View Full Version : boost figures and behavior
I've just fitted an Autometer boost gauge on my Z20LET coupe.
I noticed that boost suffers from an annoying hesitation when accelerating hard.
The turbo boosts to 15psi, hesitates half a sec, then overboosts to 20psi and decrease back to 15psi, in 3rd 4th or 5th gear of course.
I'm pleased by the 20psi overboost and 15psi hold, but I'm just wondering if this hesitation before the overboost is a normal thing or not.
BTW, I'm running EDS phase 2 with 9ltr intercooler, derestricted airbox and k&n panel filter, stainless steel powerpipe with no "DV out", precat and sportscat from courtenay and bastuck "no middle silencer" exhaust !
Thank you !
anyone ? P2 or CS3 owners with boost gauge ?
Ive got the same problem mate. Narrowed it down to either injector or ecu or maybe even the map. Sorry i dont have a guage yet. I am running cs 3 from courtenay.
did you fixed the problem?
could be bad fuel?
Stick some octane booster in it and see if it goes away!
I had to fill my gsi up at a petrol station renouned for crap fuel and low and behold every now and agin i was getting judder on hard acceleration, since then never had it again!
coupe_turbo_jon
09-08-2005, 18:54
Have you tried an air flow meter, just a thought :wink:
Have you tried an air flow meter, just a thought :wink:
have to try ...!
coupe_turbo_jon
10-08-2005, 15:51
Do, because those were the symtoms I was having when mine went
rakpeterson
12-08-2005, 01:53
had simmilar prob with mine. Thought it was maybe ecu or amm but it later turned out to be the actuator arm catching on the inside-side of the turbo heatshield. it was catching in a few places and would seem to hesitate then suddenly pick up again. Just a thought if youve removed/painted/etc. heat sheild like i did.
mantamagic
13-08-2005, 07:14
You have to remember that by the time your running 10psi of boost, the actuator has already fully cracked open.
I think the boost issue may be down to the BCS (Boost Control Solenoid), which is the device the boost hose to the actuator comes from.
It bleeds off back into the intake and may simply be slow in responding.
It does exactly the same with my car.
My car boosts up to 15psi hesitates then goes up to 17-18.
On overboost it goes straight up to 20 without a problem.
I'm sure I read about a similar issue being fixed by replacement of the BCS ?
You have to remember that by the time your running 10psi of boost, the actuator has already fully cracked open.
I think the boost issue may be down to the BCS (Boost Control Solenoid), which is the device the boost hose to the actuator comes from.
It bleeds off back into the intake and may simply be slow in responding.
It does exactly the same with my car.
My car boosts up to 15psi hesitates then goes up to 17-18.
On overboost it goes straight up to 20 without a problem.
I'm sure I read about a similar issue being fixed by replacement of the BCS ?
what's the part no of the BCS ?
I tried changing the AFM but nothing...
I noticed that the boost would hesitate to 15psi then overboosting to 20psi when flooring down in 3rd from low revs, and that it just doesn't overboost when changing gears from 2nd to 3rd in an hard acceleration ie. at high revs it just stop and hold at 15/16psi ...
It think that it isn't normal ....
MikeWarner
28-08-2005, 23:09
Luke, please let me know if you solve this. I have the exact same problem and I have check everything. I have changed the standard dump valve, changed boost pipes, upgraded pipe clamps, changed both solenoids, changed AFM, adjusted the actuator, even ran without the boost leak solenoid (no change), checked everywhere for leaks..... I spent ages trying to sort it and I've pretty much given up.
I'm running CS3 by the way. As you say, foot down, 15psi, drops for a split second and then over boosts to 18psi. From 40mph in 4th you don't get this, but I think it is down to the ECU having more time to work out what is going on. Also, I'm not getting overboost on quick spool-up (as you say) i.e. when changing gears or flooring it at higher revs.
jonstatt
29-08-2005, 08:58
Are you supposed to get overboost at high revs or when changing gears? Overboost normally only happens between 2k and 3k revs. Well thats all I get on my standard car anyway. I am sure you are changing gears well above 3k.
Jonathan
so maybe that's the normal behavior of the car and I'm just paranoid ... ?! :-/
Luke I have also heard that the BCS is supposed to solve this problem, best thing to do is try it as the BCS is another weak point on our cars.
I get overboost in mine between all gears if your revving it hard!
But it never did it untill i got the aftermarket exhaust on it!
I get overboost in mine between all gears if your revving it hard!
But it never did it untill i got the aftermarket exhaust on it!
I have a full bastuck exhaust, so I think there's a problem if I can't get overboost everytime....
Overboost appears depending on the load and rev's of the car. Overboost at all rev's isn't really possible as for our cars if it has been re-mapped. As for your turbo to provide overboost your turbo would have to have the capacity left in its speed range to provide this extra boost :). At around redline you would only get peak boost and thats it as the turbo is running pretty much at its limit on a re-mapped car.
On a standard car there is extra capacity. But what is stopping overboost at the top end of the rev range is normally the ECU settings is designed so that above a certain rpm the boost control system trys to minimize overboost. I have noticed the further up the rev range the less peak overboost I get in my car. On a standard car with a pre-cat and aftermarket exhaust the turbo spools up a lot quicker which directly translates into boost building up quicker. The standard boost control system of course doesn't realise that the characteristics of the whole boost system has changed so controls or tries to control the boost with its standard settings. This in theory would mean cars with modified exhausts would have more overboost at low and high revs.
AstraTurbo
13-09-2005, 00:17
did this problem get sorted? I have the exact same problem with mine. its really annoying keep getting very worried about it. only seems to happen in 4th & 5th. could it just be BCS?
Get a uprated actuator and see if that solves your problem :).
MikeWarner
13-09-2005, 12:06
Overboost appears depending on the load and rev's of the car. Overboost at all rev's isn't really possible as for our cars if it has been re-mapped. As for your turbo to provide overboost.....It is not so much the overboost I'm worried about, but the dip just after reaching holding pressure.
The lack of overboost is more down to timing - as in when I should be getting over boost, I'm getting a stupid dip. Once the dip is over, the ecu is no longer trying to make overboost.
When I have time in a few weeks, I'm going to go over the whole engine with a fine tooth comb and track down the problem.
benny2097
14-09-2005, 16:36
i also have the same problem i have changed bcs and afm but still the same checked for leaks etc cant find anything wrong hope someone finds the fault cos it is annoying me now
MikeWarner
14-09-2005, 18:02
Benny, do you get a wooooshing noise when you plant your foot in high gears from low revs?
AstraTurbo
14-09-2005, 23:24
I do, what would this mean?
MikeWarner
15-09-2005, 10:10
I don't know it the whooshing noise is normal as I've always had it - but it seems strange to me. Does everyone get this or is it people with the boost problem only?
jonstatt
15-09-2005, 21:45
I have a standard car and if I plant the gas at 2000rpm in 3, 4 or 5 there is an additional noise. Not sure I call it a whooshing noise, but more like a gurgly-burgly type noise. There is a bit of "whoosh" mixed in though.
Jonathan
benny2097
16-09-2005, 18:55
Benny, do you get a wooooshing noise when you plant your foot in high gears from low revs?
Yes i do it is just the boost pressure building up i think
mantamagic
25-09-2005, 00:20
Anybody know the part number for the boost solenoid ?
This is deffo somthing ecu related, when i use a dawes device the car overboosts slightly then holds the constant boost with no dips but the ecu doesn`t like this, in any gear even within the boost parameters when the boost normally drops off and the dawes device holds it the ecu throws up a fault code and goes into limp home mode.
MikeWarner
25-09-2005, 12:47
mantamagic - it won't be the boost solenoid. There are two - ones that controls the actuator and one for the dump valve over-ride. If you want to test them, just swap them over. If things are the same, then they are not at fault. I even changed both of mine and it fixed nothing.
I do think the ECU is controling the dip - but not through fault if the ECU, but down to something else causing the ECU to do this.
jamesmurray
25-09-2005, 13:08
where abouts is the boost solenoids located? i wudnt mind swapping mine over, see if it does anything to my crappy perfromance in the higher gears
jimbo
MikeWarner
25-09-2005, 20:32
One is at the front near the heatshield. You can't miss it as it has a plug on it a two vacuum pipes. The second is at the rear under the inlet - slightly to the right hand side. Both are the exact same part. I even tried bypassing the rear one by joining the two pipes together - but it still didn't fix the problem. (I was thinking that the rear one may have been releasing boost via the dump valve)
Try disconnecting the dump valve from the electronic valve at the rear of the engine and run the dump valve from the vacume pipe on the side of the inlet manifold, ive done this and its got rid of the drops in boost and delay of boost building up. The thing ive noticed is how slow the throttle responce is when i lift of the throttle as the dump valve opens with quite a delay. I think its a bit more laggy but the boost comes in earlier.
MikeWarner
29-09-2005, 10:30
I've spoken to Courtenay and I'm booked in for monday for some trouble shooting on this. Hopefully it will be fixed and I'll be able to report the findings back here.
Ive been out for another blat this morning and its certainly made a difference, the car feels really agressive now and there is no drop in power at about 4k and no pause when the boost increasing:cool: just pul pulll pull to 6.5k:D
Oh and the exhaust tone has changed and i get a nice big pop from 1st to 2nd like a rally car.
mantamagic
30-09-2005, 21:04
My BCS got exposed to the elements when I had a manual boost controller fitted, I do think it is related to my minor problem as it does not bleed the back to the intake quick enough.
Forget putting a dawes device/manual boost controller on a std mapped car, the ecu will continually override it and cause the limp home mode.
You make be able to improve acceleration and surge with the boost controller but you will end up with less boost and power overall.
The actuator is pulsed by the ecu and the boost controller prevents this pulsing therefore causing problems.
You can override it by using a fuel cut defender, but this gets messy and can quite easily cause the engine to go pop.
MikeWarner
03-10-2005, 20:15
See here for my finding on this problem:
http://www.m1gst.com/vb/showthread.php?p=479778#post479778
THE GREEK COUPE
03-10-2005, 21:54
Hi Mate The Problem Is The Softwere You Will Need A Slightly Stronger Actuator To Overcome This Problem But It Will Never Be Smooth.it Is The Way The Softwere Is Built.this Does Not Happen In P3 And Of Course It Doesnt Happen With The New Ihi Turbo Conversion Which Produces Above 330 Bhp As Seen In Jamies Car In Regals Rr Day.:)