hi all,

what is the exact behaviour of the car if it detects an overboost condition?

atm, at WOT in 3rd, 4th or 5th gear, around 4000-5000rpm, will suddenly stop accelerating and lurch (feels like hitting the rev limiter). after this, any attempt to boost over 1.2 bar on the factory gauge results in similar stuttering like u r hitting the rev limiter.

however, i'd always read that once this happens, the car won't boost over 1.2bar until you shut it off and restart it. on my car, the condition lasts for a while, but after about 5 minutes of driving (without shutting off the engine) u can get on the boost again and it will drive like normal.

is this the overboost protection, or is it something else.

cheers,

chris.

 

I know on my car(on the dyno) the car just died when hit overboost protection.

 

From the very little I know:
- KLR detects overboost
- KLR signals DME
- DME sets 'limp' mode
- Cycling ignition off/on resets the DME to normal ops.

 

I once had a similar experience. Your car wasn't near empty on the fuel gauge, was it? I had that occur on a near empty fuel tank under WOT; the car then boosted fine again. Filled 'er up - no more problems...I always thought it may have had to do with the fuel pickup being starved, or the fuel pump or FPR burping, something like that...Let us know if you find anything...

 

hmm...no, it happens all the time, full, empty (well not empty, u know what i mean ), u name it. but yeah, i don't have to cycle the ignition, it just goes back to normal ops after a while.

 

'what is the exact behaviour of the car if it detects an overboost condition?"

Well... the DME cuts the fuel... so you better have your seat-belt because it feels like you've hit a brick wall. I've cut my lip by having my face banged up on the steering wheel before. Of course, that's because I was at full-throttle when I went over the max-boost limit. If you approach it a little more carefully it will feel like the car just dies, then as boost drops, it comes back to life again. So right at the limit, it will be stumbling and jerking.

"i'd always read that once this happens, the car won't boost over 1.2bar until you shut it off and restart it."

That is more likely another fault, something that stays around. Check the blink-codes coming from the KLR and see what it reports. Sometimes, you can have several things wrong like overboosting with a bad TPS along with a bad CV-cycling-valve.

BTW, there's absolutely zero communications between the DME & KLR. There's a pass-through ignition signal that the KLR hangs onto and passes back to the DME. This allows the KLR to retard ignition if it senses knock. But that's the extent of the 'communications'. They each detect overboost independently with the KLR cutting boost and the DME cutting fuel.

facboy, sounds like you have a massive vacuum leak that opens up under boost. Check the big large hose coming out of the turbo. Feel around the backside, it like to split underneath where you can't see it. Also check the short rubber hoses that hold the intercooler pipes. Also the conical hose going into the throttle-body. This one is especially vulnerable because there's very little clamping room on the throttle-body.

 

Actually that happend to me too when I hit the overboost protection. The car ran great, then the overboost protection and it wouldn't boost for a while. But after a couple of minutes it boosted again.

Seems like their are different limp modes out there?

 

The answers to most of the questions are in this post
https://rennlist.com/forums/showthre...5&pagenumber=2
Pay particular attention to TT's posts as he has read the code and is not guessing.

 

thanks guys...i had the J-boot replaced recently, and that didn't fix the problem. i'll check those other things too. in the thread mildmax posted, somebody mentioned a bad AFM or TPS - is this possibly a cause?

 

Danno, do the GURU chips still retain overboost protection??

 

Check the line from the cycling valve to the wastegate. Mine had the same symptoms - temporary over boost cut out - when the little plastic nipple on the cycling valve cracked and leaked. It would only show up at full throttle in high gears on hot days.

 

speaking of the CV, my mech tried to pop another one in to see if that was the problem but b/c it was just a quick test, they haven't fitted it up properly - ie the banjo bolt line still goes to the CV, but there's another inlet that is currently attached to nothing (i think it's the one that goes to the j-boot). what effect is this going to have? actually, i'm not even sure that the wastegate is hooked up to the new CV either...i suppose it must be.

 

I had the exact symptoms and fixed it by replacing all the vacuum lines and cleaning up the venturi mess under the manifold. You have a definite leaks that needs to be fixed. Look for older posts by me titled "Venturi tube nightmare" I believe.

 

Hey diskzero! My wife was born and raised in Santa Clara

 

hrm...well i haven't had a chance to look at the stuff under the intake manifold yet, but i did check out the intercooler hoses and the throttle body-hose and the turbo hose, all of which looked fine.

exactly how is the CV plumbed? i've seen diagrams, but can somebody tell me how it is plumbed when looking at the physical object? assuming i'm looking at it from the top (the side that the electrical connection is on), with the 3 hose connectors facing towards me, what do the 3 connectors, um, connect to?