Cobaltchat.com

Hi,

This is such a great source of information to solve issues or point people in the proper direction, so I wanted to tap into the knowledge base. I have a 2007 220 with the 8.1 GXI. Has been running great but suddenly down on power. Was out for a drive at normal speeds and then went into a larger cove where we were just moving along at trolling speeds. When I went to get back on it, the engine was lagging for sure and slowly got up to speed but something clearly amiss. Sound was a little off but no smoke or other tell tale signs, gauges looked good, so restarted a few times to see if might clear but didn’t. Ended up bringing it back to the dock and it visually checked out.

As a first course of action, I changed out the plugs as these hadn’t been done in 2 years. Went with the NGK TR55GP gapped to .060 (add or subtract a 0 + fuel filter was just changed in the spring, as was the impeller). A quick test drive showed that this surely helped but I didn’t have time to take it for an extended run. Fast forward 1 week and I was able to take it out to see if all ok. The acceleration was much better but not what the 8.1 should have. Could only get about 4600 rpm's and a GPS app said 49 mph, so some power missing somewhere.

Any ideas? Coils? There is a low and high side so maybe the high side isn't working and only getting full output from 7 of the 8 at the top end? Fuel filter clogged? I found a post online about a Fuel Anti siphon valve from the tank that can collapse causing loss of high rpm's.

I do most of my own work on cars that have ranged from high rpm 4's (Acura's, Honda's, VW's), Turbo Boxer 4's (Subaru), V-6's (Honda, Audi's), but sadly, never a V-8. So why wouldn’t I want to jump right in and get a Big Block? Each has their own unique sounds, vibrations and challenge points, just havent had enough time with the GXI to get a handle.

Thanks in advance for your advice and consultations.

New plugs fixed my similar issue. I could also feel a 'miss' while idling. You could throw some new plug wires at it, but you might want to have it scanned so you arent doing the parts cannon.

Big Block Boys, where you be?

Does anyone know which interface I would need to hook up a scan tool? I have auto scan tools (VAG-COM) but clearly no OBD port on the VP.

Rinda makes a scan tool that's a fair bit cheaper than the Volvo Penta one, but still not cheap in any absolute sense. Different adapters are still needed for different vintage engines, so make sure you get the right one.

First thing I would be checking is fuel pressure.

Having a Rinda is not a bad thing...I have one and have detected that I had a bad coil in my present Cobalt and an under temp condition which was a stuck open thermostat in my outboard powered pontoon.

Never heard of a high and/or low side of a coil unless you are just talking primary and secondary windings

Bruce, you are correct about the coils being primary and secondary, vs high low.

Anyone have info on aftermarket coils for the 8.1? I am sure the VP units are crazy dough, and being a GM engine, has to be a cross reference for a GM coil.

Canterbury wrote: ↑Thu Sep 07, 2023 9:22 am Bruce, you are correct about the coils being primary and secondary, vs high low.

Anyone have info on aftermarket coils for the 8.1? I am sure the VP units are crazy dough, and being a GM engine, has to be a cross reference for a GM coil.

I would stick with a marine VP one if that is the issue.

Although, I've often thought since my lawn mower is air-cooled and so is the airplane, are parts interchangeable?

A quick follow-up on this issue as well. Wasnt a coil problem after all, but ended up being a combo of the plugs needing to be replaced and a bad plug wire. I replaced both of these and back to normal. Purchased the coil but never even took it out of the box so will return. Thank you all for your responses, a great community with a plethora (my 25 cent word for the day) of knowledge.

Great follow up Canterbury. Enjoy the lake again!

Glad to hear it worked out. I'd probably just keep the coil as a spare.