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Old 10-10-2020, 03:23 PM   #26
mschultz373
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I'm thinking it's the wastegate actuator. CBV spring and rubber looks good.

I plumbed in an MBC and tried turning up the boost, but couldn't get above 5lbs. however, disconnecting the wastegate actuator hose - disabling it - results in overboosting, 10, 15lbs. so i think the actuator is somehow dumping boost around 5lbs. i think I can maybe, maybe hear it opening just as I hit boost, but it's hard to say.

it could still be a boost leak? although if the car will boost to 15lbs, I suppose a leak isn't present.
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Old 10-10-2020, 03:31 PM   #27
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[duplicate message]

Last edited by mschultz373; 10-10-2020 at 03:33 PM.. Reason: duplicate
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Old 10-11-2020, 05:45 PM   #28
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Well, you know from the factory these cars are low boost cars. The stock boost on my B21FT was only 6.5psi and even when you put the intercooler kit on it with turbo+ the main part of the available boost is 8.5psi. When turbo + is enabled it goes to 10.5psi.

One thing I wouldn't do is to plumb the boost gauge in with the hose that goes to the actuator. I would connect the boost gauge to another port on the intake plenum. A good manual boost controller should be able to adjust to raise the boost quite high. Although the control the mbc has is determined by the spring that is inside it. Just like the spring in the wastegate actuator.
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Old 10-11-2020, 11:53 PM   #29
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One thing I wouldn't do is to plumb the boost gauge in with the hose that goes to the actuator. I would connect the boost gauge to another port on the intake plenum. A good manual boost controller should be able to adjust to raise the boost quite high. Although the control the mbc has is determined by the spring that is inside it. Just like the spring in the wastegate actuator.
the boost gauge is plumbed into the stock 'turbo' line under the cluster.

I have the mbc plumbed between the wastegate actuator and the outlet on the compressor. i thought that was the only way to get the proper pressure signal to the actuator?

regardless, like I said, it appears that turning up the mbc didn't break the 5lbs boost threshold. i'll play around more tomorrow.
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Old 10-12-2020, 07:54 AM   #30
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Originally Posted by mschultz373 View Post
the boost gauge is plumbed into the stock 'turbo' line under the cluster.

I have the mbc plumbed between the wastegate actuator and the outlet on the compressor. i thought that was the only way to get the proper pressure signal to the actuator?

regardless, like I said, it appears that turning up the mbc didn't break the 5lbs boost threshold. i'll play around more tomorrow.
Have you tried connecting the waste gate directly to the turbo outlet? How is the MBC connected? The waste gate should come off the port closest to the adjustment knob and the turbo outlet to the bottom of the MBC. I can almost guarantee your problem lies with the MBC, either it's defective or plumbed incorrectly.
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Old 10-12-2020, 02:55 PM   #31
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yeah, the wastegate was directly connected to compressor housing outlet prior to MBC install. then I was getting ~4lbs of boost.

with MBC installed between wastegate actuator and outlet, despite increasing the boost on the MBC, I still was topping out around ~4lbs.

I then tried T-ing the MBC pressure line off the CBV line and put a nipple on the comp housing outlet. there I topped out at ~5-6lbs of boost despite MBC settings.

then, simply removing any hose to the wastegate actuator I top out around 10lbs of boost. that's with the nipple on the compressor housing. last week, when I was running 'stock' with a line from outlet to actuator, removing that line from the actuator would result in 15lbs or so of boost. I didn't push it beyond that.

here's a picture of the plumbing currently - MBC T'd off CBV line, nipple on comp housing outlet, line to actuator disengaged in photo:
DSC-0032-1

so the actuator works, but for whatever reason, I'm unable to 'set' the pressure in the lines correctly to get it to actuate only at higher boost levels.

the hallman unit is new and just arrived friday. could be faulty but doubt it would be D.O.A.

as an aside - on one of my pulls, the oil dipstick came out of the tube. that was running the nipple on compressor outlet and T'ing the MBC off the CBV line. my turbo is also leaking oil. unsure if those would factor into this low boost issue.

Last edited by mschultz373; 10-12-2020 at 03:31 PM..
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Old 10-12-2020, 03:35 PM   #32
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The CBV line should be coming off the manifold, this is not the place to be hooking up your waste gate. This is after the throttle plate, it should be plumbed off the compressor, before the throttle plate. Where are you located? Maybe someone could stop by and see what you've got going on.
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Old 10-12-2020, 03:50 PM   #33
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the CBV line runs to a T under the intake manifold which splits for the CBV and to the egr vac regulator by the ABS/OBD boxes. is that wrong? if so, that may be the problem.

plumbing MBC between compressor outlet and wastegate will NOT raise the boost. so the MBC could be faulty. or there's some other issue, which I lean towards since I'm getting 3lbs less boost than stock level running no MBC between comp outlet and actuator.

Last edited by mschultz373; 10-12-2020 at 04:20 PM..
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Old 10-13-2020, 01:10 AM   #34
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well with everything plumbed correctly, the MBC is still not raising boost, BUT disabling the wastegate actuator results in overboost. so my conclusion is that the actuator is faulty and needs replaced. yay or neigh?
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Old 10-13-2020, 06:05 AM   #35
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well with everything plumbed correctly, the MBC is still not raising boost, BUT disabling the wastegate actuator results in overboost. so my conclusion is that the actuator is faulty and needs replaced. yay or neigh?
A spring inside the wg actuator holds the wg closed, air pressure on the diaphragm inside the wg from the turbo pushes it open and lets the exhaust bypass the turbine. If the spring in the wg is holding it closed with no air pressure then it seems as if the wg is working properly.
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Old 10-13-2020, 12:58 PM   #36
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I'll look into the MBC being faulty then. seems the only logical thing? could be cat or exhaust restriction. or my paper air filter... thanks yall.
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Old 10-15-2020, 02:54 PM   #37
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i am idiot. I just hadn't sufficiently opened the MBC. got her pulling 12lbs now. wow, she boogies!!!!
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Old 10-15-2020, 09:14 PM   #38
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Well done. Enjoy!
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Old 10-16-2020, 01:45 AM   #39
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yeah pretty fun!

my buddy and I went out for a few rips and I think I got a few backfires pulling fairly hard out of the hole. my idle is lumpy as hell so i'm thinking the car is running rich and so the backfire makes sense. but should I concerned about damage to anything? it really seemed to happen only out of the hole in 1st on hard pulls.
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Old 10-16-2020, 07:51 AM   #40
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yeah pretty fun!

my buddy and I went out for a few rips and I think I got a few backfires pulling fairly hard out of the hole. my idle is lumpy as hell so i'm thinking the car is running rich and so the backfire makes sense. but should I concerned about damage to anything? it really seemed to happen only out of the hole in 1st on hard pulls.
Check the oil and make sure it's not milky looking. Look for evidence of coolant being forced out of the overflow reservoir. These would indicate a blown head gasket.
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Old 10-16-2020, 12:12 PM   #41
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thankfully all good. but i'll be digging around this weekend trying to figure out this rich condition. still, man, first turbo volov. stock with an MBC, these guys are pretty damn fun. excited for mods down the road.
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Old 10-16-2020, 06:17 PM   #42
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You probably need to regap or replace your spark plugs. It's called spark blowout and under high load with too large of a plug gap it blows the spark out. Use .028" or you can even reduce it to .026" if it persists.
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Old 10-25-2020, 09:46 PM   #43
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i regapped them to .026 and it still seems to persist. but the past couple times it's happened, it seems like it's more like knock maybe? before it seemed to be coming from the exhaust; recently i felt it more in the gas pedal directly in the engine compartment.

i also notice my oil dipstick is getting blown out so i need to clean my pcv box. not sure if that could be related to this issue
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Old 10-26-2020, 11:58 AM   #44
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How much boost are you running? Do you have a wideband O2 gauge? Could be detonation events....
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Old 10-26-2020, 06:44 PM   #45
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~12-13lbs, no afr gauge yet. stock except the MBC. running 93 octane. yeah, i suspected it might be detonation or something. what's strange is that it only happens in 2nd or 3rd gear in the middle-range of boost, like 7-9lbs. and just to describe it further, it basically feels like a small mis-fire/back-fire 'pop' in the engine.

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Old 10-27-2020, 02:20 PM   #46
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12-13lbs is right at the limit of what the stock setup can handle. I'd say to back it off a little to 11lbs and see how it is. These engines have a detonation zone in mid range. It's why volvo only let the engine go to full boost with the turbo+ setup above 3700rpms.

What kind of plugs do you have in there? Maybe trying something that fires easier will help? Some fresh plugs may help. My engine also encountered that mid range detonation when all else was good. It made me upgrade the intercooler which took care of any issues like that.
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Old 10-27-2020, 07:39 PM   #47
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i'd have to pull one, some NGKs I think. nothing super top line. also the plug wires are old and need replaced. just been lazy on that.
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Old 10-27-2020, 08:26 PM   #48
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Stock LH2.4 goes super lean at the onset of boost and pings most of the time. Then it goes full rich to about 10.0-10.2:1 at WOT and full boost. 90s tunes are OK at best.
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