Losing boost above 7k?
08-25-2003, 09:24 PM
#1
0.5 BAR
Thread Starter
Join Date: Aug 2003
Posts: 80
Losing boost above 7k?
I have a turbo b18c1 in my 89 si, changed to a new manifold, new turbo, new charge pipe, new bov. That's it. Now, the car falls out of boost around 7k to 7400. I'm doing low boost tuning at 10psi, so the datalog shows 10psi and around 7k it falls back down to manifold vacuum. Spool time is normal, it pulls hard, then just dumps out of boost. I tried eliminate some things tonight. Tried running off the gate only, no boost controller, didn't help, pulled the vacuum line off the bov and plugged it, no help, reseated all the orings on the bov, changed the vacuum line, retapped all the holes for the bov flange and resealed it, no change. I think the bov is just letting the boost out at high rpms. driving me nuts. I'm gonna try to borrow one tomorrow that is known good. Any other suggestions?
08-25-2003, 09:46 PM
#2
3.0 BAR
Join Date: Mar 2003
Posts: 21,479
Re:Losing boost above 7k?
If the BOV doesn't fix it check for leaks. What size turbo is it? What BOV? More info.....
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08-25-2003, 10:00 PM
#4
3.0 BAR
Join Date: Mar 2003
Posts: 21,479
Re:Losing boost above 7k?
Wow. Nice. Check for leaks maybe? The BOV sounds like the culprit.
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08-27-2003, 02:10 AM
#8
1.5 BAR
Join Date: Dec 2002
Posts: 1,495
Re:Losing boost above 7k?
No, its either the wastegate or the blow off.
Can't be the piping. Most likely culprit is the blow off.
Does it have an adjustable spring? I'd try tightening it down.
Another thing to look for is the pressure that your wastegate is seeing. Its really risky, but you may try pulling that vac. hose off and run the car... be ready to let off the gas immediately (you'll be building limitless boost) but you can see if it continues to spool past that point or not. If it does its most likely the wastegate is seeing to much pressure, and forcing open to early.
Else, I'd try softening or hardening the spring in the BOV see if that produces other results as well.
Can't be the piping. Most likely culprit is the blow off.
Does it have an adjustable spring? I'd try tightening it down.
Another thing to look for is the pressure that your wastegate is seeing. Its really risky, but you may try pulling that vac. hose off and run the car... be ready to let off the gas immediately (you'll be building limitless boost) but you can see if it continues to spool past that point or not. If it does its most likely the wastegate is seeing to much pressure, and forcing open to early.
Else, I'd try softening or hardening the spring in the BOV see if that produces other results as well.
08-27-2003, 09:36 AM
#9
0.5 BAR
Thread Starter
Join Date: Aug 2003
Posts: 80
Re:Losing boost above 7k?
I swapped the bov for a known good one last night and that still didn't fix the problem. I can hear the exhaust note change quite a bit when this happens, but I'm not sure if this is due to the wastegate opening or due to my losing boost. I'm gonna pull the wastegate tonight and check it out, see if I see anything. I had someone tell me that the valve in the wg could start sticking if it sat for too long without use, this car has been apart for a month, I don't consider that too long. I'll also check out the source for the wastegate boost. I tried with and without the boost controller, but didn't change the boost source to the side port of the wastegate. I'll keep you guys updated as I find more.
