Hard Start when hot

[dan313]

My 350 mag give me a hard start when the motor is hot. im running at 160 deg and am idling at 550 rpm. I have to place the throttle in the fwd position in order for the motor to start. This is an intermittent issue. My mech changed the IAC valve thinking that was the problem. Now he wants to have the fuel rails changed.

Any thoughts,

Lenny

 

[Bay B's]

Hi, more details on the hard start please.

 

[bjdunnie]

I used to have a similar problem, cold starts no problem at all, however once the port engine was warm it needed revs to restart - this always frustrated me with an MPI engine.

Anyway, in my case it was a failed boost pump which was causing the problem. $750 for the parts and install and problem solved (in hindsight I could have installed myself)

 

[Great lakes pirate]

I had the same issue at the start of this season. Ended up being the cap and rotor.

 

[KHE]

Check the fuel pressure regulator. Pull the vacuum line off the fuel pressure regulator (FPR) - there should not be fuel dripping from the FPR nipple, no should there be fuel in the vacuum line. If there is, the engine is getting unmetered fuel which will not be a problem on a cold engine but it will tend to flood a warm engine.

You can also start the engine and pull the vacuum line and if there is fuel dripping from the FPR nipple, the FPR is bad - the diaphram is torn.

If the FPR checks OK, the problem could be a leaking fuel injector. To test for that would require the fuel rail to be lifted off the manifold (blow around each injector port in the manifold with compressed air to remove any dirt). Turn the ignition to ON (don't start the engine) to pressurize the fuel rail, then look at the ends of each injector. There should not be any fuel dripping or visible at the injector tips. If you see any leaking injectors, they will need to be replaced. I do not know why the mechanic would want to replace the fuel rail??? Sounds like he is shotgunning parts at your expense.

 

[dan313]

The mech does not want to replace the fuel rail he wants to clean it. My mistake. The motor runs strong and there is no hesitation. I was talking to a friend of mine and mentioned to check the coolant sensor. Mine is raw water cooled so I don't think that comes into play.

 

[scoflaw]

KHE makes some good points about the FPR. You can check for a leaky injector easier by monitoring the fuel pressure, as in how long it takes the pressure to leak down. Fuel pressure check is in order, hot and cold. There's a screen filter up by the fuel rail that can be examined for paint chips or whatever, that's easy to get to.