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-   -   Help Chasing Erratic Idle Please (https://www.offshoreonly.com/forums/general-q/349163-help-chasing-erratic-idle-please.html)

Tractionless 01-30-2020 06:43 AM


Originally Posted by zz28zz (Post 4722972)
You can check for internal vac leak by plugging all the holes in the valve covers except 1 where you press down with with the palm of your hand to seal the last hole with eng idling (cold eng is waay more comfortable). If you can feel that suction is building on your palm, you have a internal vac leak like suggested above.

On a side note: I once "upgraded" all the intake manifold bolts on a SBC car eng. Didn't realize the new ones were slightly longer. They would tighten down just enough to start compressing the gaskets then bottom out. Replaced the gaskets twice before I figured out what was going on. It had a internal vac leak.

Anyway, its a quick and easy thing to check for.

What's was the deal with the stripped intake plenum bolts mentioned on post #90? Could that be a potential vac leak??

Thanks for the insight. I repaired the stripped plenum bolt and replaced the gaskets to no avail, unfortunately.


Originally Posted by Trash (Post 4723058)
It could be a hairline crack some where in the intake manifold 'hat' or the surrounding gasket. As the motor warms up the expansion can cause a larger air leak. Just a thought.

Gotcha thanks.


Originally Posted by Blueabyss (Post 4723076)
Rent one of those smoke machines and do the smoke test.

Chris

Who rents them?

Tractionless 01-30-2020 06:45 AM

UPDATE

I had the boat on the water last weekend in cooler than normal weather. It seems as a result I only had one stall issue after a rev and it did not die on the hose when flushing at the ramp. Would ambient temp. affect a vacuum leak?

Thanks

AllDodge 01-30-2020 06:50 AM


Originally Posted by Tractionless (Post 4723584)
UPDATE

I had the boat on the water last weekend in cooler than normal weather. It seems as a result I only had one stall issue after a rev and it did not die on the hose when flushing at the ramp. Would ambient temp. affect a vacuum leak?

Thanks

Not seeing a difference with air temp, but the MAP could effect the fuel supply

Tractionless 02-01-2020 08:05 AM


Originally Posted by AllDodge (Post 4723585)
Not seeing a difference with air temp, but the MAP could effect the fuel supply

Yes sir, I've swapped maps side to side (twins) without a change in character to either engine, even tested the pinouts and harness. :(

articfriends 05-16-2020 01:44 PM


Originally Posted by AllDodge (Post 4721841)
With my pea brain it has to be vacuum leak because

If vac line is removed, fuel pressure increases
IAC is trying to idle but is not rich enough but is when cold

IF it was a vacuum leak, the IAC counts would head down to zero when its not at its target, IMO

articfriends 05-16-2020 01:48 PM

So aside from a weird ghostmechanical problem (I doubt) , the only thing you HAVEN'T tried is swapping the harnesses side to side? IF you hadn't bought mefi scan and saw 64 degees C for ECT Id suspect the ect or wires but no way it would read what it does, that's my only suggestion reading thru this as you asked, Smitty

Tractionless 05-16-2020 09:16 PM


Originally Posted by articfriends (Post 4739252)
So aside from a weird ghostmechanical problem (I doubt) , the only thing you HAVEN'T tried is swapping the harnesses side to side? IF you hadn't bought mefi scan and saw 64 degees C for ECT Id suspect the ect or wires but no way it would read what it does, that's my only suggestion reading thru this as you asked, Smitty

Thank you for your time!

I haven't swapped harnesses but it's worth a try or maybe I can try one of those self contained testers that takes the place of the harness. The name escapes me at the moment.

Keith

BUP 05-17-2020 12:29 AM

I forgot if this was mentioned --- have you swapped ECM s

Next is my question the master ecm is starboard engine and slave is port - on your scan do you see the reporting for that ? and are your engines interlinked ?

articfriends 05-17-2020 07:05 AM


Originally Posted by Tractionless (Post 4739294)
Thank you for your time!

I haven't swapped harnesses but it's worth a try or maybe I can try one of those self contained testers that takes the place of the harness. The name escapes me at the moment.

Keith

Since you've swapped ECM's and changed/swapped every sensor with same results, like I said , Id swap harnesses , its not as hard as you would think, Smitty


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