Ideas on a random no-start condition?

[NV325i]

^ I agree crankshaft sensor failed on mine with similar symptoms.

[Cephas]

Crank position sensor on the bellhousing. They're cheap so replace both if you can. My eta did the same thing you describe in post two - start, run fine till warm then...dead. It was that sensor.

[bddog]

I had all kinds of trouble until I replaced my bad Idle Control Valve. The Oxygen Sensor only has so many miles in it before needing replacement.

[LateFan]

We did another smoke test last night. No signs of leaking, until we bumped up the pressure a bit and one of the new rocker shaft plugs at the VC hissed a bit, then our intake plug blew out. Tightened the VC a bit, but I think we've found most of the leaks.

Today we tested the cold start valve per Bentley. Engine cold - sat all night. It did not spray ...at all. Bone dry. Testing the connector pins showed about 10.2V from one of them to ground while starting.

Then we went to the thermo-time switch. As far as I can decipher the Bentley instructions, we tested the HARNESS connector pins to ground, not the switch pins (which have no power to them unhooked, right?). One of these showed the same 10.2V. I got no signal from the actual sender pins.

Does all that mean the cold start injector is faulty?

Then we hooked everything back up and started it. Ran well, nice & smooth. Let it idle for some time while it heated up. The idle crept up steadily to about 1200. No idle cycling. I felt the coolant hose at the thermostat go hot when it opened. Temp gauge got to about 1/2.

At about 9 minutes, the engine instantly shut off. Like a switch. No stumble, no misfire, no fuel starvation, just boom - off.

It won't re-start, and is acting the same as the non-start days. Cranks and stumbles. But it's hot now and the cold start shouldn't be functioning anyway....so........??

oh...EDIT..we installed a used functioning fuel pressure regulator as well. On our old one, the vacuum pipe was spinning in the case.

[LateFan]

(EDIT - This is an 86 eta engine)

I have more homework and testing to do per The Jim Levie Basics List, but we're a bit stumped by the random no-start situation we have. My son & I have it fairly close to useable as a DD. It seems to be following an odd/even day model for starting.

We've replaced every piece of rubber on this engine, including the brake booster check valve and grommet. All new service items. Plugs are cleaned and gapped. Injectors refurbished by member MEPEH. Tested the TPS, ICV, etc. Replaced the valve cover gasket and plugs where we found a massive air leak.

It starts instantly and runs smoothly, although there is a high idle and some cycling. It hasn't done the cycling in a couple of weeks - just the high creeping idle. I pulled the oil cap off while idling to see what a major air leak does - it drops to 500 and runs roughly, tries to quit.

On odd days, it will not start. With no pedal, it just cranks (fairly fast - good starter and new battery / alt.) With some pedal, it will try to kick but stumble and die. With WOT, it will start and rev for an instant, then stumble and die. No amount of throttle feathering will keep it running.

To me it feels like flooding. After it stumbles a few times, there is gas smell. It spins fast, like maybe the cylinders are washed down (?).

Could I be fooled by symptoms? Could we have random low fuel pressure from a failing pump? It does some random whining you can hear above idle (the pump in front of the axle). But it never quits or stumbles like running out of gas.

It feels like fuel, not spark to me - it runs really well and idles for an hour without problems. We have really improved how our $1000 project car runs, but there is some system or component we haven't gotten to that continues to do this.

We are doing another follow-up smoke test tonight. We'll test the cold start valve per Bentley to see if it's leaking gas into the manifold (it's unplugged now - no effect). I bought a used fuel pressure regulator from a member and we'll try that when it arrives.

I know vac leaks are the biggest problem, but if it will run with the oil cap off, would a tiny leak we haven't found somewhere cause it to not start like this?

Thanks for your time and thoughts -