Shell Nitrogen Enriched, and its boiling point

[Spawne32]

So im having an issue with my supercharged car leaning out on hot starts and missing real bad, its prevented me from getting through inspection this month so I have been going over alot of things that could be the source of the issue.

What happens is, in this hot summer heat, I can be sitting in traffic or what not, and normally the car will idle at around 13.9-14.2 AFR (which is how i have it programmed), as i sit, and the heat builds up under the hood, not really moving very fast or at all, it will slowly start to lean out...14.5..14.8...15...15.3, etc. If i punch the gas real hard, it will go back down to where it is suppose to be, in the 14's or so. I had originally thought that this was an issue with the intake air temps heating up in a stopped position after the supercharger, and the computer pulling fuel, however this is not the case, the IAT actually stays the same and the ECU does not have any programming to remove fuel based on ECT or IAT temps.

Other times I can be driving around and I will stop at a store or something for a few minutes, get back in the car, and it will be aggressively lean, 15.5 or so AFR, and have a nasty misfire.

I have replaced...

-fuel pump with a walbro 255
-fuel pressure regulator
-new maniac electric motors alternator (oem replacement, charging much better then my factory 200k one)
-upgraded ground wires from 4awg to 2awg
-heavy duty radiator and heavy duty cooling system to keep the engine cool
-new fuel filter
-reflowed solder on the main relay for dry joints being a problem

the only thing i can think of is that the gas is sucking so much heat out of the supercharger from being on top of it, that its boiling inside the rail and heatsoaking really bad, i measured 165 degrees on the outside of the fuel rail today with my tester. Im also using shell nitrogen enriched 93 octane as well, and i was wondering if that was playing a part in the boiling point being different or not. I noticed that after a hot restart and this problem is occuring that my fuel pressure will be about 3-4psi too low compared to a cold start.

I have literally gone over every logical reason why the car leans out and misses on hot starts, ive replaced a million parts, cannot figure it out, any help would be great.

I was under the assumption that gas would not boil up to 400 degrees at atmospheric but im reading now that it could be as low as 100 depending on the additives?


edit: also forgot to mention, the car is supercharged (1995 acura integra), and it runs fantastic, but it appears to be heatsoaking the fuel rail

 

[190E26FTW]

I was having some issues with my cars running funny and not as smooth when using Shell gasoline in northern california. Went back to chevron and 76 and the car is running much better. I think shell gasolines have high sulfur content or something. I forgot where I read that so maybe others can jump in.

 

[229]

I would wrap the fuel lines.

 

[gathermewool]

Why do you have it tuned so rich at idle? What are your AFR's while cruising at steady speed?

Do you have a way of logging more than just your AFR? If so, what do your fuel trims look like? Could it be an issue with your MAF sensor (if not MAP based) or your upstream O2 sensor?

I doubt pretty highly that this is related to the fuel itself, but who knows.

 

[Smokefan1977]

I too had issues with shell gas recently

http://www.bobistheoilguy.com/forums/ubb...937#Post2308937

 

[brandini]

2nd the wrap fuel lines, also if it's a really high HP car, look into a fuel cooler.

http://www.summitracing.com/search/Part-Type/Fuel-Coolers/?keyword=fuel+cooler&kr=fuel+cooler

 

[Spawne32]

its a MAP based speed desnity tuned, so its set to whatever i tell it to, all datalogged and tuned

 

[gathermewool]

Originally Posted By: Spawne32
its a MAP based speed desnity tuned, so its set to whatever i tell it to, all datalogged and tuned


I'd love to see a datalog if you wouldn't mind PMing or emailing me a link. I only have experience (limited as it is,) with turbo Subies. I'd definitely be interested in checking out your logs, too, if you don't mind. I'm still curious why you're tuned so rich at idle (and cruise, too?)

I've never experienced it, but what every one else says about the fuel heating up makes sense, in theory. Same IDC, but lesser volume of fuel; however, wouldn't your O2 feedback add fuel to compensate to keep target AFR's?

 

[Eddie]

I been running Shell 93 in my Mazda CX7 and keep long term fuel records. I have notice no change in fuel consumption compared to other major brand fuels. If there is a difference it is lost & under the the day to day driving variabilities.

 

[friendly_jacek]

Simple, drive with you hood/bonnet removed.

 

[Spawne32]

Originally Posted By: gathermewool
Originally Posted By: Spawne32
its a MAP based speed desnity tuned, so its set to whatever i tell it to, all datalogged and tuned


I'd love to see a datalog if you wouldn't mind PMing or emailing me a link. I only have experience (limited as it is,) with turbo Subies. I'd definitely be interested in checking out your logs, too, if you don't mind. I'm still curious why you're tuned so rich at idle (and cruise, too?)

I've never experienced it, but what every one else says about the fuel heating up makes sense, in theory. Same IDC, but lesser volume of fuel; however, wouldn't your O2 feedback add fuel to compensate to keep target AFR's?


If you pm me your email address I can send you a breakdown of how it works. I run on an open loop speed density tune, or MAP tuning as you may be more familar with it. I do not run a narrow band sensor so the computer will not compensate for any changes in afr, it merely sends a certain amount of fuel based on what i programmed in for that specific cell, or rpm x map.

I keep it about 14.0 at idle in PARK (its automatic) so that when i shift into drive, it puts me at a proper afr of about 14.5. Load vs no load, etc.

Theres no real logical explanation as to why the car starts to lean out really, ive checked every single electrical system, ive replaced every part associated with changes in the fuel system, etc. Only reason i raised this idea was because it was the next thing left on the list after i exhausted all the normal solutions lol if it isnt boiling, i cant imagine it having air in the system, as its sealed and not leaking, ive checked it multiple times and it will hold 40psi while cold just priming the pump for about 8 hours or so.

 

[mechtech2]

It depends on WHERE your IAT sensor is.
Are you measuring air temps at the intake on the cyl head? Probably not. And these elevated temps will cause problems like yours.

 

[gathermewool]

Originally Posted By: Spawne32
Originally Posted By: gathermewool
Originally Posted By: Spawne32
its a MAP based speed desnity tuned, so its set to whatever i tell it to, all datalogged and tuned


I'd love to see a datalog if you wouldn't mind PMing or emailing me a link. I only have experience (limited as it is,) with turbo Subies. I'd definitely be interested in checking out your logs, too, if you don't mind. I'm still curious why you're tuned so rich at idle (and cruise, too?)

I've never experienced it, but what every one else says about the fuel heating up makes sense, in theory. Same IDC, but lesser volume of fuel; however, wouldn't your O2 feedback add fuel to compensate to keep target AFR's?


If you pm me your email address I can send you a breakdown of how it works. I run on an open loop speed density tune, or MAP tuning as you may be more familar with it. I do not run a narrow band sensor so the computer will not compensate for any changes in afr, it merely sends a certain amount of fuel based on what i programmed in for that specific cell, or rpm x map.

I keep it about 14.0 at idle in PARK (its automatic) so that when i shift into drive, it puts me at a proper afr of about 14.5. Load vs no load, etc.

Theres no real logical explanation as to why the car starts to lean out really, ive checked every single electrical system, ive replaced every part associated with changes in the fuel system, etc. Only reason i raised this idea was because it was the next thing left on the list after i exhausted all the normal solutions lol if it isnt boiling, i cant imagine it having air in the system, as its sealed and not leaking, ive checked it multiple times and it will hold 40psi while cold just priming the pump for about 8 hours or so.


If you don't have any feedback, then higher temperature fuel causing a lean condition makes sense. If you were tuned with lower fuel temps, then I believe that higher temp, less-dense fuel would result in less fuel being sprayed in for the same injector duty cycle and pulse width compared to cooler, denser fuel.

With your speed density tune, are you looking at MAP, RPM and Load for your fueling maps? If so, and if like you said, there's no AFR sensor, then you have nothing to tell the computer, "hey, the fuel is hotter, resulting in a lean condition, so please add more fuel." If this is the case, then insulating the fuel lines seems like the best option. Either that or retune so while hot. I'd rather have too rich of a mix than too lean on a FI motor.

 

[steve20]

I have a Band-Aid fix for you. Install a manual override, timed override, or thermostatically controlled switch for the radiator fan. It will run when the engine is off for a specific period of time. This was a standard feature on my 87 Grand National- fan kicked on after engine was shut off for several minutes, then shut off to keep the oil in the turbo bearing from coking