Engine boosting when I turn it off

[baker27]

Ok, this dsm (a 1995 GSX) is my first turbocharged vehicle and I have only had this car for about two months or so, so maybe its perfectly normal and I just don't know my car well enough yet. If its a normal thing, sorry for making a thread for this. I used the search, but found nothing that helped me.

Last week was the first time this happened, I drove to campus and turned off my car, but I noticed my boost gauge jumped up to about 2 or 3 psi when i turned it off. Good news is, I'm pretty sure it confirmed I have a boost leak, because the pressure drained out on its own relatively quickly. Still doesn't exactly make me smile. I figured it was a fluke and I wouldn't post unless it happened again. Unfortunately, it happened again this morning, and I figured I should ask just to make sure I am not making things worse by driving it.

Oh, and I don't know if its connected or just something random, but this morning my car had an idle surge for the first time. Might have been because it was chilly out this morning, I just figured I should tell everything I could that might help diagnose a problem if there is one.

Any advice would be appreciated.

 

[mikelv]

What kind of boost gauge do you have in the car?

Is it the stock one on the dash, mechanical, or electrical?

Also, is your profile updated? If not please do so or list what is done to the car.

Are you saying the car stays running for a second and boosts on it's own? Or when you kill it, does it turn off and the gauge spikes for a second by itself?

 

[baker27]

It's not a the stock one, its a mechanical aftermarket one. Previous owner install. It doesn't show vacuum, just boost from 0-30.

The car is completely stock besides Apexi N1 catback and aftermarket plugs and plug wires.

When I kill it, it boosts. It doesn't stay on for a second or anything like that. It took about 10 seconds to drain the boost it had built up, so it wasn't like the needle twitched or anything like that.

 

[bluegs03]

Do you know if the guy before you had a turbo timer installed?

 

[baker27]

I don't think he did, its the stock water-cooled turbo (t25, I think?). There's definitely not one on the car now.

 

[Geier]

Read up at VFAQ on how to install a boost gauge. Make sure the one in your car is installed correctly. More than likely, everything is normal.

 

[mikelv]

It's not a the stock one, its a mechanical aftermarket one. Previous owner install. It doesn't show vacuum, just boost from 0-30.

The car is completely stock besides Apexi N1 catback and aftermarket plugs and plug wires.

When I kill it, it boosts. It doesn't stay on for a second or anything like that. It took about 10 seconds to drain the boost it had built up, so it wasn't like the needle twitched or anything like that.

If your just cruising easy with the car, it's not going to build boost. You won't really build any boost without significant engine load. The car will run like any other under vacum, naturally aspirated. Unless you "give it some" your not going to boost.

Where is the gauge tapped? It should be reading pressure at the intake manifold. Unless you hammer on the car like crazy, then kill it right away, it won't boost at all. Hell, even then you won't, but you sure will heat soak it.

I'm sure it's nothing to worry about, hopefully a wiseman will back me up in here at some point.

 

[baker27]

I will be sure to check that as soon as I get a chance, sadly I have an exam on wednesday, so it might be a while.

 

[MrBoxx]

Get a gauge that shows vac and boost. Connect it correctly to the proper vacuum hose. VFAQ will show you how.

What "aftermarket" plugs and wires, out of curiosity? The stock plugs are the only ones that should be used in it. Under no circumstances should you use platinum plugs.

Oh... and do a boost leak test.

 

[noonan98turbo]

What kind of gauge do you have? I have a prosport boost gauge and the gauge itself doest zero out even when the car is off. It always reads at least 1 psi and sometimes 2 psi even when the car is tuned off. There is a thread on here that talked about this situation with the prosport boost gauge so im just curious if yours is by the same brand.

 

[r1991_4g63t]

unless your killing it while its already boosting its either a bad guage or bad install maybe, but like stated before even if you rev'd it up before you shut it off you shouldnt see any boost on the guage unless your moving.

 

[baker27]

Honestly, I have no idea what plugs or wires he put on the car.. it was done before I bought it... I can check if you think it's relevant. And I planned on replacing the gauge as soon as I get the money for it, Right now I'm a starving college student though. It's probably just a worthless gauge, it looks incredibly cheap and has no brand name on it.
I will check to see where its tapped sometime in the near future, though that will require learning how to check that.. I would hope he did it right when he hooked it up, but I guess you can't really trust strangers to do things the way they should be done.

So, not to be a noob to boost, but why cant you use platinum plugs?

 

[r1991_4g63t]

if you have seen them you'd understand, the electrode in platinum and iridium plugs is about a 1/20 of what a copper plug is, if thats not the reason i dont know.....

 

[MrBoxx]

Spark Plug FAQ

There are a few articles here, as well as the VFAQ site (VFAQ Site - Visual Frequently Answered Questions) that can show you where the boost gauge is supposed to be tapped in at. Make sure the lines are all secure, no leaks, in the proper location, etc. The gauge itself may be off.

 

[the_mork]

Here is just some speculation but it could be that your motor is stopping at a point when all of the cylinders have at least one set of valves closed making a total wall at one end and a still spinning turbo at the other, just because a turbo isn't making boost doesn't mean that it isn't pushing air, at idle it just isn't pushing enough to overcome the vacuum in your engine The fact that it bleeds down quickly doesn't really mean anything because as soon as your turbo stops spinning there is an open end and the air can flow back out of it. This situation of having all of the valves closed happens fairly infrequently.

 

[r1991_4g63t]

the turbo will spin but not fast enough to make any boost, especially without more exhaust to further compress it

 

[Defiant]

Your gauge is "bouncing" off the zero stop when the engine's turned off and manifold vacuum disappears. Either follow the boost/vacuum gauge advice, or ignore it. You don't have any magical boost coming from anything.
A turbo spinning without being driven is putting out the force of a fäggot's fart.

 

[mikelv]

Honestly, I have no idea what plugs or wires he put on the car.. it was done before I bought it... I can check if you think it's relevant. And I planned on replacing the gauge as soon as I get the money for it, Right now I'm a starving college student though. It's probably just a worthless gauge, it looks incredibly cheap and has no brand name on it.
I will check to see where its tapped sometime in the near future, though that will require learning how to check that.. I would hope he did it right when he hooked it up, but I guess you can't really trust strangers to do things the way they should be done.

So, not to be a noob to boost, but why cant you use platinum plugs?

Not sure if someone else said this, but I saw the question and felt the emergence need to answer ASAP!!

This is all you need to know at your stage of modding the car.

NGK BPR7ES

"Anything less would be uncivilized"

 

[mikelv]

Your gauge is "bouncing" off the zero stop when the engine's turned off and manifold vacuum disappears. Either follow the boost/vacuum gauge advice, or ignore it. You don't have any magical boost coming from anything.
A turbo spinning without being driven is putting out the force of a fäggot's fart.

Magical Boost huh? Hey I got some of that, it helped me break that 10 second barrier.
Magical boost does exist, don't listen to the meanie with the post delete key!!

 

[BoostedPhoenix]

Here is just some speculation but it could be that your motor is stopping at a point when all of the cylinders have at least one set of valves closed making a total wall at one end and a still spinning turbo at the other, just because a turbo isn't making boost doesn't mean that it isn't pushing air, at idle it just isn't pushing enough to overcome the vacuum in your engine The fact that it bleeds down quickly doesn't really mean anything because as soon as your turbo stops spinning there is an open end and the air can flow back out of it. This situation of having all of the valves closed happens fairly infrequently.

These are my thoughts as well...if the gauge isnt one that reads vacuum its probably tapped in somewhere in the intercooler piping. If the engine is stopped in the right position then no more air will move through it, assuming the turbo is in good shape it may continue to spin and create a small amount of "boost" in the charge piping until it spools down. Nothing wrong with the car just a non-typical gauge setup. If it bothers you then get a gauge that reads vacuum and install it with manifold vacuum as the source and all should be well.

 

[baker27]

Alright, thanks for all the help guys, as soon as I get a steady income again, I will definitely replace that boost gauge and hook it up the right way.
Maybe doing it the right way might even get me some of this magic boost I keep hearing about.

 

[Defiant]

These are my thoughts as well...if the gauge isnt one that reads vacuum its probably tapped in somewhere in the intercooler piping. If the engine is stopped in the right position then no more air will move through it, assuming the turbo is in good shape it may continue to spin and create a small amount of "boost" in the charge piping until it spools down.

No, this will not happen.