Changed engine, now won't start

[Laine_16v]

Help, just put my rebuilt engine in the car today.

Engine cranks over fine but it will not fire, not even a splutter. I have put the multimeter on coil pack plug and injector plugs, they arent reading anything (not firing), apart from the crank sensor (which worked perfectly before i did the engine swap), what would cause this? (cant see it being an immobiliser issues either?). Im pulling my hair out over this one.

Only wires currently not plugged in as im having a few issues with wiring locations is the speedo sensor, CTS and carbon cannistor plug, but again the engine should still fire with these unplugged?

Thanks in advance.

[rich-6]

I'd have thought you will need the Coolant temp sensor TBH fella

[Dan@519Automotive]

immobiliser. disconnect the battery, then reconnect and leabe ignition on for 5mins BEFORE attempting a start.

[Fred@BTM]

you missed an earth off?

[Dan@519Automotive]

i did think that too but it usually wont crank if an earth is off

[Laine_16v]

Thanks for the suggestion danny, ill give that a shot tommorow. Would it be indicate a problem on the dashboard (i have NEVER understood when the red light should be flashing or not)

Rear gearbox earth (for loom) is tight, and so is the earth strap from the side of the box to the inner arch, all the electrics seem healthy. (unless theres a 3rd earth i have missed?)

[Laine_16v]

Tried leaving ignition switch on for 5 minutes, no joy, tried for 30 seconds off, then another 30 second (read it in another post), no joy, holding the interior lock switch for 10 seconds, blipping the key multiple times e.t.c im out of ideas Red dot immobiliser on dashboard is not illuminated while cranking.

RPM gauge registeres 0rpm while cranking (not sure if this an ECU/Canbus thing until engine is actually running), is this a normal thing or could crank sensor be dodgy?

Andy told me i should get 12v at the white coil plug wire for second or no when ignition is on, i've checked it and it gets nothing.

The fuel rail is pressurised, no warning lights on the dashboard, the FBW throttle operates and buzz's away. WHY U NO START. Going to have a bit more of a gander at the relay box (not that i know what im looking for), before maybe calling an auto electrcian.

[Fred@BTM]

standard car?

[Laine_16v]

Yeah just a mapped standard ECU.

[Fred@BTM]

you've either missed a sensor off or a dodgy earth, if the TB is buzzing and the imobiliser light goes out then its something simple

[Laine_16v]

OK i've found a rather worrying issue.

Basic eletrics, each injector plug has a switched earth that is controlled by the ECU to fire the injector, no brainer. The other wire on the injector plug is ignition live 12v+. Same for the coil pack, two negatively switched earths to fire the coils, and one ingition live 12v+ for power.

ALL the 12v+ feed ignition live wires for the injectors (4 wires), and Coil pack (1 wire) ground straight to EARTH!! THis is regardless of the ignition being on or off, these wires should never see earth, AMIRITE?

im which case i think i may have damaged the wiring somewhere.

[Bobby.]

If imobilisers light it out then that's fine.

It sounds like a classice tdc sensor fault, I know you said it was fine but they can start playing about at any time especially if it been touched when removing and refiting engines. What I would have a go at if getting some one to crank it while you fiddle with the tdc sensor and wiring, never know you might have some luck...

[Jay Payne]

even with tdc sensor fault you will still get power at coil for 1 second on ignition on, this comes from fuel pump relay.

does it run for one second on ignition on(prime)? how about on cranking?

[Laine_16v]

Ive got the relay box apart and am probing all the relays and fuses with not much joy at the minute, the fuel pump definately primes as i can hear it for a split second and its pressurised. Will report back later in the day getting pressty disheartened by this, i just want to drive ths stupid thing!

[Laine_16v]

Anyone got complete wiring diagrams / manuals for a 172 please?

[Chip-mk1]

Have you not got an odb scanner you can plug in?
at least you could see if ecu is seeing crank sensor or not.

Earth, immobiliser, crank sensor are about the only things that will mean it does nothing at all.

[Laine_16v]

Unfortunately dont have a scanner, ive admitted defeat put it all together and will get it trailored to someone that has dianostics / electrical know how with these cars.

[Cr33do]

Reading stuff like this makes me nervous about putting our engine back in! Luckily we have BTM "just up the road".

Good luck anyway - let us know the outcome.

[Chip-mk1]

Unfortunately dont have a scanner, ive admitted defeat put it all together and will get it trailored to someone that has dianostics / electrical know how with these cars.

Its the original loom back in I take it?
If so it can only really be that you havent connected something somewhere given that it was working before and nothing electrical should have changed.

Worth swapping the crank sensor out for a new one though, they're quite fragile.

[Laine_16v]

Turned out it was the crank sensor wire, had pulled out the plug slightly