Diagnosis Quiz for ClassicZcar Readers:

[Wade Nelson]

THIS CAR IS FIXED!

Here's something they do on another auto repair site I frequent; one for professional technicians. An online quiz to help sharpen your diagnosis skills.

I'll present a vehicle with a problem, and you suggest the course of diagnosis you would take.

Keep it in mind --- THIS CAR IS FIXED!

I know what's wrong with it! If you suggest a particular diagnostic step I'll tell you what you would or would NOT have gotten as results. Or I'll tell you that particular diagnostic step would not bring you closer to solving the problem. Anyone can chime in at any time and guess at the underlying problem.

Ok, the vehicle is a 1991 Toyota MR-2. It's a no-start. That is, it cranks, but does not start.

Background. Vehicle has been running perfectly and reliably for years. Two days ago I went to start it up in the grocery store parking lot and I had to crank it 4-5 times instead of the instantaneous starting I'm used to. After I got it home and went to restart it later, it would crank endlessly but not start. I had fueled it up that same morning, which may or may NOT be relevant.

What would be your first step to diagnose this no-start? Battery is good, it cranks just fine, it just doesn't start. Good luck!

What would be your first diagnostic step?

[Jeff G 78]

Since it's the easiest, I'd start by checking for spark first.

[rcb280z]

Crank angle sensor

[kjohnson2444]

Check to see if fuel pump is operating. Check for clogged fuel filter.

[Wade Nelson]

Since it's the easiest, I'd start by checking for spark first.

There is no spark. Please proceed.

[Wade Nelson]

The fastest way to determine if it is a lack of fuel is to pull a hose off and add faux fuel (starting fluid). I gave it a big bolt of starting fluid and it still would not crank. No point in going to all the effort of checking the fuel pump or pressure given that it's LIKELY an ignition related problem.

[Wade Nelson]

Crank angle sensor

How would you diagnose a failed crank angle sensor OTHER than by the expensive technique of "throwing parts at it?"

[Wade Nelson]

More information.

The '91 MR2 has a digital fuel injection system but a very early one; it lacks OBD-2, so no codes are available. It also uses an early style Kamann (vortex) air flow meter rather than a more modern MAF - mass airflow sensor. It has an old-style distributor and ignitor, similar to the 280ZX, plug wires, etc. (Not the more modern coil-on-plug).

Tip: It was running flawlessly prior to the no-start episode(s), and even AFTER the first one. What would that allow you to rule out as a cause?

[LeonV]

Check to see whether the coil is sending a spark to the distributor. If not, there's an issue with spark signaling, i.e. triggering mechanism within distributor or the ignition module itself.

Sounds like it was a hot-start issue, so it may be an electrical connection failing from heat.

[Wade Nelson]

Sounds like it was a hot-start issue, so it may be an electrical connection failing from heat.

Car wouldn't restart the next day, cold. Not getting any spark.

How would you diagnose the ignition module, lacking an oscilloscope? What would you start by checking?

[cbuczesk]

I'd make sure that the cap, rotor and coil wire are good. Then I'd check the smaller ignition wires. Maybe a mouse/mole/groundhog was hungry. Yes, I've had that happen! Make sure there's voltage to the coil. Maybe the coil is going bad?

Chuck

[madkaw]

I would throw a timing light on the plug wire and turn over to see if spark is there or erratic. Whatever direction one goes, spark needs to be eliminated first.