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Latest update after track day. Drove at Sebring yesterday, kid had to work so I drove to see first-hand what was going on. Had installed new CV, spark plugs, rechecked for any vacuum/boost leaks.
1st session. Had full boost for first 3-4 laps, then boost DROPPED off. From pegging dash boost gage to only 2 marks above 1 bar. That should correspond to ~6 psi. Car still drove just fine, only low boost. I believe this corresponds to "limp" mode. I did notice that this happened only after I had pusedh up to 6400- 6600 red-line. Also noticed that I seemed to have a "two-stage" boost. Car would not go to full boost unless throttle pedal was fully mashed to the floor. At anything less than mashed throttle pedal, boost only built to 3/4 on gage. Perhaps 10-12 psi. When I then mashed the throttle to the floor, the boost gage would climb to 14-15 psi. Of course this meant I went over 6000 rpm.
2nd session. With what I observed in the first session, I drove and short-shifted below 6000 rpm. Boost stayed full for almost the whole session. Boost was variable, still only climbing to 3/4 boost on the dash gage unless I put the pedal to the floor. Car drove fine. No overheating.
3rd session. I was there with a very experience driver/racer/instructor that had past experience with 944 T's. I had him drive the car in the third session to get feed back. He came back with a grin on his face, but did confirm that my boost was "wonky". He short-shifted also and confirmed the boost stayed on full sometimes for the whole session, but that it would vary and go full/partial seeming with it's own mind. He did love the handling though ( he has a 964 race car that he says he has to muscle around the track) and remarked how easy it was to rotate the 944 T.
4th session. Last session of the day and I drove again. Short-shifted and full boost stayed with me, but was sporatic. It's hard to describe, but, for instance, coming out of turn 5 in 3rd gear, as car tracked-out of apex, I would gradually apply throttle as it straightened our (not wanting to loose the back-end) and the boost gage indicated 3/4 boost. As I gained the straight away, I would put the throttle pedal to the floor, shift to 4th, and the boost gage would fully peg, and yahoo....lets go fast. RPM's would climb fast so I had to pay attention to short-shift.
So...................could I be getting "limp" mode protection from the computer due to over boost when I rev to 6400-6500 rpm? Once it goes into this "limp" mode it won't go to full boost for the rest of the session. After the session and the car cools down and the computer/ignition "resets" upon restarting, I go out again and get full boost. Keeping the revs down, the boost will still go to 14-15 psi, but only with full mashing of the throttle pedal, Any thing less that full throttle and the boost stays at 10-12 psi. Is the computer sensing overboost?? To recap. I have stock, 33 year old computer (KLR?), with old school APE 1994-era chips and banjo bolt jet, with stock wastegate and 2 1/2" test pipe. All this started in August of 2018. Never had a problem in the previous 35 track days with the same set up. Runs fine on the street with full boost always, but then, I don't drive on the street the way the car gets driven on the track. Could something be wearing and giving me more boost than I used to have? Could the additional 1-2 psi of boost at full throttle be enough to cause the overboost protection?
Hope I described this adequately. I'm not a high level driver, just a guy that enjoys driving his car fast and safe on the track.
Last edited by eshane; 05-14-2019 at 08:24 AM.
Reason: mis-spelled boost
Just a thought...you might be running to lean at that RPM and heating the engine up enough to create issues. You may be running into reversion issues, but I would think that would happen around 17-18 psi on a 951. Could your ignition wires be sending signals to your knock wires how old are your wires? What injectors are you using? Have you thought about flow testing them to make sure their not the issue. Also the cars getting old, and temperamental, they all have their own personalities, if you replace one part all the other parts start to fail because the car knows you’ll spend the time, money and attention on it. But back to your issue, might want to check the condition of your wastegate. The valve might be sticking.
Sounds Like it is more consistent with the new CV, Pegging the Factory Dash boost Gauge seems like VERY high boost... FUN ...But potentially making bad things happen... I have never run THAT much boost, and I think the car is trying to protect itself.. Try opening up the Jet in the Banjo bolt until the Dash boost Gauge is just below the 2.... that would be Just under 1 bar over atmosphere, and at that point it should stay happy... You can make the Jets out of a regular old soft bolt, thread the outside, Drill it, and grind a slot into it for the screwdriver, Keep going up in size till the car is happy.. Sounds like you had to baby the car a bit but at least you had fun this time and didn't loose your boost totally... Running a Full Bar of Boost obviously can be done but it needs to be tuned on a Dyno with higher FP. The Turbo-Cup cars came factory with 3 Bar FP Regulators, and different Chips and they Ran 1 Bar.
The CV is a 3 ports solenoid valve.
Port#1: IN from banjo bolt (pressure).
Port #2: to WG - NO (Normally open). So if CV fails or is not energized by KLR, the pressure from IN port goes to WG to keep boost low.
Port #3: to J-boot (vent) - NC (Normally Closed). When KLR commands boost, it energizes the CV to close Port#2 and Open Port#3. By doing so the Pressure from IN goes to J-boot and the WG stays shut.
(this is the basic of how the KLR/CV work).
So for the boost to go up, Port#2 to WG must close! If it's not closing, boost remains to minimum (around 4psi). (a) CV is going bad and not executing command from KLR. Or (b) KLR is detecting a problem and is not energizing CV keeping boost to minimum (around 4 psi).
I'm troubleshooting some CV issues myself and trying to understand the situation. This seems to contradict what is said in Clarks-Garage. (quoted below) Am I understanding things correctly?
4.3 Cycling Valve
The cycling valve on the 951 is located underneath the intake manifold. It has three ports. One port is connected to the inlet side of the turbocharger between the air flow meter and the turbocharger, one to the discharge of the turbocharger via a banjo bolt on the discharge pipe to the intercooler, and the aforementioned line going to the wastegate diaphragm. Normally, the cycling valve is "open" which allows the pressure from the turbocharger discharge to be bled back to the turbocharger inlet. This is possible because the port on the cycling valve coming from the turbocharger discharge has an orifice in it. When the cycling valve moves toward the "closed" position, it is closing off the port to the turbocharger inlet. This allows pressure from the turbocharger outlet to pass through the cycling valve to the line going to the wastegate diaphragm. This causes pressure to build up on top of the wastegate diaphragm. When the combined pressure on top of the diaphragm and exhaust pressure against the valve seat overcome the spring pressure in the diaphragm, the wastegate will open bypassing the exhaust flow around the turbocharger thereby limiting boost pressure.
I trust what John is saying--I'm just trying to understand things.
I'm troubleshooting some CV issues myself and trying to understand the situation. This seems to contradict what is said in Clarks-Garage. (quoted below) Am I understanding things correctly?
4.3 Cycling Valve
The cycling valve on the 951 is located underneath the intake manifold. It has three ports. One port is connected to the inlet side of the turbocharger between the air flow meter and the turbocharger, one to the discharge of the turbocharger via a banjo bolt on the discharge pipe to the intercooler, and the aforementioned line going to the wastegate diaphragm. Normally, the cycling valve is "open" which allows the pressure from the turbocharger discharge to be bled back to the turbocharger inlet. This is possible because the port on the cycling valve coming from the turbocharger discharge has an orifice in it. When the cycling valve moves toward the "closed" position, it is closing off the port to the turbocharger inlet. This allows pressure from the turbocharger outlet to pass through the cycling valve to the line going to the wastegate diaphragm. This causes pressure to build up on top of the wastegate diaphragm. When the combined pressure on top of the diaphragm and exhaust pressure against the valve seat overcome the spring pressure in the diaphragm, the wastegate will open bypassing the exhaust flow around the turbocharger thereby limiting boost pressure.
I trust what John is saying--I'm just trying to understand things.
fast951 is right, Clark's Garage is wrong about this. The CV is normally closed, and the KLR has to actively work to open it and allow boost to get above the failsafe level.
If you check the voltage at the CV valve terminals, you'll see it's normally unpowered (battery voltage on both terminals).
fast951 is right, Clark's Garage is wrong about this. The CV is normally closed, and the KLR has to actively work to open it and allow boost to get above the failsafe level.
If you check the voltage at the CV valve terminals, you'll see it's normally unpowered (battery voltage on both terminals).
Good to know--
My problem (to highjack this thread) is that I'm only getting 1.5-1.6 bar pressure. I posted another thread recently. All connections, mechanical stuff, etc check out fine. I did replace the line from the cycling valve to the j-boot with a smaller ID vacuum line. SO:
If the 3 way valve is open on all sides under boost (12v signal), and I am restricting the return flow from the cycling valve to the j-boot, will this then bleed off some pressure to the wastegate as it tries to equalize it self internally? Thus opening the wastegate a bit? Let say so you only get 1.5-1.6 bar?
When air pressure is applied to the top of the wastegate it will help open a stock 951 wastegate valve. If bled off then the wastegate resorts to it’s spring rate inside. Sounds like you may have used to small of an ID hose. I use 1/4” drip line(you can even wrap it). Real good signal, cheap, easy to work with, can handle some heat, at any garden store. Going back to the intake side of the turbo from the CV isn’t a signal you want to restrict.
If you look at "C" on the Diagram that's the line from the banjo Bolt and it is restricted right of the get-go inside the CV. The illustration actually shows this above.. The more that's restricted, The higher the boost you will get. until the computer says...OK.. Too Much LOL...
05-12-2019, 12:12 PM
