Put the engine back in my 172 and it won't run!

[Brendan2234]

As thread title really. No spark, coil gets its 12v supply briefly when ignition turned on but nothing thereafter. Pulled and cleaned all the fuses and relays, resistance on crank sensor is 230 ohms so in spec. Possibly biggest clue is the electronic warning light (waveform) and ESP lights are no longer coming on with the ignition, making me suspect an ecu live or earth is missing but all the earths have been refitted. No fault codes present but live data with my cheap Autel scanner just shows engine RPM at 190 regardless of actual speed, very unusual for a CKP fault to do that, stuck at 0 I could see.

Only change the the loom is the pre cat lambda plug was damaged on removal so I had to fit a new plug, couldn't work out which wires went where so did a search and followed the colours suggested in a thread on here. If I got this wrong might I have damaged the ECU sending lambda heater current down and back the signal wire?

Can't find any wiring diagrams to pin check the ecu for lives and earths, any suggestions where I could find any or towards my fault would be greatly appreciated.

 

[hipwell]

Might not be helpful but if the engines been out have you made sure the earth strap has been put back on?

 

[bloke]

earth on the top of the box first port of call.

 

[STEVE.M]

earth on the top of the box first port of call.

A lashed up earth or a jump lead from battery negative to engine will confirm a poor earth.
@Brendan2234

 

[bloke]

A lashed up earth or a jump lead from battery negative to engine will confirm a poor earth.

not if it's the engine loom earth that's off though.

 

[STEVE.M]

not if it's the engine loom earth that's off though.

True, true, pinpoints the braided bit though.

 

[Brendan2234]

Battery negative that bolts behind the headlight, braided strap from chassis rail to gearbox and the ECU earth to the box above the drive shaft have all been replaced. Even though they all looked fine I might remove and clean them all to rule them out next. Going to check for injector pulse too to establish if I've just got no spark or no fuel either, rail is pressuring nicely though. Will keep you updated!

 

[bloke]

check fuses and connector on inner wing.

 

[Brendan2234]

All the fuses are good, white connector on the inner wing is clean and tight as is the earth there. There was a bit of corrosion on some of the relay pins but I've cleaned that up.

 

[Brendan2234]

Quick update, found the fault after pulling all the loom apart and checking all the ECU earths to no avail. Injectors weren't being opened either so looked closer at the crank sensor, it tested fine and the wiring was fine when it was unplugged, but when plugged back in one of the female contacts inside the plug was sliding out so it looked fine but was barely making any contact, so was giving me a rpm reading of < 200 and not logging any DTCS. What threw me and made me start off with ecu earths is the waveform light not coming on with the ignition, this still hasn't illuminated the whole time despite the car running fine. Does this light come on for everyone else? Or will it only illuminate if I've got a fault?

 

[bloke]

should do a self check with ignition on. do a dash check and see if it comes on then.

 

[hipwell]

Half of the lights on my dash have packed in. Service, and esp been 2 of them I can remember lol