eta:sorry for sniping your thread flak, im pondering over it
[Edited on 15/3/10 by cd.thomson]
Ok...following on from my original idle problems thread:
http://www.locostbuilders.co.uk/viewthread.php?tid=131856
I am now in a situation where I have a hunting idle from 800-1200RPM but the car now revs perfectly well (re-wrote the map from scratch).
I had the throttle bodies off in the search for a leak somewhere which was causing my idle to be so high. Since then the throttle bodies have been on
and off twice with the result the same, a steadily hunting idle.
The throttle bodies are sealed to the head using an o-ring on each port. O-rings are new and the face of the head is flat from what I can tell
(checked with a straight edge). I drilled a hole in each port and fitted MAP take offs. The hose tails are screwed in tight and sealed with hydraulic
thread sealant. There is then a hose from each port to a 4 way splitter block. 2 of the positions on the splitter are blanked off (linked with hose)
and the 3rd runs to the ECU. There are several joints, but all are a tight push fit using vac hose.
There is an idle bleed screw on each port, all of which are screwed down tight.
There is no idle valve.
I found a couple of problems in my map last night, I had the lamda sensor set as a narrow band when infact its wideband and still had PWM injector
setting in. Its not running closed loop lamda until 1300rpm anyway and I dont think the injector settings would make much difference.
Ignition advance was set back to 10deg.
Other than air leaks, what could cause a hunting idle?
are you sure its not a leak from your supercharger??? intercooler or boost hoses???
do you have a dump valve????
s/c not hooked up yet, TB's are just open to the air.
quote:
Originally posted by boggle
are you sure its not a leak from your supercharger??? intercooler or boost hoses???
do you have a dump valve????
have you tried backing the advance off a bit?
too advance, revs rise, run out of air, revs drop, enough air for revs to rise over and over?
advance set back to 10deg so it wont be that, but i considered that too..
eta:sorry for sniping your thread flak, im pondering over it
[Edited on 15/3/10 by cd.thomson]
quote:
Originally posted by dan__wright
have you tried backing the advance off a bit?
too advance, revs rise, run out of air, revs drop, enough air for revs to rise over and over?
do you have to run map?
do you have a damper before the map sensor?
have you checked equal draw down each one of the pipes?
Could you block it off and try it without?
it has to be MAP when using forced induction as alpha-n doesnt give the required information on the quantity of air/fuel entering the cylinders.
I am leaning towards MikeRs suggestions ref: the map sensor though as these are notoriously unreliable and when I was working on my capri a few of my
mates were having similar issues with MS/MAP
can you access your map whilst running???
had a similar thing on a subaru that was the idle controll valve, but you dont have that on yours, maf sensors cause the same problems too.....but im
thinking you dont have one of them....
inlet manifold gasket??
just trying to cover some simply stuff???
sorry if its of no use....
As Craig says, yes I do need to run MAP as its forced induction. I have a 70-80Kpa idle, which is very high, so I am hoping I wont have too many
problems tuning.
I could disconnect the MAP lines, block the 4 ports on the throttle bodies and adjust the map to make it idle at what the ECU thinks is 100kpa.
There is no idle control valve or MAF.
There is no inlet manifold. The throttle bodies bolt direct to the head and are sealed with o-rings. I will smear some hylomar around them next time I
fit them just to rule that out once and for all.
There are so few joints (throttle bodies to head, injectors to head, and MAP lines) and I cant help but think I have worked through them all. That
said I havent done the carb cleaner test at each joint yet to see if the idle speed increases, maybe I should try that.
Is there a MAP delay function on MS?
If the fluctuations are too frequent, the engine oscillates as experienced?
quote:
Originally posted by MakeEverything
Is there a MAP delay function on MS?
If the fluctuations are too frequent, the engine oscillates as experienced?
Have you tried completely covering the inlet to the throttle bodies, with a hand something similar and see if that does anything. It'll possibly
point to barrel air leak or elsewhere.
As for the hunting, have a look at the data log and see what's changing, might tell a 1000 words so to speak.
[Edited on 15/3/10 by brianthemagical]
Flak,
Sounds to me the map sensor is seeing the valves opening and closing a data log may show this if you can get the sample times down small enough.
as a test - is the map in the 'Flow' ? if so I belive running the map sensor down a bit of tube may work as this can act as shock absorber
but the map can still detect the vacume.
My Map senson on my vems is on the ECU board connected by a couple of Meters of fish tank air pipe and all is OK.
regards
Agriv8
The MAP sensor is inside the ECU as standard for megasquirt. Connected on around 0.5m of 4mm vac hose
Annoyingly I cant do any more testing tonight. But gathering ideas for the next available time is good.
Thanks for the suggestions so far chaps.
I would reduce the digital MAP filtering as much as you can for now, any kind of filtering will introduce a delay which will reduce the phase margin of your control system. If the phase margin is small enough, then you will get oscillation (hunting).
quote:
Originally posted by flak monkey
The MAP sensor is inside the ECU as standard for megasquirt. Connected on around 0.5m of 4mm vac hose
Annoyingly I cant do any more testing tonight. But gathering ideas for the next available time is good.
Thanks for the suggestions so far chaps.
Something else to try, I'll remove all the software smoothing and see what the effect is.
Yes the MAP is rock steady with nothing connected or pre start up. 102Kpa give or take.
I'm afraid you need to go back a step first. You obviously have an air leak somewhere. With the bleed screws all the way in, the engine should not idle AT ALL. Fix that first, then start tuning.
Spoken to Titan (who make the throttle bodies) and Troy at Northampton Motorsport, who have been very helpful.
Basically the idle speed with rollers will be slightly higher than with conventional throttle bodies, but not massivley so. Maybe 1000-1100rpm, which
would be fine by me.
The idle bleed screws should be screwed in tight to start with, they are solely for fine tuning the balance on the throttle bodies.
I should also be aiming to run 2 to 4 deg idle advance for road use.
So it looks like I am back on the hunt for an air leak tomorrow evening!
and i bet as you are laying in bed tonight the answer will pop into your head and you will be out in the workshop at 1am looking....
well that swhat allways happens to me!!!!
i hope you find it and its a simple fix, with the ammount of work and effort you have put in you desrve it....
its not fuel regulator surge???
any more joy on this yet Dave?
did you try running without map to rule out that / prove its an air leak?
have you tried spraying something like easy start around the joints if it suddenly increases RPM - you know which joint is at fault.
Not had chance to have another go yet 
Hoping to get it back together tonight with some sealant on all the joints. Then let it set overnight and then give it a go tomorrow afternoon when I
finish work....