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By Guest captain3chord, May 14, 2012 in Pre-1997 Toyota Corolla and Geo Prizm

Guest captain3chord


I hate to start off on a forum by posting a question, but I am at a loss and hope someone has some insight.

I have a manual 1996 Corolla DX 7afe with 267k miles. I was teaching my friend how to drive stick when it died. He was holding approximately 5k rpm and just started to let the clutch out when it died. I was staring at the dash when it happened. The tach dropped to zero as if you turned off the car (did not match engine speed).

It turnes over properly when trying to start. Battery voltage is ~12.49v

I've been diagnosing the car and this is where I am at. I figured out 4 problems spanning several areas.

1. Cannot read computer codes,

2. No fuel pump operation

3. No spark

4. No injector pulsing.

Many things would cause lack of spark and injectors, fuel pump operation and lack of codes are simpler.

I've diagnosed the entire EFI relay and fuel pump circuit, it is all working, including connection with the ECU. (Ground the green/red wire at the ecu during "on" and the fuel pump kicks on.)

ECU is receiving power and has ground across all stated power and ground connections in the wiring diagram.

The first 2 issues have me stumped. I wish I had a logic block diagram of the ECU to determine if there are any preliminary system checks which would prevent it from pressurizing the fuel system.

It is my understanding that if you have power and ground at the ECU, you should be able to read codes. Code reader has worked with this vehicle in the past and does work with another vehicle presently. This leads me to believe the ECU is fried. I replaced it with another one (granted, from a rather reputable dismantler) and same issue (nothing).

Usually when you change one element of a system and get the exact same results, that was not it. But what are the chances of a bad ECU (slim) AND a bad replacement from a working pull (slim again).

I also cannot think of any failure modes of components on the car which would fry an ECU.

Any thoughts would be appreciated.


How did you verify no spark/no fuel - did you do a spark check (ground plug and visually verify for spark) and pull plugs to see if they were damp / listen to fuel pump when you turn the pump on?

Did you check the EFI relay? As far as I know - this generation didn't have a

How about the other electricals - interior and exterior lighting, 12V power plugs, radio, etc.?

Checked distributor - coil pack - plug wires - plugs? Did you pull the cap off and see if the rotor is actually turning when you crank the motor? If it doesn't turn - the timing belt could have broke when your friend raced the engine to 5K RPMs.

Doesn't seem to be the ECM - as that already has a pretty low probability of failing in the first part, second one failing outright is exceptionally low probability. Though an bad ECM is still a possibility - I'd hold that to the end. Visually verify spark and fuel.

If no spark - check resistance on coil, check cap and rotor, check plug wires. If they check OK - look to see if distributor is functional (quick checked noted above) and see that coil is getting power.

If no fuel - check that pump is getting power. If power is good - make sure there is fuel pressure. If you haven't do so - replace the fuel filter, check that there is no water in the fuel. If pressure is good - start looking around the injector log, injectors, etc. - look for leaks, cracks, may have to pull the fuel log out and see if there is an obstruction in there. I've seen some that have so much gum.varnish inside - that the injectors were fuel starved, even though the fuel was getting to the injector log.

If fuel/spark, main EFI relay, and timing check OK - then look at the crankshaft and camshaft position sensors. The ECM is looking to these for timing information - if there is no timing information - the ECM will assume the engine is not turning over. So you can get a situation where engine turns over but never fires - no wet plugs, no injector cycling, no spark - because the sensors are not generating the pulsetrain the ECM is waiting for. Doesn't happen too often - but it does happen. You should be able test those sensors with a multimeter.

Another long shot is the circuit opening relay (COR) - usually inside the car, under dash by the fuse panel. That is what gets power to the fuel pump, you already have the fuse under the hood - which most people find OK, the relay could be partially damaged, causing intermittent issues.

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