fast951

KLR has no control over the fuel injectors, it cannot shut them off. The DME shuts down the injectors when it detects overload (stock DME code).

With the Vitesse MAF software you are running, you can and activate actual overboost yourself. This is different than the factory overload functionality

Tom M'Guinn

Thanks John. No doubt the Vitesse hardware makes most of this moot -- so more of an academic curiosity as I shelter in place. I get that the KLR doesn't have any direct connection to the injectors, but was trying to figure out how/if/why the factory literature says the injectors get shut off if the KLR detects excessive charge pressure.

fast951

​​​The KLR measures actual boost as in PSI. The DME calculates load based on air flow/RPM.
If all the variables are constants, which is never the case outside of a lab environment, then you can match air flow to boost. Start changing the engine's volumetric efficiency (VE), then air flow changes at the same boost.
Once you start manipulating VE (head work, cam, exhaust, turbo) or alter the boost curve, the stock DME overload will trigger. Many Racers experience this when they start changing the VE.

​​​​Since environmental variables are always changing, which indirectly affects VE, the DME overload protection has builtin "fudge factor" to handle the changes, the timer is part of it.
In reality, overload protection can be triggered without exceeding the boost curve programmed in the KLR. As an example, running a free flow exhaust on a cold day (VE change) , you can hit 11psi in 3rd gear and you are fine. Now go 4th gear on a slight incline, and you will trigger overload. Reason being, in 4th gear you are spending longer time at the same RPM than in 3rd (the 3 second timer kicked in).
​​​​​​​I believe there is an old thread here where a racer was experiencing this.

Up till 2007 when Vitesse introduced actual boost to the DME (via MAP sensor), there was no accurate boost control on the 951.

fast951

My opinion on this is that something went wrong in the translation. The KLR shuts down the cycling valve, maybe they are calling the CV injector???

Correction: in post #8 the factory manual is mixing both KLR and DME functionalities, which makes it less clear.

divil

Guys, they are obviously talking about the DME in that statement! Look at the last sentence: "injection" starts again after the air flow sensor plate has returned to 3/4 of it's max position. Only the DME gets that signal.

Tom M'Guinn

I think the Porsche language in post #8 is just wrong. The excessive charge pressure and nominal curve C are KLR triggers, but they list what happens when the DME sees too much load. Seems like someone got confused when writing that.

PS: john, it says gasoline is shut off, so they aren't talking about the CV. The first part talks about the KLR and the second part talks about the DME (as Divil points out). I think it's a screw up, or maybe they thought it ok to blur the two concepts if the DME and KLR triggers were intended to be the same (on paper anyway). If so, shame on them.

fast951

Yes in #8 they state "fuel injection shut" which is a function of the DME.

The text is confusing as they mix KLR and DME functionalities. DME does not know TPS angle, just IDLE and WOT. KLR knows actual TPS angle... So now they talk about barn door being open 3/4th..
So glad I'm no longer using the old stock overboost/overload.

​​​​​​

divil

So to bring this thread full-circle: do all KLR error codes cause it to go into this limp mode? I know that the TPS fault will do that, and obviously a bad MAP sensor would have to do it too. But from the documentation, it doesn't sound like every error condition would do it. For instance, the document clearly says that when knocking occurs, it tries to fix it by pulling timing, and only if that fails does it start to pull boost in very small amounts. So which ones do trigger it, exactly? Does anyone know for a fact that a high boost error code will cause the KLR to go into limp mode?

I've been working on figuring out the stock code for the KLR lately, just for fun. I don't know if anyone will find this interesting, but here's what I know so far about blink codes: the other day I found the routine that handles the blink codes. It's pretty interesting to see! I found it by guessing that the actual codes shown in the Porsche documentation would be BCD (binary coded decimal). That enabled me to search for the references to each error code. I had already figured out most of the real-time signalling and a few other bits such as the ADC stuff, so the error code logic is helping me tie it all together. Here's a few interesting things I see:

* Only one error code can be stored. They're checked in sequence, and each one overwrites any previous code. The order is:

knock/map sensor (for some reason it seems only one or the other of these is checked on any given cycle.)
battery voltage
boost too high/low
TPS signal/power

So if you have a TPS issue it will hide any other blink codes that might have come up.

* Most error conditions need 60 consecutive occurrences to trigger the code. The low battery code doesn't, it'll come up immediately. There's 2 voltage thresholds: ~10v triggers the code, ~10.5v does not trigger it, but also does not clear it if it was already there, and finally above ~10.5v clears the previous code (if the previously stored code was a low battery code).

* The boost high/low codes are more complicated. The base counter is 100 instead of 60, but that's only at full boost. Below full boost, only every 4th count is used. So if I read it correctly, at 6000rpm and full boost you would trigger a code in 1/2 a second. At 3000rpm below full boost, it would take 4 seconds.

All this stuff is based on firing cycles, not time.

I can't say definitively from the code which conditions will make it try to limit boost pressure, because I haven't found where that's handled yet. Reading mcs48 code is hard and they really pushed that chip to the limit. I'll get there though!

Oddjob

I would say that yes, all these possible KLR diagnostic faults should put the control system into "limp mode", and generate the blink codes. But I'm not sure how consistently the KLR will detect these faults/errors. For example, I have unplugged the knock sensor, to test the sensor and the car's response, and it didn't do anything. I would have expected the KLR to identify a fault with the knock sensor and go into limp mode. I believe it should, but the car I tested it on, did not.

If the KLR detects knock, it will pull timing to reduce the knock events. It's not a fault or error, so it won't go into limp mode and won't generate a fault/blink code.

In 27 years of owning and tracking 944 Turbos, I've had the KLR detect overboost and go into limp mode giving the blink code only one time. At the same boost level the car had been running for years. So I believe it to have been a problem with the KLR itself or the pressure sender within the KLR. I swapped the KLR at the track, and the problem never occurred since. I have not done any testing with the questionable KLR.

Where is the KLR high boost level set point mapped, on the KLR chip? And what is it set at?

Tom M'Guinn

I would have to think its in the KLR, no? As for the set point, see the "C" curve in post 8 of this thread.

Oddjob

That looks to be the DME overload protection being described - the hard fuel cutoff and having to back off to 3/4 throttle and 1 minute to reset.

The KLR overboost is an enigma to me. You can run an aftermarket DME chip, with manual boost controller increasing boost well beyond stock, and leave the stock/factory KLR chip installed, and it won't trip the KLR overboost fault code. So I'm not sure where it's mapped or what it's set to. And like I mentioned above, I've only had it trigger one time, and determined it to be a problem with the KLR, not an actual overboost condition.

Tom M'Guinn

Yeah, as discussed above, that language in the Technik is hopeless. It says if the "charging air pressure" hits the C curve for 3 seconds... (i.e., to much actual boost)… but then describes what happens when the DME hits its limits. That same boost chart is used when describing boost pressure earlier in the manual, so to me that C line refers to boost. My only theory is that the DME and KLR are intended to trigger at the same time (in a lab) and so whoever wrote the manual thought it was ok to refer to the two limits interchangeably... in other words, that C line is not only the boost curve limit, but also --theoretically-- the DME load limit?

Oddjob

Agree - I've seen various factory sources that supply vague or incorrect descriptions of the DME/KLR functions. Combination of the literature probably not being written by the technical/engineering design team, and then being translated to english. Important details are lost.

From what I've found over the years, the KLR overboost fault and the DME overload protection do not hit at or near the same limit. DME overload hits way lower/sooner. KLR overboost basically never, regardless of boost level. I'd be curious if what I have seen is how it's intended to work (or not work), or if others have had the KLR overboost fault kick in at moderate boost levels.

divil

You might not remember details like this, but when you had the code you mentioned earlier (due to the bad sensor) was it definitely the boost too high code (3-2)? Are you sure it wasn't 3-3 (faulty pressure sensor) ?

When you tried unplugging the knock sensor - did you drive, and go above 3500rpm? From what I can tell, knock sensor faults are not counted below approximately that value. Also, when you had the DME overboost kick in, did you turn off the car to get it going again? That clears the blink code.

I'm not trying to poke holes in what you're saying or anything. It's just I can't see how you it could have been intended to work if the KLR code is not logged before the DME overload protection.

Oddjob

It was the KLR overboost fault code, certain of it. Lost boost (limp mode) during practice sessions at the BIR club race last summer, and checked the blink code. Really surprised me, because I have never had the KLR throw an actual real world code before (only had it throw a code when I unplug the TPS to make sure the diagnostic system and my light tester work). And the car wasn't overboosting. So very likely the KLR had to have failed in some way, possibly the pressure sender. Swapped with another KLR and the problem did not return.

Testing the knock sensor was several years ago when I was trying to determine if my car had a bad knock sensor and was pulling timing. Yes, full boost, full throttle, full rpm range runs. I tried to things, I disconnected the knock sensor and I also unbolted the knock sensor from the block and wrapped it in foam to make sure it wasn't detecting knock counts. Neither had any impact on the car (DME/KLR).

The DME overload protection does not create a KLR blind code fault. But yes, cycling the ignition will reset the DME. Have had to do that on track before. But have also played with it on the street, and yes anything above 3/4 throttle will cause the DME to cut the fuel again. And after about a minute or so, it automatically resets.

>>>>>It's just I can't see how you it could have been intended to work if the KLR code is not logged before the DME overload protection.

I'm not sure I'm following what you're asking or saying here.

I've been driving or in at least 4 cars that have hit the DME overboost protection for somewhat slightly different reasons. An 86 turbo that had a k26/8 turbo installed but still had the stock DME chip, so it was boosting (air flow thru the AFM) above the intended limit at higher rpm. An 89 Turbo that had a control problem, waste gate sticking or cycling valve that was allowing it to overboost up to 13-14 psi with the stock DME chip. And a couple different 87 turbos that were running shims in the waste gate (maybe gaining 1 psi boost) but still using the stock DME chip. None of them ever generated a KLR limp mode or blink code fault. Some of these were very intermittent, occasional events. And nearly always at higher rpm in 4th gear, extended runs. So you do not see it much on the street. Generally only at the track.