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Hello all. I'm trying to diagnose a boost surge/cut issue I'm having. Long story short, the car did this some time last year, I thought it might be an issue with the diverter valve, so I put the Forge valve on, and eventually just 'pushed through' the issue. By that I mean I found if you just held the throttle down through the surging, eventually it would smooth out, though the car felt down on power after that. There were no codes then.

Catching up to a month ago, I took the car to a dyno night as I knew something was seriously wrong with it and I wanted to see the power curve. After diagnosing everything we could think of, the next logical step was to blame the wastegate. I just replaced the turbo last weekend, which solved an issue of late boost/low power in the low RPM's, but has brought back this surging issue. There have been no codes indicative of any issues. Relevant mods are JCW intake, Helix FMIC, catless turboback exhaust, Forge DV, and Manic Stage 1 tune.

Issue exists with both OEM diverter valve and Forge recirc valve. I have checked compression with good results across the board. Fuel pressure is good. AFR's are good. The surging happens both on the stock map and on the tune, and is more drastic with higher boost. No error codes, no strange oil consumption. No smoke. MAP and MAF sensors have been cleaned. Since first posting this, valve cover has been replaced as well as pressure converter and vacuum lines from wastegate/vac pump to converter and vac tank. Intercooler has also been switched out to rule out oil blockage. I have checked pcv lines for clogs.

Thanks for any and all suggestions, sorry for the short novel. In a perfect world, I'd get a CEL that would point me in the right direction, but no such luck.

Update: I smoke tested the car again and found one definite leak at the Forge DV, replaced the DV with a new OEM one (not the old one I'd previously tried for comparison) and the issue seemed improved, though still present. The surging was less prevalent, and only really present in higher boost. I'm now thinking it's just leaks in the system, though I'm surprised that the car is not seeing these and throwing codes, as it used to go into limp mode any chance it got. I'm in the process of trying to track down/fix more leaks.

RESOLUTION: Most of it was boost leaks of one kind or another. The last part of the issue was fuel injector seals, essentially lowering compression with blowby (204k miles old and seals were not changed when removed/replaced previously).

 

Hopeful bump. Wasn't the PCV valve.

 

Have you replaced the vaccum lines that go into the wastegate actuator?

 

Also do you have any oil leaking from the turbo feed line?

 

I have replaced the vacuum line for the wastegate actuator. I haven't noticed any oil leaks but I'll check again when I'm back with the car tomorrow. You think it could be a drop in oil pressure due to a leak? Thanks.

 

If it was a big enough leak to lose oil pressure you'd definiteley notice it. The reason I asked is because I had an oil leak on my feed line that was dripping down the back side of the turbo and soaking the wires causing a bad connection and some bov issues.

Do do you hear the bov vent when the surge and cutoff happens?

 

Do you have the forge complete bov or the insert?

 

Ok so I watched the video again and I can hear the bov go off after the surge. May be a stretch but it definiteley seems like a bov issue. Does it immediately open the bov when you release the throttle?

 

Ah I see. I have the full Forge recirc valve. During the surging the car isn't venting/releasing. I've tried both the Forge and the oem diverter valve, the issue exists on both. Thanks

 

Realized I didn't answer your question, sorry. Yes, the valve actuates immediately upon decel/vacuum. Thank you

 

Perhaps reinstall the stock OEM diverter valve and see how that impacts anything. So simple to swap, it could rule out an issue quickly. How is your low and high pressure fuel pump readings?...are they within spec.?

 

The issue exists both on the Forge valve and OEM diverter valve. Fuel pressure is good. Thanks

 

Are you able to graph your map and maf sensors?

 

Also do you have an aftermarket or stock turbo inlet tube?

 

Don't have the equipment for graphing unfortunately. Aftermarket inlet tube, Forge. It has been on the car for all 50k miles of this motor, and probably 100k of the last motor. Thanks

 

When you install the forge bov are you still using the oem pressure converter? Could be a damaged pressure converter not letting the wastegate open.

 

Pressure converter has also been replaced. Thanks

 

I have that same surge on my 2012 JCW N14 but only when I really get on the throttle.

It seems to go away around 5000 rpm, and throws no cel. Car has 42k on it.

 

Good to know I'm not alone on this. How long have you had the issue? Did it come up after doing any mod or maintenance that you know of? Have you tried to get it diagnosed? Thanks

 

I had a RMW tune put on the car in 2015, no issues. Then last year at the dragon I had
Helix to the walnut blasting of the intake valves. This issue started about nine months
ago, I just have not gotten around to have it resolved because I only put 2,500 minles
on it last year. Could getting the valves blasted have anything to do with it? Not the
blasting itself but removing the intake and all the rest of the pipes and hoses.

 

Thanks for the info. So last weekend I smoke tested the car myself, took my time, and found several leaks in the system. One of which was coming straight out of the Forge DV. After replacing the DV (again) the issue seemed a little better, less surging and only at higher boost. At this point I'm fairly certain it's just caused by boost leaks; I'm just surprised the car is not 'seeing' them, as it used to go into limp mode any damn chance it got. I also had my valves cleaned right before putting the new turbo on. During the smoke testing I was getting wisps of smoke back around the intake manifold as well; I'll be replacing the intake gaskets as well as the throttle body to mani gasket to see if that has any effect. There's definitely a chance that taking everything apart and reassembling, especially if the old gaskets were used, could be the cause of the leaks. I'll update as I go.

 

thanks

 

I'm curious what the solution for this turns out to be...

I have a stage 2 Manic tune on my Clubman, and I experience the same boost surging/flutter/whatever you want to call it. I have a mechanical Autometer boost gauge that I can see oscillate as the boost target is reached and attempted to control.

My mods are AEM intake, Forge diverter valve with bypass plate, Wagner intercooler, and WMW cat-less downpipe. I am still running stock S turbo with OEM wastegate, stock turbo inlet pipe, stock turbo outlet pipe, and OEM cat-back exhaust.

My theory is this: the OEM turbo and wastegate just cannot control boost very well. Or there is too much flow through the wastegate once it cracks open, and then has to close to bring the boost back up to target, rinse, and repeat. To add to the problem, the boost is electronically controlled, which makes the control cycle slower than it should be.

 

Thanks for posting. The boost control certainly isn't ideal on these cars, though mine ran fine with the same setup it has now for quite a while, so something has changed. I'm leaning towards the leak theory given the noticeable improvement upon fixing one definite leak. I'll update here as I go, thanks.

 

^^^^^Any updates?