I have a Corolla of similar vintage, but probably not the exact same engine. For a cranks but won’t start and no visible spark at the spark plugs, seems like a distributor, coil, or igniter problem. All those are part of the distributor ass’y on my Corolla I think. So the shop isn’t off base to try replacing the distributor. Since that’s not fixing the problem, next guess is the signal from the distributor to the ecm isn’t getting through reliably. Or the corresponding signal from the ecm back to the igniter isn’t getting through. The way it works on the Corolla, the engine turning somehow turns the distributor rotor, and that rotation phase is sensed by a sensor in the distributor and sent to the ECM (by a wire). The ECM then uses that signal as the time base for pulsing the igniter. The ECM varies the phasing to correspond to the amount of timing advance needed for the condition.
Where I’d start if it happened on the Corolla is the check engine test connector. There’s an output there that has some of these signals at test points. rpm pulse, igniter pulse, etc. I’d put an o’scope on those and see what is happening during cranking.
I should add that before going full blown test diagnostic on this, bringing out the o’scope and all, if it hasn’t been done recently, replacing the distributor cap, ignition rotor, and spark plug wires would make a lot of sense. Those should be replaced periodically anyway, as part of routine maintenance.
One more idea. On the Corolla there’s a critical grounding point for the ECM at the rear of the engine. There’s a bevy of ground wires. If your car has that, make sure it is making a good ground contact.
@knfenimore “Did you get her fixed?”_
I’ve gotta say I’m a little embarrassed but yeah, it’s running well now. I ended up putting an OEM distributor in, and it was STILL running rough until warmed up, then dying and not re-starting until it cooled off. So I took it back to the original mechanic, he drove it, and since he knows I do some work on the car myself, suggested that I replace the plugs and wires. I had already replaced the plugs, and since the resistance of the wires was within spec, and they didn’t look very old, I assumed they were fine. You know what they say about “assume”…sure enough, removing the plug wires and looking closer at them, I found one that looked like it was arcing through the plastic sleeve that goes from the top of the valve cover down to the plug! DOH! I put in new wires and, whaddya know, it runs fine! Even though the mechanic told me “no charge,” I felt like I should give him something for steering me right, so I dropped an envelope with some cash in the key drop slot, after hours. But hey, wait, what if that was the problem all along, and he was late figuring it out…oh well. I’ve got 220 K on the car, 50 K since I bought it for under a thousand, and I’ve had a head gasket replaced and I put some struts on. If it keeps running another couple of years with no major problems, I guess I’ve done OK although I could probably have saved some of the distributor expense by going with knfenimore’s early suggestion to replace the plug wires first, then go from there. “Live and learn,” I guess. I’m old, though…seems I shoulda “learned” more by now!
Thanks to everyone that posted here, you’ve definitely increased my knowledge in this area!
Glad you got your Camry back on the road and running smoothly @MoeParr . I would have guessed with those symptoms your mechanic would put it on the o’scope ignition analyzer, which should have spotted any spark arcing. I had a problem with a spark plug wire arcing on my truck a few months ago. Not an uncommon problem.
@db4690 … do shops still use o’scope ignition analyzers? When I took my auto shop class they had one made by “Snap On” as I recall. And it was a pretty handy tool. But at that time – late 70’s – pretty much every car used a distributor with points and condenser and a single coil. So the hook up tp the machine was simple and the same for most cars. Now-a-days there’s quite a bit more variability in the ignition system designs, so maybe it isn’t practical for shops to keep a general purpose o’scope ignition analyzer on the premises.
I believe below is what people think we use, I have seen many times where people have been advised that “often times an engine analyzer is used for ignition system diagnoses”.
The oscilloscope was integrated into the scan tool more than 20 years ago.
Yes, the one Nevada posts is the one I used in the early 80’s. I’m familiar with the Pico o’scope tools. Just a conventional o’scope functionally, but the display occurs – not on a CRT – but rather on a laptop screen. I can see how the smaller size would make it attractive for pro-mechanics. I presume the auto shop version comes w/a set of inductive couplers for acquiring the various ignition waveforms for display. I’m having a hard time envisioning how a scan tool that plugs into the obd II port could be used in place of an o’scope for monitoring ignition system waveforms.
A modern dso can record and capture very momentary glitches, something the old oscilloscope with the crt could never do
It goes without saying you can save waveforms for later analysis, and can send them to other people, again something
the old oscilloscope could never hope to do
Look carefully at the picoscope. See how it’s connected to #1 ignition coil
The picoscope isn’t a scan tool . . . it’s a scope
You need both
Either a separate scope and scan tool, or a tool which has both capabilities, such as one of the Snap On Verus models
