TheRealLefty

Thanks, good advice consistent with your handle!

Porsche-O-Phile

Get an ApecI or some other type of electronic boost controller - they're well worth the money over a manual one. Running with NO boost control is quite dangerous - even a stock k26/6 can produce a LOT of boost at peak (something like 30+ psi) and I'm sure the k26/8 on the turbo-s can produce even a little more than that. Point is, it's more than enough to cause a lot of damage. As for why the engine "cuts out", I believe there IS overboost protection built into the KLR circuit which will send a signal to the DME instructing it to kill fuel once boost surpasses a certain level, so in theory you won't boost past a certain threshold. I'm not sure this is correct, but it's what I've been told and even if true, I do not know what the "cutoff" boost level is where that would occur. In any case, running no boost controller and then having a failure of the overboost protection circuit would mean (probably) a new engine.

It is also possible that you're producing so much boost that the fuel flow rate of the injectors can't allow enough fuel to keep the mixture at stoich. and you're getting "pinging" due to a lean mixture under those conditions and the KLR is doing it's job of knock detection and sending the "KILL FUEL NOW" signal to the DME. Either is plausible as an explaination to me, but I don't know which one is true.

jimbo1111

Hook up the vac line from the bango bolt connection to the side port of the tial. That will make it run on the spring pressure .8 bar or 1 bar until you sort things out.

TheRealLefty

Tons of valuable info here. I'm going to get the car up in the air (as soon as practical here in Monsoon City, Maryland, the newly crowned rain capital of the lower 48) and see what's going on down at the waste gate. If there's anything connected to the port side of the WG (or if that's the open-to-the-atmosphere blue hose I found tucked under fuel rail) I think I am going to complete the connection from the port side to the hose running off the IC tube banjo bolt...and gingerly test drive. If all seems to be functioning under light driving, I'll park it until I do my homework and install a boost control.

blodstrupmoen

If you have 2 ports on youre Wastegate

Then youre WG wiring should look something like this..
use a t -brass fitting to fit to the line from banjo bolt at ic pipe

tconn

Blodstrupmoen
The diagram is backwards for a Tial. The pressure line from the banjo should go directly to the side port of the Tial. The regulator should be on the top port.

blodstrupmoen

Tconn, I changed it , thanks
.. confused it with the LR DP

Oddjob

Some info from an old article written by Paul Hennsler (director of power train and development) of Porsche AG on the 944 Turbo Engine (I think it was originally published in Panorama 12/85):

>>

"...In the 944 Turbo, with the onset of knock, the ignition timing of only the knocking cylinder is retarded and the boost pressure is reduced in direct proportion to knock frequency. At the onset of knock, timing is retarded 3 degrees on the knocking cylinder and then stepped back to normal. If further knocking is detected, ignition is retarded further to a maximum of 6 degrees. Boost pressure reduction occurs at throttle openings above 50 degrees. This is done by a timing difference which is compared to an rpm-dependent value. If the value is exceeded, boost is reduced as necessary by 40 mbar steps to a minimum.

....The knock control system also has a self monitoring diagnostic element, which tests the most important components for proper operation. The knock sensor is checked every 256 firing cycles. The boost pressure sensor and throttle plate potentiometer are checked each cycle. If a problem is detected the engine operates in safe mode, with 6 degrees retarded timing and basic boost pressure. The driver becomes aware of the problem by an appreciable loss of power.

The last component of the new 944 Turbo engine is the fuel injection and ignition system.... The motronic system in the Turbo has overboost protection in case of air leaks in the pressure system which could push the turbocharger speeds to unacceptable levels. The fuel injection system measures airflow and compares it to values stored in the control system. Should airflow exceed theoretical flow values by 10% for three seconds, fuel injection is interrupted in the same way as for maximum rpm control."

>>

The reason you get the overboost protection in 4th gear, and not in 1-3rd, is because of you have to exceed the designed boost pressure by over 10% for longer than 3 seconds. So its common to hit the overboost protection in 4th around 5k rpm. However, I think its a much more dramtic fuel cutouff than the rev limiter (so I disagree with the article on this). This protection is mapped in the stock DME chip and the computer is comparing airflow measurements through the AFM. Its not the KLR that controls the overboost protection.

For anyone running higher than stock boost (by whatever method - MBC, shimmed waste gate, jetted banjo, etc), you need to have some aftermarket chips that are mapped for the desired increased boost curve. If the previous owner had problems with the aftermarket chips running rich, he probably did not have the MBC set at the boost level (not high enough) the chips were designed to run. My recommendation is to find out what set of aftermarket chips you have, then setup the boost control system to match what the chips were made for (APE with jetted banjo and cycling valve, or other with MBC, etc). Or get new chips to match how you want to setup your boost control system. But you cannot continue to run without the wastegate hooked up.

The car (with stock chips) is correctly protecting itself from damage by shutting the fuel off. But only the stock chips will do this, so keep in mind that aftermarket chips do not have boost protection mapped in them, so the car will run without the stumble/fuel cutoff even if the boost is exceeding the designed level (of the aftermarket chip tuner), so you can run lean and damage the engine. That is why it is important to run the aftermarket chips with the type of boost system modifications that they were designed/mapped for.

Evan70

Some aftermarket chips do have boost protection built in. I know for a fact that Guru chips do, and I believe Authority chips do as well. I know, because I'm fighting an overboost problem similar to this right now (only occurring in 4th right at 3500rpm). What you are describing is definitely the overboost protection kicking in, and you must shut the car off and restart it to get it running normal again. After overboost protection kicks in the first time, it will limit boost to 1.1bar (on stock chips, possibly a little higher on others) and will chug/stumble if you attempt to go over that. The initial overboost protection will feel exactly like a complete loss of power, and is caused by the KLR killing the fuel system completely.

As has been stated several times, to fix your problem you need to immediately get a boost controller on your car (either manual or electronic). If you go with a MBC you'll need a good aftermarket boost gauge as well. Many EBCs come with a boost gauge built in. Personally, I replaced my MBC with a Blitz SBC-iD unit:
http://www.blitz-na.com/Blitz_Boost_Sbc_id.htm
and have been very happy with it. It didn't fix my issue (I think I've got a vacum leak somewhere that I just haven't found yet), but I like it so much that I plan on keeping it even though the MBC wasn't the problem.

Porsche-O-Phile

This thread is excellent. Good information - thanks to everyone for chiming in. Does anyone know how the KLR computer determines which cylinder is knocking? I am only aware of one knock sensor, located between the #2 and #3 cylinders. If this is true, how would the computer know which cylinder's timing to retard?

TheRealLefty

Ditto on the thread! Between Oddjob's dead on the money analysis and looking at the diagram, I understand what I'm seeing up top....one hose from the IC banjo t-connection going to the waste gate and one just going to a plugged off tube. I also see the open ended tube that probably finished the connection from the missing boost controller to the side port on the waste gate. I will scan and post aftermarket chips from the glove compartment tomorrow. I also have an OE waste gate, j-tube and bracekts in the spares box if this gets to hairy matching chips to controllers.

Evan70

Somebody around here should be able to figure out which chips you have from seeing them. The other option would be to just get a new set. Guru and Vitesse seem to have made a lot of advances over the older aftermarket chips.

tconn

I've got a set of Vitesse AFM chips off my 89 that I'll be listing in the classifieds
if your interested.
They really wake the car up!

Oddjob

Evan, thats a little bit of an unusual overboost protection symptom. You may have a couple things going on there. 3500rpm is lower than what I would expect the overboost protection to kick in at. Are you getting the DME fuel cutoff and the KLR fault detection that makes the car run in safe mode (approx 1.3 bar boost and 6 deg retarded timing)?

If the car is defaulting to the reduced/basic charge pressure, it will store the diagnosed fault in the KLR and you can get it to give you the blink code of the fault from the plug connector under the hood. Have you tried this? If so, what fault code/error did you get? What other systems/components have you checked? Knock Sensor, Throttle Position Switch, KLR Unit itself? Have you reduced the boost level you are running on the MBC/Blitz, to see if the fuel cutoff/overboost protection problem goes away at 15, 12, 10 psi?

Evan70

Things that have been changed on the car:
plugs, wires, coil, cap & rotor, all vacum lines, MBC to EBC, TPS, O2 sensor, AFM, chips.
With the previous chips it would do this in 3rd-5th, and would limit boost to 1.1 bar after the initial cutoff. With the Guru chips, it will now limit to ~1.4 bar and only occurs in 4th and 5th. I have tried lowering the boost pressure, but it takes a HUGE drop to make it eliminate the overboost problem. On the previous chips (Autothority I think) I went as low as 9psi and still had the issue. On the Guru chips I've dropped to 11PSI and don't seem to get the problem, but of course I don't feel like driving around like that so I really don't know if that really does eliminate the problem. The problem is easy to drive around, as it only occurs when going full throttle from 3000rpm or lower in 4th. If I go full throttle right at 3500 in 4th it doesn't have the issue and will pull all the way to redline at full boost.

I just blew the head gasket, so the that's being fixed right now, but I should have the car back tomorrow. While they where fixing that, they finished removing the cycling valve (had already been bypassed). I'm hoping that I might have had a leak around the intake manifold, which will be fixed when it's reinstalled. If not, about the items I've got left to target are either the AFM or the KLR itself. I haven't tried getting the trouble codes, but I will once I get it back.