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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8538
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Thanks your help. I have a 92 VR4 with no spark. I have fuel

Customer Question

Hi Doug. Thanks for all your help. I have a 92 VR4 with no spark. I have fuel at the injectors, and the engine cranks. There is a single spark when I first turn the key to the on position. I removed the ECU and had the capacitors replaced but have the same symptoms. The check engine light comes on for a few seconds when I turn the key to on, then on again during crank. I will have an obd-1 reader by this weekend but am trying to figure out where to go from here. I have checked all my fuses and have continuity on all of them. There is no movement on the tach during crank. Could my ECU still be faulty? Before I just replace the ECU, CAS, IAC, PCU, and coils, what would you have me test? Thanks Dave.
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.

Hi Dave,

Normally speaking when you have a single spark you will either have a belt timing mismatch (or perceived mismatch, if a sensor is unpredictable) or a driver failure (either in the PTU or the ECU).

Considering you do not have any tach movement which you normally will see it try to move just slightly while cranking, I would say the CAS or the PTU are the most likely suspects as both contribute to the signal to the tach. What I would want to do is check the RPM signal on the scan tool when you get the right one and see if there is a reading. If there is not, then check your voltages at the CAS. If your voltages are OK, check for waveform while cranking with it plugged in if you have access to a lab scope to see if it is outputting a signal for the ECU/PTU. If it is not, get a new CAS; if it is, suspect the PTU.

If there is RPM signal from the CAS then I would want to double check your belt timing is 100% dead on. If it is, then wiring aside and with the ECU already eliminated it would be most likely the PTU is bad. The PTU gets three low voltage (under 3V) pulses from the ECU, one for each coil, while you crank the engine. If all three are present then the PTU should output three ground pulses, one for each coil. If you have the low voltage input but not the three ground outputs, then the PTU is bad. Of course if you are missing the low voltage inputs then you would be back to either a timing mismatch or a bad ECU, wiring excluded again.

Customer: replied 1 year ago.
Okay I will do all you have suggested. Is there a way I can just to be sure my ECU is alive? I did not send it out to a lab for repair I simply had a local repairman replaced the capacitors. That being said I am reading that even after replacing capacitors that you see you may still be fried. Is there a way to test it for life?
Expert:  Doug replied 1 year ago.

The ECU can only be tested by swapping into a known working vehicle or sending out for repair to a facility that has the equipment to bench test them. There is no way to bench test these yourself, nor can a dealer do it... special equipment is required.
It is best to send these off for repair for that exact reason. While you may not have leaking capacitors now, the old ones may have shorted the board and done untold damage to it.

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