paulf
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| posted on 2/4/06 at 11:41 AM |
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High MAP readings
I have now got my car running but although i have no problems gettingh it to idle i cant get the MAP reading below 65kpa.It is a 1600 crossflow with
an unknown cam and increased compression.I dont know if it is due to the cam or just bad ve settings ,it is drivable but runs rich all the time i
think the high map readings are also affecting the ignition timing as i am using MAP for the ignition control also via a megajolt..
I have tried a few settings to generate VE tables but dont actually know the exact power and torque figres for my particular engine.Some tables looked
ok with figures from 30 to 85 but others have figures as high as 215 in places and look completely wrong.
I am using a V2.2 with v3 software and megatune 2.25.
Paul.
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CairB
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| posted on 2/4/06 at 03:16 PM |
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The VE map that gets generated tends to be on the rich side, for obvious reasons.
I believe that it is only intended as a rough starting point and can get it a bit away from the final tuned values depending on the values for peak
torque, power and their rpms.
If you've put in the correct injector flow rate and capacity etc then I would be surprised at needing VE of 215. I would have expected more in
the region of 100 - 120 for an NA engine.
The tuning process must then be followed to get fueling optimised for your particular setup. The minimum would be with a narrow band O2 sensor
although I feel that it is well worth investing in something like an LC1 as it makes life so much simpler.
The tuning guides on the megasquirt forum are worth a couple of reads to get an understanding of the tuning process.
Have you tried datalogging and feeding the results into one of the analysis applications such as megatweak?
When I did mine I kept the throttle and rpm down initially and worked my way up and across the map.
The idle MAP is affected by the afr so you could tried adjusting the VE values around idle to get the lowest MAP at idle. There are several tricks to
getting the idle steady by 'boxing in' the VE table around idle.
FYI at present I have milds cams and the MAP is about 44kpa at 800rpm.
From my experience throttle bodies can cause the final VE table required to be very different from the estimated one.
That's why I am running a version of Alpha-N.
Cheers,
Colin
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britishtrident
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| posted on 2/4/06 at 03:27 PM |
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65kpa would be about 270mm hg below atomospheric -- "very little suck !"
BUT
Depends if you are really getting a reading in absolute units reason I say this is 65kpa below atmospheric is about -490 mm hg at around what
I would expect a fast road tuned xflow to idle at.
Stick a cheap vacuum gauge on it and do a sanity check.
[Edited on 2/4/06 by britishtrident]
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paulf
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| posted on 2/4/06 at 06:44 PM |
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That is the correct reading ie 270mm hg confirmed with a gauge, im just modifying the vacuum connection rail so as the takeoff is in the middle
instead of one end , not sure if it will make any difference though
Paul.
quote:
Originally posted by britishtrident
65kpa would be about 270mm hg below atomospheric -- "very little suck !"
BUT
Depends if you are really getting a reading in absolute units reason I say this is 65kpa below atmospheric is about -490 mm hg at around what
I would expect a fast road tuned xflow to idle at.
Stick a cheap vacuum gauge on it and do a sanity check.
[Edited on 2/4/06 by britishtrident]
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paulf
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| posted on 2/4/06 at 06:54 PM |
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I re did the VE calc and now have figures from 20 to 85, Im not sure how long an oxygen sensor will last as im running on lead replacement additive at
present but have decided to drain the tank and fill with unleaded to allow me to fit one to get the initial tuning done.
Ive been reading on the megasquirt site , but its not easy to put the thery into practice without O2 feedback.
Will i get any worthwhile info from a datalog with no oxygen sensor fitted?
Im back to work tommorow so wont have any time for a few days, so am going to print out as much info as possible to read at work ready for the end of
the week when I can try again.
Paul
quote:
Originally posted by CairB
The VE map that gets generated tends to be on the rich side, for obvious reasons.
I would be surprised at needing VE of 215. I would have expected more in the region of 100 - 120 for an NA engine.
The tuning process must then be followed to get fueling optimised for your particular setup. The minimum would be with a narrow band O2 sensor
although I feel that it is well worth investing in something like an LC1 as it makes life so much simpler.
The tuning guides on the megasquirt forum are worth a couple of reads to get an understanding of the tuning process.
Have you tried datalogging and feeding the results into one of the analysis applications such as megatweak?
When I did mine I kept the throttle and rpm down initially and worked my way up and across the map.
The idle MAP is affected by the afr so you could tried adjusting the VE values around idle to get the lowest MAP at idle. There are several tricks to
getting the idle steady by 'boxing in' the VE table around idle.
FYI at present I have milds cams and the MAP is about 44kpa at 800rpm.
From my experience throttle bodies can cause the final VE table required to be very different from the estimated one.
That's why I am running a version of Alpha-N.
Cheers,
Colin
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CairB
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| posted on 2/4/06 at 07:48 PM |
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Paul,
I would say that you need the O2 sensor to make VE table tuning reasonably painless, so yes, use the O2 sensor for the datalog. Ensure that you get O2
sensor cross over points for megatweak to work with by setting the O2 sensor ego limit high enough.
If your worried about the sensors failing perhaps a few from the scrappy would be useful just in case you suspect one as being damaged by your
setup.
I used to check my narrow band sensor by measuring the output after the sensor had self heated by putting the tip in the oxygen starved section of a
low blowtorch flame.
I would have thought that you should be able to do a fair few VE table iterations, i.e. datalog - update VE table then repeat, on a tank of fuel.
If your nervous you could swap the O2 sensor for a M18 plug, pinto spark plug?, and run on your new improved VE table for a tank of lead replacement
for a while to recoat the valve seats, ready for another dose of tuning.
Cheers,
Colin
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paulf
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| posted on 2/4/06 at 08:04 PM |
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I think that is the way to go, i will fit an 02 sensor and collect a few spares from scrapyard to play with, Hopefully I can get it somewhere near
using the sensor without damaging the valve seats as i wont be at full throttle until set correctly.
Paul.
quote:
Originally posted by CairB
Paul,
I would say that you need the O2 sensor to make VE table tuning reasonably painless, so yes, use the O2 sensor for the datalog. Ensure that you get O2
sensor cross over points for megatweak to work with by setting the O2 sensor ego limit high enough.
If your worried about the sensors failing perhaps a few from the scrappy would be useful just in case you suspect one as being damaged by your
setup.
I used to check my narrow band sensor by measuring the output after the sensor had self heated by putting the tip in the oxygen starved section of a
low blowtorch flame.
I would have thought that you should be able to do a fair few VE table iterations, i.e. datalog - update VE table then repeat, on a tank of fuel.
If your nervous you could swap the O2 sensor for a M18 plug, pinto spark plug?, and run on your new improved VE table for a tank of lead replacement
for a while to recoat the valve seats, ready for another dose of tuning.
Cheers,
Colin
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paulf
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| posted on 10/4/06 at 08:18 PM |
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I managed to get some oxygen sensors from the scrapyard and fitted one over the weekend.I have been out on the road in it today and manged to get
some datalogs and make a few adjustments .It runs reasonably well now but has a few flat spots and a bad stutter at about 3000rpm but am makeing
progress.I can still only get the map reading down to about 55kpa at idle of 800revs but have found that increasing idlespeed to about 1100 revs
brings it down lower but cant work out why at present.
I have downloaded Mstweak 3000 but cant find the usage instructions for it yet am going to try with that latter in the week when im off work
again.
Paul.
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MikeR
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| posted on 10/4/06 at 10:52 PM |
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How long do you think O2 sensors will last on LRP ?
hadn't occured to me before that it would kill them.
(just planning ahead)
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britishtrident
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| posted on 11/4/06 at 06:36 AM |
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Valve timing OK ? also possible tappet clearance too tight.
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paulf
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| posted on 11/4/06 at 08:32 PM |
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Yes i should check that , i have noticed it occasionally pops lightly through no 4 inlet only on light throttle openings.Just means having to pull off
the rocker cover for a look.
Paul.
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