At WOT Diacom is only showing 28 degrees of total timing.Adding to this is the fact that I run a DUI ignition module in the distributor.I think this is what is returning the low reading.
The car runs too good for the 28' to be accurate.Would like to see 34-38 degrees.
I have run Diacom on other Vettes and have not seem total timing this low.
Any thought?
Maybe I should post this in the new ECM section.
Thanks....Phil

 

Unless your car has a crank position sensor, and an LT1/4 MAY have, I dunno that much about opti-crap.....sorry about the slam there, ....
the computer has no way of knowing how much initial is cranked in there,...
so add your initial to your computer readings....and it should be 8* so you are right in there at 36* total....

 

I should have mentioned this is a L98.1991 Corvette.or was that in my sig.Diacom gives you a total advance from initial and a total that includes the initial.
Phil


[Modified by wheelsup, 10:27 AM 12/21/2001]

 

FYI, a (typical) '91 A4 stock L98 chip has the following spark programmed in at 100 kpa MAP and 5000+ RPM:

6* initial
18* main
7* PE
for a total advance of 31*

The distrib module has nothing to do with what the ECM chip program calls for (in my experience). Diacom just reports what the chip says it's doing.

Maybe you have 3* of knock retard, or the program is modified?

drj

 

Dr.J, I have a TPIS stage V chip.I have 6' of initial advance and the k. sensor has been desensitized.
Let me understand,if the Diacom at WOT is reading 28 degrees:That should include the advance built into the chip?? Right or wrong? If the 28' DOES include the chip advance then Iam back to my original question.
Thanks...Phil

 

Phil-

Not sure I understand your question here. Let's go back to basics:

Diacom has no way to know what the spark plugs are doing - there is no sensor in an L98 that measures when spark occurs relative to crank position. Diacom just talks to the ECM, and reports out what the ECM program thinks the distributor is doing (or more correctly, what the ECM is telling the distrib to do).

The ECM program (chip) calls for a certain spark advance at some RPM and MAP (those are both measuring sensors). You could disconnect half the plug wires and ship them to China, the ECM program will still call for the same spark advance, it has no idea whether the plugs are even in the car or not.

[All the ECM/chip sees are sensor values for RPM, MAP, Coolant Temp, etc. You can pull the ECM and put it on a test bench, hook up some resistors and a signal generator, it will think it's running at Indy.]

Diacom is only a commo program. Its job is taking the ECM signals from the ALDL and printing them on your computer screen. By itself has no control or measuring ability over the engine whatsoever.. Does that make sense?

If Diacom reports 28* at WOT, then that's what TPIS put in the chip. You need a timing light to verify what is actually happening in the 'real' engine. But a tuner would typically take a TPI chip and cut some of the excess PE fuel out of what GM uses - then normally I see them add spark to the GM values, not take it away. Maybe you got a chip for an iron-head engine? Anyway, Diacom is just reporting what the program says - there is also usually a line that reports spark knock - is there a value for that on the same frame where you see the total 28* advance?

HTH
drj

 

Dr.J, I guess what I really need to know is what the "real" engine sees as total timing.Need to put a timing light on it and let it rip.There is no knock retard....zero.
Still confused.I have seen other Diacom readings of other L98's that had more total timing.May call TPIS,I'll really be confused then.lol
Thanks Again
Phil

 

If your 28 degrees total including the 6 degrees advance then one of two things are happening.

1. Your car is not going into PE mode which adds more fuel and advance spark.
2. Your car has a custom chip.

Jason

 

Jason,I have a custom TPIS chip.The car run great.Guess I'am trying to determine if I could use more timing.
Thanks...Phil

 

Phil,
My Ease Diagonostic software reports both values, total and relative to initial. I'm not sure if Diacom does that or not. Also my custom chip (started life as ARAP bin) is very aggressive when it come to timing. I get up to about 42 degrees total timing. Then again my 10:1 compression is relatively low for Alum. heads.

Also, are you picking up knock counts? Your total of 28 might be because the ECM is pulling timing out. Just a thought.


[Modified by GlennS87, 1:53 PM 12/21/2001]

 

Glenns87,No knock counts.I have a 10.25 cr with alum. heads.Yes,Diacom shows both total and relative to initial.
Thanks...Phil

 

Phil-

Just a thought, people on the chip boards (I've never seen a TPIS chip myself) have said that TPIS deliberately try to obscure their chip work to prevent copying - it might be as you suspect, the 28* has no relation to where the spark is actually running. They could do that by buggering something else in the code I guess, and still have it work right.

We could probably figure it out, but I don't have time this week at all!

One quick test - with that chip at warm idle, does the spark advance jump around like 20* total? If not, they just rearranged the spark offset - if so, they changed something else - and you will have to pay them again to get the chip revised, if you want different results. That's why it's cheaper in the end to program your own!

Happy Holidays

drj

 

No that does not affect Diacom display. At what RPM did Diacom show 28 degrees timing? I run 35 degrees total in my 89. That includes a little adder for PE. More fuel needs more spark advance generally. Formato runs 32 total and Ed Wright runs about 36 total. Please keep in mind we are talking only about WOT 100% load spark values. During cruise, you will see values like 44 degrees or so.

The 89 Vette 6 Speed stock chip runs 23 base + 8 PE spark adder for a total of 32 at 4800 RPM WOT
Jason


[Modified by 89vette, 1:30 PM 12/21/2001]

 

Jason-

Not sure what the 'no' relates to :). If I wanted to hide my timing number, I'm thinking I could change a scalar value in hex and make it read any number I want, without affecting the voltage sent to the ESC module - but that's just a hypothetical on my part, 'cause I never tried it. Just a guess, maybe it's something even more simple, like changing the interger value of the initial offset in hex. Or maybe that's the spark they really used - I was just wondering why Phil's chip would have a reading like that. Dunno, & it's academic to me anyway - but has anyone examined a TPIS chip? I'm curious.

drj

 

Diacom reads what the ECM is telling the componets to do. TPIS goofs up thier chips by changing the location of some tables. Formato cuts one leg off the chip fter its programmed. Jumper around it and it can be read. TPIS actually has thier own mask code. But what Diacom is showing is what's going on. To get thier spark table, you would have to record all the different load and RPM points which would be very hard to say the least. Most chips are just smoke and mirrors anyway. I have Formato, Lingenfelter, Fastchip, Hypertech and Exotic Muscle chips in my bag of tricks. Ed Wright by far chages the most and tries the hardest. Most have idle speed and fan temps only and maybe a copuple more degrees of timing. Sounds like your a little mad at me.

Jason

 

Nah, no way. Am I starting to sound like 'grumpy'? There's just too many dogs and people running around this house right now (singing Christmas Carols) to form a coherent thought.

I didnt know whether the 'no' meant TPIS wasn't trying to report a false number, or that Diacom couldn't be made to report a false number.

I've looked a little at Moates' source code, but never at what the chip uses to put those outputs on the ALDL bus, so I wondered if you knew. It was an interesting problem, and I put a couple of minutes into wondering how I would disguise a timing number if I were selling expensive chips. No big thing, sorry if it sounded wrong.

Anyway, I gotta go enjoy Christmas vacation with this crew (even if they can't sing). Happy Holidays, all.

drj

 

Man, am i sorry i opened this, cause i feel completely ingorant.

How about a simple test...the old fashion way....LOL

after warm, use a timing light to determine the timing at a few different rpms...then compare it to what the diacom is telling you.

if timing light says 30 and diacom reads 22.....it will tell you something.

BTW, Happy holidays to you dudes!!!!!!!


[Modified by ralph, 3:19 PM 12/21/2001]

 

So... If you start with 8deg initial and Diacom shows that the computer is putting in 22deg you have a grand total of 30deg. If I want more than 30deg total I would assume I could do one of two things:

1) Increase the initial timing
2) Change the cal of the computer

If a person wanted to go from say 29deg total to 33deg total what problems would arrise from simply adding 4deg inital timing?

Mark

 

Well, I don't want to trip you up. If you start with initial spark advance of 8 degrees, that is 2 more degrees than the chip is set for. Diacom does not know that your engine is timed at 8 degrees, so it will still base "Spark advance relative to Reference" as (spark timing in chip + 6 degrees). Diacom will always report 2 degrees less in your case of having 8 degrees than the engine is actually getting.

So in your situation you mentioned above, YES...you would be a total of 30 degrees advanced when the spark plug fires in relationship with the crankshaft, but Diacom will only be showing 28 degrees.

The ways you mentioned to get more than 30 total degrees are correct.

I will not get into the last part about problems that can arise because there are many that could happen, but some basics are this: You could run into problems with spark knock. You run the risk of overheating. You will round off the electrode on the sparkplug quicker. You are possibly increasing the pressure in the combustion chamber.

Of course those are things that CAN happen. They might not, and a lot of people DO advance their timing. Be forewarned though. I have started learning how to read plugs here in the last few months to help me with my decesions.

Good luck, -Matt-

 

Ok.. Let me further explain.. <grin>

I have a 1991 car that had some custom work done on it -- and it has a custom chip programmed. I was told by the previous owner that the "timing was conservative for pump gas" and that he thought it was at about 28-29 total degrees. Something tells me that some additional timing with good gas might be worth some ponies. Lets be safe and say 32-33deg total.

I have Diacom on the way.

When I get the Diacom in place where will I need to start to determine what the heck the car has for timing? How do I need to go about checking the initial settings etc? If I want 32-33 instead of 28-29 will simply dialing in some extra initial timing accomplish those goals?

I am very familiar with distributers and whatnot but this will be my attempt at trying to decipher this car.

Any and all help is greatly appreciated.

:-)

Mark

I am going to nee