986 S 3.2 engine cranking but not starting post-rebuild - any suggestions?

[HarveyRacing]

Hi!

We've been completely rebuilding a 986 S 3.2 engine for use in a race car.

We've finally got everything back together and into the car and now when trying to turn it over we get a crank but no start.

First thoughts were that it would be fuel pump related, so we checked that and we have both fuel and a spark. We primed the pump via the diagnostic, and this is what we get:

Video: https://imgur.com/edyhXsH

Can also confirm that the tacho is moving when she cranks and we have full lights on the dashboard.

Some thoughts I had:

- Could be immobiliser related (we have 10 immobiliser faults but no code for them from a generic reader), but if this were the case then the car would be completely immobilised and wouldn't even crank, right? That seems to be what happens from reading up on it.

- Are there any sensors that would prevent the car from turning over? At the moment there is no exhaust fitted and I'm wondering if the O2 sensors don't like that and that's causing the problem? I have a new complete exhaust system arriving on Monday so cannot test this until then.

Before stripping the car and rebuilding the engine, it's fair to assume that the car hasn't been started for something like 6 months (it was purchased as a non-runner).

If anyone has any suggestions of where to go now to debug in the meantime, I'd be happy to hear them.

[blue62]

Originally Posted by HarveyRacing

Hi!

We've been completely rebuilding a 986 S 3.2 engine for use in a race car.

We've finally got everything back together and into the car and now when trying to turn it over we get a crank but no start.

First thoughts were that it would be fuel pump related, so we checked that and we have both fuel and a spark. We primed the pump via the diagnostic, and this is what we get:

Video: https://imgur.com/edyhXsH

Can also confirm that the tacho is moving when she cranks and we have full lights on the dashboard.

Some thoughts I had:

- Could be immobiliser related (we have 10 immobiliser faults but no code for them from a generic reader), but if this were the case then the car would be completely immobilised and wouldn't even crank, right? That seems to be what happens from reading up on it.

- Are there any sensors that would prevent the car from turning over? At the moment there is no exhaust fitted and I'm wondering if the O2 sensors don't like that and that's causing the problem? I have a new complete exhaust system arriving on Monday so cannot test this until then.

Before stripping the car and rebuilding the engine, it's fair to assume that the car hasn't been started for something like 6 months (it was purchased as a non-runner).

If anyone has any suggestions of where to go now to debug in the meantime, I'd be happy to hear them.

From what I see and hear in the video it is firing up just not staying running.
Possible fueling problem.
I would check the fuel pressure at the fuel rail. there is a pressure spec. for key on not running and key on running. See if you fuel pressure at the fuel rail meets spec.
That is what I would check first.
If fuel checks out then it could be the immobilizer overriding starting.

The O2 sensors are not active at cold start. so they are not the problem.

[Dllrd23]

Originally Posted by blue62

From what I see and hear in the video it is firing up just not staying running.
Possible fueling problem.
I would check the fuel pressure at the fuel rail. there is a pressure spec. for key on not running and key on running. See if you fuel pressure at the fuel rail meets spec.
That is what I would check first.
If fuel checks out then it could be the immobilizer overriding starting.

The O2 sensors are not active at cold start. so they are not the problem.

Blue62 is spot on about the o2 sensors and I also agree about the fuel pressure. I would also add to check injector pulse. Interested to see what it is doing when the thing dies. I suspect you have pulse initially but immobilizer could be cutting either injector pulse or fuel pump power so watch both at the moment it stalls.

[itsnotanova]

I suspect it's a fuel issue too, but I have seen a bad DME do the same thing

[HarveyRacing]

No fuel issue, but a problem with my rebuild skills.

Slightly embarrassingly, I missed the part in the manual that told me to turn the crankshaft 360º clockwise during the rebuild, meaning I had essentially timed Bank 2 360º out of phase.

Corrected and now she is purring. Very pleased.

Thank you to everyone who replied!