turbo overboost issue - maybe

[abporsche1]

car is an 1987 951 purchased in 1995 totally stock. 1998 added LR boost enhancer and a stage II chip burned by someone in Portland, ore. it dynode at 225hp at the wheels. also added suspension in 1999. it has operated with virtually no issues through out the 45k miles driven on track, long road trips and carving mountain twisties.

last October I was attempting a pass and what I think happened is overboost protection kicked in. but there was no power at all while on throttle. doesn't OBP cycle rapidly on-off, on-off? is OBP cutting fuel or spark? since then the car sat except for short in city heat cycle drives every 6 weeks until a week ago. went on a 1150 mile long weekend drive this last weekend - CanAm 2013 - prior to this trip I added a LR 3" turbo back exhaust with test pipe.

it happened again on sunday, but not until after 1000 miles. the first time it happened was at ~ 800 ft elevation. this time it happened at ~ 4500 ft making a pass up a steep mt. rainier pass. scary **** when you loose all power. what's happening?

[Ky914Newbie]

When overboost protection kicks in, you have to wait 60 seconds for the fault to clear while driving. Additionally, you can clear the fault by cycleing the key off and on and it will be back to normal.

Overboost is often removed or set significantly higher by aftermarket chips. If it isn't behaving as I have described, you may have a different issue.

[Pete R]

The boost enhancer may be sticking. Take it off for a while and see if you have the same experience

[abporsche1]

I did the key cycling 1/2 dozen times with no change. I think the chip had a higher threshold OBP burned in, but not positive. I'll try removing the BE and see what happens.

Thanks, Barry

[nize]

Originally Posted by abporsche1

I think the chip had a higher threshold OBP burned in, but not positive.

just for the record, this has never been possible with the factory stock klr in place (at least as far as anyone is aware). read here for more info;

Boost Control - Engine Protection Questions

[Pete R]

Originally Posted by nize

just for the record, this has never been possible with the factory stock klr in place (at least as far as anyone is aware). read here for more info;

Boost Control - Engine Protection Questions

+1 Porsche designed everything so that in the event of a failure of any component it would lose boost and not over boost

[abporsche1]

hey, it was 15 years ago with no paper work, crs happens (o: the red line was raised 400 rpm. thanks nize, i'll read all and see if it matches my symptoms.

[nynor]

i too have a new overboost issue, after putting the sport exhaust back on the car. it seems to get up to about 16lbs of boost and the car just loses power for a second, then it comes back, rinse and repeat as long as keep my foot in it. i have a stage II chip-set and the standard autothority banjo bolt. i've checked the hose from the banjo bolt to the CV, among other hoses, i don't see a problem. at full boost, the AFR is 11.2:1 or lower. any ideas?

[nize]

nynor; what is your boost set at? any non-stock parts other than the authothority chip and banjo?

[nynor]

thanks, nize, i was getting ready to start a new thread....

nope, everything else controlling the boost is stock. it has the autothority stage II chips and the autothority banjo bolt. last year, i would see some boost creep, but never had it cut out. the boost does seem to be creeping higher, this year, after i put the performance exhaust back on (2.5 inch, no cat, straight through muffler).

i do have an updated blowoff valve (billet, rebuildable, etc.), but i don't think that would cause overboost issues.

thanks!

d.

[Rogue_Ant]

Put in the stock banjo bolt and see if the problem goes away...
If it does, you are hitting the DME's "overboost" (overload) protection.

[nize]

yeah, i was about to say make sure the banjo bolt is not clogged.

[Ky914Newbie]

Originally Posted by abporsche1

I did the key cycling 1/2 dozen times with no change.

I don't think it is overboost because cycling the key would clear the memory and be back to normal.

[nynor]

Originally Posted by Rogue_Ant

Put in the stock banjo bolt and see if the problem goes away...
If it does, you are hitting the DME's "overboost" (overload) protection.

i KNOW i am hitting the overboost protection.

Originally Posted by nize

yeah, i was about to say make sure the banjo bolt is not clogged.

that would be way too simple! i'll check that out.

Originally Posted by Ky914Newbie

I don't think it is overboost because cycling the key would clear the memory and be back to normal.

yep, at least for a while. time to make the LED thingie and see what the error code is.

[jkb58]

The factory overboost protection is mapped on the DME chip. The overboost condition is determined by excessive airflow thru the AFM. Most aftermarket chips raise the overboost threshold, thereby allowing the car to run more boost w/o triggering the overboost protection. The DME overboost cutoff is a hard fuel shutoff (injectors), so the engine stumbles hard under acceleration. Its a very hard stumble, not a loss of power/boost or a weak spot in the powerband. Car will actually buck. And it will stumble hard at anything above mid to full throttle for about 45 seconds to a minutes after the first time it is triggered. Then it resets. No KLR diagnostic codes are generated by the DME overboost protection being triggered.

According to the factory manuals/info, there is also an excessive boost diagnostic function of the KLR. So if the KLR ever identifies an excessive boost condition, it would supposedly go into "limp home" mode, which would limit boost to a basic level, somewhere around 1.2 bar abs, or so. This is the same as if there are other KLR faults, like a bad TPS for example, anything that generates the diagnostic blink code faults. Now with that said, all the testing and boost levels I have played w/, I have never had the KLR identify an excessive boost condition, so I don't know what threshold boost level would have to be exceeded for this to actually kick in.

I have run some pretty high boost levels (for testing and a few times unintentionally) w/ Autothority chips and never hit a DME overboost protection, upwards of 20 psi. If or where the DME overboost protection has been set on the Autothority DME chip, its very high. So it would be very unusual to hit the DME fuel cutoff protection on an Autothority, or most any aftermarket chip.

My guess is that both the posters (abporsche & nynor) are having some other problem than the DME overboost protection (which typically is only a problem w/ stock factory DME chips).

[nynor]

here is why i think it is an overboost issue:

1. the car stumbles, hard, just as you describe.

2. it only happens when the boost level reaches 16+ lbs, per my aftermarket boost gauge.

3. the fuel mixture stays good at full boost, 11.2:1 or richer.

4. it happens at just about any RPM range, as long as it meets the above boost level.

5. it will stumble hard, then recover, then stumble, etc., but at a certain point, it will go into limp mode. however, if i don't allow the boost to get that high (throttle control ), it will run fine at about 15 lbs boost.

6. the boost only started going this high after i put on the performance exhaust (no cat, straight muffler).

thanks,

d.

[abporsche1]

nynor, your symptoms 1-5 are exactly what i experienced - but - the first time it happened it had the stock exhaust. 2nd time it happened was with LR 3" turbo back w/test pipe. i drove it hard with lots of full throttle for 2.5 days and 1000 miles with no problem. then once it happened it continued for 150 miles. do you have the boost enhancer and have you checked it?

Barry

[jkb58]

Originally Posted by abporsche1

I did the key cycling 1/2 dozen times with no change.

Originally Posted by nynor

4. it happens at just about any RPM range, as long as it meets the above boost level.

5. it will stumble hard, then recover, then stumble, etc., but at a certain point, it will go into limp mode.

These descriptions make me think its something else. But any chance this is a custom mapped set of APE chips? Not a standard off the shelf set of Stage II's? Only reason they would hit OBP would be if the parameter was intentionally left in place by the chip tuner. I have run APE chips (and others) over 16 psig for years w/o issue.

Couple things:

Because of the way the air flow is measured, OBP is typically only triggered at high rpm, and has to be near a full run thru the rev range, as the DME measures airflow over a period of time. It will never trigger in 1st or 2nd gear, and sometimes in 3rd, but it needs to be a long pull in 3rd and it will hit at high rpm. Often it takes until hitting 4th gear for OBP to trigger.

Again, OBP and the KLR are unrelated. So if you are getting a limp mode, definitely check for a blink code. Faulty TPS can cause various fuel delivery problems. Not a KLR fault, but even a failing DME relay can cause stumbling, as the fuel pump kicks in & out.

[abporsche1]

my chips were custom made 15 yrs and 40,000 miles ago with ~ 5000 miles of track without a problem until last october.

it definitely happened in 3rd gear, i generally don't do high rpm full boost in 1st and only a little in 2nd.

i was with a traveling group so i didn't do low speed, low gear tests for the symptoms.

it didn't go into limp mode.

Barry

[nize]

i still think the banjo bolt (or boost enhancer) is clogged or gummed up.