'Sup everyone. I've run a few searches and didn't find any help. I'm new here too so you can't get mad at a dumb question. So if I roll into WOT from low RPMs and the boost creeps up slow it stops at .11 bar. If I go WOT from about 3300+ my boost spikes to .12 then falls to .7 then back to .12 then falls to .7 and on. I don't have any mods I'm aware of (second owner) other than Cobb #2. I noticed it for the first time today, and I've had the Cobb for ~ a month??? I'm guessing it may be: leaking BPV leaking vaccume line somewhere needs a tune (I'm so broke... I hope not!) Any ideas??? A cracked line would be such a PITA to find, but I'm going to look around tomorrow. By the way, what's "normal" boost for AP stage 2? Thanks! Mike EDIT: I'm talking about MPa up there, not bar... sorry. I type without paying attention sometimes.
well with the boost spike then going down is normal but it does sound like a vaccume leak. i would make sure that all the tmic lines are nice and tight. Check the lines to the boost solenoid to the turbo and the vac line to bov. If that is not working revert back to the stock map see if its working. but if it wroking normal then download the new maps for the ap and reflash to stage 2. i think that stage 2 is about 15 psi.
.12 bar is still way to low anyways. At stock you should be boosting close to .98 bar. If you convert it thats high 14 psi. The only time I really hit max boost is when I am accelerating very rapidly. If you hold boost in the gear, the boost will not stay constant. This is because the small turbo can't maintain those high pressures when your engine is sucking it up. If anything is cracked or disconnected its very easy to find, because all boost components for the most part are on top part of your engine. Check the lines on the front side of intake manifold. Then check the turbo to intercooler connections. Finally, look at your CDV connections from your intercooler to your intake.
stomping the pedal should cause it to spike whereas rolling into WOT should not... im guessing your issue is the tune since when its spiking, the ECU is over correcting... then the boost falls too low and it overcorrects again and so forth i dont think its a mechanical issue since it only does it if u stomp the gas and not when u roll into WOT... in both cases, if ur WOT at ~3500 RPM, u should see high boost and a leak (if present) should occur in both cases... also clemsonscooby is right... 0.12 bar sounds too low... for AP stage 2, i'd expect it to spike around 17.5psi (~1.2 bar) (dont quote me on those numbers) here's a conversion chart between bar-psi
Nope, my fault, I was using MPa. I don't know why I typed "bar"... sorry about that. Yeah, if I were "spiking" .12 bar I'd have a totally different problem. My concern isn't the spike to .12 MPa/1.2 bar/17.39 PSI, it's the yo-yo between .12 MPa/1.2 bar/17.39 PSI and .7 MPa/.07 bar/10.14 PSI. In 4th/5th gear it can surge up and down 4-5 times before I'm going too fast to count more surges. I wouldn't guess the ECU feels the need to vent pressure at a max of 17.39 PSI... my uneducated guess is a boost leak on a spring loaded valve. But what do I know... :dunno
Did you buy the car new? Do you know if there were any previous modifications to it? I'd start with making sure the 'T' of hoses on the turbo/solenoid are stock, that the 'pill' is in the right place, and that the hoses themselves aren't damaged in any way. There have been reports of boost fluctuations with AP Stage 2 in the past, and pretty much all of them turned out to be troubles with the boost lines. Also, make sure you flash realtime stage 2 map over the base map if you haven't, as well as ensuring you have the latest versions of the maps.
I'm the second onwer. The pill is stock (one ring and brass) and in the correct spot. There's no visible damage to any of the hoses. I'm going to change the maps around tonight and see if it helps. I really just think my BPV isn't holding when the boost kicks in hard. Is that even possible? What boost do those normally fail?
Unless the BPV is damaged somehow, it'll hold fine til at least 19-20 psi. The boost 'hunting' you're seeing, I believe is from the ECU not being able to hit the target boost properly within its allowed parameters. If the hoses are fine and the pill is the right size and in the right place, you can always see if the wastegate arm has been fiddled with.
Sorry for the slow responce time. Yes, it's just a 93 map. I didn't have time to fool with the AP over the weekend. I crushed my BPV a bit and it did nothing. Thanks for trying to help me brainstorm... I need to find the money to get tuned. You get what you pay for.
Something like this is NOT likely to be a "vacuum" leak, or a leaky BOV (don't crush it anymore). The only "leak" that would cause something like this would be a leak in the boost control lines. (From the turbo to the T, then to the wastegate and the boost solenoid) What happens is that there is a "Boost Target (BT)" table and a "Wastegate Duty Cycles (WDC)" table. These work in conjuction with the mechanical boost control setup to try and give you smooth, appropriate boost. Generally when there you have too high of a WDC setting, or too aggressive of a mechanical boost control setup (too small of a pill) for the BT, the car "overshoots" (makes more boost than the BT) and then pulls back HARD on the WDC. Then it "undershoots." When the boost drops under the BT it ramps back in the WDC until it overshoots... and oscillates until it gets it under contol or you lift. The easy way to see if it's mechanical or tuning - flash the stock map. It should get almost to 0.1 mpa, then drop towards redline. It should all happen fairly smoothly. If it still oscillates on the stock mapping, it's a mechanical. If it's perfectly smooth stock, and only oscillates on the Cobb, it's a tuning thing... SS