EFIDynoTuning Forum

yeah the ml2872 hardware code that matches your tunes for this is actually rare.


talking cheapest I can find used is $200 and the cheapest reman is $400+

If I could find the pinout differences between ml2871 and ml2872 to figure out if the ml2871 hardware coded PCM's are useable that would be awesome.
'

the ml2871's PCM's are cheap and plentiful.

So my PCM has been reporting Vref errors on forscan for a hot minute, like 1.5 years now.


Previously it would report voltage, not the right voltage, but it would report voltage.


No symptoms previously, other than the reported inferred vacuum reading was oscillating wildly. No biggie, PCM baro is locked at 1 atmosphere in tune right?


Well, I accidently flipped polarity on 2 alternators after installing a new engine, it hasnt wanted to run for ish since And Forscan is just erroring out on the reported VREF now.


I have checked the sensors being fed a 5v and the only one that is off is the IAT plug by .5v, the rest report 4.97v



Symptoms include running like trash with the MAF and TPS plugged in, Rolling misses, backfires after unsuccessful start attempts and backfires at key off idling.



Ive got an alternator on it with known good diodes now, and all of my sensors are testing out fine.



Just looking for some way to confirm the PCM is dead besides setting more money on fire.

is there any reason I just cant delete the dropping resistor from the pump circuit?

Im aware.


I will continue to use your old tune with the 2 speed pump trigger accesible I guess.

Ok.



Is there anyway for me to set the trigger to like 100rpms?

Well if thats the case why do you have regulated return listed as an option under fuel system selection in your notes for the xdf?


Also, yes there is a "voltage control" on all 98's


Uses a 2 speed system that halves system voltage at the pump through a resistor. PCM triggers a relay based on RPM and that shorts the resistor and jumps voltage to 12v+


You even had the option to control the trigger RPM in earlier craj0 tunes man.

gotcha. When you change it, it changes the SP**MAF values. only reason I ask.


Ive managed to troubleshoot my problems down to fuel pressure issues. Still.


Im only getting 25psi at idle at the rail with an on3 320lph fuel pump and a brand new FPR. And around the 8-10min idling mark it drops further to 20psi. Also it doesnt climb when throttle is applied, it drops until high speed triggers. And even then, it only holds steady at its current pressure.

Ive set the fuel type switch to 0 for the unregulated return, ive even put 12v's in the voltage table for it.


Got any ideas what Im missing here? Am I chasing bits and bytes? electrons and relays? Possibly a physical hardware issue?

Sorry, I use Forscan for diagnostics. Has the ability to show OL, OL-drive and OL-error

Forgot to set fn320 when I switched to the new bin.


Can you elaborate on the raw MAF transfer function you added?

Dude!


Soooo many new things to screw with lol! Was a little worried about granularity of control with almost a 12-1 static and no knock sensors, not so much now!

Questions

Im running an on3 320lph pump on my 98 gt. What Mhz should I hit her with in the FPUMP_FREQ scalar? Been having severe low RPM fueling issues, like it just aint coming sometimes.



Also, Im not sure if I fried my PCM or the cat layed on the laptop when I wasnt looking, but the damn thing refuses to go to CL logic after warmup. Drops from OL straight to OL-drive?

Thanks!