Few months ago I took the car out one morning to cars and coffee, sat for about 2 hours and when I went to leave the car would crank but not start.
Turns out the ECU was losing its signal when the car cranked, so it thought the key was off but the starter would obviously turn. Remove the small wire from the starter and jumped it with a screwdriver and drove it home.

Figured it needed a ignition switch so I got a new one and put it in- well this didnt work, same issue as before.

Never had a issue like this so Im not sure where to look next, someone else had suggested the clutch safety but the car does crank so that seems like it would be working.

Anyone have any other ideas? Im putting the car pretty much in storage today for the winter and it would be great not to have to start it with a piece of wire again.

thanks

 

How did you figure out that the ECU was losing power? If that were the case then maybe it's the Main Relay at fault as its job is to provide power to the ECU w/key to on or the start position. You can bypass the relay by jumpering the wires in the four wire plug at this relay. B/G to B/Y and W/L to B/W. Jumpering W/L to B/W will provide constant power to the ECU at pin 2I (Main Relay). Jumpering the wire(s) is for diagnostic purposes only as jumpering will eventually drain the battery over time.

 

i have a aftermarket ecu and it has a diagnostic light, not wired with the factory relay.
the light goes off when the car cranks where it should normally be flashing.

 

Wires powered by the IG1 fuses have power w/key to on and start while those wires powered by IG2 fuses have voltage w/key to on and not start so this could possibly explain why the light goes off unless it had been previously working. So how is your ECU powered up specifically if it doesn't use the Main Relay (which circuit)?

And the ECU doesn't play a role in the starting circuit other than to select how much fuel to use as measured by the Water Thermosensor. To get the car to turn over can always be done w/o an ECU plugged in so your problem lies elsewhere such as the Starter Cut Relay perhaps and the wires to check can be provided, but it doesn't state whether the car is an S4 or S5.

 

when the car is cranking it basically has no fuel and spark ( no information from the ecu ) it just cranks.
its a s4.

i know the computer is getting direct power from the battery, and it has a turn on lead . At first I thought this turn on lead was where to look, but obviously it is turning on with the key it just cuts out when cranking.

The big question here is why did it do this suddenly? this is what worries me

 

Are you powering the ECU via IG1 or an IG2 circuit as it makes a difference. Also, does the wire powering the ECU go through FEM-01 or FEM-02 or is it a straight shot to the ECU (and not talking about the wire from the battery).

 

this I do not remember, I have to take it all apart to get to that and I wont be moving the car for a few weeks ( weather permitting ), at that time I am bringing to a fabricator for some IC/exhaust clean up work as I go to a different UIM, then I will be bringing it back to my shop to swap out 2 injectors and change a fuel fitting. If there is snow on the ground the car will just end up sitting.

 

The factory ECU is powered at pin 2I which is the B/W wire from the Main Relay and this wire passes through a connector which mates the Front harness w/the Emission harness via one of the Orange connectors above and to the right of the ECU. So you've used a different circuit to power the ECU I gather?

 

That's 3I.

Maybe your starter is drawing down the battery too much when cranking the engine over? And maybe this MYSTERY ECU has a feature where it shuts down when the voltage is too little??? I mean, it worked prior to this, so why not now?

Cranking a normal RX causes the batt to drop to ?? 9 vdc or less, so maybe you batt or starter is dragging things down way too far and this causes the MYSTERY ECU to shut down?

 

the mystery ECU is a wolf v500. It has a whole new harness that has been running in the car for 3 years. On the advice of my tuner he suggested it have its own dedicated ground and a power right to the battery. No changes were made to the car, it cranked right over that morning and fired up. Drove it and it now has this issue. I drove it pretty easy that day too my wife was following me and I always take it easy on the car when I haven't driven it in a while. It had been sitting for like 2 months.

I doubt the ECU cuts power with low voltage because I just changed the battery this summer and the old battery was always being depleted from the car sitting but it would still fire the car up.

 

No other suggestion other than to remove the power wire for the ECU from the battery and make sure its clean and then reinstall it. Other than that it seems a ECU problem????? Maybe monitor the voltage of the battery while cranking the engine over and see how low it goes.

I guess check the gnd to the ECU also wouldn't hurt.

 

I am hoping its a bad connection where the ecu gets its turn on signal.
But then I wonder because it does turn on when the key is turned, going to ask my tuner who is also the distributor for the ecu, meanwhile I am going to look at the wiring diagram again

 

even though I dont have the car handy its in storage this is still going through my head.
is there a relay the starting circuit goes through? where is this relay located?

I need to dig out my service manual, I have a print copy somewhere.

 

Post a picture or paste a url where we can look at the wiring of YOUR Wolf ECU. You don't have a RX ECU so we don't know.

Is'nt there a WOLF EDU forum on this site?

 

its not with the wolf itself, it has to be where the turn on lead is tied into the vehicle

 

The start circuit goes through one relay (Starter Cut Relay, located in the bay next to the clutch master cylinder) and powers another (Circuit Cut Relay, located under the dash by the steering column.

 

thanks!

 

The Starter relay has but one 4 wire plug and it's located next to the Main Relay.

 

standard relays right? I dont know why I cant remember off the top of my head seeing a relay by the clutch master, maybe I just never paid attention to it

 

His starter turns over so the start circuit works.

IF we had a wiring diagram for the thing we could see where the turn on signal comes from. For the WOLF ecu. Is it a Wolf v4x or a Wolf or V500 or V1, V2, V3, V4????????

 

its a v5, it has a single turn on lead, which is turning on when the key is turned, just not when cranking
maybe if I have time later I will go down to the car and check.

 

i went down the car last night, didn't have much time. I was really just hooking up a battery tender.
I see the relay under the hood.

I noticed last night, which I don't think I had before and if its even related to the starting issue the seat belt warning lamp is very dim when the car key is turned OFF.

 

The seat belt sensor places a ground on its wire which would cause the light to turn on so perhaps the sensor is not working properly to cut the ground signal on the wire as it should be doing.

 

I cant recall seeing wires coming out of the seatbelts when I did the seats and carpet, but then again I wasnt exactly looking for these things either.

I did try plugging in the seatbelts with no change, I ended up pulling the BTN fuse so the light would not draw on the battery. I dont even remember ever seeing that seat belt light before.

 

I didn't see the "w/key to off" in your post so there's something else at play here.