low BLM numbers

[dadmomcat]

Car at idle is running 98 BLM's ( car has warmed up ) my MAF is 6. TBS at .40 and IAC is 21, 02 reading is high at 835 WOT. Car is running rich.
I have used Thrasher 93 and armstrong 93 chip, both had low BLM nunbers. no malfunction codes.

Did not record BLM numbers at WOT. What can i do to get the BLM into the right range at idle ??? All reading is from scan master.

Thanks for the help.

 

[T-top87GN]

Well, if your BLM's are low then you are runing too rich. The ECM is pulling fuel from the engine.

Post some recorded files so we can check them out, if you have a laptop based scan tool that is.

 

[PaulRV6]

But if its idling in closed loop then won't it still be trying to run 14.7 A/F ratio? Unless it is trying to pull out more fuel than it is able. Is this correct?

paul

 

[T-top87GN]

The ECM will be targeting whatever value is in BLM cell 0.

Once the car hits closed loop the ECM will richen the engine until it sees the O2 voltages hit a certain value and then it will pull fuel out till it sees the O2 at another value. The ECM will go back and forth between these two at normal idle.

There's a better write up at: http://www.gnttype.org/techarea/faq/BLMINT.html

Easier to read that than have me explain it actually. Back to the problem at hand.

If the O2's are high at WOT that really has very little bearing on the idle. But those O2's are kinda high.

Hook up a fuel pressure guage to the fuel rail, with the engine at idle, pull the vacuum line off of the fuel pressure regulator and see what the reading is. You are suppossed to have it set at 44psi with a Thrasher so see if you are above that. If you are trim it down to 44, put the vacuum line back on, and then check everything again. You may need to pull more fuel out but I would be wary of going below 42psi with the Thrasher chip. HTH

 

[Gbody5]

Don't know about Armstrong chip, but isn't a Thrasher open loop at idle? I show open loop at idle and I also run rich, but I thought the Thrasher was designed that way to get the smooth idle, esp at start-up.

 

[T-top87GN]

Yes the Thrasher chip is open loop at idle. Basically ignoring the O2 sensor at idle. The Thrasher chip uses the idle tables in the chip and never switches to closed loop. It does it's idling based on coolant temp vs target A/F programmed in the chip and then idle based on the coolant temp vs idle/park target RPM value.

Since the Thrasher is totally idling the car based on tables and values in the chip, then you must have the FP set at 44psi vac off to make the calculations work right. Each car is a little different but I can't see having to back more than 1-2psi down from 44 to get the car to idle right.

The O2 values you are seeing via the scan tool are still right, however. The sesnor is still functioning and sending data to the ECM. The ECM is just ignoring it during idle.

 

[NC87GN]

Send it to anyone who can read and burn an Eprom and up the injector constant. Reference tables are on gnttype.org

Mike Banas
87GN