Need help diagnosing an engine problem

[optimist_prime]

You know , I found something interesting, turns out you can scan Mefi 1-4 without the tool, there are multiple sources of people doing that, but here is the link

Make a Marine EFI code tool for less than $1.00 - Offshoreonly.com

I'm aware of that trick. But I try to avoid crawling in my engine compartment as much as possible lol.

[Hyperlite]

I did the scan using that method. No error codes. So going to have to keep investigating.

[vr5200]

I did the scan using that method. No error codes. So going to have to keep investigating.

Does your boat have a microwave?

Is shore power available?

Either use a hairdryer or heat up some rags and put them on top of the ECT sensor while the engine is cold soaked.....give it some time to warm up the sensor and surrounding metal .....then start the engine....see if the behavior changes.

Even though there are no codes......and the ohm check seems acceptable, the ECT could still be skewed a bit.....and it is a cheap test to perform.

All of these things are DIY attempts to diagnose the problem....a true scan tool that can display live data would be the best resource......but that often comes with the cost of hiring a technician and paying a possible trip charge plus diag time.

If you can use the hair dryer method, you could also blow warm air into the intake IAT sensor area while cold soaked and see if the behavior changes during a cold start.

A sensor that is somewhat inaccurate my not throw a code.

================================================== ===

Next idea- the possibility of a vacuum leak.....................

Maybe a small leak exists when stone cold but the gap closes some when it warms up?????

............and/or the ECM is able to compensate for it once it has warmed up a bit?????

Once the motor is warmed up, spray something around the intake area and see if the RPM changes a bit.

================================================== ==

I know you want to figure this out.............. and many of us want to know what the root cause is as well!.

[Hyperlite]

Does your boat have a microwave?

Is shore power available?

Either use a hairdryer or heat up some rags and put them on top of the ECT sensor while the engine is cold soaked.....give it some time to warm up the sensor and surrounding metal .....then start the engine....see if the behavior changes.

Even though there are no codes......and the ohm check seems acceptable, the ECT could still be skewed a bit.....and it is a cheap test to perform.

All of these things are DIY attempts to diagnose the problem....a true scan tool that can display live data would be the best resource......but that often comes with the cost of hiring a technician and paying a possible trip charge plus diag time.

If you can use the hair dryer method, you could also blow warm air into the intake IAT sensor area while cold soaked and see if the behavior changes during a cold start.

A sensor that is somewhat inaccurate my not throw a code.

================================================== ===

Next idea- the possibility of a vacuum leak.....................

Maybe a small leak exists when stone cold but the gap closes some when it warms up?????

............and/or the ECM is able to compensate for it once it has warmed up a bit?????

Once the motor is warmed up, spray something around the intake area and see if the RPM changes a bit.

================================================== ==

I know you want to figure this out.............. and many of us want to know what the root cause is as well!.

Interesing, i will give it a try tomorrow, thanks!!!!