boatjohn75
New member
I have a Mercury 20 HP EFI to which I decided to add some automotive sound deadening insulation (4-5mm thick) on the inside of the top cover. After this installation, the engine stumbles and loses power when running for about 30-45 minutes at higher settings (e.g. 4500+ RPM). If I let the engine idle or stop for a while, or If I remove the cover (within minutes, and can run hour+ without cover), everything is back to normal and it runs fine.
maybe or maybe not, since I don't remember using it this long when it's hot before)
The insulation is tight only near the intake manifold (where it rubs against the plastic housing a bit). Looking at the engine diagram (https://www.boats.net/catalog/mercury/outboard/20hp/20hp-efi-0r833820-up/intake-manifold) it looks there's a throttle position sensor and air temp/pressure sensor in that area. I'm wondering if the insulation is causing some of these to overheat and read erroneously (and causing the ECU to reduce power), or whether they're going bad. I haven't run this engine for this long at WOT before, so not sure if it's the insulation or the cover in general.
Checked the fuel sytem (had a bulb issue before, but that's not it this time, venting is fine, fuel is fresh) and all seems good. I'm trying to decide whether to remove the insulation or replace the sensors (or something else?). Has anyone else run into similar issues in the past? Here's a video (note: this is happening without touching the throttle):
maybe or maybe not, since I don't remember using it this long when it's hot before)
The insulation is tight only near the intake manifold (where it rubs against the plastic housing a bit). Looking at the engine diagram (https://www.boats.net/catalog/mercury/outboard/20hp/20hp-efi-0r833820-up/intake-manifold) it looks there's a throttle position sensor and air temp/pressure sensor in that area. I'm wondering if the insulation is causing some of these to overheat and read erroneously (and causing the ECU to reduce power), or whether they're going bad. I haven't run this engine for this long at WOT before, so not sure if it's the insulation or the cover in general.
Checked the fuel sytem (had a bulb issue before, but that's not it this time, venting is fine, fuel is fresh) and all seems good. I'm trying to decide whether to remove the insulation or replace the sensors (or something else?). Has anyone else run into similar issues in the past? Here's a video (note: this is happening without touching the throttle):