LNF: Turbo boost high when let off the throttle

[Mr.Uncontrollable]

Hi All,

I've been searching all over the internet and couldn't find an answer for my problem. I have Saturn sky Redline with Magnaflow exhaust and K&N drop in air filter plus 3 bar sensors. My tune is stock for two reasons, first I had lot of KR (maybe its the fuel, sensors .. etc), second I was boosting so high at some points (around 30 psi).

My issue now is that even with the stock tune, I'm still boosting relatively high (up to 23 psi). After checking my scans, I noticed that the high boost happens when I let off the throttle, exactly when it reaches zero, the boost just jumps to high value before going down. I need to fix this is in order to boost more safely. If I add any more boost with this issue existing I will end up with extreme unwanted boost. Please help

I believe the below pictures are better than my English

Boost.PNG
boost2.PNG

Please find the scan attached.

Thanks

[cobaltssoverbooster]

That's normal as it takes the LNF a while to build vacuum and open the recirculating valve. This is usually more pronounced when a ATM BOV is installed with out correcting the spring pressure.

Alot of the scans here will agree

[Mr.Uncontrollable]

That's normal as it takes the LNF a while to build vacuum and open the recirculating valve. This is usually more pronounced when a ATM BOV is installed with out correcting the spring pressure.

Alot of the scans here will agree

First I would like to thank you bro for being always here to help us

I really did not have any clue about the high boost until I was told about it at in this forum when I posted about my KR issue. No one said its normal at all. Below is a link to the post.

http://www.hptuners.com/forum/showth...d-heart!/page2

The problem as said is that I have this issue on my stock tune as well, which means if I add any extra boost I will end up with very high Boost when I let off the throttle and this may be very bad on the engine. Any ideas

[Iam Broke]

The boost goes high as the throttle plate closes as there is no place for the air to go before the BPV or BOV opens. The engine never sees it. Worst that will happen is you pop a charge pipe hose off or damage a plastic IC end tank. Get a good aftermarket intercooler with metal end tanks and boost away.

[Mr.Uncontrollable]

The boost goes high as the throttle plate closes as there is no place for the air to go before the BPV or BOV opens. The engine never sees it. Worst that will happen is you pop a charge pipe hose off or damage a plastic IC end tank. Get a good aftermarket intercooler with metal end tanks and boost away.

Please excuses me for asking much

- Isn't the boost being measured on the manifold? which means the high boost is already inside the engine?
- Shall I install an after market BOV to get rid of this issue?
- What does it have to do with the intercooler?


Thanks

[Iam Broke]

The spike you see is on the MAP sensor in the lower charge pipe. It's the only one that can read higher than 255 kPa (~22 psi) no matter what the range of the sensor is. The ECU range is limited for the MAP in the intake manifold in it's hard coding to 255 kPa.

I have never been a fan of a BOV on an LNF, too much MAF metered air escapes the system fooling the ECU and causing massive fuel trim issues during the transition. One solution is a MAF relocate, but it causes other tuning issues, especially at low flow/idle (at least with the ZZP pipe).

Plastic end tanks on the stock intercooler are weak and might crack under high boost.

I'm an old feeb and sure someone will correct any errors.

[Mr.Uncontrollable]

Thanks bro. I think I'll just ignore this issue and go ahead adding some extra boost (between +2 and +4)

Just another problem I'm having those days is that my automatic gear is jerking while downshifting, especially on low gears. I saw some posts online that says you can tune the car for this to go away but no one says what to tune exactly. Do you have any clue about that?

[Iam Broke]

Never tuned an auto LNF, COB will chime in.

[cobaltssoverbooster]

well on the auto if you have transmission settings you can tune the shift pressure on the downshift which should smooth it out.
you can take some timing out in the lower rpm ranges where the auto trans shifts from 2-1 or 3-2 at slow speeds but any changes from the middle of your map down to the lower right corner should be tuned for cruise or wot only. lowering the timing can help reduce the load on the torque converter some. other table would be camshaft movement at low rpm and dal/optimum torque tables. the optimum torque is a sensitive table and is recommended to be changed only after you understand what goes on behind the rest of the ecu tables first.

this is a log from my car earlier today. boost is set low for break-in and DD but its about 18-20 psi. you can see on the line my tps and etc pedal % are almost closed but i still have 230 kpa which is ~18.7 psi
reno 04.png

[Mr.Uncontrollable]

Thanks bro.

I don't have transmission tables so I'll try with the other suggested tables. For the boost I think I'll just forget about this issue as it seems to be totally normal (your scan has cleared it out , thanks) . As said I may add some extra boost on the high end of rpm only.

That was lot of help to me .. Thanks again

[cobaltssoverbooster]

the spike happens in such a small amount of time that its something we can overlook. plus the load usually goes down where the spike is which means we can adjust timing to prevent a detonation event. setup your histo as a general kr pid and you can tune it out in the tuning process of copy and paste special.

i would try dal shifts first as the tables function is to have a set value of airflow commanded. lowering the number is the fastest way to reduce load on the trans in the shifting range.

good luck and dont forget to post any problems with standard info (log, current tune, vcm scanner config., mod list first post only, and issue of course)

CSSOB

[Mr.Uncontrollable]

I have tried before to tune my timing to get rid of the KRs using copy and paste special. The KRs went away but the car became heavy and not as responsive, so i just returned everything back to what it was and decided to get my hands little dirty. First I adjust my KR sensors rotation as some recommended in other forums to get rid of false KR, and that really helped. Then I installed the K&N air filter to get better more air and installed the Magnaflow 3" exhaust to get engine to breath easier. The mods worked fine to me so I went ahead installing base GMPP tune (I have the 3bar sensors installed already).

Now the maximum KR I'm getting is 4.5 with max average of 3.5 on GMPP tune , is this considered safe? or I have to tune my timing?

I'm using the best fuel available to me here at Bahrain, Octane 95 RON - 92 MON.

The attached scan on my first post is for my car with stock tune. I'm attaching here my last scan with GMPP tune along with the tune file itself

Attachments:
06 Saturn Sky 2008_GMPP.hpt
37 from work stock saturn sky gmpp - Exhaust.hpl

Thanks

[cobaltssoverbooster]

Did the dealer install the gmpp programming because its more restrictive than s modified factory tune.

if you did to late now but its ok. I'm doing injector Testing for kr but its taking some time to get results.

[Mr.Uncontrollable]

Did the dealer install the gmpp programming because its more restrictive than s modified factory tune.

if you did to late now but its ok. I'm doing injector Testing for kr but its taking some time to get results.

The GM dealer at my country refused to do it so I had to take other route. This tune is based on my stock tune and multiple GMPP files sent to me from friends and from hptuners repository. I noticed many differences from one gmpp file to another so I took to closest to my stock tables.

What do you mean by the injector testing ?


Thanks

[cobaltssoverbooster]

good that makes yours a stock modified stage 2. the stock file has less turbo protection safeties.

my injector testing is for window time vs knock retad. trying to see if the injection window start angle has anything to do with detonation events. after adding an extra 10 psi over factory base tunes im sure its not calibrated correctly.

[Mr.Uncontrollable]

Good luck with that bro .. let us know how it goes.

[|V3nom|]

yes i would like to know this. do you think the ghost kr could be real due to an uncalibrated injection window? maybe even uncalibrated enough in stock tunes?

[cobaltssoverbooster]

well im running 20* no kr on supreme pump in nevada which i believe is 91. im still new to the area and have a lot going on so i haven't really payed attention to the octane rating. once i get enough logs together i will put up a post.
the first to figure this out was gmtech. its been a long time since i have moved injectors due to military service so its taking me a little longer to remember what i was doing and how i wrote my notes out. so far its looking promising and remembering a lot about the window timing and value representation.

[|V3nom|]

wish i could run 20* without being paranoid about possible ghost knock...

too bad gmtech doesnt chime in anymore, he sounded like he had a good handle on how the lnf ecm worked.

[cobaltssoverbooster]

Yes he did or does probably a better word.