Boost fluctuating, stuttering up high, but not in 4th???

[MyEclipse5]

I have the boost controller set around 10psi, mods in profile.

So when I go WOT in 2nd it will stutter and the boost fluctuates around 4000RPM, but when im in 4th I can floor it and it hits 10psi and stays fine...seems a little slow though.

I tried doing a leakdown test, but I was by myself so I don't really know if the system was pressurized.

I'm thinking:

Boost leak
plugs/wires
dirty inj

Anything else? Am I correct to think these?

 

[Loewen21]

How far into fourth gear rpms wise do you go? I had a weird problem similar to this that progressively got worse over time. After driving for x minutes the car would start to stutter at 15 psi and would over time start stuttering at lower boost until eventually it would stutter at 0 and into vaccuum! This was of course after well over an hour of driving. But to the point, it was my ecu going and the circuits would overheat themselves and cause the stuttering. Could be your problem, could also be something simple like you said too, fouled plugs shot wires or the injectors. Good luck

 

[romeen]

IMO, boost leak is the most likely cause. If the stuttering was misfire due to the plugs or wires it would probably be more prevalent in higher gears (higher load) than in lower gears like what you are describing. Although fuel injectors can definitely get dirty which will affect the spray pattern as well as volume of fuel delivered per pulsewidth it is not a real common occurence due to the detergents used in modern gasoline.

Do the boost leak test. If that checks out ok then move on to the less likely causes.

 

[MyEclipse5]

Ok so I'm almost positive its not a boost leak...hear me out on this one.

The only reason boost would leak would be under load, correct? Like if you are WOT its trying to stay at 10psi or build up higher and the charge pipes aren't tight enough to hold on so they leak.?

I tightened up all of my charge pipes, I even tightened up my BOV (I'm thinking it might be this? its a greddy type S and the screw thing in top is about 1/2-3/4 screwed in, dont' worry, no surge) I also put new vaccum lines on because I found out one was leaking a little...this didn't help.

SO I took it out for a drive, and even 1/2 throttle, only getting to about 5psi, as soon as I get over 4200RPMs it will spurt, boost jumps around, and it gets to the point that tis so sperattic I have ot let my foot off of the gas. IF before I could hold 8psi under 4000RPM's when it was building, don't you think I should be able to hold 5psi throughout the powerband? Doesn't this rule out boost leak? Anyone?

 

[Smevans]

Does this happen as soon as you start driving or after a little while? Check your plugs.

 

[wvturbo2]

NO boost leak isn't ruled out. Do a test to rule it out. I've tightened up my pipes thinking that i fixed it and still have found a leak. It sounds like a boost leak to me. Test it and make sure then check plugs and wires.

 

[romeen]

NO boost leak isn't ruled out. Do a test to rule it out. I've tightened up my pipes thinking that i fixed it and still have found a leak. It sounds like a boost leak to me. Test it and make sure then check plugs and wires.

Completely agree. No matter how much you tighten and check things the only way to know is to pressurize the intake. Use soapy water via spray bottle on all areas and look for the telltale bubbles.

I am using t-bolt clamps on all my couplers. I have still found leaks that were fixed just by slightly repositioning them.

 

[MyEclipse5]

NO boost leak isn't ruled out. Do a test to rule it out. I've tightened up my pipes thinking that i fixed it and still have found a leak. It sounds like a boost leak to me. Test it and make sure then check plugs and wires.

Thats the problem. I bought a 30 gallon tank, filled it with air, and when I put it on my homemade boost tester it doesn't seem to pressurize the system. I can't hear any leaks and if I hold it on there nothing....Maybe ill try again. I'm going to get some new plugs/wires with tomorrows pay check.


And it happens as soon as I start the car.


Also I have a 255 walbro, with a FPR set at around 36psi. Its still untuned, but I didnt think this would be a problem, or that it would cause the problem I'm having.

 

[romeen]

Thats the problem. I bought a 30 gallon tank, filled it with air, and when I put it on my homemade boost tester it doesn't seem to pressurize the system. I can't hear any leaks and if I hold it on there nothing....Maybe ill try again. I'm going to get some new plugs/wires with tomorrows pay check.


And it happens as soon as I start the car.


Also I have a 255 walbro, with a FPR set at around 36psi. Its still untuned, but I didnt think this would be a problem, or that it would cause the problem I'm having.

1) Try the boost leak test again. It is possible that when the motor shut down some of the intake and exhaust valves ended up in overlap and the pressure went right on out the exhaust. Which test device are you using? Make sure it is sealed well with the compressor inlet.

2) Just to confirm, you set your base fuel pressure with the vacuum hose disconnected from the FPR and the end of it plugged, correct? BFP for a 1G is actually 37 psi with the line disconnected. Assuming an ideal vacuum of 20inHg at idle the fuel pressure should be about 27 psi with the vacuum line connected.

 

[MyEclipse5]

1) Try the boost leak test again. It is possible that when the motor shut down some of the intake and exhaust valves ended up in overlap and the pressure went right on out the exhaust. Which test device are you using? Make sure it is sealed well with the compressor inlet.

2) Just to confirm, you set your base fuel pressure with the vacuum hose disconnected from the FPR and the end of it plugged, correct? BFP for a 1G is actually 37 psi with the line disconnected. Assuming an ideal vacuum of 20inHg at idle the fuel pressure should be about 27 psi with the vacuum line connected.

Alright, so I tried it again and It sounds like the only leak is from my BOV? Maybe that pipe isn't as good as I think. I dunno, It holds a little better now when I repositioned the coupler on the pipe right there.

And yes, the BFP was set with it disconnected and plugged.