catamax944

Went to a friends today to put together a few last things on his 951 after an engine swap .
Engine fired first try after the swap a few days ago and was running pretty well apart from hunting idle.
Today i noticed it had a huge leak on one of the intake runners so we pulled the manifold and changed the gaskets ,leak solved but now it wouldnt start anymore.
We have fuel,spark and tach bounce but it doesnt even try to start.
Any ideas ??

944hal

How do you know you have fuel? Are the injectors firing?

catamax944

Yes they are , pulled the rail and cranked the engine, they fire good.
Spark is strong and timing is fine.
The issue started right after we pulled the intake manifold , before that is would fire first crank .

mytrplseven

Did you disconnect the TPS or AFM plug? Are the vacuum lines all connected as they should be, ie., FPR, FPD, etc?

odonnell

Is the cap and rotor intact? If you can verify spark at the plugs, it almost has to be related to injector pulsing which implies either a bad harness connection or a faulty reference signal from the speed and position sensors. Someone correct me if I'm wrong, but a good speed sensor will still drive the tach. Maybe the position sensor is bad? You can switch them to check for inconsistencies.

catamax944

I didn't disconnect anything , just pulled up the intake manifold a few inches enough to change the gaskets without disconnecting anything .Same with the fuel rail , just unbolted it and pulled it up.
Vac lines are a bit of a mess, can they cause a no start scenario ??
Injectors are firing fine with good strong spray and it also has strong spark but the engine doesn't even tempt to fire up.
It also has tach bounce so that would indicate good speed/ref sensors right ??
Something definitely happened when i pulled up the manifold but what , whats under there that can cause no start ?

odonnell

Idle control valve, if it's open, it will allow too much air past the throttle body to facilitate starting

divil

Have you done a compression test? Checked your timing belt? If you have fuel and spark and still no start, that is where I'd be looking.

Tom M'Guinn

If the hose on the FPR came off (at the regulator or somewhere downstream) you're engine may be flooding, and you may have fouled the plugs. Did you check the spark at the plugs (not just at the coil) and double check the firing order? Does the cam belt marks line up?

Why did you have a huge leak at the intake gasket? That's unusual unless the intake is hanging up on something - like when the throttle body hits on a larger turbo. Are you sure you really fixed the huge leak? Can you slide a feeler gauge between the intake runners and the head?

Are the fuel injectors pulsing fuel, or just spraying constantly? A short somewhere can sometimes just turn them on full force -- have you pulled a plug and looked to see how much fuel is going in? Or confirmed with a fuel injector test light that they are actually pulsing.

Sure something big -- like the ISV hose or I/C couplers -- didn't come loose when you pulled up the intake?

catamax944

Thanks Tom! You were spot on..
It's the injector harness , sometimes they are on full force like you said and sometimes they are dead.

Tom M'Guinn

That's the benefit of listing a dozen possibilities.... Glad you found it!

catamax944

Short update,
The problem persisted after fixing the injector harness and i found the DME temp sensor wiring also had a short. Now it runs great ,all good ....for the time being.