5.0 GXi Rough Idle

scfdbc9

Seaman Apprentice
Joined
Jun 15, 2021
Messages
35
I have a 5.0 GXi that was repowered towards end of last summer. Since getting it back we have chased a rough idle at first crank and/or difficulty on a warm restart. Would usually require clear flood on throttle to start. From there, once idled it would stay at idle and run as expected all thru throttle range. After doing some research we have completed the following:

1. Replaced IAC: No noticeable change
2. Replaced injectors and plugs: Several original plugs appeared to be fouled and definitely were wet and had a smell of gas when pulled. This was after boat had been sitting several days and had not been cranked prior to plugs being pulled.
3. New distributor cap and rotor
4. Checked fuel pressure at rail and stays 55psi
5. Found corroded pigtail on fuel pump, cleaned and applied dielectric

Boat will now start and idle as expected for about 10 secs . At that point it will begin to idle lower as if about to stall and will have a shake to it like a beefed up cam. Sometimes it will stall out when throttle is applied, other times it will take the throttle after which it will idle slightly better and run as expected through all throttle ranges.

After letting it sit for a bit after the described rough start/idle, you can crank it and it idles perfectly as if no problems at all. No shaking, just smooth idle.

My nearest Volvo mechanic is 2 hrs away....any thing I'm missing or suggestions to try?
 

Nheels

Petty Officer 2nd Class
Joined
Mar 8, 2021
Messages
126
Do you know what the pressure is in the low pressure side of the fuel pump? Any whining coming from the fuel pump?
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,348
Was this replacing the exact same engine before it ? Was the ecu from previously used ? I’d check the injectors were doing what they should and that it’s not running rich thinking it’s cold too. Check the plugs for water perhaps too. In case your risers or manifolds are slightly weeping in there. Check your plugs are iridium too.
 

scfdbc9

Seaman Apprentice
Joined
Jun 15, 2021
Messages
35
Thanks for all the replies… honest mistake on my end, the engine coolant temp sensor was left unplugged from the motor swap…motor is a champ now.
 
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