Volvo Penta 8,1 low idle, dies while shifting.

Figge

Recruit
Joined
Mar 18, 2014
Messages
1
Hello.
I'm a boat mecanic in Sweden. Please try to understand my horrible english.

I have a customer who bought an VP 8,1 engine from another dealer. (Thank god I did'nt deliver it). This engine have too low and unreliable idle. Aprox 500 rpm.

I have checked:
The compression. Ok on all 8 cyl.
Fuel pressure. Ok.
Fuel in fuel pressure control vacuum line. It's dry.
Top rpm. Ok.
Condision of the fuel. Ok. The owner uses the boat.
The ECM soft were was already up to date.
Electrical connections.
Trubel codes. None.

I have changed (on cost of the dealer who delivered the engine):
IAC valve.
TPS
MAP sensor
Sparkplugs.

How do I check the IAC function and circuits?
Any sudiestions?

Best regards Figge.
 

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
8,776
Re: Volvo Penta 8,1 low idle, dies while shifting.

Hi there, welcome to iboats!:)

Have you ran a EFI scan tool to see if the live data is out of the ordinary specifications that you might be use to seeing? Do you have another like engine to compare to? Be sure all 8 spark plugs, wires and coils are working and within specifications as any of these items will lower the RPM if out of specifications.

To test the IAC you could:

1. Idle the engine until the IAC counts are 0 or stabilizes. (or, if no scan tool is available) start and allow the engine to idle until it stabilizes.

2. Disconnect the IAC connector while the engine idling.

3. Shut the engine off. Remove the IAC, inspect the IAC position.

4. If the IAC is fully extended so no air is getting though the IAC port, check for a vacuum leak.

5. If the IAC is not extended, check for open or shorted IAC wiring to the Powertrain Control Module (PCM).

6. Using a test light, check for a blinking light on each IAC harness wire while revving the engine up and down slightly.

7. If all OK, replace the IAC.

Also for more marine diagnostics of the IAC, see page 6-82 & 83: http://www.marinepowerusa.com/pdfs/MarinePowerUSA_8.1L_MEFI_4_Service_Manual.pdf
 
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