Kurt

Unfortunately, I have not found a definitive answer to my question in the many "overboost" threads that have been posted in the past. So here goes my best explanation.

3rd, 4th, & 5th gear, it abruptly shuts off the fuel - the violent manuever that a few people have experienced. One time (fortunately, off the highway), the engine refused to accelerate until I turned her off & restarted her.

I've had a few discussions about this on Rennlist chat, but is it true that the overboost protection should never kick in if everything is in working order? I want to get the car and myself into 1 or 2 DEs this summer so I can learn how to operate this machine as it was truly intended, but I really want it in working order first (i.e. capable of acceleration at high speeds).

Basically, my questions involve the exact nature and behavior of the overboost protection (when everything is in working order), and what exactly might need to get fixed - wastegate, whatever comes to mind.

Thanks a lot in advance

Update below

rhesus

My car was doing this when I first got it. Turns out one of the oil-change monkies left an intake hose slightly disconnected. Can't remember which one but hopefully that helps you a tad.

Jon Moeller

Check your cycling valve, too. I found that the signal line was broken off, and as a result the car was overboosting. Since my KLR has the Autothority chips, no overboost protection was present. The result was a blown hg.

That's my evaluation of what happened to my car. Hopefully, that's all the damage that was done.

-Jon

Jake951

I'm not familiar with the particulars of your car, but the first thing you need to do is to monitor boost with an aftermarket gauge (not the one in the dash). Under what conditions do you get the fuel cutoff? Are you running completely stock? If so, then stock overboost protection kicks in a bit above 11 or 12 psi because peak stock boost is around 11 psi. If you are getting more than that stock, then it could be a faulty wastegate or cycling valve, or an obstruction or leak in the line to the wastegate. A faulty KLR is also possible, but I think it's less likely than the other causes. If you have a non-stock setup, like aftermarket chips, MAF, MAP, etc., with manual or electronic boost control, you should have some means of turning down the boost. If that doesn't work, then look again at the wastegate, cycling valve, and line to the wastegate.

Kurt

Yes, sorry to skip out on some of the details.

Car is completely stock and I do not have an aftermarket boost guage, yet, as it's on its way.

Danno

Sounds like it perhaps could be an intake hose that's leaking under boost. Everything runs fine across the entire RPM range at 25% throttle. Even 50% throttle is OK right? But it's only when you have full-throttle and max-boost hits around 3500- 4000rpm, then you get a BIG stumble that throws you through the windshield?

I had this very problem after getting my headgasket repaired car back from a SoCal "tuner" after he blew up my car on the dyno (AND charged me for the headasket repair). Thus GURU Racing was born...

Anyway, on the way back, I was getting violent stumbles at anything over 75% throttle. Pulled over on the side of the freeway and inspected everything. Found that only two of the front belt-cover bolts were on there and tightened (lots of rattling). Then most the large hose-clamps on the intakes hoses were completely loose. The large clamp on the throttle-body hose was dangling down by the intercooler-pipe, and the throttle-body hose had blown off. So I pushed the throttle-body hose back on and tightened down the hose-clamp. No more than 5-miles down the road, the stumbling started up again. This time, it was the small rubber hoses that come off the intercooler that I found was loose. I took off the intercooler-pipe between the intercooler-outlet and the throttle-body to find that there was a humongous dent in the end where a screwdriver was used to pry the intercooler pipe into the hose.... grrr. . So I took an extra 30-minutes to inspect and tighten each and every single hose-clamp on the entire car. Also plulled some bolts from non-essential areas and installed them on the belt-cover housing to reduce the rattling.

Kurt

Correct, only happens at full 100% throttle and full boost in the top three gears. Exactly as you described -- however, no rattling or strange noises whatsoever.

So did fixing/replacing the part with the dent, the intercooler pipe, fix the problem? I'm going to put all of these items on the list, so the more the merrier.



Haha, excellent story (and reasoning).

Danno

"So did fixing/replacing the part with the dent, the intercooler pipe, fix the problem?"

I don't think the dent in the end of the intercooler pipe did much except restrict flow. What helped was tightening down the hose-clamps that were loose. I also found that the big hose coming out of the turbo was loose as well.

What really bugged me was this guy gladly took my check and gave me a car that he knew the repairs were incomplete.

Jfrahm

What if he had no signal to the WG at all? I think you need to get into 3rd (or on a really long hill) to see full boost in 2nd.

-Joel.

Danno

Hmmm, yeah. If he had a plastic nipple on the CV break or some other leak that diverts pressure away from the wastegate, he'd get more than normal boost and trigger overboost protection.

Didn't ask the important question: "How much boost are you actually hitting when the car stumbles?"

Kurt

Yes, the million dollar question...that can't be precisely answered yet. Don't have an aftermarket guage (as it's being shipped now), so the overboost kick-in is happening at "full boost"/ 2 bar as indicated by the stock guage.

But...a working boost guage is about 2 days away.

Jfrahm

Sounds like no signal to the WG to me. You could pull the WG line off of your CV and see if there's anything connected to it. A piece of vacuum tubing and a M-M connector will help, just put one end in your mouth and conenct the other to the WG line. If you can pull a vacuum on the WG line, check the other lines on the CV.

-Joel.

Kurt

Thanks Joel, I'll add that to the list.

Additionally, one question that hasn't been answered - is it true that the overboost protection should never actually kick in if everything is working correctly? So essentially, the overboost is a built-in device, purely for safety, that deploys solely if something goes wrong?

Danno

"- is it true that the overboost protection should never actually kick in if everything is working correctly? "[

Yes, it's a safety mechanism. In your case, something isn't working correctly because max-boost on a stock care shouldn't ever go over 1.75-bar on the dash gauge. You're 33% over max-boost already.

"So essentially, the overboost is a built-in device, purely for safety, that deploys solely if something goes wrong?"

Yep, pretty much so. Even then it's still dangerous to hit it. In your case, with 33% more boost, with chips mapped for stock flow, you can be getting dangerously lean and are risking a headgasket, or worse, a complete engine-rebuild.

So keep your eye on the boost gauge and learn to feather the throttle so that boost never gets above 1.75-bar and you'll be fine.

Kurt

Yes, precisely what I've been doing to "deal" with it.

Thanks for all the help everyone, particularly Danno. Next week I should have the necessary time to check everything out, and I'll be sure to share whatever news comes of it.