GPA951s

Not Sure How the J boot affected his situation in that thread because it is simply atmosphere,(Maybe a slight vacuum due to venturi affect) although there is a Little Diaphragm in the CV and If it was plugged when it hit 12v the Diaphragm couldn't lift because it was plugged.
Anyhow, good thread and lesson learned, stick to basics. I get a kick out of how sometimes things get overly complicated in these threads.. It seems many people want to break out oscilloscopes and get all engineering technical and they get lost. In the course of 18 years I have owned and worked on (Mine and other peoples) Numerous 44s I have never used a scope, . I have fixed more issues by wiggling wires, tracing lines using a VOM Tie-wrapping a Voltmeter to the windshield wiper and going for a spin... Or re-tracing something that got disturbed when some "other" thing was changed, Ask the Question, What changed? What got Stressed due to? High RPM, Heat, ect. and of course Time, for the cars that were sitting.. Let un know what you find..

Droops83

You do make a good point that a scope is not absolutely necessary for most diagnosis on a 951----a good DVOM will suffice in most cases. Like many tools, a digital storage oscilloscope (DSO) is only as good as its user. As in, it takes some practice in getting reliable probe connections and it takes experience to know which settings to use and what the waveform should look like, etc. A newbie DIY scope user might spend more time trying to figure out the scope than it would take to solve whatever the electrical issue is!

I am a professional Porsche/BMW technician (from vintage all the way to the latest cars), and I have access to 3 different scopes at my shop. I know some techs who use their scopes every day, but I probably only break one out once or twice a month, if that. They do come in handy for checking analog AC signals (think 944 engine speed and reference sensors), older-style ABS wheel speed sensors, etc. I also sometimes use a scope to test fuel injectors and DME functions such as primary ignition current (just last week I needed to be 100% sure that a couple of ignition drivers were faulty in a $2,000 DME control unit of a modern BMW before condemning the part).

However, the "what did you do last" litmus test can often help lead to the cause of a suddenly recent drivability problem, especially on these old cars where components can crumble in your hands! I my experience most 951 issues can be traced to vacuum/boost leaks, followed by old/deteriorating wiring and sensors. Followed by whatever was disturbed when work was done .

As for the original poster's boost issue, I would install a proper boost gauge at the next track event, which will greatly aid diagnosis and help determine if it is indeed a "low boost" or "no boost" issue.

eshane

Update Gentlemen. Track day at Sebring yesterday. Filled gas tank with Sunoco 98 octane to establish if engine knock was causing computer to lower boost. No change evident. Full boost on drive to track from Orlando. No issue. Dash boost gauge indicated full 2 bar boost, as indicated on dash boost gauge, reached at full throttle pedal travel. At track, on 1st session, car made full boost for 2 laps, and then boost dropped. HOWEVER, driver indicated some boost, about 5-6 psi, or 2 short lines above 1 bar on dash gauge. So, it doesn't seem to indicated an issue with the wasted gate or cross-over pipe. Car never indicated an overheat problem per the dash water-temp gauge. It was 85 F at the track yesterday (sorry northern brethren). After car cooled a bit, I tightened all turbo system, vacuum-line clamps I could reach; some were a 1/4 to 3/4 turn loose. Second session same issue, full boost for 1-2 laps, then drop-off to low boost, per the dash boost gauge. Have videos showing gauge, coming out of turn 16 down the back straight. At shift to third gear, its like running into a wall of jello. Car still accelerated, up to 115-120 mph, and no hesitation or stumbling, just low boost. Last 2 sessions the same issue repeated. Car ran fine with low boost, finished last 2 sessions, still no overheating per the temp gauge.
My rudimentary knowledge makes me think that the computer is telling the engine to dial back the boost, when it is heat soaked. Other thoughts are, vacuum leak somewhere that opens when item becomes hot and crack expands. Line from intake manifold to KLR? Crack nipple on CV? Electtrical wire lead insulation bad and grounding on metal somewhere? Electrical connector not fully connected and backing-out? TPS issue? Checked throttle cable to throttle-body and getting full rotation. Injectors not delivering full psi? Fuel pump weak?
It's difficult to diagnose due to issue only appearing at track, no issue on street at all, drives as if there is no problem with boost, yet at track, low boost issue is present.

eshane

Thoughts..................could the wastegate not be bleeding off properly, sending too much boost to the turbo, resulting in over-pressurization of the intake manifold, and telling the computer there is an over-boost issue? Could the BOV not be functioning properly and , again, telling the computer there is an overboost issue. The line to the KLR goes from the manifold. Does the KLR line "read" manifold pressure as "overboost"?

eshane

More thoughts..................The cycling valve "reads" pressure from the banjo-bolt in the turbo hard line to the intercooler. Can the CV be malfunctioning and "mis-reading" the pressure from the banjo-bolt line? Can the CV bleed line to the BOV be blocked, resulting in the CV "mis-reading" it's internal pressure because it is not bleeding, and send a signal to the KLR to lower boost?

eshane

More............will the CV read turbo over-pressure through it's connection to the hardpipe BEFORE the manifold pressure goes too high and the KLR connection steps in to lower boost?

eshane

Could my banjo-bolt Jet be getting clogged and not sending a proper signal to the CV?

fast951

A clogged banjo bolt will create overboost not lack of boost. From what you describe, you are experiencing "limp mode".

The CV does not "read" nor monitor anything. It's just a 3 port valve. The CV routes the pressure to the J-Pipe to keep the WG closed (more boost). Or send the pressured air to the WG to open it (less boost or boost control).
When the CV is de-eneregized, it routes signal to WG. It defaults to low boost.

From what you describe, the CV is failing and shutting down. Or the KLR is forcing limp mode. Check the KLR codes by following the factory test procedure.

In addition to fixing the boost issue. I strongly recommend monitoring knock. On the track, always mix some high octane fuel.

zmf

Nothing useful to add except that I've had to do the same troubleshooting. But if you're getting around 14 psi when the system is working, what would be the boost if the wastegate remained open? Could it get as high was 5-6 psi? I don't know what turbocharger you're using.

eshane

John, am I not understanding this correctly? With a clogged banjo jet, no pressure from the turbo hard pipe is sent to the CV. The CV stays "dumb", doesn't know about boost. The overboost goes through to the manifold and the KLR get the overpressure and goes into "limp" (overboost protection mode).

Or, if the coil in the CV diaphragm is dying with heat and not properly functioning, and the banjo jet sends the high pressure correctly to the CV, does the over-pressure go to the WG or to the J-boot?

fast951

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).

If the IN port is not getting pressure (clogged banjo), then you get lots of boost, as there is no pressure to open WG.

​​​​​​The DME senses overboost (actually overload) it will activate a fuel shut. The car feels as if you hit the rev-limit.

Again, my guess is the CV is going bad (had this problem on my car years ago).

Of course, I'm against replacing parts unless proven bad. So I would pull the KLR codes when the problem happens and before shutting down the engine. However, if this only happens on the track, I'll be tempted to replace the CV as track time is expensive. BTW if you want to save some $ you can use an aftermarket solenoid valve in place of the CV and test it on the track.

Note - I have seen APE KLR chips do all sort of weird things. The above description is for stock KLR code.
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GPA951s

Just Grab the signal off the CV its 12v or its not... My guess is youre going to see 12v when you mash the gas,, running round town, as the car heats up (on the track) when your problem rears its ugly head you will see 12V and low boost meaning the CV is bad, If you DONT (highly doubt it) then its limp mode,

I bring a spare with me to the track... The cost of track days, gas, Tires, Time off work is worth more than 25 min it takes to change it out and (Roughly) $100 part - Havent priced one lately...

It is an Electrical part... Subject to Heat.. That is why it only happens on the track... AND on the Street its not "ON" all the time on the track its ON almost all the time.. Every time your foot is past 1/2 throttle.. Its a Coil of wire that is an electromagnet pulling on a disk to a diaphragm...

Good luck!

eshane

New CV on order, will be installed for next track day and..................................we'll see. Also, can I read the codes with a simple multimeter plugged into the proper connector slots? will the meter detect the slight current and swing the arm just like it's a light pulse?

eshane

Also, checked the wastegate temperature at idle and it stayed cool as the exhaust heated. I conclude that the wastegate is not damaged and leaking, at least at idle.

eshane

New cycling valve and spark plugs go in today, with a check for any leaking vacuum or boost lines/hoses. Sebring track day May 11, taking known good coil with me. Will also try and get any codes read. Will report results..................