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.

My my only thoughts at this point is Maybe a bad ignition relay, bad crank sensor wire issue, or maybe bad ecu. Bad ecu would make most sense to me, since it has been intermittently not working for a few months now, typically from a cold start, but nothing points to it for sure.

Anyone have any ideas?

aletz12485

iTrader: (1)

Mine has this intermittent issue as well. 90% of the time i see the CEL with key on, no start. Starts up fine. The other 10%, the CEL doesnt illuminate, i have to pop the hood and tap (gently) the top of the fuse box. This trips the CEL and the car starts up everytime. I was originally pulling the EFI relay in the fuse box eveything, then figured out tapping on it worked, then figured out just tapping on the top of the entire fuse box would work. I have no idea. Runs fine once started. Does it mostly when warm. I even swapped the relay to see if that helped. No change. I suspect my ECU is starting to go out.

tenac2215

Tired 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?

72corolla

Check both ignition coils?

tenac2215

havent gottwn a chance to test them yet, but I can't imagine that both of them would have gone out at the same time. It idles fine once/when it starts

aletz12485

iTrader: (1)

Does the CEL still come on with the key on? I saw you said it did in the OP, just wondering if anything changed. Did you try pulling the efi relay with the key on, re-installing it and hear the fuel pump prime the injectors?

Did you actually verify no spark? Like pull a plug wire and verify?

tenac2215

yes, I can hear the fuel pump, have a walboro pump installed.
Also yes, pulled plug to verify no spark

72corolla

My 92 sc400 does not start when a coil is disconnected,it does stay running and misfires when I disconnected a coil while it's running tho.hope that helps.coil to distributor cap wires can verify coil has spark if you don't have a multimeter.

tenac2215

i will test the coils and get back to you all

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 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

aletz12485

iTrader: (1)

With the key on, pull the efi relay from under the hood fuse box. See if that triggers the cel. If it does, try to start it. If not, your ecu is probably the culprit. Sent it to Tanin for repair.

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.

albert0108

Hi there , were you able to solve this issue with cranking but no start / spark ??

tenac2215

read the post above yours lol. Yes my problem ended up being the EFI relay. Pretty cheap fix.