Jump to content

Fuel Temp AFR Impact

Brody Walker

Recommended Posts

G'day legends,


I have a G4+ running my Rb25det neo setup on flex fuel using the modelled fuel mode. The problem im facing is my AFR's lean out after a heat soak. I have 2 logs, one was the first drive of the day with AFR's a bit rich, 2nd was after the car sat for an hour or so & the day warmed up resulting in lean AFR's.

I suspect this is due to my fuel temperature not IAT/charge temp. The reason for this is I have compared 2 identical spots in the logs & the the difference is fuel temp, see below

Log 1 (no heat soak)

  • RPM: 2019
  • Lambda: 0.978
  • IAT :43c
  • ECT:90c
  • Charge Temp: 44c 
  • Fuel Temp: 47c
  • Inj Eff pulse width: 1.084


Log 2 (heat soak)

  • RPM: 1930
  • Lambda: 1.088
  • IAT :44c
  • ECT:88c
  • Charge Temp: 45c 
  • Fuel Temp: 59c
  • Inj Eff pulse width: 1.070

I also noticed the higher my fuel temp was the leaner my AFR's got. I stopped the log but fuel temps got to 63c whilst in my driveway & AFR's went to 17:1. This issue doesn't seem to happen when I have e80+ in tank, only when the E% is lower which was E34 during this drive. I have twin walbro 460's in tank running all the time which I know causes fuel to heat.

The question is, any other thoughts on other causes for this or have I got it right? Then is it possible to build in a fuel temp correction map? 

Map uploaded, can send logs across too if needed. 

Idle tweaks 03-01-24.pclr

Link to comment
Share on other sites

maybe you can upload the two logs on google drive or dropbox for example.

from the data you posted, it maybe be due to injector non linear operation (what injectors are in use?)

or also due to different MGP value (cold engine most likely higher MGP) leading to more air but somehow commended IPW is about the same

Link to comment
Share on other sites

Thanks for your help. I'm using Bosch 2200 INJ-139 injectors.

The MGP value is the same in each of those examples. The cell on the VE map is the same cell for each log.

Log files are uploaded here:


Link to comment
Share on other sites

it appears to be the injectors Adam refers to as bosch CNG injectors, and they seems to be fiddly (and big!) so likely some variation there too.

less problem with e85 because more volume gets injected and you are likely less in non linear injector zone. 

I would rather vote to be an injector "issue" than fuel temps. gasoline beeing a mix behave maybe differently in those CNG injectors von temps differs

Link to comment
Share on other sites

  • 6 months later...

Did you ever figured out if that was your injectors or fuel temperature? I have exactly the same problem running FIC 2150 injectors (bosch injector) and the longer I drive ( the warmer fuel temp) the leaner afr I have on cruise and wot. I made Main fuel table overlay and put fuel temp in axis to add fuel when fuel temp is warmer. Seems to work but no perfect. I am wondering if my injectors might do this? Thanks!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...