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Location:
sunny coast, qld
Registered:
October 2002
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fuel tuning question
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Tue, 13 September 2005 11:31
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I have been out tuning my 1jz with wolf 3d v4. before.
Basically what is happening is that between 5000 and abou 5500 it is at about 13.0 - 12.8 then it is getting richer and heading to 12.4 at about 6000 then gets to mid 11's between 6000 and 7000.
That is at 15psi the whole time. The strange thing is that the fuel map is at 7.8ms from 5000 to 5750 or so and at 6000rpm it goes down to 7.3. Yet it is at the same time that the fuel amount decreases that the engine gets richer?
How can this happen?
The only thing I can think of is that the acceleration enrichment is not quick enough as it is really coming on boost hard at about 5000rpm.
I thought of duty cycle on the 550cc injectors but that doesn't make sense either as if they were running out of flow it would be leaning out in the top end of the rev range.
Any other ideas?
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Location:
Bottom of the hill, Sydney
Registered:
April 2004
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Re: fuel tuning question
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Tue, 13 September 2005 12:01
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I don't have any experience with tuning ecu's and I don't know if it would make a difference but do you have a rising rate fuel pressure regulator? An increase in fuel pressure could give the extra fuel.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: fuel tuning question
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Tue, 13 September 2005 12:34
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| BradW wrote on Tue, 13 September 2005 22:01 |
I don't have any experience with tuning ecu's and I don't know if it would make a difference but do you have a rising rate fuel pressure regulator? An increase in fuel pressure could give the extra fuel.
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Brad, that completely defeats the purpose of having a tunable standalone ECU.
Chris,
for injectors, if they get above maybe 80-90% duty cycle, they may not close properly, giving a higher effective pulse width than commanded.
are you giving 1 or 2 squirts per enging cycle? at 8000 (iirc) 80% duty is 12ms per cycle, but at 6000rpm this is 16ms..
the only other thing i can think of quickly is that you are running out of cams or headflow, such that you still have the boost, but not as much air is getting into the cylinders, and so the result is a rich mixture....
from the commanded pulse widths and AFR's, you could plot the VE (or ar consumed) vs RPM... see if it makes sense..
or combustion is being affected at thoe rpm, resulting in an exhaust mixture that looks rich but possibly isn't?? (clutching at straws here.. ie misfiring etc..)
Cya, Stewart
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Location:
Montrose, VIC
Registered:
May 2002
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Re: fuel tuning question
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Tue, 13 September 2005 12:38
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I'll go with running out of puff. Does it still have the standard rat munchers, I mean turbos?
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Location:
sunny coast, qld
Registered:
October 2002
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Re: fuel tuning question
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Tue, 13 September 2005 13:00
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BradW: standard FPR and same boost so same fuel pressure
Stu: by 1 or 2 squirts you mean sequential or batch fired ignition right? If so the injectors are batch fired so they are firing twice per cycle. On the dyno, the power did drop off in the upper rev range so that could be because of lack of flow in the head.
I am not sure how to calculate the ve from the pulse widths and AFR's? ve is something that I never truly understood 
Doesn't feel like it is misfiring but I have noticed a slight miss when I hold about 1200rpms in neutral so...?
mrshin: I am running a HKS ta45s so it should be pumping a fair bit more air than the stockers would at 15psi
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: fuel tuning question
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Tue, 13 September 2005 13:31
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ahh, i mean, for each complete engine cycle (ie two engine revolutions), how many times does a particular injector fire?
and the reason i ask is because you say you have 7.3-7.8ms PW..
assuming the injectors fire twice per cycle (once per engine rev) at 6000rpm, you have 16ms in which to inject, and still be 80% duty cycle... 7.8ms x 2 = 15.6ms = 80% duty.
at 8000rpm, you have 12ms to inject, so 7.8ms = nearly 100% duty, which might have weird things happening.. which would begin around 6500-7000rpm perhaps..
wait, Wolf reports duty cycle no? what does it say?
umm umm.... VE is basically how much air is getting in as a percentage of 100% being the actual swept volume of the engine
the calculation would go something like this...
fuel injected = max flow of injector X duty cycle (probably in cc's).
convert cc's of fuel into mass then into Moles of fuel (approximate as octane for data).
work out how many moles of oxygen are required for nominal combustion, turn that into litres of air (24.47 per mole at 25C),
then divide by 0.21 to get moles of air. (or 0.06 for tokyo  )
that tells you roughly how much air the engine is pumping thru for stoichiometric AFR..
to convert air used to a certain measured AFR, divide air volume by 14.7, then multiply by the measured AFR (ie 11).
that gives you amount of air used for given AFR..
from there, you can easily work ut the VE, as you can calculate how much air the engine would use if 100% efficient (ie half swept volume X (1 + boost in BAR), x RPM. then divide the air vlume calculated before, by this 100% VE number, and you get the VE at a given RPM...
since the only variables are injector duty cycle, AFR, boost and RPM, you can probably just make it into an excel calc sheet and plug in the numbers...
maybe this doesn't help the original problem much.. 
i guess my vote is for intake tract restriction (taking a very simplistic view of the situation), or cam timing not allowing as complete cylinder filling.
on the dyno this will show up as a decrease in torque (before power tapers off), and since torque is directly proportional to VE.. it sorta makes sense....
hmm, you could read the megaquirt Megamanual  .. the MS is tuned by using nominal VE% which is multiplied by the "required fuel" for 100% VE.. making it intuitive to tune as far as the numbers go..
Cya, Stewart
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Location:
sunny coast, qld
Registered:
October 2002
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Location:
Adelaide
Registered:
June 2002
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 Re: fuel tuning question
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Wed, 14 September 2005 00:22
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Chris-what you are seeing is completely normal, and as mentioned by Stewart, it is linked directly to VE of the engine.
The point in the rev range where your engine is making max torque is where the engine is ingesting the maximum amount of air (the point of greatest efficiency-and hence requiring the maximum amount of fuel.
Although you rev the engine more, even though it is at WOT, physical characteristics mean the engine is ingesting less and less air. (IE as you rev the engine more the lower the VE becomes).
As the revs build, although the power may be increasing, the torque is dying away, and hence following yuor max torque point, the injection time should gradually decrease.
(Note that the above description must be considered whilst the engine is at a constant manifold pressure.)
Don't fret mate-that's exactly what you should be seeing.
Cheers
Sean
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Location:
sunny coast, qld
Registered:
October 2002
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Re: fuel tuning question
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Wed, 14 September 2005 00:40
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Thanks mate. It makes sense to me now
So I need some big cams to get more flow and make more torque in the upper rev range then 
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