Thread: vacuum leak?

Hi all,

Lately I've been noticing that my 98 GTP doesn't seem to be as strong at WOT than it is at let's say 3/4 of throttle. I first thought it might be the fuel pump or the injectors, but I've been reading about vacuum leaks on the forums and eventhough the DIC boost meter is not the best indicator, I've noticed that the bars will not reach all the way up sometimes.

I did some tests on the way to work today at WOT and the bars would stay 2 bars short of reaching the full boost meter and thus I felt some power loss at high RPM.

On the last test I did, I went WOT and the bars went all the way up since the start and I didn't feel any power loss at high RPM.

I replaced some vacuum lines and T's back when I first bought this car but I left the thick line that runs from top of the SC to what I believe is the MAP sensor as it was. It seems to have been patched with electrical tape, but I'll replace that one this weekend I guess.

My question would be that given this sympthoms, should I begin looking for vacuum leaks, then see if the bypass valve is working correctly or check the fuel pressure and injectors?

Thanks,

Start looking for vacuum leaks. Start the car and spray starter fluid around potential leaking spots. If the idle changes, then you have found a leak

Thanks guys. I checked that vacuum line that runs from the side of the SC right after the TB and goes up and across the SC. That one seemed to have been patched with electric tape. But after further inspection, I found out that there was actually NO hose left under the tape. It was just tape rolled up acting as a vacum hose! LMAO! I replaced the whole line with a new hose and I'll test it more later today.

With the new line in place and the car stopped, I go WOT and the boost gague goes all the way up expept 2 bars. By the time the engine is around 4-5k RPM, the boost gauge is at full bars. I didn't notice any power loss as before, but I'll do further tests, maye I'll also take it to the track this weekend. I haven't taken my car since I bought it and I've done some minor mods and othe repairs so far. I also want to know if there has been any changes.

Hey Bio you got me thinking about the belt slip too. I replaced the accesories belt a few weeks ago when I put in a new coupler, but I used the same SC belt that it had. I never thought that belt slip could be an issue and I don't know how old that belt is, but one of the belts does squeak when the car is cold in the morning, it goes away after 1 or 2 minutes and I'm guessin it's the SC belt that's squeaking. I applied some of that anti-slip thing on the belts today to see if it also slips tomorrow morning, but I guess I'll just change it to be sure. I know the tensioner pulleys are fine, we checked them when we did the coupler.

I just have one question, wouldn't the SC belt squeak if it was slipping at high load? I don't hear it doing that.

Ok I've got another question, I noticed that ever since I started messing with the CAI, that sometimes the boost gauge wouldn't register any bars at all, but this goes away after a few minutes of driving the car, i think it's after i've been stopped at a traffic light, then the boost gauge starts registering bars again.

This only happens now when I first start the car in the morning and not always. would this also be related to vacuum leak and or the bypass valve? I don't seem to feel any power loss when this is happening, by the way, the SC still whines if i give it enough gas.

ok I'll add the engine starter to the groceries list! hehe thanks!

Ok so i've been working on the vacuum lines. i've done some research and I found schematics for 3 main vacuum systems in the GTP: the line that's shared by the bypass valve, map sensor and fuel pressure gegulator, the EVAP line and the A/C line.

I've replaced most of the line that runs from the SC to the bypass vavle, fuel pressure regulator and MAP sensor. I replaced all connectors and checked all lines and replaced as necessary.

I haven't worked on the EVAP lines since I'm assuming that if I had a leak in this system, I would be getting some ECM codes.

I haven't looked at the A/C vacuum lines since the A/C ports are working correctly.

I also think these lines that go further away from the engine are less exposed to high temperatures and would have the lowest probability to leak.

The thing is that I still don't register any boost on the DIC just in the morning for like 5 or 10 minutes and then the boost registers bars normally for the rest of the day after I drive it for a while. Even though the DIC doesn't register any boost at this time, there's no power loss either. The Idle is not rough, it could be a little jumpy sometimes, but almost not enough to notice, most of the time it feels as is the engine was turned off when in neutral. The MPG is average, 18mpg in the city.

Another thing that I notice is that at WOT in 2nd gear between 3k rpm and 4k rpm or so I feel the car hesitate and then it goes away past 4.5k rpm. I'm not sure but I think I can hear as if there was some random pressure leak comming out from the car, but it's hard to pin down as it only ocurrs at this point and I don't think that I can even assure that it's air pressure leak.

So my quesiton would be what the next course of action should be? Are my assumptions regarding the EVAP and A/C correct?

I'm thinking of getting a cheap pressure gauge and hook it up to see what kind of pressure readings i'm getting. By the way am I supposed to hook it up to the vacum connector located near the SC snout? This is the only one that seems to have pressure based on it's location.

I still need to test with the engine starter, but not sure where would I try it if I've checked all the lines next to the engine. I think I need to test the LIM gasket.

Any ideas will be appreciated.

Thanks!