boost spikes and missing/low boost

[zingZACH]

Originally Posted by saabkid37

my viggen has NEVER run oover 9.5 psi.

Yeah, 99's seem to run low for some odd reason. I was seeing about 11 - 12 stock. I would see 10 on some days... and that was with full 3". Now that it's tuned and has cams and a bigger inlet pipe from an 02 Viggen, it runs about 15 - 17.

[jssaab]

CHeck that accordian looking hose on the BPC, mine had a crack in it that you could not see unless you bent it.

I had the saem kinda thing and it took forever to find

[pete93t]

my 9-5 is doing the same thing. it will get low boost then climb to 20-22psi then drop and sometimes it feels like it spikes or im hitting fuel cut or something. for a wile i thought the psi drop was from heat soak after a few WOT runs but idk. could be so many things i dont know were to start. just got nordic stage 3.

[DeLorean]

Originally Posted by zingZACH

Yeah, 99's seem to run low for some odd reason.

If there is something wrong, sure... My 99 9-5 with the GT17 according to the open SID is seeing what equated to approximately 17 PSI. The fact that it's a 99 has nothing to do with it. It's the same motor and same engine management system.

I would do all the preliminary things you need to do with any turbo car first off. Vac leaks, plugs, DI. Be sure your BPV is holding pressure (blow into the vacuum hose, it should not leak). Since you have another 9-5 that runs well, try swapping some parts between the 2 and see if anything changes. I would swap the air flow meter for one. I would not be shocked if there is some massive boost leak that has developed, finding it could be the hard part though... Running issues are like a shot in the dark trying to diagnose without seeing the car, but there are a few "off the top of my head" ideas you might take a look at.

[zingZACH]

Originally Posted by DeLorean

If there is something wrong, sure... My 99 9-5 with the GT17 according to the open SID is seeing what equated to approximately 17 PSI. The fact that it's a 99 has nothing to do with it. It's the same motor and same engine management system.

I would do all the preliminary things you need to do with any turbo car first off. Vac leaks, plugs, DI. Be sure your BPV is holding pressure (blow into the vacuum hose, it should not leak). Since you have another 9-5 that runs well, try swapping some parts between the 2 and see if anything changes. I would swap the air flow meter for one. I would not be shocked if there is some massive boost leak that has developed, finding it could be the hard part though... Running issues are like a shot in the dark trying to diagnose without seeing the car, but there are a few "off the top of my head" ideas you might take a look at.

I was talking about 99 Viggens... and no, not everything is completely the same in a 99 Viggen.

[mike d]

Did you pull the maps from a tdo4 car? if you didnt you could have an error in the PID maps, these are dialed in based upon what turbo is on the car,, make sure these are changed properly

how many MG of air are you requesting at the peak? are you certain there are not torque limters that need to be adjusted?? T7 is a bitch like that....

[abdukted1456]

Originally Posted by jssaab

CHeck that accordian looking hose on the BPC, mine had a crack in it that you could not see unless you bent it.

I had the saem kinda thing and it took forever to find

You mean the hard plastic "hose" that covers the wiring to the electrical connector? yeah, it is completely cracked and coming off.

Originally Posted by mike d

Did you pull the maps from a tdo4 car? if you didnt you could have an error in the PID maps, these are dialed in based upon what turbo is on the car,, make sure these are changed properly

how many MG of air are you requesting at the peak? are you certain there are not torque limters that need to be adjusted?? T7 is a bitch like that....

it is a nordic tune, not a self tune, I couldn't answer that. it should be correct though.



I swapped in a different BPC and the boost is steady (no more spiking) but still seems low from what I would expect from a td04 tune... (peak at 9 or 10 psi)

I will look further, just have been too busy to dig really deep. swapping the MAF with the aero to try is definitely on my list though.

I do suspect a boost leak, or maybe the WG is partially open or sticking open or something.

[koriminal]

Did you ever get this figured out? I'm having similar issues with my viggen stage 2 nordic. Peaks around 10 and will hold steady. I figured it was just less pressure because I added a downpipe, but it just doesn't seem fast. Before the DP I was peaking at 17psi or so. Wondering if I should be looking for leaks etc, or if this is it...

[abdukted1456]

I don't know if it really feels like a stage 2 aero still, so I don't know if this is "solved" yet... BUT here are a few things I know:

• I am used to a stage3++ Aero with e85 so a stage 2 lpt with a td04 might still feel "slow" to me.
• The aero has a big ETS intercooler and this lpt has the stock one that blows chunks
• The ambient temp has a massive effect on the car, with the stock IC this car feels like there is no turbo and then when the temp gets down to say 65 degrees, it feels peppy again. Again, compared to my aero and my old 9-3 with uprated IC, this is a very dramatic loss in performance...
• I recently replaced the CPS and now I can see 14psi + and holding on cooler days when the car doesn't heat soak as easily.
• I did not find any obvious leaks, but I could have easily missed something.
• the car is OLD with 180K, so there is bound to be some things that don't work 100% as they should at this point.
• I swapped BPC's with no change.
• DI and plugs are still pretty new
• Still did not try a MAF but it is running better now with a new CPS.