Thread: E85 very rough idle.

Hello all,

I just converted my 07 supercharged Grand Prix to e85. I installed the pump and 60# injectors. Problem is very rough starts and really rough idle. It drives perfect and has nice power. I don’t notice the issue under driving acceleration. It is 70* here so not really a cold start. I’m not sure what’s going on. Does anyone have any suggestions on what is causing this????

How did you tune for e85? I'm guessing you just need more fuel but can't say without seeing logs. There are tables for startup that you can add fuel. We'll, yours probably has more tweakability than my 01. I had to really richen it up to get it to start right up, even cold starts on warm days. U hav wideband?

I figured it was a tune issue.

I set stoich to 9.67, IFR changed for injectors and aslo open loop vs coolant temp. here is a link of my tune. Any help is appreciated.

Transfer - Dropbox

That might be your problem. I think changing stoiche to 9.67 is not the best way on these pcms. It effects other tables as well that you might have to change. Best way for me was basically only changing a table for injectors, I think it's called offset? From 1.00 to 1.30 after changing IFR, then all u have to do is tweak the MAF table. I'll have to double check when I get home.

Edit: I think it's injector scale. Btw, there's a really good e85 tuning guide on this site. Think it's a sticky.

Thanks Bandook! I will start over again and follow that way. Thanks for the suggestion. I will let you know how it turns out.

question, in the "Defacto Guide" it says only to change the injector skew(cylinder gain). Is this correct. Should I also adjust the IFR? 33/63= 0.5238. do I multiply positive (x 1.5238) or negative (-1.5238) I am having a brain fart. Thanks for the help. i probably should have posted this in the tuning forum. :-/

Yeah, gain... couldn't remember. For IFR, I can't remember exactly how I got mine. I read so much trying to figure out the best values to use. But since there are no exact numbers to be found for these injectors, you basically multiply your IFR table the percentage that the 60's are larger than what u have. Then you can tweak the MAF table from there. I really don't think it has to be perfect. Don't worry about the other injector tables unless you know how to calculate those. If going from 33 to 63, is basically 48% bigger. So maybe start by multiplying by 1.48xx. If your skew is 1.30 or 1.28 or whatever and you only changed the IFR and your wideband shows terribly rich or lean, then I would multiply your IFR by 5% until it looks closer to stoich, then start tuning MAF.

That's just my way, not saying it's the best. Everyone has their own way on this platform, but I will link you to a really good guide for tuning real quick. I can now take a gnarly tune and get it real close with just a few edits, with this guide.

Here is the link. I see you are already on the hptuner forum. Good luck getting much help there, lol. If you don't have a small block you won't get much attention. But this guide is the simplest and quickest I've found and is very easy to follow. If you have any questions just hit me up.

Thanks a ton for your help. I took your advise and changed those two parameters. It worked great. I changed the gain to 1.225 and multiplied the IFR by 1.5238 (33/63) the trims were within 4% of zero. so pretty much dead on.

Originally Posted by bandook

Here is the link. I see you are already on the hptuner forum. Good luck getting much help there, lol. If you don't have a small block you won't get much attention. But this guide is the simplest and quickest I've found and is very easy to follow. If you have any questions just hit me up.

HPT forums suck!!!! Zero help there and outdated information. Once in a while 5FDP pops in and helps.

Nice! Time to drop that pulley! You could easily run a 3, if not a 2.8.

I dunno anything about going by E85 stoich values. Did you adjust the other tables to same stoich? But I think you should take your timing way down before and work on your fuel, then slowly bring timing in. If you use that guide i linked i bet you get your trims locked in at 0 wot. But yeah, being too rich can cause knock. You don't want to enter PE and be adding or subtracting fuel.

Nice. Are you going to pulley down now?