Volvo Penta 8.1 Hard/wont start

[Cooler]

One other "weird" thing to check out. You mentioned an oil change before the rough running. A friend of mine discovered that if he overfilled his oil level, he would have these same symptoms. Engine would actually shut down after cruising for an hour. That was also an 8.1. He drained a quart out and no more problem. Good luck! er

[Jskhome62]

Hello all. Another update. Last time I posted I thought maybe this problem was solved but I’m actually still chasing it. I had a mechanic come out with a computer but nothing specific showed up so they did some old fashioned troubleshooting by swapping port and starboard parts to see if problem moved. They were pretty sure it was the IAC because the problem moved with it (reportedly - wasn’t there) so I replaced it on the port engine. Seemed like it helped for a brief while but now back to the hard starting, more frequently on a hot engine restart but occasionally cold as well.

Next tried ChatGPT and it suggests I either have a weak fuel pump that is unable to keep prime so I’m getting vapor lock off the hot engine preventing a restart or I have a plugged fuel tank vent that’s drawing a vacuum preventing starting on either a hot or cold engine. I have been able to get things going again by loosening the fuel cap (and maybe removing the fuel filter did the same) but that doesn’t always work.

I have a replacement pump ready to go but I’m hesitant to replace it just yet. I’d like to check the tank vent for blockage as ChatGPT recommends (apparently spiderwebs and dauber nests in fuel tank vents are very common in Florida) but it also says the vent is a thru hull fitting near the fuel cap. The only thru hulls I have are near the waterline and none of them are for the fuel tank.

So that is the question for the group. Where is the fuel tank vent? I know they sometimes can be inside the fuel fill spout which is where I’ll look next, but should I look elsewhere? Is the fuel cap itself vented - not seeing any type of breather there?

As always - appreciate any help or guidance. I’m relatively convinced this problem is related to something simple because everything runs so well/stable/strong once it starts.

[Jskhome62]

Hello all. Another update. Last time I posted I thought maybe this problem was solved but I’m actually still chasing it. I had a mechanic come out with a computer but nothing specific showed up so they did some old fashioned troubleshooting by swapping port and starboard parts to see if problem moved. They were pretty sure it was the IAC because the problem moved with it (reportedly - wasn’t there) so I replaced it on the port engine. Seemed like it helped for a brief while but now back to the hard starting, more frequently on a hot engine restart but occasionally cold as well.

Next tried ChatGPT and it suggests I either have a weak fuel pump that is unable to keep prime so I’m getting vapor lock off the hot engine preventing a restart or I have a plugged fuel tank vent that’s drawing a vacuum preventing starting on either a hot or cold engine. I have been able to get things going again by loosening the fuel cap (and maybe removing the fuel filter did the same) but that doesn’t always work.

I have a replacement pump ready to go but I’m hesitant to replace it just yet. I’d like to check the tank vent for blockage as ChatGPT recommends (apparently spiderwebs and dauber nests in fuel tank vents are very common in Florida) but it also says the vent is a thru hull fitting near the fuel cap. The only thru hulls I have are near the waterline and none of them are for the fuel tank.

So that is the question for the group. Where is the fuel tank vent? I know they sometimes can be inside the fuel fill spout which is where I’ll look next, but should I look elsewhere? Is the fuel cap itself vented - not seeing any type of breather there?

As always - appreciate any help or guidance. I’m relatively convinced this problem is related to something simple because everything runs so well/stable/strong once it starts.