What octane gas to use

Have a compression test done on all cylinders and compare to what the compression should be. If there is carbon build up in the cylinder heads this would cause knock with 87 octane and would throw a code like you got.
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If this is your problem, I'm sure the dealership, if you brought it there, would recommend pulling the heads to clean everything up. That would fix the problem but would cost you big $$$$$$$. Get a can of SeaFoam and run it through the intake using the brake booster vacuum line. You can look this up on the internet. The SeaFoam will break down the carbon without pulling the heads.

I've never heard of Cataclean nor the slightly clogged cat causing this kind of problem but if you trust your mechanic then give it a try. If that doesn't do the trick get the compression test done and go from there.

I dont know how many miles you have or how often you run a full tank through but you may have gotten bad gas with excess water or if you leave the RV sit with a partially filled tank and no gas treatment, condensation can accumulate and either turn the gas bad or settle in the bottom and then mix when you start moving.
I always put Starbrite marine gas treatment in the last fill up just before I get home if I know I wont be travelling for more than a month.

I had this problem once on a previously owned rig with the Chevy 6L.

I had bought some of that rotgut 85 octane in NM at higher altitude because that was all they had and I was out in the boonies. When we got closer to home (Oklahoma) the light came on. Now, that is an altitude change of about six thousand feet decrease. I filled up with good old Oklahoma purchased 89 octane pure gas (about a 1/4 of a tank of the 85 was still in the tank) and that was the end of the problem. The engine was cutting out a bit above 60 mph. The problem stopped within five miles and never occurred again.

Now, this forum has repeatedly educated me on the fact that lower octanes at higher elevations are just fine. I only know what happened to me. Normally, I always filled this rig with 87 octane containing ethanol and never had a problem the entire time we had the rig. I just always assumed that when I mixed the 85 and 89 pure I made an acceptable fuel for that tankful. And no, the gas cap was tight and never created a problem. That is, however, a very normal source of problems like this one.

Paul

If you haven't already, I'd recommend dumping some gas preservative in the tank, like Sta-Bil or Star-Tron.

I get 13 mpg to 13&1/2 it's only 22 ft long and driving around 60 mph. My job makes it difficult to go camping more than once a month. So it will sit until April.

Wow - to take my tank from full to 1/4 seems like all I have to do is drive it around the block once or twice. :)

9 MPG.

Friend says the catalytic converter is a little dirty and said use Mr Gasket Cataclean exhaust treatment. Use 1or 2 times.I read the reviews and they seem to be mostly positive so I will try it. The problem I have now is my fuel tank is full and will have to get the tank below 1/4 so it will be awhile before I get to try this treatment.

Yes I got the message incorrect fuel. I don't remember the code but if it comes back up I will let you know. The friend said he will put their diagnostic machine on it but since I erased the code I will wait for the check engine light to come back on. I will keep ya'll posted.

malojeer wrote:
The gas cap is brand new. I always make sure of the fuel grade I use. I wish it was simple solutions y'all mentioned but I've been told I'm snake bit. I probably consult a friend of mine who works for a dealership. Thanks for all the help

Ok - but you're hearing from us that have the same engine and run on the lower octane gas with no problems.

Did you really get a code that says you're using the wrong fuel? What's the code?