5.0 GXI recent rebuild stalling at idle and crazy tach reading during crank.

[Powerstroke in a Prius]

So I bought this used boat with the Volvo Penta 5.0L GXI that is so clean I can eat a meal on it (50 hours on the engine). It runs perfectly - until it warms up and stalls while at displacement speed or at idle.

Observations:

• Once it stalls, it sometimes starts right back up... sometimes not.
• I watched the tach while the engine is in its "no-go" mode, and the tach jumps all over the place while cranking. I saw 3000 RPM on the tach (no start) during one round of cranking, and a jump to 6000 RPM during another round of cranking. When the engine is running, I see no weirdness from the tach at all.
• I forgot my pressure gauge, so I can't speak to the fuel pressure, but the engine behaves "digitally" - it runs perfect, or not at all. I suspect a bad fuel pump would whine, make the RPMs drift, cause a miss, or something other than just abruptly halt the engine - then maybe start right back up (or not).
• During one long crank of not starting, I got a strong whiff of fuel from the engine compartment, so I let it set and breath for a while.
• While running, the dash gauge says 175 degrees F, but the heat exchanger shows closer to 150 degrees F on my thermometer gun. I forgot what the oil filter showed, but I want to say 177 degrees F. I checked the fuel pumps and they read over 90 degrees F.
• Once I let the engine settle and cool, I can fire up and motor back to the launch. I haven't had a stall on plane yet, but that's not to say it won't happen.

Ideas?

 

[alldodge]

Need to get the motor scanned for codes. Being a 207 I'm guessing its a gxi-E possibly. With what its doing I would look first at the CPS (crankshaft position sensor) and its connector. It should be located on the distributor.

 

[bajaunderground]

What quality of fuel are you using? lower octane can boil and create vapor lock like situation if it sits after running. You said after "it warms up" so I'd try a higher octane fuel or add octane booster to your fuel...had this same issue and the higher octane cleared it up. I'm not inferring that higher octane is the way to better fuel, better power, it's merely a rating of how hard it is to compress to burn.

All gasoline has a boiling point of 100deg F-400deg F.

 

[Powerstroke in a Prius]

I can't know what fuel was in there before, but the PO had the money to put in "the good stuff". I put in 30 gallons of high-octane non-ethanol fuel, and the tank is allegedly 56-gallon capacity.

I strongly suspect the Crankshaft position sensor, but I didn't know where to find it - and a shop told me they had never seen one of those go. Being from the diesel world, I've seen plenty of them go - so I have some familiarity with the symptoms. I won't dispute input from those with far more experience on VP engines of this era... my last VP had a carb and points.

 

[alldodge]

Vapor lock only can develop after the motor stops running and its all warmed up. It comes from heat soak of the fuel, doesn't happen while running

 

[Powerstroke in a Prius]

Need to get the motor scanned for codes. Being a 207 I'm guessing its a gxi-E possibly. With what its doing I would look first at the CPS (crankshaft position sensor) and its connector. It should be located on the distributor.

I ordered Diacom, it will be here Friday... such is life in the modern world.

 

[Powerstroke in a Prius]

Fixed! Diacom was of no help with this particular problem, but I learned how bad my trim sensor problem was.

I had a bad fuel pump connector and it showed corrosion on the contacts. When I first found that, my thinking was "Aha! This has to be the root cause of the randoms stalls and no starts." As it turns out... I was mostly correct: The poor connection on the fuel pump damaged the fuel pump relay contacts, and it wasn't until I repaired the connector and swapped out the relay that the craziness stopped.

I talked to a tech about the crazy tach reading, and he speculates the voltage spikes from the noisy fuel pump relay was messing with a lot of things in the engine electronics.