Did I Experience Overboost?

SpeedRacerX

Well-Known Member
Took a nice little drive yesterday. Temps about 45. Drove for 15 miles, no issue. In recent weeks, car has been running great. 93 and Alky. Usually 24-25# boost. 6262 turbo, HD actuator, front mount, 295 drag radials.

Getting close to home, I decided I wanted to stretch its legs one time for the week. I opened the dump. Turned the corner at my usual rural farm area road and nailed it.

Seemed strong through 1 and 2. As it shifted from 2-3, in a blink of the eye, the light on my tach lit up, felt like either a tire spin or a shift slip and right in that split second as I was lifting, I looked at the boost gauge and it was climbing toward 30#. Oh crap. I backed out in a fraction of a second. Checked the scanmaster and the O2s where low 700s but it showed about 7 knock. Hmmm. Had me concerned.

Got home, ran fine, no leaks, nothing visible, oil looked fine, coolant looked fine, etc.

Trans was built this Spring and I've never even taken it to the track yet so I can't imagine it was a trans slip.

I wonder if it over boosted, broke the tires loose (45 degrees) and caused it to rev up which set the shift light off??

If it was overboost, was it the cold weather and opening the dump that caused it? The wastegate hole in the turbo was opened up when the new turbo was put on this Spring.

Any thoughts?


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Frederickdav

Active Member
Not a Turbo-Guru by any means but I would guess you broke the tires loose. I know my T runs best when it's cold too bad up here along with cold come snow then salt and rust. So well before the rust season, T gets put away.
 

1KWIKSIX

Well-Known Member
I don't run Alky in my car so can't say for sure, but I believe I've read in the colder weather you must adjust your tune when your'e running Alky or risk engine damage. Hope that's not the case here.
 

SpeedRacerX

Well-Known Member
Not a Turbo-Guru by any means but I would guess you broke the tires loose. I know my T runs best when it's cold too bad up here along with cold come snow then salt and rust. So well before the rust season, T gets put away.
Yes, it should be put away by now. Wanted just one more ride. I hope it just spun.

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Pronto

Believe nothing you hear and half of what you see.
I've always had to add fuel with colder weather. Opening the dump didn't help either. You may have lifted a head just enough to start a fail. You'll know in the spring.
 

grass doctor

Dream Catcher
it finally got cold down here in north FL last week and mine has been loving it , chirped the tires in 1,2,amd 3rd gear wow
when I experienced an overboost situation car felt a lot faster than normal and had loud pop 2 -3 seconds after I floored it
it blew a lot of my vacuum lines off , but everything was okay, it happened when then vacuum line came off the solenoid got nice write up on that, just sharing my experience but my car is mostly stock hope she is okay
 

Mr.Spool

Well-Known Member
If it was overboost, was it the cold weather and opening the dump that caused it? The wastegate hole in the turbo was opened up when the new turbo was put on this Spring.
25 to 30 is a big jump,that will eat up alot more fuel.2/3lbs from the cold weather and 2lbs uncorking the exhaust roughly.need a fuel cushion there.
 

SpeedRacerX

Well-Known Member
Checked the scanmaster and the O2s where low 700s but it showed about 7 knock.
knock could have been on the 2/3 manual shift, always hit the mph recall then you can compare where it happenened and what o2s you had.
Knock occurred at 56 mph, right around the 2-3 shift, shift light, boost rise. Does that mph seem low to be shifting into 3rd? I know things are different on the street.

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Mr.Spool

Well-Known Member
Knock occurred at 56 mph, right around the 2-3 shift, shift light, boost rise. Does that mph seem low to be shifting into 3rd? I know things are different on the street.

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depends,manual shifting and valve body,and wheelspin are factors that affect that.low 700s is something you cant carry much past the 1/8 depending on how much you shoot in.need more fuel there,if you got out early your probably ok
 

marleyskater420

still needs to learn
tire spin can and often does trigger the knock sensor

^^This.

CLIFFNOTES FOR STORY BELOW:
*Tire shake can trigger false knock. Not just tire spin, but tire shake as well.
*Find a road with a long incline to help put weight on the rear tires for traction, and make a hit. If the car has no tire shake and shows no KR, then it was probably the tire shake. If the car has no tire shake and it shows KR, then it is real KR, and make tuning adjustments accordingly.

I was tuning a friend's car this summer and we kept seeing a few degrees of knock whenever we made a long WOT blast, however the car would always do the G-Body shuffle because it was struggling for traction.

To locate the culprit, we hooked up the laptop to the Powerlogger in the car, and we made another hit but this time I had my friend focus on when the tire shake would happen, and I focused on when the knock happened. After we made the hit and we compared at what point in time the KR and shake happened, we found that the KR was happening exactly when the tireshake took place.

To be completely sure it was the shake, we went to a stretch of highway with a long, progressively steep incline that was a few miles long. This incline was steep enough to put some extra load on the engine, but also help keep the weight of the car on the rear tires to help with traction. We made a hit, and sure enough there was no KR. Exact same O2 readings, and exactly the same target AFR on the 6.1 wideband chip.

We exited the freeway to turn around to hit it again to be sure, and on the freeway hit going downhill, sure enough the scanmaster registered KR. The 2nd hit going up the incline showed zero KR again.

I wrote you all that to say that it could very well be false knock from tire shake. Do you have a strech of road like the incline I described, that would help load the rear tires for better traction so that they won't shake or spin? If so, try a few hits on that road and see if you can make a hit with zero tire shake and if the car still shows KR.

Hope this helps!
-Tyler
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
Low 700's...7 counts of knock...you've damaged the head gaskets. Boosting it when you get it out next year will push them the rest of the way out. Colder dryer air requires extra fuel...lots of it.
 

SpeedRacerX

Well-Known Member
Low 700's...7 counts of knock...you've damaged the head gaskets. Boosting it when you get it out next year will push them the rest of the way out. Colder dryer air requires extra fuel...lots of it.
You had to tell me this right before Christmas? Lol. I'm hoping it was wheel spin.

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