I've noticed when datalogging that the cruise BLM's and WOT O2 mv's seem to change with the ambient temperature even when the engine operating temperature is in the 180's. When it's cold out I'm lean, and when it's warmer I'm not so lean. The daytime temps right now swing from 60's one week to 30's and 40's the next. So I'm wondering, should I wait for more moderate temperatures before getting way deep in the tune? I'm figuring that if I tune during 50 degree weather then when it's summer I'd be off again. I don't want to be chasing BLM's and such all over the place. If I tune to ambient temps in the 70's then the computer can adjust for summer/winter. Any thoughts?

 

wish i could help, but I have been chasing the same issue for 2 winters now, I've almost accepted that I would use a summer tune, and a winter tune. , but I'm not a quiter, it's not part of my core values, so I keep trying to figure it out. lol

 

The maf is air temp related, remember the hot wire and air flow cooling. BLM's
will float day to night and summer to winter. +-5 is not uncommon.

If you are running the wells type with the circuit board/heat sink. they can be more temp sensitive than the Bosch.

I seem to remember Rbob or Grim Reaper adjusting the intake temp table, to stablize the blm.

Do not remember which bin/ecm or how. CRS Been reading posts for six months. So much knowledge and so small of a brain.

 

RednGold you out there? Care to chime in?

 

I'm on a engine testing trip, and melting spark plugs in a methanol engine (trying to figure that one out still). Gotta love arriving on the scene halfway through a damaged engine. Hope the problem was caused by the lack of oil during the first few minutes when they first installed it. Or, by a warped block or cracked rings from when the water pump failed at 6000 RPM. Or perhaps something from the broken exhaust valve damaged the piston. After watching the compression drop a little (normal 12 bar, then 10 bar), melting a few plugs (even when run at 11.5:1 AFR), melting some aluminum to the plugs (during sustained >5000rpm testing), and finally now the compression is 3.5bar. Should be ring damage overheating the piston. Methanol is 119octane or so, so I don't think it knocked to death. Maybe some preignition from an already overheated piston, though. Or perhaps the exhaust valve is glowing... If another plug fails on the new engine, I'm going to go a step a colder on them.

Anyway...

The only other thing I'm thinking of than a MAF issue is a Purge control issue. When colder, less purge vapors will come from the fuel tank. When warm more. The fuel RVP will probably be specified for the colder weather, and when warm will vaporize much more easily, and need to be purged.

 

I currently have my purge can disconnected to eliminate the possibilty of a vacuum leak there.

Ok maybe this is a stretch...

I modded my MAF (x-screens/fins) so the reported flow is less than the actual flow. So, some air is "leaking" past the meter, if you get my drift here. When the air is cooler and denser, a greater "mass" of air is "leaking" past the meter. Conversly, when the air is warmer and less dense, there is a lesser amount of "leakage" past the meter. Could this explain why I observe a more lean condition when the ambient air is colder?

I experiance an overall lean condition at cruise and wot. Cruise BLM's are in the 132-140 range and O2 is 850-869 wot. Not bad really and I'm planning to adjust the injector constant, but believe I need a little tweak in the MAF tables too.

Should I stick with changing the injector constant and leave the MAF tables alone?

 

It has been recomended that when the screens and fins are removed it is best to reset maf tables.

Do a search and learn from the past.

 

How much difference are you seeing from a cold day to a little warmer day?

I've never tuned the MAF setup in cold. Left the country when I was just getting going into the actual tuning on that car, but it was basically stock too, with everything connected. So, basically I'd be speculating based on my other experience in EFI.

The MAF was theoretically designed to automatically compensate for air temperature differences. Not sure how accurate it is. I don't know if it compensates for humidity very well, but I don't think the humidity will affect it more than a percent or two in the temperature ranges you're dealing with.

You'd probably be fine with adjusting the injector flow rate to compensate, as it's probably a general % difference when you increase the effective "diameter" of MAF. The flow readings wouldn't be accurate anymore, but it's just bytes in a chip that are "converted" to show an engineering number. You can probably counter it with a change to the LV8 scaler, to get the LV8 back to correct, in order to make the spark lookup normal again.