I understand that, but the fact that his tuner is saying, "it's the fuel pump" when in reality, even if it is the fuel pump it is due to the tune, is unsettling. I'm already skeptical of the tune from the other comments. 13.2 AFR @ WOT? I don't have much experience with DI, so I may be worrying unnecessarily, but on any other application that is LEAN. Before anyone tells me, "e85 is different" ask yourself first if you understand that widebands read in terms of lambda.

 

Ok, I see what you are saying, and I agree with you. It is very unsettling to not be able to see what your car is doing. The 13.2 AFR was bothering me too but I don't know much about the cobalt so I assumed that maybe that was normal for a turbo cobalt on e85 (I'm only targeting 12.1 to 12.4 max on my car which is DI as well). If he is running to lean an afr at WOT then I wouldn't doubt that there could be some KR present which would deffinitely be causeing a demand for more fuel when it happens. Also, I don't see many (if any at all) other turbo cobalts maxing out fuel pumps.

 

Unless you go WAY too far on the timing, it is impossible to make a DI Cobalt knock on E85. On the dyno, we found that you can advance the timing PAST MBT and there's not a lick of KR.

What does happen on the DI Cobalts on E85 is the HPFP (high pressure fuel pump) gets run past its capacity, which causes a drop of fuel pressure at the rail. The ECM compensates by lengthening the pulsewidth, which can lead to injection window misfire. This is where the ECM is still trying to inject fuel at the same time it is trying to ignite the mixture. This is analogous to peeing on a fire as someone else so eloquently put it once. Once injection window misfire sets in, the combustion quality is terrible, and this can cause what appears to be an enrichening of the mixture via a wideband.

The DI Cobalts run AFRs in the *14s* on the stock tune. We richen them up on gasoline to help stave off knock, but again, because knock isn't a problem on E85 we can safely run leaner mixtures (high 12s - low 13s). They make the best power in the 12.8 - 13.5 range on E85, based on my dyno experience.

The rules are all different here. Very different from tuning port injected motors.

 

Exactly, there is zero extra power to be made beyond 12.5 in such an application and it is unsafe. I don't understand what the point of a 13.2:1 target AFR is and imo it's likely the source of your problem and future potential problems. I'd recommend getting a dyno or street tune rather than a mail-order tune. No offense to your tuner, but it sounds like even if he is the best balt tuner ever, something isn't right with your tune specifically.

Edit: didn't see your response before my post vince.

 

the 13 afr's are fine for the di cobalts on E85 because thats where the peek power out put is, and at zero kr... he just informed me that my car has no kr at all and that was really my only concern.... the "sweet spot" for power on E85 is about 20*, timing wise, and on 93oct you can only get about 13* if your lucky and thats about to fall off the edge into kr....
the capibilities of E85 are completly different than that of regulatr 93oct, that difference allows for more timing and a leaner mixture but without knock

so end the end all i need to make peek power is a better hpfp.....

 

this isnt a "mail-order" tune....i log everything and he see's how the car responds just as if he was logging it him self in the passanger seat..yea i have to send the log to him via "emial" but that doesnt change that he gets exactly the same info as he would as if he was in the car....
how do you hink he got to where he is without a dyno?? of course he has his own dyno that has been used countless times in finding out just what our cars can do..

 

I prefer the term "remote tuning". Lol

 

trifecta was the only tuning solution i went with when i had my cobalt hands down

 

this^^ its not even close to mail-order....
no can tune at all, all custom tuning which is why he has so many faithful customers imo
didnt say he was the "cobalt tuning god" but he knows what hes doing....

 

Its still a street tune though. I would like to see a cobalt on the dyno having the AFR increased a little at a time to see where the peak is before it stops gaining power. An afr of 14:1 is very lean and seems to be pretty risky at WOT.
Not questioning his abilities, just curious to see for myself as our cars are similar but what works for the cobalt (as of right now) does not work for the speed when it comes to tuning...

 

thats the thing alan, his has been on his dyno and that how he knows what he can do with the tune on E85 cause there has already been experimentation on his own dyno at his shop...

 

Who said anything about tuning to 14:1? That's what the stock GM tune runs on these. The engine can take it (presumably because it is DI), but they don't make best power at 14:1 (not even on E85). I figure GM did that for emissions or economy reasons.

 

You said it runs 14 afr stock.I'm not doubting you cause I don't know. I'm just saying that sounds very lean for a WOT afr. Stoich is 14.7:1... Were you talking about WOT or part throttle cruising?
I'm really interested to learn anything I can about the turbo cobalt as it could help to shed some light on some of my own tuning issues.

 

On the stock tune (at WOT), it runs at the richest .87 lambda and at the leanest .95 lambda (which I guess is technically 13.965:1 assuming a stoich of 14.7)

It of course runs stoich during idle, cruise, etc.

 

What allows the cobalt to run so lean?

 

To be clear - this discussion pertains only to the LNF (DI Cobalt).

Why can the LNF run so lean? Who knows for sure, you'd have to ask a GM engineer, but it probably has to do with it being DI.

However, other DI engines from GM don't like to run that lean. The V6 Camaro which is a 3.6L DI engine likes to run in the high 11s / low 12s for best power.

The LNF doesn't like running that lean, either, if you turn up the boost.

 

nice runs!

 

thanks man itll be better with me and the cobra next time

 

Hmm... My car is DI turbo 4cyl like the LNF and it runs pretty rich. Infact, it likes to run in the 10's on stock tune. Tuned we run around 11.76 to 11.8 and with meth, 11.9 to 12.1. E85 is still mostly unproven and I need to do some reading to better understand the difference between the two fuels and the difference in tuning for them.

 

Yeah, it could have more to do with the engine design itself than the fact it is DI by itself. Really all we can do is tinker with them and see what they like, and what they don't like.

 

ive never seen you in the vs section vince what are you doing here lolz

 

My attention was called to this thread so I jumped in and made some clarifications. Lol

 

dosnt anybody use the search button, it has been concluded that on the cars the pump is a hit or miss.

 

What do you mean by hit or miss? There is always a reason for any occurrence, just a matter of finding it. No offense to vince and I'm sure he's perfectly accurate in his answer, but just trusting tuners without other input and discussion when there's a problem is what leads to blown motors and crying owners. Thanks for clearin' it up with info vince.

 

What he is sayimg is that every cobalt is different. Some rum out of fuel on e85 some can run it. some cant even rum e47 its differemt car to car and how each hpfp responds.