CAUSE OF INTAKE PRESSURE DROP??

[stevolution]

Hm.. what causes intake manifold pressure drop? When I press accelerator at about 4~5000 rpm, the turbo stalls for some reason then starts spooling up again gaining boost after 1~2 seconds of pressing down on the accelerator.. I can tell cause normally I can hear air wooshing through my intake through my filter. I don't think its the stock BOV either cause it works fine under 4000 rpm... can hear it passing it onto the intake manifold..

Hm.. questions should be more like what causes the turbo to stall..

Any suggestions would be appreciated

Thanks

 

[Black88GTA]

Boost leak? Or, maybe a bad vacuum line or something? My old Conquest loved to blow vacuum lines off the fittings under boost...one in particular, I had to ziptie the end in place so it would stay put.

 

[SVT Cobra]

If your car was supercharged I'd say it was the pully slipping, which sounds exactly like your problem, but because it's a turbo I would say a leak maybe?

 

[compman25]

Are you just cruising at a constant rpm? If so, you lose the boost because it isn't needed to keep you going at that speed. Then you nail it, and nothing for a few seconds. It has to spool up again and build boost. Turbo lag.

 

[thedarkwolf]

There won't be lag when you are already cruising at 4k rpms. The turbo is already spooled up.
Checking for leaks won't hurt but it doesn't make sense that its not also leaking at lower RPMs. Could be a timing issue. What car is it?

 

[compman25]

yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

 

[otispunkmeyer]

Originally posted by: compman25
Are you just cruising at a constant rpm? If so, you lose the boost because it isn't needed to keep you going at that speed. Then you nail it, and nothing for a few seconds. It has to spool up again and build boost. Turbo lag.

there wont be lag at 4000rpm

the turbo will still be spinning since its turbine is connected to the exhaust and exhaust gases will be flowing, turning the turbine, you'd have to block the exhaust or have some kind of bypass to shift the flow down another pipe or soemthing to stop the turbo spinning.

the compressed air it will be generating however will probably just be vented away to atmosphere or something by a valve, until you put your foot down again.

if it was a leak, then wouldnt he be loosing boost a bit if not completely?

could it be that something is loose or sticking? like a valve or something? and its sticking for a couple of seconds before it actually operates?

 

[DivideBYZero]

Overboost conditions will cause the ECU to drop pressure via the wastegate, slowing the turbo. I had this a couple of times in very cold weather. It was ~-6c so it was sucking in very cold air and this just pushed it over the 13 or so lb boost limit. The cut was fierce and felt like someone stamping on the brake and letting off right away.

Subaru, if anyone is wondering.

 

[compman25]

Originally posted by: otispunkmeyer

Originally posted by: compman25
Are you just cruising at a constant rpm? If so, you lose the boost because it isn't needed to keep you going at that speed. Then you nail it, and nothing for a few seconds. It has to spool up again and build boost. Turbo lag.

there wont be lag at 4000rpm

the turbo will still be spinning since its turbine is connected to the exhaust and exhaust gases will be flowing, turning the turbine, you'd have to block the exhaust or have some kind of bypass to shift the flow down another pipe or soemthing to stop the turbo spinning.

the compressed air it will be generating however will probably just be vented away to atmosphere or something by a valve, until you put your foot down again.

if it was a leak, then wouldnt he be loosing boost a bit if not completely?

could it be that something is loose or sticking? like a valve or something? and its sticking for a couple of seconds before it actually operates?

You are wrong.
Control by turbine-side bypass
The turbine-side bypass is the simplest form of boost pressure control. The turbine size is chosen such that torque characteristic requirements at low engine speeds can be met and good vehicle driveability achieved. With this design, more exhaust gas than required to produce the necessary boost pressure is supplied to the turbine shortly before the maximum torque is reached. Therefore, once a specific boost pressure is achieved, part of the exhaust gas flow is fed around the turbine via a bypass. The wastegate which opens or closes the bypass is usually operated by a spring-loaded diaphragm in response to the boost pressure.

Today, electronic boost pressure control systems are increasingly used in modern passenger car diesel and petrol engines. When compared with purely pneumatic control, which can only function as a full-load pressure limiter, a flexible boost pressure control allows an optimal part-load boost pressure setting. This operates in accordance with various parameters such as charge air temperature, degree of timing advance and fuel quality. The operation of the flap corresponds to that of the previously described actuator. The actuator diaphragm is subjected to a modulated control pressure instead of full boost pressure.

That is from Borg Warner Turbo info

 

[compman25]

Originally posted by: DivideBYZero
Overboost conditions will cause the ECU to drop pressure via the wastegate, slowing the turbo. I had this a couple of times in very cold weather. It was ~-6c so it was sucking in very cold air and this just pushed it over the 13 or so lb boost limit. The cut was fierce and felt like someone stamping on the brake and letting off right away.

Subaru, if anyone is wondering.

And if you install a boost guage and watch it as you cruise at a constant rpm in your WRX, the boost drops to almost 0.

 

[DivideBYZero]

Originally posted by: compman25

Originally posted by: DivideBYZero
Overboost conditions will cause the ECU to drop pressure via the wastegate, slowing the turbo. I had this a couple of times in very cold weather. It was ~-6c so it was sucking in very cold air and this just pushed it over the 13 or so lb boost limit. The cut was fierce and felt like someone stamping on the brake and letting off right away.

Subaru, if anyone is wondering.

And if you install a boost guage and watch it as you cruise at a constant rpm in your WRX, the boost drops to almost 0.

Agreed. I was fully aware that at constant rpm/no load the Scoob was off-boost.

Search for the keyword 'rollers' on http://pics.bbzzdd.com to see the Scoob I used to own on the Dyno.

 

[jupiter57]

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

14 Liter?
WTH are you running 850 Cubes in?
What kind of HP are you making?

 

[thedarkwolf]

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

I have two turbo charged cars neither of which will lag if I am cruising at anything over 3k rpms. The turbo is already spun up so if there is any lag it isn't noticeable. Lag happens at lower rpms when you floor it not so much upper. If yours is lagging you either have a massive turbo or there is something wrong with it.

And yes both of my cars have boost gauges and I know I am not making boost while cruising. Turbo is still spun up though.

 

[MercenaryForHire]

Originally posted by: DivideBYZero
Agreed. I was fully aware that at constant rpm/no load the Scoob was off-boost.

Therefore, employ brake-boosting when doing a highway start, or fix that little "ECU defect."

- M4H

 

[nakedfrog]

Originally posted by: MercenaryForHire

Originally posted by: DivideBYZero
Agreed. I was fully aware that at constant rpm/no load the Scoob was off-boost.

Therefore, employ brake-boosting when doing a highway start, or fix that little "ECU defect."

- M4H

He hasn't got that car any more.

 

[compman25]

Originally posted by: jupiter57

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

14 Liter?
WTH are you running 850 Cubes in?
What kind of HP are you making?

A truck for hauling 105,000lbs. It makes 500hp and around 1500ft lbs torque.

 

[thedarkwolf]

Well I wouldn't be surprised that you have lag in a rig. Huge turbo and high rpms is anyhing over 2k rpms .

 

[JulesMaximus]

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

 

[Toastedlightly]

Originally posted by: JulesMaximus

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

Diesel!

 

[SVT Cobra]

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

LOL sure kiddo. Pics then or dyno charts?

 

[Vic]

Either a boost leak or a sticky wastegate actuator, I would say.

I'm thinking the latter. If you're cruising at 4k rpm, the turbo is going to be spooled up and boosting more than then engine needs, so the ECU will be wasting the excess. The boost won't be at "almost 0" in such a case, the intake manifold will be in vacuum (meaning negative boost if want to think of it that way) due to the mostly-closed throttle valve. Then when you go WOT, the wastegate should promptly close. If it doesn't, then the engine could almost choke from lack of getting the air the ECU would expect it to get.

 

[Vic]

Originally posted by: JulesMaximus

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

Freightliner Detroit Diesel.

 

[SVT Cobra]

Originally posted by: Vic

Originally posted by: JulesMaximus

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

Freightliner Detroit Diesel.

In a WRX?

 

[DougK62]

Originally posted by: SVT Cobra

Originally posted by: Vic

Originally posted by: JulesMaximus

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

Freightliner Detroit Diesel.

In a WRX?

He obviously has a WRX for his personal vehicle and drives some sort of big truck for work. Seems clear as day to me...

 

[Minjin]

Originally posted by: SVT Cobra

Originally posted by: Vic

Originally posted by: JulesMaximus

Originally posted by: compman25
yeah, actually there will be a lag if he is at a constant rpm. Manufacturers have to make fuel mileage ratings, one way they do that is to bleed off the pressure so the engine doesn't use more fuel if you are cruising at a constant rpm. While accelerating upto 4k it will be building boost, but once he levels off at a constant rpm it drops. If you don't beleive me, come ride in my WRX, or come to work with me. my 14 liter engine builds 35lbs of boost while accelerating, once I am cruising at a constant speed it drops to almost zero. If I then floor it, it takes a few seconds for the turbo to build up pressure again. That is how modern systems are designed.

Your 14 liter engine? 35lbs of boost? SHENS!!!

Freightliner Detroit Diesel.

In a WRX?

Might want to reread that sentence again, especially the second part of it.

As for the thread, its so filled with misinformation, I don't know where to start.