What causes negative spark timing

[AL]

The 96 GP I just bought has around negative 30 degrees of timing and I am wondering why its that bad? Could the knock sensor be bad? Would that cause this situation? What else could cause negative timing? 96 GP Sedan 3100

[RobertISaar]

WHERE does it have -30*? what RPM/kPa/MAF whatever?

 

and are you sure you're reading whateverr you're reading correct? i've seen certain scanners and software report negative numbers because that's what they are depending on how you define timing.

 

since you fire the plugs long before the piston gets to TDC, it could be considered -30* when the plugs are fired, which is somewhat normal depending on load.

[AL]

Just in daily driving... Its about -20* at idle and around -30* at around 2k rpms

[hotrodolds]

Negative is actually positive. What -30* means is that the plug fires 30* BEFORE TDC.

[RobertISaar]

Negative is actually positive. What -30* means is that the plug fires 30* BEFORE TDC.

 

that's the simpler way of saying what i was getting at. sounds normal.

[AL]

So Im not having any problems then? Thats pretty good

[hotrodolds]

Nope...I'd say you are good to go.

[RobertISaar]

So Im not having any problems then? Thats pretty good

 

if it was somehow even running at say 30* ATDC, then you are some type of God...

[AL]

Its weird because my 91 has positive timing and so does my 03 and my gmas Equinox and my moms G6 and this is the only car I have ever scanned where there is a negative timing number

[RobertISaar]

then whoever wrote the datastream definition for the 96 needs to be hit in the face with a shovel.

[94 olds vert]

then whoever wrote the datastream definition for the 96 needs to hit in the face with a shovel.

 

Dare I say repeatedly?

[AL]

You mean x2?

[94 olds vert]

no hit with a shovel more than once.

[AL]

Oh I see... I need to scan another 96 GP

[RobertISaar]

Oh I see... I need to scan another 96 GP

 

and you've come to this realization why?

 

what you're experiencing is normal, it's just that someone was lazy when they wrote the specific definition that the 96 uses...

[AL]

What if the other 96 I scan does NOT have a negative number

[RobertISaar]

think of it this way: if it really was 30* retarded, then lets say it's firing exactly at TDC(since my 3100 likes around 20* at idle and somewhere around 30* depending on load, i'll say the one you're scanning is acting normally): it would NEVER make enough power to get to any repectable speed. there just simply would never be enough pressure in the combustion chamber. it would basically be misfiring 100% of the time.

[AL]

I dunno tho cause this car seems pitifully slow...

[RobertISaar]

if you can hit 55MPH using a 3100 that's firing at TDC, you have found a miracle engine.

 

go ahead and scan another 96 3100, but it WILL be the same.

 

take it from someone who has made at least 50 OBD1 datastream definitions, it's normal, it's just that the converted data is coming out negative because someone decided to make a horrible equation...

[AL]

96 is not OBD I

[RobertISaar]

96 is not OBD I

 

true, but the basis for communication is the same. the ECU pushes out a datastream of bninary numbers, then a scanner(or laptop) then decodes the binary signal into useable numbers, such as spark advance, vehicle speed, RPM, etc...

[19Cutlass94]

last time i looked at my spark, it was like 15* advanced at idle and jumped up to 3x* advanced when i hit the gas at 2k rpm. I have no idea why you are saying yours is retarded by that much, cuz it shouldnt be. If im reading things right

[RobertISaar]

last time i looked at my spark, it was like 15* advanced at idle and jumped up to 3x* advanced when i hit the gas at 2k rpm. I have no idea why you are saying yours is retarded by that much, cuz it shouldnt be. If im reading things right

 

is that directed to me or Al?

[19Cutlass94]

last time i looked at my spark, it was like 15* advanced at idle and jumped up to 3x* advanced when i hit the gas at 2k rpm. I have no idea why you are saying yours is retarded by that much, cuz it shouldnt be. If im reading things right

 

is that directed to me or Al?

 

Al. that was with my 3400. I still have data scans of my 3100. I do not remember seeing the timing being retadred at all. and that could be he doesnt have much power, or it doesnt feel like it.

[BXX]

Ugh, here. Read this..

 

From my HP Tuners setup. It displays negative unless I set a proper PID and modifier. My last jobs Snap-On Modis displayed negative timing too.

 

"Converting negative reported timing advance to positive

 

Application: GM V6 based vehicles

 

For many late model GM V6 based vehicles (those derived from the 3800 Series II platform) the factory computer will report positive timing as a negative number.

 

VCM Suite 2 allows two solutions to this:

 

Solution 1

Create a user defined PID and insert into the table as follows:

Name: Timing Advance - V6 Fix

Abbrv: Adv - V6

Sensor: Timing Advance

Units: °

Function: -3.0 * [PID.14]

How it works: The scanner will average the values of all sensors of same type currently being scanned. What we have done here is create a new PID that returns 3x the spark advance in the positive direction so that when it averages the two values you get the actual spark advance in the positive. You shouldn't have to change your histograms, charts, gauges etc. as they all log as sensor based by default.

 

Solution 2

This method is similar but uses -1.0 * [PID.14] as the function. You would then have to go switch your histo's and charts etc. to plot the PID value rather than the sensor value. "