How does the ECU determine to pull timing?

Mallard · Feb 1, 2005

Exactly as the title says. I did 4 dyno pulls and on 3 timing was pulled at various points. I allowed 15-20 minutes between runs with a big fan blowing on the engine/intercooler/radiator to cool down.

So how does the ECU determine whether to pull timing or not? Is it just the air intake temperature sensor or are there other factors?

BlkZoomZoom · Feb 1, 2005

how do you know timing was pulled?

Mallard · Feb 1, 2005

Well I don't have a datalogger/scan tool so I can not say with 100% certainty, it was both my and the dyno operators assumption. Both the HP and torque curve dipped 10HP at a point, then jumped back up just before redline. My good pull had smooth curves and the other runs followed it exactly except for where I'm assuming timing was pulled, and then it had the same slopes but 10hp lower.

I have the Split Second AFC so under boost my fuel is controlled and would not differ between runs. I had a boost sensor logging boost and those curves are identical between runs.

BlkZoomZoom · Feb 1, 2005

There are a ton of inputs the pcm uses to determine timing... let me thing of how many I can come up with...

brake light switch,
a/c pressure switch,
IAT,
ECT,
MAF,
CKP,
CMP,
VSS,
TP sensor,
Neutral switch,

also I believe battery voltage is used as an input. There may be more that I can't think of right now.

Mallard · Feb 1, 2005

BlkZoomZoom said:
There are a ton of inputs the pcm uses to determine timing... let me thing of how many I can come up with...

brake light switch,
a/c pressure switch,
IAT,
ECT,
MAF,
CKP,
CMP,
VSS,
TP sensor,
Neutral switch,

also I believe battery voltage is used as an input. There may be more that I can't think of right now.

Ouch, that's quite a few possibilities... Since this was a straight dyno pull and did not happen every time can that be narrowed down a bit?

If battery voltage is an input then a dip in voltage could case it? When my fans turn on my lights dim for a second; If the fans kicked on during a pull could that cause a dip in voltage that could result in timing being pulled?

Mallard · Feb 1, 2005

Oh, I should add, on two of the dyno pulls it dipped at the same rpms, the other one was different. I'd post the sheets to show what I'm talking about, but they're on my work computer.

Focus · Feb 1, 2005

Don't forget the knock sensor !!

Mallard · Feb 1, 2005

Focus said:
Don't forget the knock sensor !!

On 93 octane under stock boost?

Focus · Feb 1, 2005

Mallard said:
On 93 octane under stock boost?

I am stating that the knock sensor is another input that can make the ECU pull timing.

Mallard · Feb 1, 2005

Focus said:
I am stating that the knock sensor is another input that can make the ECU pull timing.

Gotcha. I'm just trying to narrow it down.

Mallard · Feb 2, 2005

Here's my dyno so you can see what I'm talking about. The green line was my best run so compare that to the red and blue lines. I put arrows under where I think it pulled/advanced timing.

If anyone has any ideas as to why it might have done this or how I can try to prevent it when I go back to the dyno let me know. So far I'm leaning towards the IAT sensor and I might try cleaning the MAF.

ND4MSP · Feb 2, 2005

not a bad run there. tourqe especially. How does the car feel. I'd say that the fans kicking in that you mentioned could have caused the slight dip. The graph showed a pretty quick recovery after the dip though.

KyRaceFan · Feb 2, 2005

What other mods do you have? 160hp seems kinda low for a fuel tuned car. Even with no tuning and bolt ons i made about 195hp.. in 100 degree heat.

BlkZoomZoom · Feb 2, 2005

I would bet more of a fuel problem than timing problem. It looks as if it dumped fuel. Wheres the a/f reading?

Mallard · Feb 2, 2005

I didn't have a wideband hooked up on these pulls so I'm not sure what the a/f was, but keep in mind that the ECU isn't controlling my fuel under boost, the S.S. AFC is running tables. So the fuel should be the same as long as the boost is.

My car is completely stock other then the AFC.

It may have recovered after the dip, but it lost 10hp where it did dip.

I'll hook up a wideband next time to make sure my a/f's are flat if you think that could actually be it. An Innovative LM-1 will be installed before summer.

igdrasil · Feb 5, 2005

Timing will be determined after coolant temperature, AIT and MAF output mostly, or at least those are the sensors that may do drastig changes to timing.

One thing you have to remember, never dyno a car if you just started the engine, let it run like a normal street for at least 1 minute, then do the pull.

Another thing is that, the O2 sensor reads too rich when cold, so its better to run a dyno plot when the O2 sensor is in good running temperature.

igdrasil · Feb 5, 2005

Ah, one question, how are you controlling fuel? are you clamping the MAF? If you manipulate it to run leaner (example: MAF output is 3.5 while the Split Second is sending 3.3 to the ECU) it will also decrease the timing advance....

I havent monitored total timing but Im pretty sure what Im saying.

Mallard · Feb 5, 2005

igdrasil said:
Ah, one question, how are you controlling fuel? are you clamping the MAF? If you manipulate it to run leaner (example: MAF output is 3.5 while the Split Second is sending 3.3 to the ECU) it will also decrease the timing advance....

I havent monitored total timing but Im pretty sure what Im saying.

I believe that's how the Split Second works, but I can't say for sure. It alters both the MAF and the O2 signal going into the ECU in order to control the amount of fuel being injected. As far as I know it just re-scales the MAF voltage; so your statement would be correct.

Well on one pull it didn't pull timing so I will also make sure of the other stuff you mentioned when I go back. Thanks for you help.

jtmp3 · Mar 1, 2006

does th mp3 have a knock sensor? or only a MSP? do all protege's have a knock sensor?

boostisgood · Mar 1, 2006

All cars have a knock sensor (at least all odbII cars do). As far as your dip, I would have assumed that is the spot that all the stock PCM's give us our sluggish feel at WOT, but you got an AFC, so I couldnt even begin.

Your best bet, get BACK on the dyno with a WBO2 and a datalogger to see whats going on with that AFC.

How does the ECU determine to pull timing?

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