Did you ever just loose 10 degrees timing? Math?

[1project2many]

Not sure diagnosis was the intention here but try locking min and max timing within one degree and see what shows up at crankshaft. Code won't violate those numbers so anything different at crank is a problem outside pcm.

[EagleMark]

Already locked timing as a sanity check, still off by 10 at crank. Going to check uncheck/check 400B-Bit 0 while watching timing as another sanity check? I've already done several sanity checks. After sleep too! Yes 10 degrees interferes in my sleep!

That code is not in my DSM so I'd never have found it. I guess the ASM is more important...
Why does it say LCA7C? LCA7C is $CA
When $12 is at LCA7D? You did say LCA7D first time?

What exactly is this doing? Besides checking timing should I look for something else?

[jim_in_dorris]

I'm not typing too well right now, trying to fix wife's office chair and hit my thumb really hard on the meaty part with a bfh. Anyways, LCA7C is CA and LCA7D is 12. That is what ORAB #$12 assembles to. It means that you want to set bits 1 and 4. Those are then output to port D. What I think needs to be there is bits 1, 4, and 5.

[EagleMark]

Let me know if anything else. Vehicle is not here, but I'll be with it in AM.

[1project2many]

Already locked timing as a sanity check, still off by 10 at crank.

Then it's not the code.

Loop REF to EST and apply 5V at bypass. Use timing light to measure change. If any measurable difference inspect distributor / module / pickup coil for problems.

To keep truck running for this test must also send REF to pcm. I've used two high impedance test lights connected B+ to GND and taken jumper from light to light connection point to get 6V for this test.

[EagleMark]

But when I locked timing it was still 10 off? It's also 10 off Jeepsandguns?

[1project2many]

If problem only occurs with mpfi code selected, don't select it. With the memcal mode selection pin shorted the injectors are triggered every fourth reference pulse by hardware, not by the selected cpi / mpfi option bit. There are configuration problems if you select the wrong options anyway, so skip the potential problem.

Are you sure the distributor / coil / module isn't the problem? Looping REF to EST allows you to ensure the distributor isn't the problem. With a scope you could measure actual spark latency corrections too.

[EagleMark]

That was the first thing I did today, turned off CPI/MPFI mode 400B-Bit 0 while watching timing. No change! Still short by 10. So I knew it was not a code issue.

Went ahead and did the $12 to $32 to $12 (I forget, it's on other PC) and no change in timing. Still short by 10.

Added 10 to timing table and man did it run better and was accurate on Data to Crank timing. But Spark Advance table is now 10 high.

Not my truck, he had changed the MSD EST/ICM module to GM long ago to avoid Spark Latency issues. But looking in the MSD distributor I found a common part with JeepsandGuns $0D MPFI conversion. He has a Duraspark pickup to trigger EST/ICM module because of non GM motor, guess what is in the new MSD distriburtor? Switched the wires just incase but it did what I though and made timing backwards like you would on a reverse rotation distributor in a conversion.

We're changing out distributor to GM distributor with GM pickup coil and we will see if this is where the 10 degrees went?

It also has a MSD coil... not sure how a coil could change timing?

[1project2many]

Added 10 to timing table and man did it run better and was accurate on Data to Crank timing. But Spark Advance table is now 10 high.

So the ALDL spark matches the crank? But the timing table reads ten degrees high? Was this thing off at all rpm, or did it get worse as rpm increased? If it's the Duraspark pickup coil then it might be interesting to see a scope pattern of the output.

I seem to remember something about the Duraspark coils. Some of them have two magnets, one for low voltage cranking and one for engine running. Any idea what the part number and / or p/u coil wiring is?

[EagleMark]

Yup ALDL matches crank and Spark Advace table is 10 degrees high. Checked several TBI $0D logs to bins and they are spot on. They also have GM distributor.

Yes across all RPM consistent 10 off, give or take a couple, same as stock TBI with GM distributor.

Distributor
http://www.msdignition.com/Products/...stributor.aspx


Replacement module.
http://www.msdignition.com/Products/...8366/8367.aspx

[jim_in_dorris]

Well, I guess it's not a code issue then, I will remember that Duraspark will cause a CPI/PFI/TBI problem. (I hope)

[EagleMark]

Have not got the distributor changed to non duraspark pickup yet, so we don't know for sure? I've never noticed 10 degrees misisng in duraspark TBI conversions, but when doing them I was not looking as hard, didn't know then what I know now! Next time I get my hands on one I will be checking.

But a recent development has made me suspect it still may be code? CPI uses MAT and no one I know of has implemented it yet in TBI or MPFI conversion, until now! JeepsandGuns has installed and turned on MAT and engine runs much better by feel of butt and data logs! So another place to look in ASM would be what MAT does with spark when turned on/off? CPI bins come with no main spark bias and 9.8 MAT spark bias. TBI comes with 9.8 main spark bias and no MAT spark bias, so they swapped? He is going to check timing at crank to see... data has not changed, but we don't know until then if it changed across the board.

Alos I can't find where the MAT does fueling changes? Spark changes are in tables in XDF so we know it's there, there is a lot missing or never done to ASM in what I have is DSM so who knows what is accurate?

[1project2many]

Doesn't matter what MAT does to spark. Max and min limits are god compared to MAT spark table.

Pretty sure MAT isn't part of TBI fuel routine. Intake air is heated so GM assumes little temp compensation needed after engine is warmed up.

[EagleMark]

Right MAT is not part of TBI fueling. But he is now MPFI, added MAT and BLM and INT have come together as stright lines compared to the zig zag ups and downs of past.

He does not have coolant through intake. Watching MAT temps are close to coolant temps at idle and go down 40+ degres a 2000 RPM. I would have to assume MAT does play a fueling part in CPI/MPFI because of the steady INT/BLM readings now.

Ah.. I think the fueling is answered with MAT enabled "
MAT & CTS Blend Multiplier vs. Airflow" L4AD9
and
"Inverse Air Density @ Sea Level vs. Blended Intake Temperature" L4AEA

Spark is effected with MAT enabled:
"MAT Spark Advance Compensation vs. Vacuum vs. Temperature" L4433


Still does not answer this 10 dam degrees!!!

[1project2many]

Right MAT is not part of TBI fueling. But he is now MPFI

You said you unchecked MPFI bit?

Still think 10 deg outside ecm / pcm.