts, I think that's probably close enough to the specified 12 volts. But, maybe not?

I then pulled the ignition coil to test it. The primary coil resistance is supposed to be 0.81 - 0.99 ohms, I measured about 1.2. Not sure if that little bit out of spec would cause the truck to suddenly die. The secondary coil resistance is supposed to be 6 - 30 k-ohms, it tested right in the middle of the range. Not sure if there's anything else to test with the coil. The manual mentions using something called a 500V megger to test the insulation resistance between the primary coil terminal and the case, but that's greek to me, I don't really know what that means.

I then tested for spark using one of those little spark testers. Got good strong spark at the distributor end of the lead running from the ignition coil to the distributor. Then tested spark at the plug end of a couple of the plug wires and got no spark at all.

I have had the ECU repaired by AvPro a few years ago, but just in case, I tried swapping it out for an older one I have. This old ECU has issues, but did at least let the truck run when it was installed in a different truck a few years ago. No difference, still cranks without starting. Also, when the ECU started going bad before I got it repaired, the symptoms were more driveability related, like poor running, hesitation, stalling, etc. So, I don't think it's the ECU.

At this point it seems like the spark is disappearing somewhere between the end of the ignition coil to distributor lead, and the plugs. I just replaced the cap and rotor 30 minutes ago but that didn't help. I'm kind of left thinking that there's something else inside the distributor that isn't working, but I don't know how to test anything in the distributor. Or, maybe that slightly high resistance in the primary coil of the ignition coil is causing the voltage to drop just enough, that the spark from the spark tester looks good, but it's not enough to make it to the plugs.

I also think that losing all compression suddenly without an accompanying noise of a broken timing chain is unlikely (also I verified that the rotor turns when cranking, so the camshaft is turning). It also seems unlikely that all of the spark plug wires went bad at exactly the same moment with zero warning. I did test the main coil to distributor lead with an old, but working, lead and that made no difference at all.

The Distributor is a pretty pricey part (welcome to Canada!), so I hate to order one if I don't have to. The ignition coil is at least under a hundred bucks, so I could try that. But, it seemed to test okay except for the slightly high main coil resistance, and it gave good strong spark.

My manual (the official Mazda shop manual) also tells me to test the igniter, but I have no idea what that is or where I might find it, and the test they describe uses a special Mazda tool. So, I haven't done that.

I'm kind of getting a bit stumped...and I'm looking for advice. Anything I've missed, or maybe something that isn't in the manual. Any suggestions would be appreciated.

Thanks!
Kevin

Open the ECU case and check for leaky capacitors.

thanks, I should have mentioned that I did crack open the ECU and it looked fine. This is the one that AvPro rebuilt a couple of years ago.

How far will the spark jump? 1/8" is plenty to bridge the gap in the cap and at the plug, but should jump wider gap. Check the center contact in the cap. It did not fall out or something? Rotor, even new has the center to end correct? Sounds like problem is between the end of the lead from the coil and the start of the plug leads (assuming the leads each check out good next), strange, but your work is cut out for you, good luck.
Try each plug lead plugged into the coil and check spark to ground (use old plug in lead with gap widened). If you got spark, I got nothing, sitting here.
You got spark, parts in the distributor and ecu are doing their job, it would seem.
Can't wait to hear the solution.

Hey Geterdun,

The spark looked pretty good. I used one of those little spark tester things that have one end that looks like a spark plug, that plugs into the lead, and the other end has a clamp that clamps onto part of the block. Near the clamp there is a little circle of metal around an electrode, so you can sit and watch the spark. The gap there is probably 1/8 - 1/4 inch and the spark was nice and bright blue when attached to the end of the lead that comes out of the coil, but there was no spark when attached to the spark plug end of the leads going from the distributor to the plugs. Strange, for sure!

I think the distributor has some other stuff inside that you can't replace separately so I've ordered an entire new distributor. I can't think of anything else, either, at the moment. I hate throwing parts at things but at this point it seems like a pretty likely culprit. I'll let you know if it does the trick...

Kevin,

Did you try plugging each spark plug lead into the coil and check spark on each plug wire like that?
Again, if the coil is firing, the pickup coil in the distributor and the ignition module in the distributor should be good, as well as the ignitor. So you did not spring for plug wires first? That distributor is pricy.

I figured the plug wires must at least be okay-ish since.it.was running just fine and then just stopped. My previous experience with bad plug wires is that even with one totally dead the truck will run, if incredibly rough, but it will run. It wasn't even trying to catch, though. I also figured the odds of more than one plug wire going bad at exactly he same time were pretry slim to nonexistent...

But, i got to re-learn the most basic lesson (again) tonight...always check all connectors, etc. Unplug everything and plug it back in. I unplugged and plugged back in the connection o the ignition control module/igniter (or whatever the small black box is beside the coil), and after that it fired right up like nothing had ever happened! Ran like a top as usual.

I'm not.really certain that the connection was it, as the terminals were shiny and looked good. But unless something else is wrong intermittently and decided to correct itself at that exact time, then I'll assume it.was.as simple as a bad connection.

Yeah, the distributor is pricey but it was going to take 10 days for it to arrive (rock auto to canada) and i have a lot of yard work to do...so i just bit the bullet. Oh well, live and learn!

Thanks for your help, Geterdun!

I did recheck the spark from the coil.again before i got it running, and this time I noticed that it was more orangey-orangey-white than blue-white. So maybe the coil is putting out a weak spark, not always enough to fire the plugs? Maybe it is on its last legs. It did test just out of the spec in resistance on the primary coil side but just barely out. If i quits againaybe I'll look more closely.at.the coil.

Luckily i bought the cheapest distributor that rock auto carried : )

Glad you got it done. I believe the black thing by the coil is called the ignitor, and you see if it goes bad, everything shuts down. If this happens again, maybe take the bottle of water you will start carrying around with you and cool it off. If it starts , you know what to do.
Now the process starts, accumulating spare (known good) parts.

Keep on Truckin'
______________________-
'93 B2600 Extended cab, no bot
Major regret, selling my '77 6.6 T.A. Smokey and the Bandit TransAm in '81

Yeah, I've accumulated a few spares over the years (this is my third B2600i) but it seems like what I need is never what I have! These trucks have become quite rare in wrecking yards around here. I'll have to keep my eyes peeled for anyone parting one out and glean some more stuff.