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383 Mag Stroker Hot Start ICM Problem

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Franics

New member
Hi all,
Looking for some advice and also hoping this might help someone somewhere in the future...
For reference I'm mechanically inclined but don't really know what i'm doing.

I've been helping someone with a 383 Mag Stroker having consistent hot start issues for 2 years(!!) now:
Engine starts cold perfectly, runs perfectly with no power issues but shut it down hot (even with 15min idling cool down and hatch open) and it refuses to restart normally, even if done immediately
It is possible to restart by doing a clear-flood (full throttle) start but if you miss that then it flat out refuses to restart whatever you do until it totally cools Next morning it fires right up at idle.

Checked a lot of things... fuel pressure and leak down, coolant temp sensor resistance, replaced TPS, bled off a load of fuel from the rail to try and eliminate vapour lock but problem remained. It's been scanned by Mercruiser dealer and nothing other than replace TPS advice.

With the help of this forum I found a post regarding the ICM getting hot, after a hard run I felt the ICM and it was warm rather than hot but I tried something weird which was to spray canned air (Staples keyboard cleaner) upside down to give a cooling but not wet blast to the ICM and the Aluminum fins next to it - the engine starter perfectly at idle.

Any recommendations for better fixes than cooling the ICM with canned air?!
Checking grounds? Repotting ICM on silver thermal paste? Replacing ICM but after 2 years probably would have failed by now?

Thanks!
 
HVS index is a good question, not to say it's correct but it hasn't been touched from the factory.
I can check the ECM temp but it was cooling down the ICM that did the trick.
Thanks for your help.
 
Heat is the number one cause of operational failure of ICM's. The answer here is obvious.
 
Last edited:
Franics said:
HVS index is a good question, not to say it's correct but it hasn't been touched from the factory.
I can check the ECM temp but it was cooling down the ICM that did the trick.
Thanks for your help.
Click to expand...

When the wiring harness fails and heats up the 555 controller, you cannot touch the controller, it will burn you.... If yours is just warm, its normal.


As for the coil
Pull the ignition coil, take a look at the where the coil wire and the weather pack plug attach, are the angled away from each other?...
When these coils start to fail they do un-explainable things.
Mercruiser only sells the coil and module as an assembly.
 
Chris, how hot is too hot for an ECM, like 160F?

After a winter hibernation we replaced the ICM/coil recently and the issue remains.
Fuel pressure still good, spark ok, can hear injectors firing with stethoscope.

If it's not an ECM or related harness issue, maybe something is throwing the timing when hot?

Cheers,
 
160F is too hot....

Look up ServiceBulletin No. 2011-11R2 OEM No. 2011-07R2 From Mercruiser.... Go right to page 14 and Ignore the rest. The procedure that starts on page 14 applies to all HVS engines like yours...

The HVS (Dist) needs to be re-indexed when too far out the make the ECM run extremely hot.
 
Franics said:
Chris, how hot is too hot for an ECM, like 160F?

After a winter hibernation we replaced the ICM/coil recently and the issue remains.
Fuel pressure still good, spark ok, can hear injectors firing with stethoscope.

If it's not an ECM or related harness issue, maybe something is throwing the timing when hot?

Cheers,
Click to expand...

I have the same engine and the exact same issue.
My local Mercruiser mechanic checked , iac valve, fuel pressure, injector leakdown and on and on...
my boat only does it a couple times in the season but when it happens it horrible.
I seen where others have mentioned full throttle or even a quarter throttle start.
That has worked sometime but not always.
I have also unplugged the fuel pump and had it start. i think it's a flooding issue.
when home after it wouldn't start hot oneday i started it on the trailer.
looked like tons of fuel ciming out of exhaust.
i called Mercruiser and they only directed me to dealer.
Last time it was $2K and no answer.

Please help if you get an answer.

Thanks Gord
 
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