How does PCM calc fuel amount?

[AndyL]

How does the 99 PCM calculate fuel amount, look up table, actual calculation?

I am trying to understand the effects the Turbo Master has the on the fuel delivery amount. I am guessing the PCM uses boost pressure as part of the calculation equation or some kind of amplifier or offset. When I increase boost from say 5 to 10 PSI how much does fuel amount increase?

If it is a calculation I was also thinking I could build an automatic fuel compensation device. A small Basic Stamp could easily read the EGT and automatically offset the necessary sensors to increase/decrease fuel delivery amount to achieve a desired temp. It would basically be the same as the PCM de-fueling due to intake temps, except from a more accurate EGT reading.

Would anyone be interested in a device like this, would it even be helpful? If so I will build it.

Andy

[gmctd]

Throttle angle from APP module, coolant temps, rpm, boost press modified by initial baro offset at each startup, fuel temp in IP, intake air temp IAT, cylinder balance from Fuel Solenoid closure and Hi Res IP pulses, to start with.

If boost press does not equate to pulse rate at wastegate solenoid, will check for IAT, IP fuel temp, coolant temp and will pull fuel on deviation limits.
Would seem to indicate tables.

Your '99 factory manual\Diesel Supplement goes into more detail than the '94 manuals.

[Kennedy]

The computer calculates fuel rate in mm3 and displays on the datastream. This is kind of an assumption, and can be more consistent than accurate, but not bad.

They use Fuel rate x engine RPM / MPH on the late model DIC to factor instant and trip fuel economy.

It has been my experience that boost increase will not alter fuel rate directly. Additionally, a mechanical boost device will not directly regulate boost. It will regulate back psi only which does affect boost psi. The active duty cycle of the OE wastegate solenoid can give you more back psi to spin the turbo up faster at initial spool up, then relaxes when the target boost is achieved.

[AndyL]

John,

Do you have a BIN of the 99 ECM I could decipher?

[Kennedy]

Sorry, I don't.

My '96 has a new home in Texas :( which is a bittersweet deal. I needed to move on and all, and Texas is a much friendlier climate (rust) for it. I still say the 6.5 had CHARACTER lacking in the more sophisticated modern diesels.

Anyhow, long story short, the new owner has done quite a bit of work for me on some of the Eprom stuff, and is optimistic that he can cover some ground on the OBD II stuff now that he has one at his disposal.

Suffice to say though, the '99 stock program is pretty darn good as is, and if you want to improve upon it, you'll need a bigger turbo as the major gains will be above 2600rpm...

The best gains for the 98-99 are exhaust, electronic boost control, intercooler, and HF injectors.

[AndyL]

Thanks John,

I am not wanting to change the PCM code, just figure out the exact variables used to calc fuel delivery. Then I could better understand the direct effects of additional boost. With a BIN dump (or a spare 99 PCM I guess) I could pull that from the assembly code.

I guess then I could also find the enhanced PIDs I have been looking for.

[Turbine Doc]

Andy,
Educate me on what a BIN is and I might be able to assist.

[AndyL]

Originally posted by tbogemirep:
Andy,
Educate me on what a BIN is and I might be able to assist. It is slang for the ECM/PCM Program memory. The computer code that is running in the vehicle computer.

[Turbine Doc]

Oops sorry I asked, too much for me to help you with thought it might be some number I could access from my scanner looking at my 99 PCM

[JohnC]

Boost does not have a direct efect on fuel rate. the only effect is if boost is too high the PCM will limit the fuel rate in an attempt to prevent overboosting. Simply, the PCM looks at RPM and throttle and a couple of other more minor things, then looks up both fuel rate and boost level in a map.

[gmctd]

Logically, that would appear true - note the number of 'black smoke, no power' posts.

Nice rig, JohnC! :cool: