What controls timing advancement?

[Scaramoche]

I have a wd21(like yall dont know hehe) and i have been having a constant backfire issue. I had thought i had fixed it, untill over the last few days i had to drive 200+ miles a day. I thought everything was fine, but after about 1.5-2 hours of driveing i could feel it slowely loosing a little power, then it would begin to backfire(around 3k rpm), i could drive if sat below 2,5k rpm. i retarded the timing a bit, and seemed to clear it up, but i would now have loss of power issue and some backfiring on idle(1k rpm).

 

either way i got home and put a timing light on it, and found that my timing, which i had set at 12-15 degrees(at temp, after warming up) was now sitting at like 30 degrees. so when i had retarded my timing on the road, it lowered got rid of the backfire.

 

so what devices tell the ECU how much to tweek the timing? something is obviously crapping out at temp and causing me some issues, or could it be the ecu?

 

in a nuttshell, how can i limit the amount of timing adjustment?

Edited July 14, 2010 by Scaramoche

[GrimGreg]

IIRC it uses the MAF and O2 sensor readings to determine air/fuel mixture in versus a rich/lean burn reading out and bases timing to burn most efficiently. It changes ignition timing based on the crank angle sensor readings.

[MY1PATH]

Timing advance is a constant starting @ 1,100RPM

It reaches a total advance of 30degrees @ 4,500RPM (yep a motor that revs to 6~7k runs out of advance 1/2 way to redline.**)

The advance is controled electronically so our rotor has a wide sweep, unlike centrifugal or vacum type units that use a narrow rotor.

If there is a knock or poor ratio detected the ECU Retards 5 degrees from whatever position it is on the advance curve. It also applies this same fixed retard when the engine is warming up.

This is TBI and MPFI 1st gens. I do not know if 3.3 is differant.

 

 

**this works well for turbo motors becuase as preasure rises from High RPM spool you need less advance anyway.

Edited July 15, 2010 by MY1PATH

[Scaramoche]

Timing advance is a constant starting @ 1,100RPM

It reaches a total advance of 30degrees @ 4,500RPM (yep a motor that revs to 6~7k runs out of advance 1/2 way to redline.**)

The advance is controled electronically so our rotor has a wide sweep, unlike centrifugal or vacum type units that use a narrow rotor.

If there is a knock or poor ratio detected the ECU Retards 5 degrees from whatever position it is on the advance curve. It also applies this same fixed retard when the engine is warming up.

This is TBI and MPFI 1st gens. I do not know if 3.3 is differant.

 

 

**this works well for turbo motors becuase as preasure rises from High RPM spool you need less advance anyway.

 

ok, that makes sense, and seems to follow what im seeing.

 

when cold, or at lower rpm's(below 3k) i run fine, but once engine is at operating temp, and i get up towards 3k, i start backfiring. I have cleaned my mass airflow, no change, but what i HAVE CHANGED is my o2 sensor. Infact in a previous post a few months ago i was having these issues(thought i fixed, ie ab valve, and timing), and they all started after i replaced the o2 sensor. so my question is, if i disconnect my o2, will the ecu default to a basic air/gas mixture curve? and if i do this, do i have to "clear" the ecu, ie battery etc?

 

 

Basically in the morning, im going to get engine to operating temp, then set timing again(cause it runs like crap now due to being severly retarded) ill set it at 12-15 degrees(probaly closer to 12), disconnect the o2, reset the ecu(disconnecting battery i assume) and see what happens.

 

also i would like to note at the same time i did o2, i also added an msd 6a ignition system(if this could be an issue, please let me know)

 

any advice would be greatly appreciated.

 

thanks

scara

[MY1PATH]

also i would like to note at the same time i did o2, i also added an msd 6a ignition system(if this could be an issue, please let me know)

 

any advice would be greatly appreciated.

 

thanks

scara

 

YES! MSD can cause troubles and personal injury as I have learned first hand lol (ZAP!)

The points on the TBI cap are close togeher. this can lead to misfires and stuttering when upgrading to a system like MSD. ESPECIALLY if you use an aftermarket coil in adition to the system.

 

The solution Is to get a 90-95 pathfinder dizy(need to change base plate too) and drop it in.( the whole thing is larger so arcing is more dificult.)

the vavle cover needs to be dented or swapped for it to fit and the wire clip on the new dizy needs removed so the plug will reach your harness. but the plug and sensor inside are the same.

Search my posts for more info...

this may not cure you but it will help you narrow things down and prevent future issues.

[Scaramoche]

Woot,

 

that was it, ie msd. I just disconnected and no more backfires.

On payday ill go pick up a dizzy from a newer model, my question is, will the valve cover fit from a 90-92?

 

thanks all

scara

[MY1PATH]

It will fit but I don't know if the intake PCV hose is the same or if its even there.

I honestly think denting your existing cover to clear the larger Dizy is the solution. It can be done in place so that saves ALLOT of time.

lemie see if I can find my original thread....

 

Here ya goes;

http://www.nissanpathfinders.net/forum/index.php?showtopic=25870&st=0&p=475362&fromsearch=1&&do=findComment&comment=475362

Edited July 17, 2010 by MY1PATH

[tmoore4512]

So...with that being said, and me having a 95, there technically SHOULD be a way to manually over ride the timing advance/retard for "performance" instances...

 

I know on my old Civic it was all controllable...

[MY1PATH]

not really, If you try to advance the timing on the MPFI it just holds that timing untill it reaches that point in the advance curve and then resumes normal operation.

Unfortuantley you cannot lengthen the advance curve either.

[tmoore4512]

I guess the only real way to do it would be to completely re-do the entire ECU. New program and all.

 

It is not something I would want to do, just a thought...and besides I can barely afford the steering components I need at this moment...

[MY1PATH]

sopposedly you can buid a megasuirt for about $200 and fit it for not much more. Its allot of learning but you can get complete and total control of everything.

VS jet/jwt re-programs $400

I think indignet was messing arround with re-mapping Might wanna give him a buz if you want something to start with that don't cost you a leg.

 

The megasquirt uses an advanced MAP sensor instead of a MAF sensor. Their data states that this sensor also tracks barometric preassue when the engine is off so that it self calibating to altitude, ambient temps and other common variables in barometric preassure.

 

I works in conjunction with an o2 sensor just like ours does.

Edited July 19, 2010 by MY1PATH

[Indigent]

Just for reference for this post and posterity and whatnot, the ECU only retards timing due to knock in the 400-800 RPM range at like 90-100% MAF load. So basically only when you are pushing the gas pedal down all the way while climing a steep hill, or during takeoff from a dead stop while towing a heavy load.

 

If you want to know more I put a comment similar to this in a post a while back. You can turn on or off knock sensor monitoring at any point in the timing map, or just replace the knock map with the regular one. I wouldn't recommend it, as knock in those conditions will cause big problems.

 

I have fully disassembled the ECU bin and have figured out a TON. I tried to get people interested in tuning this ECU a while ago, but didn't get much response. I have noticed I have been posting a bunch about it here lately, so if people are interested and need help, I could get off my ass and do somewhat of a writeup.

Edited July 23, 2010 by Indigent