Mercruiser 5.0 mpi problems with warm start

[honzaskopek]

Hello everybody,

I am little bit desperate, because I am fighting with this problem more than 3 months. The first problem is that sometimes when I turn off engine (running great, no problem) I cant start again. There is no one beep alarm and I cant hear fuel pump. After some time it finally beep and I can start engine...

Yesterday I discovered another problem. After more than hour - when I had to wait for that one beep for start - it finally beeped, but I still couldnt start engine, it was still only cranking. When I push more gas on idle - it started and beeped two times per minute ( I know it is IAC) so I changed back that old one IAC and finally I could drive. I was lucky that I had that old one on the boat...

I spent a lot of money on some mechanic from Mercruiser and it was same. I spent a lot of money on some electrician and it is same (but better, it does only sometimes)

All sensors could be ok, I think the problem is IAC - it is still very hot I think it shouldnt be. But it is new...

Occasionaly the engine turn off when I drive...

No of engine is OM658178.

Do you have any ideas?

Thank you very much,
Honza

 

[tpenfield]

From what you described, I would check the kill switch at the helm (near the throttle) for signs of corrosion and also check the connections to the key switch for corrosion.

 

[honzaskopek]

Key switch is new that was first what I changed. Electrician told me that he checked kill switch. I will check it alone to be sure

 

[alldodge]

There are two relays on top the motor, one is main power and the other is fuel pump. The relays are the same and can be swapped with each other. Check the connections on the relays. If it won't start put your hand on them and have someone turn the key to see if you feel the relay energize/click.

 

[honzaskopek]

Yes, computer said fuel pump relay is bad, I bought new one but it is true that I didnt know which one of these two relays is it. So you think this is problem of not beeping on the start = not working fuel pump? There are now two absolutely same relays - same part number.
But why I could start it with more gas?

 

[honzaskopek]

but if the relays are same, it should be ok when they are swapped with each other or?

 

[alldodge]

Yes, computer said fuel pump relay is bad, I bought new one but it is true that I didnt know which one of these two relays is it. So you think its problem of not beeping on the start = not working fuel pump? There are now two absolutely same relays - same part number.

When the key is turned ON the ECM and main power relay energizes, then the ECM checks to see if everything is working. If all is working then you hear 2 beeps. The beeps go off the same time the fuel pump is turned ON. If fuel pump will not energize then no beeps

But why I could start it with more gas?

I would say it was just coincidence.

 

[alldodge]

but if the relays are same, it should be ok when they are swapped with each other or?

Yes, they can be swapped

 

[honzaskopek]

ok, I will try swap that relay..
when there is no beep there is also no power at dashboard, I will try it and let you know if is it better. Thank you very much

 

[honzaskopek]

By the way you think there is no problem with IAC?

 

[alldodge]

By the way you think there is no problem with IAC?

Nothing that I have read leads me to an IAC issue. If there was a IAC problem, the boat would start and then die, and the only way to keep it running would be to give it some throttle. If the rpms drop the engine would die again

 

[tpenfield]

Engine starts fine when it is cold (right?) and also runs fine even once warmed up (right?).

So, that would leave me to believe it is electrical in nature and has to do with what the ECM goes through during the starting process. Agree the sensors are probably fine unless there are other symptoms

 

[honzaskopek]

That happened on tuesday. I had to start with more throttle, after that there was 2 beeps per minute and when I turn it back to idle, engine died. After that I changed IAC and it was ok. But before this I had to wait more than hour to hear that beep and fuel pump. That IAC is old one month, I dont understand this. Third IAC this year.

 

[honzaskopek]

Engine starts fine when it is cold (right?) and also runs fine even once warmed up (right?).

So, that would leave me to believe it is electrical in nature and has to do with what the ECM goes through during the starting process. Agree the sensors are probably fine unless there are other symptoms

In most cases engine starts good when it is cold. But I know about one case when it didnt start when it was cold...

and runs perfect when is warm, thats right

 

[alldodge]

Does the IAC get hot?

 

[honzaskopek]

Yes IAC gets very hot

 

[alldodge]

Yes IAC gets very hot

There should be a pigtail going from the IAC to the harness. Need to replace it, and many auto stores have them, they are Ford windstar if I remember right

 

[honzaskopek]

Do you think it couse all the problems?

 

[alldodge]

Don't think so, but it could be pulling so much power that it drops it below what the ECM needs. Don't know for sure, just guessing

 

[honzaskopek]

Could you show me the number of that part? I am not sure if I translate it right, thank you very much