Boost "Spike" [Archive] - SaabCentral Forums

: Boost "Spike"


martin.nicoll
18th July 2007, 08:38 AM
I have replaced my d/p from Abbott with their "newer" version.... this cured the hesitancy and the engine light.... :)

Problem is the car has developed massive boost spike when on WOT in 3rd & 4th but mainly in 5th. :cry:

Abbott said it is nothing to do with their d/p or ECU, as it would have happened before if it was. They did mention possible pipes and vaccumes being split or off....

Any ideas what these pipes could be and where they are... also an ideas what else could potentially be causing this? :confused:

Saabohème
18th July 2007, 08:55 AM
First order of business - check the three larger vac lines that run to your BPC. Run, do not walk. Report back.

martin.nicoll
18th July 2007, 09:22 AM
Just checked... all lines from the BPC are fine, no cracks and all are securely on.

Sap
18th July 2007, 09:55 AM
boost spike as in your hitting fuel cut off?

this thread may be of use

http://www.saabcentral.com/forums/showthread.php?t=100608

Saabohème
18th July 2007, 09:58 AM
Next order of business - you have a 2002 Abbotted Aero, so I hate you. Perhaps that is too strong - I envy you and covet your automobile. But let's see what we can figure out now. Please provide more information about the boost spike, now that we are satisfied that the BPC solenoid is connected. (We may discover later that your BPC has gone bye, bye). Please describe the boost spike in detail:
Where on the stock gauge it goes (or the psi rading if you have a real pressure gauge);
The duration of the spike (how long it is sustained at the spike peak);
What does it do if not a sustained spike peak and how does it do it and how quickly (that is to say, does it spike and then immediately fall to a sustained lower reading, does it spike and then flutter at or near the spike peak, or does it spike, drop, re-spike, drop and so forth).

martin.nicoll
18th July 2007, 10:06 AM
:lol: Sorry to hear of your envy... I am however very grateful for your help!


Right.....

Ths "spike" seems to be mainly in 4th and 5th, but has happened in 3rd.

What happens is when I accelerate hard the boost rises quickly and smoothly to beyond the red on the stock gague (not got a real one yet), it holds for about half a second then 'hiccups' back to about half way in teh red and then slowly rises again to about 3/4 in....

This is happening every time in 4th and 5th and about 50% in 3rd, not had it in 2nd as of yet.

I had a rolling road done last week and peak boost (before suffering from teh spike) was 1.3 bar (approx. 19psi I believe) and this was sustained at about 3/4 in the red, so not sure now......

Thank you for your help with this, I really appreciate it!

martin.nicoll
18th July 2007, 10:14 AM
boost spike as in your hitting fuel cut off?

this thread may be of use

http://www.saabcentral.com/forums/showthread.php?t=100608

Ooooh wastegate chatter... I have this too....... didnt realise that was a problem and not normal?! :confused:

So... possibly BPC and/or wastegate?

Oooh oooh oh... also dump valve, I have an uprated one (£30 ebay job) and have teh stock spring in, maybe this is an issue? I have stronger springs, should I put the harder ones in maybe?

Sap
18th July 2007, 10:16 AM
did you perform any adaptation runs after installing the new HW?

martin.nicoll
18th July 2007, 10:18 AM
did you perform any adaptation runs after installing the new HW?

The problems were today since teh DP was fitted..... I havent changed anything since, just checked the vac pipes.

Saabohème
18th July 2007, 10:43 AM
You may never experience it in 2nd if Abbott limited the boost in 1st and 2nd like Saab and some of the other tuners do.
Let me get this clear in my head - you refer to this being a spike. What was your previous best on the stock gauge before this began happening - where precisely did it go? Since it is going to 3/4 now and then dropping, I am assuming that you previously did not reach 3/4 red? If this is true, was your previous best 1/2 where it now settles to and sustains before attempting to climb again? If so, maybe the 3/4 is your new best boost peak but simply cannot be sustained - perhaps due to some other factor like the strength (or weakness) of the BPV spring or heat soak on the IC (although this is unlikely since you say you can get spike and drop in third, then fourth and then fifth, which would not happen as you go through gears since the heat soak could not be dissipated between gears quickly enough). This could be a new boost peak that cannot be sustained due to inadequate fuel - and thus knock detection is pulling timing and boost to sustainable levels. MAYBE, the new DP has decreased the pumping loss on the exhaust side sufficiently that you are temporarily leaning out for a second and the boosts drops for this.

martin.nicoll
18th July 2007, 11:03 AM
Right.....

Before.... Boost would rise to just over 3/4 in the red and was sustainable, with slight fall on prolonged runs.

Now.... Boost rises very quickly to beyond the end of the gague sustained for about 0.5 seconds and then falls to 1/2. It then rises again to about 3/4 and is sustained after that.

Saabohème
18th July 2007, 11:27 AM
Before.... Boost would rise to just over 3/4 in the red and was sustainable, with slight fall on prolonged runs. This was probably IC heatsoak.

The picture is clearer. Your earlier responses were somewhat ambiguous.
I now concur that you have an uncontrolled and undesirable boost spike. It seems that this spike is triggering Trionic overboost protections causing your boost to fplummet or taper to safe levels, before climbing back to the Abbott programmed peak, where it then sustains. The hiccup you mention could be and probably is fuel cut, but you will need to elaborate on that before it may be conclusively stated.

The only variable in the equation that we have thus far identified in comparing the before and after is the introduction of new DP in place of an earlier Abbott DP that was in some way defective, IIRC. (Please verify this assumption on my part and make corrections where warranted).

So, why is the DP not to be suspected in this scenario? Please provide a more detailed description of what Abbott told you by way of explanation as to why the DP cannot be contributing to the problem.

martin.nicoll
18th July 2007, 11:45 AM
The only variable in the equation that we have thus far identified in comparing the before and after is the introduction of new DP in place of an earlier Abbott DP that was in some way defective, IIRC. (Please verify this assumption on my part and make corrections where warranted).

So, why is the DP not to be suspected in this scenario? Please provide a more detailed description of what Abbott told you by way of explanation as to why the DP cannot be contributing to the problem.

The old downpipe has a problem with teh cat, basically it was FUBAR'd....

They said that the ECU was programmed to set levels and that the new d/p was slightly more restrictive when working than the other one and that their d/p & ECU couldnt be contributing to boost spike as it has only just occured and if it was the ECU it would have happened before.

They also said that teh d/p cant affect the boost on its own? I couldnt argue as I dont really have a clue!?

Saabohème
18th July 2007, 02:42 PM
I am no T-7 expert but this I know: T-7 will adapt to most hardware changes to stay within its mapping. Your T-7 was re-mapped by Abbott, so assuming everything is working properly and in harmony, the car should continue to work just as before, with the boost coming on aggressively-progressively and peaking and holding at 3/4 red on the gauge. However, it is not doing this. After the single change from the one Abbott DP to the new Abbott DP, you are now very aggressively boosting (read "too rapidly boosting"), shooting past the previous peak and off the gauge, most probably triggering fuel cut, causing boost to fall to about 1/2 way on the gauge, before it begins progressively climbing back to its former peak and holding there.

Electrically test the BPC per Haynes or WIS.
Test the mechanical function of the BPC.
Verify that the large vac hoses are connected to the proper ports.