2007 Tahoe Q6 merc 5.0 305 MPI motor won't start after running it

[perkins71]

I have a mercruiser 305 5.0 fuel injected motor. I can start the motor fine, I can run it 30 min or even 2 hours with killing it or having any issues. But when I kill it, and try to start it, it acts like its flooded. Sometimes it will start sometimes I have to wait 30-60 min. Another thing when the motor is running and you give it gas it hesitates. I just overhauled the motor and didn't have this issue before that. Brought to shop they put on computer and said it could be the TPS sensor or the Idle air valve, changed both and still doing the same ,.. I need help
my motor - OW665431

 

[Bt Doctur]

what does the engine temp read, and dont say normal.Too hot of an engine may cause vapor lock issues.

 

[perkins71]

160-180

 

[alldodge]

Howdy

What's your fuel pressure at the rail?

 

[perkins71]

never checked it, I was trying to lookup how to check it

 

[alldodge]

never checked it, I was trying to lookup how to check it

Pick up a gauge which reads at least 100 psi. The gauge can be found at most auto stores and on line. There is a shrader valve (item 19) which the gauge is attached to. It has a screw on cap over the valve.

http://www.mercruiserparts.com/bam/s...31852/12840/90

BTW, when you kill the motor can it be restated right away without issue or it doesn't matter if its right away or has been sitting warmed up? Or does it matter

 

[perkins71]

99% of the time It will not start right after killing it, I have waited as long as 1 hr. before it would crank

 

[alldodge]

Well its not vapor lock.
Have you tried starting by opening the throttle just a little?
Is this an Alpha or Bravo drive?

 

[perkins71]

it's a alpha, and yes tried starting by opening throttle. That how I have to start after running it, but when it does start it's like it's flooded or want start

 

[khe]

There should be a fuel pressure regulator on the fuel rail - If there is a vacuum line that connects to it, disconnect the vacuum line. There should not be any fuel dripping out of the regulator nipple. If there is, the engine is getting too much fuel when warm and that could explain the difficulty in starting when warm.

When the problem exists, if you open the engine hatch, can you get it to start quicker than the 30-60 minutes?

 

[alldodge]

Being an Alpha you have Gen II cool fuel and the pump is behind the port motor mount. I'm thinking your regulator is the issue but checking fuel pressure will get us closer.

 

[perkins71]

yes when I open engine hatch and wait it will start, tonight I will check the fuel pressure

 

[Bt Doctur]

Your injected so fuel should not be getting into the motor with the motor off unless the injectors are leaking down. So with a gauge installed , turn the key on, let the fuel pump cycle and watch the pressure. Should get to around 40 psi and stay there .It should not drop quickly.

 

[perkins71]

I had 40 PSI all the time

 

[alldodge]

I had 40 PSI all the time

The rules out the fuel pump, that is when it won't start. All this info we need when it won't start. You have the HVS distributer and many have trouble with the cap but don't see that as the issue now. When you crank over the motor does the tachometer move up around 200 rpm or more?

The crankshaft position sensor is on the timing chain cover. Remove the connector and check for any corrosion on the pins.
Next check for 12V at the coil (There is a pink and a pink/white)

Need to find out if there are any codes

 

[perkins71]

I will check for corrosion this evening when I get home. But when I crank it over the tachometer jumps all over

Two weeks ago put it on computer and they said had wire off or loose wire, and they said my throttle sensor or my idle air valve might need to be changed. I changed them both and still do the same thing. I still have the 2 beeps every min or so, but before overhauling motor I never had the alarms.

 

[alldodge]

But when I crank it over the tachometer jumps all over

With the tach jumping around and not steady this is a good indication of the issue. You have a bad connection to the tach or your tach is shorting out. Disconnect the wire going the tach and see if you problem goes away of changes

 

[perkins71]

The tach only jump when trying to start but when it starts it's fine
The crankshaft position sensor no corrosion

 

[khe]

The next time it won't start, disconnect the wire going to the tach. like AllDodge said and see if it will start. If it starts, then you will have confirmed the issue is in the tach or the wiring to the tach.

 

[perkins71]

ok just tried it, I let it run and warm up. killed it and tried starting , it wouldn't start. disconnected wire going to the tach, still didn't crank up