Hi all,
In the last couple of months my car has been doing something strange:

Under load it would climb through the RPMs normally and as the boost came on would hesitate, hard (almost like a rev limiter, but not quite). So bad, I thought misfire so I let off the gas.

It's completely driveable, just under some hard acceleration that it does this. A few times I got brave and it powered through the hesitation and it can take off again after a second or so and keep climbing.

No check engine lights or even warnings / pre-faults.

Stock EVO 8, ~ 85k miles.

Got the Torque app and an OBDII BT transmitter and logged some data. I can't see the hesitation (not enough data points per second) but I did notice that it's reporting ~25psi boost peak with one run peaking at 31psi!!!

So now I'm poking around trying to figure out what's wrong and how it might be fixed. First thought is wastegate, not even sure how to check that. I found a box in the wastegate boost line, which I assume is some sort of EBC -- again not sure how to check that for functionality.

Any thoughts on what to do next?

Thanks,
Anthony

 

If you have a stock car, the boost readings are not accurate, the MAP sensor only reads up to one bar (14.7psi). Have you tried a fresh set of spark plugs gapped to .020"?

 

I do have a new set of plugs to put in. That was my first thought a month ago before the datalogging (fouled plug, blowing spark out, etc).

Have not put them in. May re-prioritize that.

Interesting that it does not report more than 1 bar from the stock MAP. It reports values that seem to track and make sense well above that (boost tracks RPMS to a point, boost correlates with MAF data except when shifting / BOV engaged, etc). But I have never calibrated it or even tried to read these values before.

Thanks.

 

The stock boost curve is a 19-21psi spike, which tapers to about 15psi out the top. Unless you know for sure the car has a JDM 3 bar MAP, or an OMNI power upgraded MAP sensor with the rom updated/calibrated to read them properly, you are not reading real boost numbers.


Also, on a stock tune, if you were really seeing that much boost, you would be getting a lot of knock counts.

 

Interested in this as mine does something similar, usually only in cooler Temps though. It will accelerate hard and then around 5500 to 6k its like it hits a brick wall and hesitates really hard. Will backfire and throw an over boost code.

 

Well it was the plugs.

Replaced all four. Right side plug (not sure if that's 1 or 4) was also loose, not so loose that it came up with the plug wire, but I hand-unthreaded it without the wrench.

See pic of the plugs.

Drove it hard this morning and wow, what a difference.

Thanks for the help and I now know not to use the Torque app as a boost gauge as well!

Anthony

 

Glad you got it figured out and was an easy fix. I just replaced plugs not long ago but I guess I'll give them a check and see how they are.

 

These were likely changed at 50k. So 35k of wear on them. I lost my notebook where I used to keep these things (now they are on Google Docs), but my maintenance log doesn't go back that far.

But I'm really glad I don't need to do a full vacuum line inspection, wastegate test, and boost leak test.

 

Yea, those things were done. Lots of erosion on the electrode.