Thud, then CEL at highway speeds

Hey,

A couple times now, I accerlated hard on the highway, and as if traction control braked (big thud) and then the CEL came on disabling the cruise control ect.

Is my MAF messed up? I have noticed hesitation under acceleration recently. Anyone else have this happen? CEL disappears after about 100 miles of driving.

Have you tried to have the code read and see if it was stored? There are a ton of things that can cause the CEL/blinking cruise so it would be best to know what triggered it.

When this happens are you in 5th gear and just step on it or do you come down to a lower gear and then step on it? I believe this is overboost.

chances are u overboosted. also check to make sure you do not have a boost leak anywhere. are you stock?

I am stock, there is an MBC installed on it when I bought it but its disconnected, and turned off as far as I can tell. The car was obviously abused and ragged out when I got it which is why I got such a good deal Ok so I will try to find a place that can take out the MBC then and check hoses ect. The car has 93k on it, I am not going to upgrade it because I think at its age you are asking for problems, and its fast enough stock.

I will go to autozone to see if they can pull the code, the CEL has since turned off. Weird I did have MAF problems when I put in a drop in filter a while back.

Yes I was in 5th and just floored it. You can feel it hesitating if you push it too hard.

Take your negative terminal off your battery and step on the brake for about 20 seconds, reconnect it and the CEL should be gone. I would find a tuner that is local to you and have him check your car out. If you're stock, you should connect your stock BCS. And make sure you're not running a tune on a "what seems to be stock" car.
Remember this, when you do the above your car will act weird for about 30 miles or so, maybe even more depending on your car. It might even shut off when you come to a stop light.

you had an MBC on it. and you removed it. without retuning. you can't do that.

you're overboosting. and probably knocking like crazy which explains the hesitation.

The mbc is still connected but turned off. I want to remove it and do a reflash if that's possible. I had some MAF issues when I did a drop in filter and took it in and they data logged and didn't detect anything other than MAF issues at the time. Knocking is usually pretty obvious and my engine would be toast by now if it were, driving cross country on no problems.

Originally Posted by GT_Red

The mbc is still connected but turned off. I want to remove it and do a reflash if that's possible. I had some MAF issues when I did a drop in filter and took it in and they data logged and didn't detect anything other than MAF issues at the time. Knocking is usually pretty obvious and my engine would be toast by now if it were, driving cross country on no problems.

What do you mean by "turned off?" This is pretty important... because it sounds like you're driving your car without any form of boost control!

And you don't think hesitation followed by a hard jolt and a CEL is "pretty obvious" enough for you? Hesitation can easily be explained by pulled timing. The jolt and CEL under heavy load, high boost (WOT) is most likely overboost.

Stop driving the car like that (in boost) until you figure out the problem.

Originally Posted by GT_Red

I am stock, there is an MBC installed on it when I bought it but its disconnected, and turned off as far as I can tell.

Originally Posted by GT_Red

The mbc is still connected but turned off.

So again, what does this mean?

Get the code, so we can stop guessing about why your CEL lit up.

Lots of auto parts shops will loan you a code reader to use in their parking lot.

Originally Posted by iNVAR

you had an MBC on it. and you removed it. without retuning. you can't do that.

you're overboosting. and probably knocking like crazy which explains the hesitation.

Chances are if it has an MBC it's not tuned.

Your car looks like an 05, they did not have VDC systems on the 05 LGT.

Originally Posted by GTTuner

Chances are if it has an MBC it's not tuned.

Your car looks like an 05, they did not have VDC systems on the 05 LGT.

Eh, true enough, I'm thinking of a hybrid setup.

But it sounds to me like it's an overboost condition. If the PO had it setup as a hybrid, it would easily explain why he's overboosting since hybrid setups have 100% WGDC dialed in across the board.

He also says he disconnected the MBC. Did he even reconnect the stock BCS?

I've been reading the information you guys are giving me. Upon talking to a Subaru tech, they suggest changing the MAF first. I noticed the MAF is after market anyway, made by Denso. I will start there, the dealership does diagnostic for $60. I think that's not bad considering in Arizona they charged 125 just to test drive it for you.

The part is only $132 and the dealer wants $245. I am going to fully remove that MBC, and it's turned all the way to the closed position. Does that not mean its shut off? If not then I will move sooner to get the system restored to stock.

Thanks

Fine, do what the dealer says and ignore everything we said. Good choice. And keep paying them too. And keep stomping on the gas. I'm sure that will do wonders for your car.

BTW, a useful bit of information for you: the stock MAF sensor is Denso. So much for being aftermarket!

Did you ever get a fault code?

Sounds to me like the dealership is just trying to empty your wallet. If they really thought it was the MAF sensor and wanted to help, I'm sure they could find a known-good one to swap in (takes about 5 minutes) and see if the problem goes away.