GOLFMK8
GOLFMK7
GOLFMK6
GOLFMKV

1.8T, Cant find 93 fuel anymore in my area, misfiring on bad gas, can I mix 91 and e85?

MK7AlltrackBlack

New member
Location
Edmond, Oklahoma
Car(s)
2017 Alltrack
I have a 2017 Golf Alltrack with a IS38 swap, unitronic stage2 plus, and stage 2 Unitronic TCU tunes....with this tune it calls for 93 oct. I live in OK and the last gas station chain around here that had 93 oct no ethanol (which my car loved) stopped carrying it... There is one other place I know of that has 93 gas with ethanol. When I tried it, my car started misfiring under hard acceleration and the epc light came on. Maybe it was a bad batch of gas there and had nothing to do with the ethanol but I havent been back since. Since then locally I have been using 91 no ethanol with octane booster and it seems to be alright most of the time, but honestly I am hesitant to really drive aggressively with it so I dont know for sure... Recently took a long road trip over the holidays (900 miles to GA one way) and was able to get 93 w/ethanol once I got further east. But I ran into the problem again...car misfired when I had to suddenly hard accelerate on the Interstate, car misfired, epc light came on and had to pull it over to stop and restart engine, ran ok after, just had to take it easy. Coils, plugs, and turbo were all brand new about 7 months ago when installed and car ran great for about 3-4 months up until I started putting in the different gas...

Ok, so here's my question, barring any issues with the plugs, and coils which I need to rule out as maybe contributing to the issue....can I mix 91 oct and say 2-3 gallons of E85 (if I can get it) to get to 93 and run it in my engine without causing anymore problems? Will it hurt it if the mixture ends of making it higher then 93 octane (say for some reason like 95 or 96 oct)?
 

Dog Dad Wagon

Autocross Champion
Location
Innnnn West Philadelphia...
Car(s)
19 Alltrack 6MT
What Jim said. Lots of people run E30+ on fueling systems that aren’t upgraded for ethanol resistance. I believe all VWs are flex fuel ready since VWs are sold worldwide and some countries use more than others. Pretty sure Brazil has like E20 in their “regular” fuel
 

MK7AlltrackBlack

New member
Location
Edmond, Oklahoma
Car(s)
2017 Alltrack
Thanks for the info, is there a conversion chart or something for E85 and 91 that determines how many gallons of each you will need to get to a desired octane level? To answer your question dtfd the unitronic tune for an IS38 swap on the 1.8T is mapped for 93 octane so I am told. You can use 91 but apparently its doesnt adjust to the lower octane properly and causes problems under heavy acceleration...which in my case meant misfires...I am not an expert by any means at this stuff but thats more or less the problem..
 
Last edited:

Dog Dad Wagon

Autocross Champion
Location
Innnnn West Philadelphia...
Car(s)
19 Alltrack 6MT
Thanks for the info, is there a conversion chart or something for E85 and 91 that determines how many gallons of each you will need to get to a desired octane level? To answer your question dtfd the unitronic tune for an IS38 swap on the 1.8T is mapped for 93 octane so I am told. You can use 91 but apparently its doesnt adjust to the lower octane properly and causes problems under heavy acceleration...which in my case meant misfires...I am not an expert by any means at this stuff but thats more or less the problem..
“E85” =/= 85% Ethanol. It can range from E40-E85, usually somewhere in between the two. You need an ethanol sensor to know what your E% / effective octane is
 

tigeo

Autocross Champion
Run some E - it will sort out the Unitronic fuel quality drama - try 2.5 gallons to start. This is not a plug issue, it's a fuel quality issue. Uni's tunes are v. sensitive to it b/c they use quite a bit of timing advance vs. many tuners (I see upwards of 15 deg at redline with the right fuel vs. 6-8 or so for many tuners but of course less boost) and under hard acceleration this can be an issue where you are getting a lot of KR. I run 2.5 gal of E85 (actually E80 here) with 93 in my IS38 4Mo GSW - runs like a top. If I don't, I get the same issues in the winter mainly...summer blend 93 seems to be fine but e is easy to get and it runs so good with it I usually run a blend all of the time. Remember, Uni shows E10-E20 for this tune on their site.
 
Last edited:

tigeo

Autocross Champion
Thanks for the info, is there a conversion chart or something for E85 and 91 that determines how many gallons of each you will need to get to a desired octane level? To answer your question dtfd the unitronic tune for an IS38 swap on the 1.8T is mapped for 93 octane so I am told. You can use 91 but apparently its doesnt adjust to the lower octane properly and causes problems under heavy acceleration...which in my case meant misfires...I am not an expert by any means at this stuff but thats more or less the problem..
It's not that senstive - just start with 2-3 gallons of the E85 (whatever it is) and go from there. There are online calculators and you can get a test kit (a small graduated cylinder) but honestly, I've been doing this for 2 years, I just put a few gallons in and drive it. Winter blend fuels seem to be the main culprit which can have increased susceptibility to detonation.
 

tigeo

Autocross Champion
If you reach out to Uni (John), I believe they can get you a 91 IS38 tune with a less aggressive timing map...I'd just try to run a few gal of E.
 

MK7AlltrackBlack

New member
Location
Edmond, Oklahoma
Car(s)
2017 Alltrack
Lots of great info, thanks tigeo. I am going to give the 93 and E85 blend a try, maybe getting a hold of that 91 IS38 tune would come in handy as well since I plan to do some more travelling this year. I wonder what the power differences are rated... Two questions....with the 93 and E85 blend you use....now this might be a stupid question but Im assuming it doesnt matter if the 93 is already 10% ethanol? and I noticed your plug gap is .028 with similar UT tunes (or maybe not). I have Denso IKH24's in mine that have a .031 gap that came recommended with the IS38 swap for my car, but the OEM plug gap on the 17 Alltrack is .32....the Sportwagen has the same engine right...whats your take on .028 gap?
 

tigeo

Autocross Champion
Lots of great info, thanks tigeo. I am going to give the 93 and E85 blend a try, maybe getting a hold of that 91 IS38 tune would come in handy as well since I plan to do some more travelling this year. I wonder what the power differences are rated... Two questions....with the 93 and E85 blend you use....now this might be a stupid question but Im assuming it doesnt matter if the 93 is already 10% ethanol? and I noticed your plug gap is .028 with similar UT tunes (or maybe not). I have Denso IKH24's in mine that have a .031 gap that came recommended with the IS38 swap for my car, but the OEM plug gap on the 17 Alltrack is .32....the Sportwagen has the same engine right...whats your take on .028 gap?
No stupid questions dude. Yes, the 93 is ~10% ethanol and that's factored into my calc as well as assuming the ethanol "flex fuel" that Sheetz sell is 81% which is the max they say, it's really a range so could be less. There are online ethanol calculators you can play with but 2-3 gallons just works and there is some trial and error, you aren't going to blow up your car running a little like this. I run the same IS38 Unitronic tune as you (for 93) and run Ruthenium plugs at their stock gap (0.028"). I've run stock plugs, Denso IKH24s, and NGK "RS7s" - all stock gap and all worked/no discernible differences between them. My personal opinion is that folks are too obsessed with spark plugs/gaps and that it actually doesn't make that much of a difference. I will post my spark plug table for you in a bit. The stock plugs come gapped 0.028"-0.032". Yes, Sportwagen and Alltrack are the same car more or less and have the same engine. I'm a big fan of the Ruthenium plugs from NGK - they are cheap ($8 ea @ Rock Auto) and the stock heat range. I don't think we need the colder plugs unless *maybe* you are tracking it.
 

tigeo

Autocross Champion
plugs.JPG
 

MK7AlltrackBlack

New member
Location
Edmond, Oklahoma
Car(s)
2017 Alltrack
Interesting, I had rutheniums in my car before the swap but opted for the one step colder Densos because they were "recommended" with the IS38. If only I knew then what you are telling me now...oh well, someone upsold me, no biggie I suppose. I still have the NGKs actually sitting in the box, they only had a few thousand miles on them. Anyway, Im looking forward to burning through what I have left in my tank and then putting in 2-3 gallons of E85 and the 93 w/ethanol. My car really hasnt been the same since they stopped carrying that 93 no ethanol around here. Do they have a private email option on this site? You mind if I contact you from time to time about your setup and pick your brain a bit? Also I am going to call John over at unitronic tomorrow to see what the deal is with the 91 is38 tune. If need be for any future cross country trips would be nice to have the option to use the 91 tune if necessary (i use uniconnect). I appreciate the info, Thanks
 

tigeo

Autocross Champion
Interesting, I had rutheniums in my car before the swap but opted for the one step colder Densos because they were "recommended" with the IS38. If only I knew then what you are telling me now...oh well, someone upsold me, no biggie I suppose. I still have the NGKs actually sitting in the box, they only had a few thousand miles on them. Anyway, Im looking forward to burning through what I have left in my tank and then putting in 2-3 gallons of E85 and the 93 w/ethanol. My car really hasnt been the same since they stopped carrying that 93 no ethanol around here. Do they have a private email option on this site? You mind if I contact you from time to time about your setup and pick your brain a bit? Also I am going to call John over at unitronic tomorrow to see what the deal is with the 91 is38 tune. If need be for any future cross country trips would be nice to have the option to use the 91 tune if necessary (i use uniconnect). I appreciate the info, Thanks
Sure there is a private message function.
 
Top