I have a 1997 7.4L Gi, DP-S drive, that will die when I shift into forward or reverse gear.
This only happens when the engine is up to operating temperature and idling at 600 - 614RPM (digital tach). When the engine is cold, idling at 650 RPM it has no issue going in and out of gear. I tried to remove the rear prop and it has no problem at operating temperature spinning 1 prop.
There are no engine faults detected, the fuel pumps were replaced a year ago, along with plugs, wires, distributor, and IAC. For kicks I pulled the vacuum line of the fuel pressure regulator, the extra air sucked into the intake with the line off bumped the idle RPM up to 650, and the engine had no trouble shifting into gear.
Is it acceptable to adjust the throttle cable to force the Idle up to 650 RPM even though the ECM is trying to control it to 600? Is there something that I should be looking at to explain the somewhat weak idle when its at operating temperature (>130F water temp)?
7.4 Gi Dies shifting into gear
Re: 7.4 Gi Dies shifting into gear
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So glad you found us Craig O.
Those sound like symptoms of a bad idle air control valve (IAC). Hard to diagnose over the internet though.
Others will chime in shortly.
And welcome aboard mate.
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So glad you found us Craig O.
Those sound like symptoms of a bad idle air control valve (IAC). Hard to diagnose over the internet though.
Others will chime in shortly.
And welcome aboard mate.
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2002 Cobalt 262
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
&
2005 Cobalt 263
496 MagHO
(sold )
Erie, PA
Currently boatless (for now)
will fly for food
(CChat moderator)
Re: 7.4 Gi Dies shifting into gear
Thanks for the welcome!
The IAC was replaced about a year ago, and based on the checks in the service manual it appears to be operating correctly. The book suggests to run the engine, shut it down, then disconnect the IAC. Fire it up disconnected, verify it's idling At least 200 rpm higher, then reconnect and ensure it drops back to 600rpm. The IAC had no issues with this test.
I'm open to any suggestions.
The IAC was replaced about a year ago, and based on the checks in the service manual it appears to be operating correctly. The book suggests to run the engine, shut it down, then disconnect the IAC. Fire it up disconnected, verify it's idling At least 200 rpm higher, then reconnect and ensure it drops back to 600rpm. The IAC had no issues with this test.
I'm open to any suggestions.
Re: 7.4 Gi Dies shifting into gear
Have you changed spark pugs, cap lately? Fresh fuel?
Do not adjust throttle cable to compensate.
Do not adjust throttle cable to compensate.
2017 R5 350HP Mercruiser Bravo III
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
Re: 7.4 Gi Dies shifting into gear
Should be good on plugs, cap, and fuel.
I understand adjusting the cable isn't preferred, it's just 40 RPM from making it and it's really tempting.
Interested in hearing any other suggestions. The boat seems to run great otherwise. Tops out at 4,800 RPM on the high side, fires right up. No service engine codes.
I'm a little bit at a loss right now.
I understand adjusting the cable isn't preferred, it's just 40 RPM from making it and it's really tempting.
Interested in hearing any other suggestions. The boat seems to run great otherwise. Tops out at 4,800 RPM on the high side, fires right up. No service engine codes.
I'm a little bit at a loss right now.
Re: 7.4 Gi Dies shifting into gear
It's definitely odd especially since you replaced the IAC already which is what should be keeping this from happening. What was the reason you replaced the IAC a year ago...same issue?
Ever thought about getting your injectors cleaned.
Ever thought about getting your injectors cleaned.
2017 R5 350HP Mercruiser Bravo III
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
Re: 7.4 Gi Dies shifting into gear
I just bought this boat, assumed this would something easy enough to tackle myself.
The service records I have show that the complaint was hesitation when accelerating from idle.
The shop replaced plugs, wires, cap, distributor, and noted the IAC was not functioning and replaced it too. 6 months prior they put new fuel pumps in as well.
I thought about injectors but the engine seems to run really strong in all conditions except this scenario. It's strange that with a cold start up this issue isn't there. My thought was the injectors would be a more consistent issue and not temperature dependent.
Do you have a recommendation for getting injectors cleaned if that ends up being the issue?
The service records I have show that the complaint was hesitation when accelerating from idle.
The shop replaced plugs, wires, cap, distributor, and noted the IAC was not functioning and replaced it too. 6 months prior they put new fuel pumps in as well.
I thought about injectors but the engine seems to run really strong in all conditions except this scenario. It's strange that with a cold start up this issue isn't there. My thought was the injectors would be a more consistent issue and not temperature dependent.
Do you have a recommendation for getting injectors cleaned if that ends up being the issue?
Re: 7.4 Gi Dies shifting into gear
Just google it. There are a bunch out there. Typical cost is around $20/injector plus shipping.
I had low speed and idle issues with a vehicle I owned that had a little less than 200K miles on it. I just replaced the injectors and it made the vehicle run like new again.
2017 R5 350HP Mercruiser Bravo III
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
Northridge, CA
Big Bear Lake, CA
South Lake Tahoe, CA
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