Sc400 cranks but won't start. No spark, has fuel

[tenac2215]

so for the past 4 months I've been having intermittent starting problems with my 93 sc400. I'll go to start it sometimes and it just won't fire up, no problem cranking. I can usually wait a day or so and it will fire up like nothing was ever wrong with it. Since last week I have had zero luck getting it to start at all now. Same
thing cranking fine.

Here's everything I've done so far to see if I can fix the problem:

replaced fuel pump and fuel pump ecu
replaced both camshaft position sensors
replaced crankshaft position sensor

i know for sure it's getting fuel. Pulled the plug to test for spark and it is not getting any spark. Tested igniters and they are fine

it is currently giving me Obd codes 12 and 24.

When i I changed the crank sensor, the old one had a bit of oil on it and the plug (from seeping oil pan), not sure if it was enough to cause any sort of shorting issue. There was also some kind of black build up on the old sensor. Tried to clean out that opening the best I could, but may be more grime In There than I thought?

Check engine light comes on when ignition is switched to on, so the ECU is not totally dead.

Tried tapping the ecu, and fuse box, as well as really clean out the crank sensor hole. Still no spark. About a week ago I installed imf headers on it. Started fine before a jacked it up and started fine once I installed the headers. Started it with open headers and drove it around my block. Had issues idling but I'm guessing that's because the downstream 02 sensors weren't getting any input. Stalled a few times and started back up. Went to start it up again 3 days later and it just will not get any spark. Cranks fine.
I'd imagine if it jumped timing it wouldn't be enough that it wouldn't still run. And either way, it should still be getting spark right?


im completely lost on this thing right now.
Any more ideas?

 

[Zuffen]

Are the Spark Plugs wet?

They don;t take to flooding well.

 

[tenac2215]

I don't think so, but I can verify. what would cause that?

 

[gloverman]

I would be checking the crank signal is getting to the ECU. Ive had a few with broken wires to the crank sensor later or poor connections between the front loom crank loom and the main engine harness. Using an LED test light onto the pin at the ECU it should pulse when the engine is turning , or a multimeter it should give a small a/c voltage. I would then trigger the ignitors from the ECU wires to see of the whole circuit produces a spark on both sides. It needs the ECU powered up, crank input and one camshaft sensor generate the ignition output signal and then one functioning ignition circuit to make spark.

A bit of dirt on the crank sensor shouldnt be an issue. Giving it a clean never hurts but as they are inductive oil or dirt shouldn't bother it.

 

[gloverman]

And cam timing. That doesn't take much to check. But it shouldnt stop spark.

 

[George_R]

read trouble codes, make sure both ignitors are well grounded

 

[tenac2215]

So was checking signal to the ecu... now when I turn it on, then take the key out, the fuel pump stays running, and the cel is dimly lit. Also the cel does not come on anymore with the key on. So I'm thinking it's been a bad ecu all along? Unless I just created another problem lol

 

[George_R]

sounds like earth problem or ecu problem

 

[tenac2215]

So Ecu ended up being fine, I think I just didn't have it plugged in all the way. Changed the EFI relay and started right up. So I guess that was my problem all along.