Erratic idle + Erratic power under load

[kstanton]

Hi all,

I tried searching for similar issues but, was unable to find any what were both happening at idle and under power. I took my 2004 GTX 4tec 155hp 103hrs out today and noticed that during idle it will jump between 1k rpm and 2k rpm erratically and then sometimes run smooth. Also when getting up on plane I noticed that it felt like it was bogging down but, then would randomly kick in and run normal. I have read about all kinds of idle problems but, my case seems to also include under power issues. The gas was old and we siphoned it out and replaced with new fuel. Is there anything obvious that I should check? I am trying to get it running before the 4th of july week so I appreciate any help!

Kevin

 

[kstanton]

I should also note that the old fuel did have stabil in it. I also checked it for trouble codes but, none have been registered.

 

[Michael211_2000]

I should also note that the old fuel did have stabil in it. I also checked it for trouble codes but, none have been registered.

How old was the gas? I filled my RXT up last November, added StaBil fuel stabilizer and winterized it... I didn't start it again till earlier this month (some 7 months of sleep!). It runs just fine, took it to the lake twice already and runs just as good as it did last October.

Put some Seafoam fuel system cleaner in it and run it for an hour or so and see if it doesn't clear up. Also you may want to change your spark plugs (I changed mine when I winterized it last year, so mine are new).

- Michael

 

[kstanton]

How old was the gas?

From last season. It's odd that it is off and on, I would assume if the fuel plugged up the injectors that it would be continuously sluggish. Then again I don't know much about the fuel system in this thing.

 

[Michael211_2000]

If the fuel is less than 1 year old, and you added Stabil to it, then it should be fine... maybe not quite as powerful as brand new fresh fuel, but the difference should not be significant to anybody other than a pro racer. How old are your spark plugs? They should be changed yearly when you change the oil, IMO. Also it may be that you're having an electrical problem going on, corrosion may have set in somewhere over the winter... every time we had clear dry weather, I went out and took the cover and seats off mine to let it air out inside! And still my starter relay has gone bad over the winter... grrrr! So you might want to take your battery cables loose (both from the battery and the ground wires that go to the front of the engine) and clean them with a small wire brush on a rotary tool or something. That's all I can think of.

- Michael

 

[kstanton]

How old are your spark plugs? They should be changed yearly when you change the oil, IMO.

The plugs haven't been changed but, that's the first thing we are going to try. They look fine though.

 

[Michael211_2000]

I'm inclined to think the electrical system isn't getting good power for some reason... remember the carb and ignition timing are all computer controlled, if there's a corroded terminal anywhere it could be causing power fluctuations that may disrupt the engine computer but not be noticable on the instruments.

I've no other ideas. Sorry. Good luck!

- Michael

 

[kstanton]

Thanks for the suggestions. We got it running smooth again. Replaced the plugs, cleaned some corrosion off the contacts for the plug and put some Dielectric grease on em. Put in some fuel system cleaner and ran it through the system checking each cylinder one by one to make sure it was firing. Not sure which one it was but, it's running good now.

 

[Michael211_2000]

Excellant! Have fun!

- Michael