Low boost issue, need to know what to do next
 

I seem to have a hard time making boost. I use to be able to easily get boost and reach almost 2 bar. Lately I'm only able to get to about 1.8 +/- bar (on the car gauge) and it doesn't pull hard. The car revs to red line and I don't think the clutch is slipping.

I pinched the line going to the WG and I'm only getting 1.2 bar (per the gauge).

I've been able to visually check the vanes and play of the cold side of the turbo and they seem fine.

I had the car leak down and compression checked and it all turned up good, so no problems there. I replaced all the small vacuum lines. I replaced the pop off valve on the J boot.

I pulled the waste gate exhaust pipe off and the valve was fully seated though I don't have a tool to pressure test it other than compressed air tank. Not sure its a good idea to use that.

I know the OEM gauges are not that acurate, but it is a constant I've been working with.

I bought a cycling valve, but have not tried installing that yet since from what I've read if it fails I should only be able to hit 1.2 bar. I have a hard time getting past 1.2bar unless I just floor the throttle, but I can achieve about 1.75-1.8 if ever so briefly before boost falls off.

I don't think its a WG issue since Im not making boost with the line pinched - something else would seem to be at play.

I'm not sure where to go next?

Thanks for any help you all can give.

heeeeeeeelp

failed wastegate or leak in the intake system. check all of the hoses and clamps, especially the big one just before the throttle body.

Agree that a slow build up of pressure is most likely a leak issue, whether intake or exhaust is 50/50. There's also a chance that the double walled crossover inner pipe has collapsed if you've chopped the throttle while on song.

Well I pulled the intake and have installed to a new CV I had and replaced all hoses running to it just to eliminate it as a variable.

I did pressure test the system from the J boot. The only leak I had came from the Air/Oil separator. But that system should only be under vacuum right? I don't think it would show up as a boost leak since its never under pressure (other than blow by?).

I intend to put the system back together and test run it. If the boost doesn't change I will pull the WG and check the crossover with a bore scope to see if it has collapsed.

If it hasn't collapsed then It must be the turbo or something electrical. Can a DME produce low boost or difficult boost?

I bought a new boost gauge I will install to verify actual boost as well.

What is strange is that the car is more or less (maybe a tad less) powerful than before I put the Lindsey 3" exhaust (with cat) on it. Then for several days it felt like a totally different car with great pull. Then is went back to pre exhaust levels.

Do these cars have the sophistication to learn new power curves when things are added? Wouldn't think so.

Well, it's the KLR computer that controls the Cycle Valve, and takes the inputs from the Knock Sensor and such for Turbo health, DME computer is more a Timing, Air Flow and Fuel control device. Still, on again/off again, and the fact that the Exhaust has been disturbed, makes me want to run a Feather across all the Exhaust joints, cold and hot, there's some real growth and shrinkage with 400 degrees.

I had an issue similar to this on my car several years ago. I normally boost 2 bars but would fall off to 1.8 bars above 5500 rpm. The problem was a faulty wastegate. The way I isolated the culprit was to fabricate a blind flange and attach it to the wastegate so no exhaust gases could bypass the turbo. Then I did a test by first accelerating the car to 5500 rpms at no boost. Then I momentarily floored the accelerator. Car leaped ahead as boost jumped way up beyond 2 bars. This proved the wastegate was at fault. Needless to say flooring the accelerator must only be a momentary test else you'll get into trouble quickly. Prior to doing this test I tried pinching off the line to the wastegate. It had no effect on the boost problem.

Sounds like exhaust Leak check Headers and seals.

Vacuum Gauge test -17hg if perfect..., Intake manifold typically leaks at Idle control outlet. Fix (Remove & Tig)

Later

Hi, just wanted to share my experience and ask some questions. Bought the car half a year ago. During the winter did the general maintenance work and started to drive it this spring. Still have done less then 1000 miles. I soon noticed that the factory boost gauge shows the boost of only 1.4 to 1.45 bars and the boost builds up only after 3000 rpm. I brought is to a workshop (not experienced in Porsche's) and asked to look for a problem. They found out the following:
1) the actual boost maximum was 1,55 bars (the factory gauge is showing 0,1 bars less boost than actual) by using other boost gauge, thus still 0,2 bars below the factory specs,
2) they could not identify any leaks in the intake or exhaust pipes (I do not know how they did that test);
3) They put on for a test new Bosch bypass valve and there was no difference in the boost pressure;
4) The boos with disabled factory chip was around 1 bar and they said that his is less then K26/6 turbine should produce (it should be at least 1,5 bar)
5) They think that the issue is with wastegate (worn out spring).
6) They propose to program new chip that would consider the worn out wastegate specifics until permanent solution can be done (e.g. wastegate restoration). One big part of their business is chip-tuning that they say it can be easily done.

I am not sure about such solution. I have also sent some info from this forum about dealing with boost issues.

If anyone has any further suggestions (especially about wastegate restoration), please feel free to comment.

a new waste gate is what ... 500 bucks, and the car needs it. a much better solution than chipping it around the problem.

you also might try shimming the waste gate.

Replace the wastegate. I cannot imagine a shop telling you to chip it if they know the wastegate is bad. Wastegates don't fix themselves.

Which wastegate would you recommend? Lindsay Racing offers single and dual port wastegate. They mention that for dual exhaust wastegate the minimum boost that you can set is 9 psi, that is still higher then the standard maximums boost for turbo (according to clarks garage it should fall to 0,52 bar that is around 7,3 psi at 5800 rpm). Could it be issue or the difference is quite minor. Or should I just use the single port wastegate that is direct replacement for the original? I might chip the car in the future but do not plan aggressive chip or any other significant modifications.

This is an extreme test but I have performed it to ferret out a boost problem on my 951 a few years ago. It proved the problem was indeed the wastegate. My problem was that the boost would fall off to 1.8 bars (from 2.1) once the engine exceeded 5500 rpms at full throttle. I am one who does not throw parts at cars in order to fix a problem. I determine what is wrong and fix only it. It saves money.

The test I did to isolate the wastegate was to fabricate a blind flange which is basically a sheet of metal with only bolt holes in it. The flange is placed at the wastegate exit to the dump pipe to prevent any gas from not going to the turbocharger. Once installed I ran the engine up to 5800 rpms at no boost (light throttle), then momentarily floored it. Car leaped forward like it was hit behind by a semi and the boost gauge nearly broke its needle. Naturally, I immediately let off the gas so I would not damage the engine. It was a radical thing to do but it definitely proved the spring in the wastegate was defective. I should mention that prior to this test I pinched off the control line to the wastegate so that the test totally isolated the wastegate itself.

Intake-leaks come after the AFM, and will cause too-rich mixtures and stumbling if you're loosing boost on the intake side.

Dual-port wastegate only makes a difference with an electronic boost-controller using twin-solenoids in a push-pull configuration. Otherwise, the pressure-differential between the two sides of a dual-port wastegate using manual-controllers is exactly the same as a single-port wastegate.

If you're familiar with programming, set up a finite-state machine test-table and determine the pressure-differential at no-boost, zero-boost and any amount of boost for both single & dual-port wastegates with manual-controllers. Then add a 3rd test using dual-port wastegate with electronic-controller w/twin solenoids in push-pull.

As for the actual wastegate, the issue is the stock spring is weak and starts opening at 4-5psi in the diaphragm. Over the decades, the spring weakens and opens at 2-3psi. That's weak enough that exhaust pressure alone will open the wastegate at high-RPMs with zero pressure in the diaphragm (wastegate hose clamped shut). That test itself will give a clue if the wastegate's leaking exhaust. It doesn't rule out collapsed wall in the crossover.

Lawrence's test is the only definitive way to completely isolate the wastegate for testing. After you've blocked off the wastegate, if you're still having low boost, then most likely it's a turbo problem or collapsed exhaust.


On an aside note, people seem to think that big wastegates go along with big power. Strange logic considering that the wastegate's function is to dump exhaust and lower boost. If you're going to try and extract the most power out of your turbo, then you want as little exhaust dumped as possible to maximize boost and power. Just a little clipping at the highest-flow peak to keep it level at the desired boost-level. For example, a turning up boost on a TO4E turbo to go from 300rwhp to 400rwhp required reducing the amount the wastegate opens in the 4000-5000rpm range from 3mm to just 0.5mm. With electronic-controller, it even clamps the wastegate completely shut from 5000rpm onwards to deal with the dropping torque-curve.

Some of the ricer guys run completely sealed exhaust with no wastegate, maximum boost is whatever the turbo can do all out. Can hit 40-50psi in its most efficient range and drops off after that. They just size the turbo to match the engine's flow based upon displacement and its RPM range. Then tune the fuel/ignition maps accordingly. A 2.0l 4v engine with 10,000rpm redline can actually flow more air than our 951s and a K26/6 will run out of steam at 4500rpms, even with the wastegate completely closed or no wastegate at all :(

Thanks for the provided info, Danno. I am thinking of getting new dual port wastegate from LR, with their boost controller ("Boost Enhancer"), new bypass valve and new 3'' exhaust. After that I would chip it but I would go with quite conservative chip with 13 psi at the lower rpm range and at read line dropping to maybe 9 psi (I have K26/6). The workshop gays are saying that generally If I have under 300 crank HP I do not heed 3'' exhaust, but as I plan to put a new one then there is no significant difference in price between 3'' and 2,5'' set-up.

I would appreciate is anyone with experience could comments on the below questions:
1) Do I have to increase the fuel system pressure (I assume, no)?
2) Is there any gain from dual port wastegate combined with LR "boost enhancer" or can I go with their standard rebuilt WG combined with boost enhancer and achieve the same results?
3) Is there any benefit for 3'' exhaust vs 2,5'' exhaust considering the above?
4) Would this set-up be aggressive for the K26/6 turbo/the engine?
5) Is there something else I could/should do considering that the car ill be just used for some Sunday driving and occasional track days? I am not looking for max HP but rather at more mid range HPs.

Thanks, any comments and experience is appreciated.

1) Do I have to increase the fuel system pressure (I assume, no)?
No need. There's an inverse-function between pressure and total flow. Increasing pressure decreases the maximum volume the fuel-pump can deliver. It's a balancing act, and increasing pressure slightly from 2,5 to 3,0-bar will let you get more from the stock injectors. Up to about 300rwhp with modified programming. The chips must be programmed for a specific fuel-pressure, or have adjustments to allow for mutliple pressures and injector-sizes.

2) Is there any gain from dual port wastegate combined with LR "boost enhancer" or can I go with their standard rebuilt WG combined with boost enhancer and achieve the same results?
You won't get any difference in boost-control with single or dual-port wastegate if you use a manual controller. So go with the single-port if you want the LBE. Otherwise dual-port if you plan on getting an electronic controller in the future. The LR is a rebuilt factory wastegate, I prefer using a Deltagate, Tial or HKS. Also do not use flexible vacuum hose for wastegate-control. Use hoses similar to the stiff 15mm hose that Porsche installed. Soft hoses is one common source of fluctuating, variable and dropping boost.

The nice thing I like about electronic controllers is programmable boost-curve per gear. That's 3D-mapping like with fuel & ignition. 1st-gear typically has mid-range max-boost of about 12psi with a increase to 15psi by redline. Second-gear has 15psi mid-range max-boost and increase to 18psi by redline. Third/4th/5th-gear has 18psi mid-range max-boost increasing to 20-21psi by redline. The lower-boost in lower-gears act as traction-control and keep the tyres on the chirping-edge of traction for maximum acceleration and control. The rising boost-curve also counteracts the dropping torque-curve to yield a flatter dyno-chart and gives higher peak-HP than torque; a sign of good high-end efficiency.

3) Is there any benefit for 3'' exhaust vs 2,5'' exhaust considering the above?
Get the 3,0" as it will allow for future upgrades. I like the SFR 3" exhaust, lightest and highest-quality construction. Get the muffler configured with a slip-fit using posts and springs to mount. Then you can quickly change it out for a straight-pipe at the track.

4) Would this set-up be aggressive for the K26/6 turbo/the engine?
Not at all. I've gotten over 320rwhp out of K26/6 with 3" exhaust, larger fuel-pump & injectors, EBC, MAF/MAP, standalone-ECU, etc. Might as well get all the components that will work with future upgrades.

5) Is there something else I could/should do considering that the car ill be just used for some Sunday driving and occasional track days? I am not looking for max HP but rather at more mid range HPs.

• Cometic MLS headgasket - you will thank me later when things don't blow at the track
  
• cooling - change both the main and smaller turbo thermostats to make sure they won't fail on you at the track. Do some full-throttle runs on a hot day with AC full-blast and verify that the temp-gauge never goes above horizontal (9-o'clock)
  
• oil - pick a high-viscosity synthetic oil with high levels of solid-lubricant additives (ZDDP,ZDTP,boron,moly, etc). Make sure the oil-level is at the upper-maximum mark on the dipstick.
  
• brakes - change fluid to DOT-4/5,1. Get pads designed for high-heat track use, such as Pagid Yellows or the various Hawk compounds.
  
• tyres - make sure all four are dynamically-balanced (weights on both inside & outside rim-edges
  
• alignment - front: camber & caster set to maximum end of adjustment-range listed in manual. rear: camber set to maximum end of range, zero toe.
  
• gasoline - look up the Gasoline FAQ and Rocket Fuel FAQ and develop a mix of 92-oct pump gas and whatever race-gas is available at the track (typically 100-oct) to arrive a final 96-octane mix. Use weighted-average for the calculation. This will give you a larger safety margin if you run into issues such as hot days, overboosting or non-optimal chip-mapping for the particular hardware-configuration of your car. Use this 96-octane mix for the next step.
  
• Dyno-tuning - regardless of what boost-level you run, any modification from stock-configuration requires re-mapping the chips. Even pre-programmed chips for a certain boost-level are never 100% spot-on as other variables such as engine wear-and-tear (rings & valve sealing), turbo condition, etc. will be different than the test-car that was used to model the chips. Most likely your car will not match the car used to create the chips. I've seen two K26/6 cars with exactly same Tial wastegates and boost-controllers set to the same max-boost settings. Both hits 15psi max-boost, but one drops to 12psi by redline while the other holds 15psi all the way. Best to verify the mapping with dyno and fine-tune.

This is a small list of what I consider the minimum things to do before you track your car. The cost is minimal compared to the +$10000 or more that you'll be spending when it blows up. These cars are old; many are prone to blowing headgaskets after modifications without any track usage at all. Be safe, cover all the bases you can and make sure the tuning is spot-on.

Thanks again Danno. Lot of valuable information for me as new 951 owner. I will take a look at the other wastegate options you mentioned. Regarding other to do things some of them are already done before the first track day I will participate next Sunday, like OIL (Bred Penn), brake fluid with increased boiling temperature, EBC yellow pads, tyre balancing, gasoline (I use only 95 or 98 octane), but still some work to do.

Currently the car is at the workshop for upper strut bar instal and as a next thing I plan to change the alignment. Also thinking about changing out koni sport shocks as people with track experience are saying that those do not "work" properly on track and suggest putting on Bilstein's B6.

Danno, I did little internet research regarding wastegates and have found that many recommend TiAL MVS MV-S V38 for our cars. What is your opinion about that wastegate? Would it be good fit considering the other planned upgrades I mentioned before? I see that I ill need adapters, but considering that I will instal other exhaust system, I should not hurry up with ordering the adapters for the standard system or can I reuse them?

Yes, Tial 38mm wastegate is good unit. Will work well with stock and any upgrades you do in the future. The adapters are available from many sources. Most aftermarket exhaust are configured to use the stock wastegate. So if you get adapters to fit Tial to stock exhaust, it will also work with aftermarket exhaust later.

One big benefit is the exhaust-flow and pressure pushes the valve closed, compared to pushing it open in the stock & LR wastegate. No high-RPM boost-drop due to exhaust pushing the wastegate open.

You're outside of the U.S.? Most likely your gas is 95 or 98 MON octane. Similar to U.S. 91-92 gas (RON+MON)/2. You'll want to get a mix that gives you around 101-102 MON octane for safety at the track. With constant full-throttle usage, the engine heats up, the coolant heats up, turbo, etc. This can result in pinging/knocking and quickly burn up & blow headgaskets.

Have fun! I'm also doing a trackday on Sunday 1-June at Sears Point. :)

Thanks again. Yes, I am from Europe. Did not know about RON/MON octain differences. Found that 98RON usually equals 94MON in terms of octane.

Good luck at the track!

All oem intake manifolds leak because of a design flaw.....get it fixed/modified. Then work from there. Vacuume /boost is off until properly addressed.
Pm me for details. Later.

I wasn't getting more than about 1.4 reading on the stock boost gauge so just did the wastegate hose clamped shut test. Took it easy and the gauge read above the usual 1.4 BAR. So I decided to giver her a little bit more and the gauge did not go passed 1.8 at full load/throttle. Does this pretty much guarantee the wastegate has gone soft? I just put on the down pipe about 200 miles go and it looked fine! Plus all hoses, all vacuum lines etc have been replaced.

Thanks
Mike G.

Anything after turbo doesn't matter as much. Exhaust issues is typically between header and turbo. Dual-layer crossover section can get clogged by inner-layer melting. Usual test is to see if golf-ball can be rolled through. Many 951s have collapsed crossover.

Also clogged cat can reduce boost, but usually only 1-2 psi. Test max-boost by driving with catalytic section removed.

You'll also want to test wastegate as well. Remove it and apply pressure to diaphragm (bicycle hand-pump w/gauge) and measure two values:

1. pressure where wastegate valve just begins to open
2. pressure where wastegate valve is fully open.

https://drive.google.com/uc?export=d...QLkfRLqY-ivvf4

These numbers will tell you condition of wastegate. There are actually several ways to increase spring-rate of factory wastegate if it opens too easily. I've used factory turbo & wastegate up to 25psi without any issues (custom chip-mapping or aftermarket EFI system needed).

I can't read the values on the gauges. What should they be for those two conditions?

Thanks
Mike G.

Measure actual values on yours and we can compare.
Max-opening is about 13-15mm on wastegate valve.

Also test your CBV - compressor bypass valve. Simple test is to blow through each big port. Should not flow pressure in either direction. If it has ruptured diaphragm, you'll hear fluttering or turkey-gobbling sound when building boost or shifting. Replace with part# 993.110.337.50 which is little stronger with brass-reinforced diaphragm.

5 psi for lift off
11 psi full open

Thanks
Mike G.

Ok, that great testing! Yes, perfectly good wastegate. Weak ones tend to start opening at 2-3psi and fully open by 5-6psi, so yours is in great shape. To regulate to stock 1.6-bar boost, wastegate only needs to open halfway, about 5-6mm.

I suspect combination of issues:

1. Cycling-valve is most likely culprit as confirmed by your pinched-hose test. By default, cycling-valve is fully-open and letting all pressure to wastegate and dumping boost. Working cycling valve is controlled by KLR and diverts pressure back to intake (away from wastegate) and allowing boost to build. Getting 1.8-bar with pinch test shows either KLR or CV is not working. You can test KLR’s CV control line with noid-light and see if it’s sending signal to CV

2. CBV - apply vacuum to little port. Can you see plunger opening bottom port? Does it hold vacuum and keep bottom port open?

3. Collapsed crossover pipe. This is next most-common source of low boost as exhaust is not hitting turbo hard enough to generate boost. Might be only slightly collapsed as you’re still able to get 1.8-bar boost.

4. Clogged cat is also very possible. Easy to test by removing catalytic, and holding rear exhaust up with coat-hanger. Test pinched-hose test again in remote area (loud) and see if you get 2.0-2.2 bar boost. Not likely as DME will cut off fuel at 1.8-1.9 bar. But i’ve seen many that won’t do that until 2.1-2.2 bar

5. Worn turbo. I’ve seen many of these. Do you have oil pooled up on back of intske-valves when car is stopped? Do you get grey/blue smoke when getting on boost? Most common cause of worn turbos is inadequate cooling. Does turbo water pump work to cool turbo for 2-5 minutes after stopping? Have you verified that water-port for turbo on water-pump has been drilled out? I’ve seen many, many of these in default 944NA blocked-off state.

Try to feel and measure radial and axial-play of turbo-shaft at compressor wheel nut. If it’s more like than 1.25-1.50mm in any direction, turbo’s kaput!

Can the BOV by itself be the cause of the low boost problem?


Thanks
Mike G.

It's possible bad CBV is sending boost around to turbo-inlet instead of into engine. Simple test is remove it and plug vacuum-hose with bolt and two big hoses with cork or something. Then gently try some test-runs. Don't let up throttle too quickly as shock-wave bouncing off closed throttle-plate can shatter turbo's compressor-blades without CBV installed. If it's not holding vacuum, then definitely needs replacing anyway.

Cycling-valve and collapsed crossover most likely culprits at this point.

Applied 12V to the CV and it clicks!!! DOH! Need to get Noid light next. Can this be done with just a test light?

Thanks
Mike G.

It may be locked up inside and still click. Really need to test flow-conditions of CV. Be really careful with plastic nipples on CV. Pull hoses straight off, do not bend them or they'll break nipples off CV. Might be safest to cut hard crispy hoses off with dremel and replace with new soft hoses. I like to lay triangular filet of epoxy where nipples join body of CV to reinforce. Can attach hose to port C and blow in it and see where it comes out. Power on CV no more than 5-10s at time to avoid overheating it. To test CV:

https://drive.google.com/uc?export=d...srlau53Oll3a-t

1. With no power-applied to CV, confirm you have flow between ports C and W

2. With power-applied to CV, confirm you DO NOT have flow between ports C and W

3. With power-applied to CV, confirm you DO have flow between ports C and R

If you have defective CV, don't need to use crappy old plastic part. Get modern all-metal boost-solenoid:
https://www.aemelectronics.com/products/sensors-connectors-accessories/boost-control-solenoid
Which is actually just MAC control valve https://www.ebay.com/itm/153357750198


As for testing signal, not sure duration is high enough to light up test light (it's PWM signal like injectors). Wouldn't hurt to try. Noid-light has duration-extending circuitry to ensure it lights up with shortest of signals. Oscilloscope would also work.

Damn! I wish I didn't have to work today!!

Thanks
Mike G.

YES! There is flow.

NOPE! There is flow.

YES! There is flow.

Thanks
Mike G.

Well, that confirms it, CV is not working. When activated by KLR, it should stop flowing pressure to wastegate and return it to intake to allow turbo to build boost. Easy enough to replace with MAC valve.

Still possibility your crossover is slightly restrictive as well.

I'm not convinced this is true. I tested a brand new Porsche CV and it behaved the exact same as the one on the car!!! Flow still occurred between C and W.


Thanks

Mike G.

Got this from a German Forum!

The timing valve has no diaphragm, it clocks a piston. The line C-W is always open. Via the piston, the line R is released intermittently to lower the pressure in C-W.

Test the timing valve

You should blow in "R". If the cycle valve is closed, "R" is also closed (almost). The full charge pressure is therefore on the wastegate. If 12V is applied to the timing valve, "R" is open. The boost pressure is for the most part back into the intake area and the control pressure on the wastegate is minimal.

Thanks
Mike G.

RE-tested CV just to make sure and the old CV is fine. New BOV and sealed the throttle shaft. Did a test run still only 1.4 BAR. Hmm! Going to check the boost press with a gauge now. Wonder if the stock boost gauge has a way to be calibrated?

Thanks
Mike G.

Checked boost pressure with crappy Harbor Freight test gauge that has a max press of 10 psi. Looked like about 9 psi max in 3rd gear. Pinched off WG hose, again, and the gauge read 1st-8.5, 2nd-10ish, 3rd-pegged at 10+psi.

What does the vacuum typically read on these beasts?

Thanks
Mike G.

it should be -18 to -20 inHg vacuum at idle.

What kind of boost do most see when pinching off the WG hose with a stock engine?

Thanks
Mike G.