boost cut due to cold weather?
 

Ok so i have an evo 8 with evo 9 turbo intercooler and bov. intake. exhaust. tuned on e85 at 32psi. I bought the car this way. it turned the boost down like a week ago to around 28psi. It ran just fine like that. Today i went WOT and it started shaking really hard and wouldnt build boost past 20 psi. In 2nd gear it spools up to 20 psi and starts shaking real bad at about 3k. it was really cold today (-25 F) and i was wondering if it is boost cutting because of the cold?

Boost cut (or more properly fuel cut) would be the instant stoppage of fuel by the ECU if you were exceeding load limits set by your tuner. It would not explain a drop from 32psi to 20psi.

That sounds more likely to be a boost leak, boost controller problem, wastegate problem, or some combination thereof.

What are you using to control boost? If you have the ability to datalog your car, you should look at what load values you are hitting, and post the log for us to see.

It doesnt get up to 32 psi because right when it gets to 20-25psi it start shaking and doesnt build anymore boost. (its kinda like a violent rev limiter). it is a manual boost controller. also when it starts shaking the check engine light flashes.

i do have a video of it doing this if that would help.

Well there weren't any boost leaks and all the vacuum hoses going to the boost controller are ok. So what should I check next?

What do you run for engine management? Stock ecu on a maf? Have you checked out your A/F? Is it going lean on you? If it's going lean, it could be a pump going bad or something else fuel system related. If it was a boost cut, you would hit at least what it was tuned for before it would cut (32psi).

If it is MAF on the stock ecu (which I assume as you still get check engine lights), you want to make sure no unmetered air is getting in between the MAF and the turbo. It definitely sounds like a fuel cut, but the question is why. Make sure the vacuum line on your fuel pressure regulator (passenger side of the fuel rail) didn't come loose or pop off as well.

Also make sure the vacuum line to your EGR valve which is located on the drivers side of the intake manifold way down low hasn't come off. The vacuum lines also run across the back of the manifold in a forest of craptastic wonder. This is the reason I nixed all that crap, to clean it up.

yeah its the stock ecu with maf air flow sensor. Im wondering where the fuel filter is now so i can see if it's the reason to not getting enough fuel

When was the last time you put a new set of plugs in it? NGK BR7ES gaped to .022

Fuel filter is in the fuel pump housing itself and is not serviceable.

Is your ECU flashed or are you using an AFC or some piggyback? If for some reason you are using an AFC, make sure the signal input is set to Karman and NOT hot wire. I remember having some crazy crap like your having happen when I accidentally left my AFC on hot hire instead of Karman. Karman is frequency based and hot wire is voltage based. I use an AEM with MAP (Manifold Absolute Pressure) instead of MAF (Mass Air Flow), so no issues there anymore.

The fuel filter is just the sock on the pump. You can replace it by taking out your back seat (1 minute pulling 2 release snaps) and then it is on the drivers side under the cover there. Just have to leave the car off for a bit with the fuel cap open to relieve some of the fuel pressure and then pull the fuel lines and electric connector off. Next, remove the small nuts and then wiggle the pump assembly out (a bit tricky) and replace the sock on the bottom. I am sure you have a walbro if you are running that much boost, so you can find replacement kits all over the place for the whole pump or just the sock on the end.

If you don't mind pulling it out a few times you could try the sock first and then the pump or just splurge on a new $90 pump and do it once. If the old one wasn't bad, you can always keep it for future use.

It really doesn't sound like bad plugs, as that is usually not as harsh of a cut. Bad plugs should just be like a misfire and not a fuel cut bucking like he is getting. You can always try it though. Also bad plugs usually don't completely stop you from revving like he is experiencing, usually it will just miss here and there and still let you rev it out. The only way I would say it is plugs is if for some reason one or more of them have come loose.

Also realize his ignition has been fine at that boost level before, so I seriously doubt he needs a new ignition. You can certainly try plugs first though as it is cheap. I would be surprised if that fixes the issue though.

You need to get a wideband and get a good A/F ratio measurement. Unfortunately widebands are not cheap, but really a must have for modified turbo cars.

+1... sounds like bad plugs to me as well....swap em out

sounds like missfire. time to go spoolinup. for now you could change your sparkplug or gap it down a bit.

really?
 

:confused:

Put some new plugs in it, save yourself a butt-load of time.

I boxed the filter sock. There is a built-in filter in the assembly itself (12 on your diagram as shown), but the sock is the first filter the fuel sees and is where all the crap gets caught first. I wouldn't be surprised if it was clogged if he is switching between pump gas and E85.

From what you have explained it definitely seems like a problem with the spark plugs. Check all 4 plugs and make sure they are all tightened. At first I would think a leak somewhere between MAF and the turbo. With the Evo's vented hood it's also possible for water to get into the spark plug cylinder. Believe it or not it happens. If everything wasnt tightened appropriately and all sealed up, that could be the problem. Let us know what you find out when you fix it!