jmj951

Also sometimes called the diverter valve, and on other cars this can also be called a BOV (blowoff valve, only that's not the case on 944's because it recirculates/diverts the air within the intake, it doesn't vent to atmosphere like a real BOV).

Just google 944 turbo bypass valve or 944 turbo diverter valve and you'll see lots of pics. It's connected to the j-boot and the intercooler pipe between the IC and the throttle body, and has a vacuum line connected to the top of it.

If you have the stock bypass valve with the diaphragm and it's old, it might be slightly deformed/warped enough to cause this problem (even if the diaphragm is not technically damaged and doesn't fail a leak test). If you have a Forge diverter valve or other piston-type diverter, the piston might be sticking and you might need to relubricate it.

divil

Thanks, I do know the part in question...just wasn't sure about the term "bypass valve" as I knew it as a BOV. It is stock, and tests ok, but I think I'll put it on the "may replace even though seems OK" list...same list that most of my car's parts is on right now lol!

Ronin-951

Have you seen Rogue's write-up on Coils? Stock was not the best to begin with, = falls short in the upper range, so a replacement will help no-matter.
Gap on the Bosch 'Super Plus' WR 7 DC+ Plugs should be at .028

divil

I have read it. It was interesting. But if I replace the coil I am probably going to replace it with a stock one anyway.

In Rogue's write up he doesn't mention any advantage to using a better coil with a stock chip, and in fact he says that it's harder on the driver transistor (because the coil charges more quickly, meaning more time at peak current). In the thread he posted here with that write up, he says the point of using a better coil is that you can get away with less ignition advance, which makes sense if you're tuning (and then you can also fix the peak current issue while you're at it).

That plug gap sounds familiar...whatever it was, I looked it up an made sure at the time. But I need to pull them and take a look anyway.

ehall

What have you done to check fuel? This could also be an injector issue. My car was doing this, and then it got worse. We turned over the car and watched each injector fore it's stream into a clear 2 ltr. It was not good, nor was it consistent from one to the other. Just an idea. Good luck!

divil

I had the injectors cleaned and resealed and tested by Witchunter a few years ago. Looking back I don't think the car was running any better back then, but I hadn't had it for very long and didn't know any better.

More recently I've replaced the fuel filter and tested the pressure at the rail. Fuel pressure passes all the normal tests, although there is a lot of fluctuating on the gauge. I haven't been able to find out if that is a problem or not.

Also, not sure how good a test this is, but I have driven with a volt meter hooked up to the O2 sensor to see if it would show any obvious signs of running rich or lean. I thought if it was way off it might show up on the sensor. So far it looks normal, i.e. it just keeps switching back and forth from around .2v to .8v when connected. When disconnected it hangs a bit higher, around .6 - .8 pretty much all the time. I don't think that really proves anything, but I will probably take a closer look with a scope. It switches too fast to really see anything with the multimeter. But when disconnected it is more stable, and the car doesn't seem to drive any better that way.

I have not actually watched the injectors firing. That is something I will make a point of checking. Another thing I haven't done is a volume test on the fuel pump. I had the pump off recently to replace the lines and the electrical contacts looked fine.

divil

I was curious about this, so I pulled the vac line off the valve, plugged the line, and put my Mityvac on the valve port. Then I pulled a good strong vacuum on it and went for a drive. No question, it was *way* worse than the problem I'm chasing. It took forever to build any boost...I'd say it was almost as bad as the limp mode when you pull the TPS plug, except that I did eventually start to see some boost.

Still, I wonder if it could sometimes be stuck partially open. That might cause the issues I see. I'm curious to know if yours was getting stuck fully open, and how you figured it out?

Tom M'Guinn

Did it hold the vacuum? If you cranked it wide open, you will indeed find it hard to generate boost. Mine was just not sealing well, so was just leaking a bit. I frankly don't recall exactly how I figured it out (is was a decade ago) but I probably blew through it while applying vaccum and pressure.

divil

Yes it holds vacuum and pressure no problem, so the diaphragm must be fine. When I had it off the car a while back, it seemed to work fine - it would open with vacuum, and seal with pressure. If I left the diaphragm port open at atmospheric pressure, then the main port would leak kind of unpredictably...but I don't think that could cause a problem, since the diaphragm port will always see the same pressure as the side port.

Tom M'Guinn

Sounds like that's not your issue. Have you checked the TPS? On the DME and KLR boards, focus on the solder pads where the main connectors attach to the board. Those pins get pulled and pushed on when the harness plug is removed/installed so are the most common ones to crack. Take the boards out in the bright sun and look for hairline cracks around those solder pads -- use a magnifying glass or readers if you don't have great close up vision. Google cracked solder joints for images if you don't know what you are looking for -- they don't jump out at you -- you really have to know what you're looking for.

divil

Yep have checked the TPS. The idle switch works, the wiper part works, and the KLR generates the WOT signal (checked at the diagnostic port). But my issue is evident even before WOT anyway.

I actually got a spare DME and KLR from a low mileage car...they look very well preserved. Today I swapped my KLR chip into the new KLR put that in the car (it was from an early car). Still doesn't feel right. It did fix the boost gauge however (if you remember my other thread here)

I have to open the new DMEs to convert to 28 pin and swap the chip so I will check very carefully the way you described.

Tsmith84

Pm me your address and I will send you a coil from my parts car. Ran fine when I took it apart. Unless your past that, haven't read through all the posts.

divil

PM sent...thanks!

ehall

Outstanding! That's what RL is all about.

Jeff N.

Don't you hate threads like this where the OP never does a final post on how the problem was resolved?