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Stumble on cold start after tune up...

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So went back out this evening to change out the plugs to what Michigan Motorz recommended. I had put in AC Delco 41-101 and called them to make sure hey were the right ones and they told me they’re hotter and to change them out to 41-993. Thought they were essentially the same but whatever...
Previous to this I did a full tune up... and replaced fuel pressure regulator which had a bunch of gunk in the screen. now when I start cold, the motor fires right up, idles down and sounds like it wants to die, then catches and clears itself up. It’s done this both times I’ve had it out on the water and on muffs after the tune up. Sounds like a vacuum leak somewhere at first but then clears up. After it warms to operating temp, it runs great. No stumbling at all, gets up on plane better than ever and no issue up to 4800 rpm. What could be causing the stumble at the cold start?
thanks. 

2004 Volvo 5.0gxi-D w Michigan motorz block in 2016

thx

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Maybe a bad plug.

Other things that come to mind are IAC or MAP.

The MEFI ECU is an open loop system so nothing to “learn” from the potential increased fuel being delivered as a result of new reg.

If you have access, hook it up to diacom or similar and do a power balance and take a look for anything out of the ordinary on MAP, IAC, injector pulse width, spark dwell to start. If not, try swapping/checking the plugs.

 

 

 

 

 

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13 minutes ago, CaptScott said:

Maybe a bad plug.

Other things that come to mind are IAC or MAP.

The MEFI ECU is an open loop system so nothing to “learn” from the potential increased fuel being delivered as a result of new reg.

If you have access, hook it up to diacom or similar and do a power balance and take a look for anything out of the ordinary on MAP, IAC, injector pulse width, spark dwell to start. If not, try swapping/checking the plugs.

 

 

 

 

 

Thanks for the reply... plugs are brand new and it did the same when I had the 41-101 in there yesterday. Changed them out for the 41-993 today and same thing.  Checked the gap of each plug before I installed so I don’t think it’s that. If one of those sensors where bad wouldn’t it affect overall performance or throw and alarm? Same of the plugs or wires were bad; I’d think that would affect its running characterstics more than just at a cold start. Unfortunately I don’t have a diacom or similar or access to one.... seems like the injectors aren’t stayin open long enough at cold start or something. Doesn’t the ecu control how long the injectors stay on at a cold start?  Think that’s how it works in a car...

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10 hours ago, Further said:

Thanks for the reply... plugs are brand new and it did the same when I had the 41-101 in there yesterday. Changed them out for the 41-993 today and same thing.  Checked the gap of each plug before I installed so I don’t think it’s that. If one of those sensors where bad wouldn’t it affect overall performance or throw and alarm? Same of the plugs or wires were bad; I’d think that would affect its running characterstics more than just at a cold start. Unfortunately I don’t have a diacom or similar or access to one.... seems like the injectors aren’t stayin open long enough at cold start or something. Doesn’t the ecu control how long the injectors stay on at a cold start?  Think that’s how it works in a car...

How many hours on new engine?  As a rebuilt, the valve guides may still be a bit snug and that problem would cure itself after about 25 hours.    W

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1 hour ago, Wingnut said:

How many hours on new engine?  As a rebuilt, the valve guides may still be a bit snug and that problem would cure itself after about 25 hours.    W

Not sure... The boat overall has had very little use - I bought it this past winter with 139 hours total; its an 04'.... The block was purchased/installed in 2016 (confirmed by Michigan Motorz) but not sure how many hours it had when it was installed.  Don't think too many cause it wasn't used all that much.  I've put about 10 hours on it so far.  Prior to the tune up i just performed, It didn't have this stumble....  

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I dont know the answer to your question, but I have 2005 220 with a Volvo 5.0, and it will do the exact same thing on a cold start, except for me it will rev up, struggle, then die.  Every cold start requires 2 starts, the first one that dies, then the second and everything is fine. Warm starts are not problem and starts right up and idles fine.

Nothing else is affected, and boat runs great after 2nd start.

The only thing I can correlate it too is after my fuel pump died and I replaced with a new one, I started having this "feature".  I assume it has something to do with fuel pressure building up? Since nothing else seems to be an issue, I have not tried to fix it...dont want to make things worse.

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Not normally where I would start but seeing as this only began after you replaced the regulator and plugs (and you have eliminated plugs as the cause), check the fuel pressure at the rail.

Sounds like you've already checked vacuum lines. 

Where are you located?

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5 hours ago, CaptScott said:

Not normally where I would start but seeing as this only began after you replaced the regulator and plugs (and you have eliminated plugs as the cause), check the fuel pressure at the rail.

Sounds like you've already checked vacuum lines. 

Where are you located?

Yep thanks. Planning to check fuel pressure and all vacuum lines tonight. On my way over to the marina now. 

I’m located on Lake Hopatcong in northern New Jersey. 

Thanks for the help!

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Fuel pressure is good I think...  50-52 at idle on the rail and 12 steady on the low pressure. Nothing loose and all lines are connected firmly. Started up cold without stalling but still stumbles and sounds like a vacuum leak somewhere but clears up pretty much right away. Weird...  guess I’ll just have to live with it. 

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26 minutes ago, cyclops2 said:

IAC filter failing ? The whistling noise ?

Check all oil levels.

IAC filter?  It’s a valve isn’t it. And symptoms would be erratic idle or rpm which i am not experiencing. Nothing I’ve read regarding IAC valve resembles what my motor is doing. But maybe it’s on its way out. Time will tell. 

Oil was just changed and levels are perfect. 

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Forget what part on some Hondas created a whistle like a turbo. Not critical. So guys left the defect alone.

Is the whistle from the main throttle valve in the air intake ?  E F I add more fuel during a cold start.  They also can raise the idle with a richer mixture.

Is the engine going to a over 1,000 rpm fast idles for 5 to 15 seconds ?

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