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Old 31st October 2006, 07:04   #1
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Default Relation between Ignition retard/advance and AFR

Hi guys,
Is this safe to say a lean mixture will cause a Ignition retard and a richer mixture will cause a Ignition advance ?
So is it ok to say that if the LTFT is high the car will be running with a higher retard to mantain the AFR ??
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Old 31st October 2006, 19:33   #2
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Quote:
Originally Posted by chetanhanda
Hi guys,
Is this safe to say a lean mixture will cause a Ignition retard and a richer mixture will cause a Ignition advance ?
So is it ok to say that if the LTFT is high the car will be running with a higher retard to mantain the AFR ??
Why dont you tell us why you think this is safe to say that these relationships exist..and maybe we can get some people to comment.
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Old 31st October 2006, 22:59   #3
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Quote:
Originally Posted by Mpower
Why dont you tell us why you think this is safe to say that these relationships exist..and maybe we can get some people to comment.
ok, I'll explain further my question :

Im getting LTFT readings varying from 1.6 to 2.3 % indicating that the AFR is lean.
1] At 0% throttle angle my LTFT is 0
2] At about 30% the LTFT climbs to between 1.6 and 2.3

I also observed that the ignition was
1] 12 degrees at 0%throttle
2] went upto 20 to 30 degrees at 30% of throttle
Im considering negative = ignition Advance(BTDC) and positive = ignition retard (ATDC)
looking atthe above values I was asking if lean mixture means ignition retard , so in other words High LTFT = ignition retard in order to stop knock.

Last edited by chetanhanda : 31st October 2006 at 23:10.
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Old 1st November 2006, 01:31   #4
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Quote:
lean mixture means ignition retard
The AFR is decided based on engine rpm, engine load (which is measured through MAP or MAF sensor), engine coolant temperature, charge (air-fuel mixture) temperature etc.
1. At high rpm , high load condition the air-fuel mixture is made richer because more power is needed.
2. At high temperatures (engine and charge) the air-fuel mixture is made richer since the lean mixtures burn hotter and can lead to engine damage.

So both the AFR and the ignition timings are ECU controlled parameters based on the sensor readings not cause and effect as evident from what I have quoted above.

Quote:
in other words High LTFT = ignition retard in order to stop knock
Three ways among many in which the knocking can be avoided are:
1. Run the engine on a richer air-fuel mixture.
2. Retard ignition (spark after TDC).
3. Use higher octane rated gasoline.

Essentially LTFT is a learned parameter based on the fact that engine ran rich or lean over certain period of time. Whereas the Ignition retard (Ignition any later than the optimum point for given rpm, load, temperature) is immediate action taken on detection of knock.

So I would say ignition was retarded because of knocking. And high LTFT (I assume that means richer AFR) because either the engine was knocking for long beyond which could be handled by ignition retardation or it was running hotter than it should or both.
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Old 1st November 2006, 06:17   #5
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Quote:
Originally Posted by Pankaj401
The AFR is decided based on engine rpm, engine load (which is measured through MAP or MAF sensor), engine coolant temperature, charge (air-fuel mixture) temperature etc.
1. At high rpm , high load condition the air-fuel mixture is made richer because more power is needed.
2. At high temperatures (engine and charge) the air-fuel mixture is made richer since the lean mixtures burn hotter and can lead to engine damage.
So both the AFR and the ignition timings are ECU controlled parameters based on the sensor readings not cause and effect as evident from what I have quoted above.
Thanks !!
Guys u have misunderstood me .. Im not trying to explain a theory here.. Im trying to ask for suggestions to solve my problem of having a high LTFT of 1.6 to 2.3 %
Also along with this high LTFT Im also noticing high retard, so I was trying to guess if this retard is due to my lean AFR ? maybe the ECU is retarding my ignition based on my knock sensor input

Do you guys think I should get the injectors cleaned maybe they are being clogged causing my mixture to go lean ?
I dont have feature to view the IPW or the IDC or anything to do with the injector pulse to come to a decision that my injector pulse width is high in order to compensate for lean condition ..
but is it safe to assume its the injectors may be clogged and get them cleaned 1st and then trouble shoot after the cleaning ??
plz suggest as its going to cost me 200$ for this..

Im sure its not my 02 sensors that are faulty giving incorect readings as they very reactive to changes and the sensor readings are perfect !! oscillating between 10 and 1000 mV.

Last edited by chetanhanda : 1st November 2006 at 06:23.
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Old 1st November 2006, 06:28   #6
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Quote:
Originally Posted by Pankaj401
So I would say ignition was retarded because of knocking. And high LTFT (I assume that means richer AFR) because either the engine was knocking for long beyond which could be handled by ignition retardation or it was running hotter than it should or both.
I was also coming to that conclusion that :
1] Due to lean mix it is causing my ECU (after getting input from my 02 sensor) to increase the STFT, which after sometime is pushing my LTFT to 2.3%.
2] Meanwhile also in parallel due to the lean mix the engine is knocking and triggering my knock sensors to inform the ECU to retard the ignition...

right ?
guyz plz suggest..by the way Im running Premium 91 Octane gas.
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Old 1st November 2006, 12:46   #7
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Quote:
Im trying to ask for suggestions to solve my problem of having a high LTFT of 1.6 to 2.3 %
The problem could be anywhere from fuel delivery system to fuel injection system to ignition system.
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Old 2nd November 2006, 02:18   #8
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Chetan,

I would like to add C.R as well for relation between Ignition Retard/Advance & AFR. Let me try to explain that but before that i would like to state few terms which will help you understand the relation between all these, now most of us are aware of four stroke cyle so i will not explain that, we will be concentrating more on the power stroke of an engine, The power stroke can be thought of as an avearge (theoretical) pressure which is result of combustion of air/fuel mixture in a combustion chamber which excerts pressure on piston to rotate the crank, This theoretical average is called mean effective pressure M.E.P

take for eg 2 identical engines in terms of cc valves a/f ratio etc but one engine has C.R of 9.1 & other engine has 11.1 ,

The engine with 9.1 C.R will have far less M.E.P than an 11.1 C.R engine because C.R controls the heat in chamber before its ignited,lower c.r will have low burn rate the temperature rises depending how much fuel is compressed, thats why lower C.R needs more timing advance because it takes more time to burn/heat & raise pressure in chamber, therefore to time peak cylinder pressure for a slower burn rate & slow pressure riser requires more advanced ignition timing. where as for a high C.R engine less advanced ignition timing is required beacause higher c.r engines the fuel burn rate (here octane rating comes in to picture ) & cylinder pressure rises quickly so you want to retard the ignition to time peak cylinder pressure. now what is this peak cylinder pressure for that look at the diagram below




Its quite obvious that how quickly the cylinder reaches maximum pressure after ignition is determined by the rate at which fuel burns & C.R, in left pic if your peak cylinder pressure occurs at T.D.C the Piston, Rod & Crank are in aligned with the centre line of crank the energy released instead of turning crankshaft rotation is absorbed by block, head, bearings this is no good & very dangerous if your Car is NOS or Turbocharged cause they increase the burn rate of the fuel mix, by having peak cylinder pressure at 12-14 ATDC (right pic) the Rod is at angle with crank centreline when cylinder pressure puts force on piston it spins the crank. So you want max peak pressure at particular degree so that the force is used to turn the crankshaft.
Most street cars with up to half throttle are tuned to run at 14.7:1 air fuel ratio for N.A engines which is also called as Stoich condition which gives maximum fuel economy,it gets richer by approx 13.1 on full throttle, Honda ecu in open loop mode are self monitoring it takes feedback from various sensors learns & adapts, it makes long & short term fuel corrections based on inputs if you advance your distributor it will learn & retard to make up for that ,if your fuel pressure raises & it runs for long it will trim down the fuel supply by reducing injector pulse width.

in your case chetan i would recommend you following things.
> get your ECM Reset first (just unplug the battery & leave it for some time)
> Check your CAM timing is set to factory Spec
> Set your Ignition timing set to factory spec (16-BTDC) pls chk.
> Check the condition of sparkplugs
> Check your intake air temperature sensor if any
> Your Oxygen sensor could be bad
> Check for loose connection in wires/joints or connectors.
> Check for fuel Pressure & all injectors clogged if any

Do tell us more about your car engine Yr ECU (Part # & Code) whats current c.r ? have you opened the engine or any other work & whats current ignition timing is set at, pics would be great.

Rocam

Last edited by Ford Rocam : 2nd November 2006 at 02:30.
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Old 2nd November 2006, 11:41   #9
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Quote:
Originally Posted by chetanhanda
I was also coming to that conclusion that :
1] Due to lean mix it is causing my ECU (after getting input from my 02 sensor) to increase the STFT, which after sometime is pushing my LTFT to 2.3%.
2] Meanwhile also in parallel due to the lean mix the engine is knocking and triggering my knock sensors to inform the ECU to retard the ignition...
This is weird as if your LTFT is going up it means that your injectors are working fine, the only culprit I can think of would be your O2 sensor, also as far as I know the ECU can only retard the timing from the existing curve and advance it to the preset curve and not beyond.

At times even the IAT (Intake air temp) and the water temp sensors can cause this fault by giving lower values that what they should.
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Old 2nd November 2006, 12:30   #10
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Hey ..thanks for the detailed reply guys !!
I just got my car back from the dealer - they did the following
- Injector cleaning
- throttle body cleaning
- valve clearance check

.. the car feels a little better, I will be logging fresh parameters again today to check if it made a diff.

I also had a long talk with their chief "OBD2 guy" at the dealership .. and showed him a playback of the parameters I had logged on my laptop.
He said my LTFT was ok and not too high, according to him the malfunction threshold is 19% and I was way down at 1.6% so I should be OK. He also gave me a xerox of the data sheet of all the ideal operating conditions of all the sensors and the xerox said I was in good shape..
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Old 2nd November 2006, 12:32   #11
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Quote:
Originally Posted by Psycho
At times even the IAT (Intake air temp) and the water temp sensors can cause this fault by giving lower values that what they should
I will investigate this also
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Old 2nd November 2006, 12:35   #12
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Quote:
Originally Posted by Ford Rocam
in your case chetan i would recommend you following things.
> get your ECM Reset first (just unplug the battery & leave it for some time)
done, LTFT goes to zero and rises to 2.3 % at 3000 RPM

Quote:
Originally Posted by Ford Rocam
> Check your CAM timing is set to factory Spec
> Set your Ignition timing set to factory spec (16-BTDC) pls chk.
> Check the condition of sparkplugs
done

Quote:
Originally Posted by Ford Rocam
> Check your intake air temperature sensor if any
> Your Oxygen sensor could be bad
> Check for loose connection in wires/joints or connectors.
done

Quote:
Originally Posted by Ford Rocam
> Check for fuel Pressure & all injectors clogged if any

Do tell us more about your car engine Yr ECU (Part # & Code) whats current c.r ? have you opened the engine or any other work & whats current ignition timing is set at, pics would be great.
engine -D16Y8
no engine work done
ignition timing details I will get from the VEci sticker under the bonnet

pics need to be resized, befor I upload tham ..

and thanks again !!
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Old 2nd November 2006, 14:37   #13
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Hi Chetan, I would recomend having your MAF and TPS sensors also checked.
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Old 2nd November 2006, 14:56   #14
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Quote:
Originally Posted by Sideways
Hi Chetan, I would recomend having your MAF and TPS sensors also checked.
Farhan theres no MAF sensors on a honda.
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Old 2nd November 2006, 19:02   #15
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Quote:
Originally Posted by Ford Rocam
Farhan theres no MAF sensors on a honda.
I appologise. Have the MAP sensor checked. I was under the impression that most Honda's ran MAF.

Last edited by Sideways : 2nd November 2006 at 19:04.
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