I agree.

If the OEM recommends 89 octane, but says that 87 is acceptable, I would (and do) run 89. Does Dodge really care if you have piston ring and land failures at 120K miles?

I end up plugging in and using my Superchips to show real time data logging when I drive anywhere that takes more than 10 minutes or more. I run the perforamce tune and 91 octane, and data log the ignition retard. I am still amazed at the number of times I see the ECU pull back timing to keep the engine out of knock.

Dodge already has the Hemi's from 06 on over a barrel due to the constraint of running 5w-20 for the MDS system, rather than 10w-30 oil. 5w-20 is recommend for my '05 (non-MDS), but I run 10w-30 because I want the engine to last longer, rather than save a few pennies in gas milage.

Give yourself a break and run 89 octane.

 

I doubt an octane change will effect MDS.

As far as running 87 or 89. I had an 04 with the 5.7L( no MDS )and now have an 08 with the 5.7L( MDS ). No major mods just full synthetics all around, exhaust, and CAI( 04 ). I do some towing now and then( duck boat ).

I have tried numerous times - NUMEROUS - upping from 87 to 89 to try and see better MPG. Just does not happen for me. I am talking resetting the computer and running 4-6 tanks to give things time to adjust to the different octane rating. Just ZERO difference( hand calculated MPG figures not overhead ). I also notice no change in performance.

For me 87 works just fine. I know many claim improved performance with 89. For me it is just not there and not worth the 20 cents extra p/ gallon.

 

My MDS will stay on while coasting (basically until I come to a stop). I know 100% that it will come on in 2nd gear and higher, not 5th only.

Your problem is interesting, and I have absolutely nothing useful to offer from a troubleshooting perspective. However, I would like to know what you eventually find to be the root cause.

joe

 

Read it again. "All engines (except 5.7L engines) ... octane 87 ..." "The 5.7L engine ...The manufacturer recommends the use of 89 octane for optimum performance."

The Fram filter is not likely the cause. A PCM reset is worth a shot.

 

Joe, I'm glad to hear that someone experiences what I have. Now that the darn thing just won't stay in MDS at coast, it's driving me crazy.

I haven't yet reset the PCM, but I hope to have time tomorrow to do it. I'll keep everyone posted.

 

True but you left out the part before that where they say "The 5.7L is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high quality unleaded gasoline having an octane rating of 87 to 89. The manufacturer recommends the use of 89 octane for optimum performance."

The bottom line in this discussion is that "optimum" does not mean "required". As I stated I have run both to truly see if there is any difference and in my 2 5.7L Rams I have found none that was noticeable. I am sure on 87 the PCM messes with timing to avoid knock a bit with the 87 and I lose a couple HP but it is not something noticeable. Literally there has been zero MPG difference with 87 and 89.

Dodge is just not going to say it is ok to run 87 if it is not. I have heard people say it is because they know it will take a long time to do anything so it is out of warranty so they don't care. That argument does not hold up to me since the fuel recommendation has stayed the same from the start with the 5.7L in the 3rd Gen's including being there during the 7/70 and Lifetime Power Train warranty time frame. If there was any long term ill effects of using 87 in a stock 5.7L Dodge would not say it was ok to use. Especially when they are on the hook for the engine for it's life span.

Actually, they are still saying the exact same thing for the 5.7L even in the 09+ 4th Gen Rams with the redesigned more powerful 5.7L...

2011 Dodge Ram 1500 Owner's Manual
Starting And Operation
Page 440

Fuel Requirements( copy and paste from online Dodge/Ram truck site owner's manual ):
"This engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high quality unleaded gasoline having an octane range of 87 to 89. The manufacturer
recommends the use of 89 octane foroptimum performance. The use of premium gasoline is not recommended, as it will not provide
any benefit over regular gasoline in these engines."

For some 89 may be beneficial( tow a lot, serious mod's, really heavy foot, etc... ))but for the average person, IMO, 87 is all you need in the 5.7L. Certainly in my experience with my 2 it has been all I need.

No offense to anyone. Just discussing.

 

That sucks that you guys have to pay more for 89. Here, because they add ethanol, 89 is .10 cheaper than 87 and .25 cheaper than 92.

 

We only have ethanol blended fuels here( 10% ). All of them from 87 to 93 have it.

 

I'm in for my post PCM reset report.

After doing the "pull the fuse on PCM" procedure (oulined in this forum somewhere), here's what I found.

For the first 5 miles or so, MDS would not come on at all and shift patterns were "odd". Once the PCM re-learned or assimilated driving habits, MDS starting coming on but only when I had my foot on the throttle. As soon as I let off, MDS turned off.

I'm right back to where I started, so PCM reset did not work.

I'm using 5w20 Castrol conventional oil with Fram oil filter. The only change to the truck was my oil change about a month ago, yet this problem started last week.

I really feel like some small thing is causing this to happen. My oil is super clean, filled properly, and correct weight. Engine temperature doesn't seem to matter.

I'm at such a loss as to why this behavior has changed. It's driving me crazy. My next fill up should be in a day or two, and I'm going to see if my MPG has changed any now that I can't coast in MDS.

My last fill up was at 15.3 according to my mileage app. Let's see what we get now.

I still welcome other suggestions to try.

 

Next thing I'm thinking of trying is to do a "key dance" and see if I pull any codes. My MIL is not on when I drive, but that doesn't mean there isn't a code stored.

As I read online after Googling, I see that sometimes cold weather than cause the computer to throw an "incorrect oil weight" code which would make MDS not kick in as much. I wonder if this is my problem.

However, I thought that by reseting the PCM by following this procedure
https://dodgeforum.com/forum/2194740-post2.html

would clear any codes. Perhaps I was wrong.

Another alternative is to have a mechanic friend of mine with a Snap-On scan tool read codes from my PCM and manually clear them that way.