Got spark, but engine not firing - ECU issues?

Started by johnnydread · Oct 3, 2012 · 10postsSMF 2010–26

johnnydreadOct 3, 2012, 10:22 am · #1

The engine is turning over and we verified that there is spark, but it isn't firing. We put an oscilloscope on one of the injector leads and it doesn't look like it is getting a signal so we suspect something is not wired right with the ECU or the ECU is bad. Any suggestions? Is there a way to bench-check the ECU independent of the car wiring to verify it is good?

sideways_s12Oct 3, 2012, 1:43 pm · #2

So basically your not getting fuel check your fuel pump and if you take a screwdriver and place the plastic end to your ear and the other end to the injector while trying to start it you can hear the injector pulsing if you can't most likely the injector is bad look at those 2 things before assuming it's your ecu.

Also check the codes on your ecu you can put it in diagnostics mode and it will likely tell you what's wrong

VG30DETTOct 3, 2012, 1:55 pm · #3

Check everything from cheapest to most expensive. Start with fuses and filters, then test your injectors with a multimeter (which should read around 12 ohms iirc), then check fuel pump for priming and running, then proceed to check fuel pressure. If all that shits the bed, test your pump. If all that fails, try and borrow an ecu to test with.

Also, is this a fresh swap? If so, did you connect the fuel pump power?

rednucleusOct 3, 2012, 3:18 pm · #4

Do easiest 1st - pull fuel line from motor, turn on key and see if pump primes and gives good fuel flow. Then can move on to injectors. Good idea to test codes too.

johnnydreadOct 3, 2012, 5:15 pm · #5

Thanks for the replies - we've checked the fuel pump (it works) and the injectors by listening to them as you suggested and by measuring them with a scope. They aren't firing. I didn't check resistance on them, I'll try that, but they are all brand new.

The ECU does not show any LEDs at all. We've tried putting it diagnostic mode and it doesn't show anything.

VG30DETTOct 3, 2012, 5:17 pm · #6

your ecu COULD be screwed, wouldn't harm it swapping it out for a known working one to see.

sideways_s12Oct 3, 2012, 6:38 pm · #7

the leds aren't blinking when in diagnostic mode? then ecu could be screwed or is not getting power do any of the wires to the ecu looked frayed or broken...

johnnydreadOct 6, 2012, 2:05 pm · #8

It was bad wiring - runs now!

rednucleusOct 8, 2012, 8:42 pm · #9

Where was the wiring problem?

johnnydreadDec 20, 2012, 3:33 pm · #10

Where wasn't the problem might be the better question. This is a crapcan racecar where everything had been stripped out, including all of the original wiring, so we had to rewire it from scratch. We found a couple of places where we had incorrectly wired in a couple of things and we ended up using a different harness - the first one was pretty mangled.