924Board.org

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Last fall I bought my Euro 931, it had a slightly dry-rotted intake boot, (the boot below the sensor plate/ above the turbo). Well, my turbo started leaking alittle, (come to find out it was an O-ring at the oil intake). I put it up in storage till this spring. I replaced the boot and rebuilt the turbo just the same, (already bought the kit)... the car ran great. Soon after I noticed a missfire was coming to be. It wasn't idleing that great, and occationaly backfired under heavy boost. I checked the plugs, they were a little toasty from age, but I also found that my coil wire had a pin hole in the top of it. The connector at the distributor end was corroded as well as that one connector in the cap. I ordered and replaced the old AC plugs with the proper Boshe. I also ordered and replaced the wires, the cap, and the rotor button. The backfire problem was solved, the idle problem was not.
Now all the sudden it takes off crappy then you feel some of the torque kick in at about 2k RPM, but it's short lived. By 2200 RPM your torque feels to be gone, but it's beginning to boost. At this point there is so little power that it feels like it wont make it too 3k RPM, but when it finaly does it sets you back and just burns the tires.
I know these cars are a little sluggish before the boost comes in, (compaired to some cars), and when they boost they boost strong. But this is a very noticable differance from before this problem. It's also seeming to have alot harder time starting now. When I first start it in the morning it stalls, and I have to start it 2 more times, on the 3rd start it stays running like it never had a problem in the first place. I can go out driving, come home, shut it down, and while it's still warm go to start it back up and it takes about 10 seconds of turning over to start.
Maybe these things are not related, but I can't help but think they must be. The car still runs very strong over 3k RPM.
Please if anyone can help me figure this out I'd greatly appreciate it.
Oh... one more thing. When this bogging first started, it wasn't all the time. A couple times it was bogging, so I planned it to at the next light aswell. I gave it a little more gas then at the light before and it decided not to bog but instead just go... ass end slipping sideways. This is way it's so mind boggling to me, I'm sure it's nothing too serious, but I'm a little afraid it's gonna be expensive. I'd be so happy to figure this out the first time, I can't really afford not to.
Please help, and a big thanks for your taking the time to read this.
Aaron
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81' 931

924RACR · Posted: Fri Apr 04, 2003 9:58 pm Post subject:

Have you adjusted the mixture and idle? Might be very off, if it was adjusted to compensate for a leaky boot.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Smoothie · Posted: Sat Apr 05, 2003 7:30 am Post subject:

Also double check the plumbing between the turbo and throttle - check those orange o-rings. Especially the lower one between the turbo compressor outlet and lower pressure pipe. Make sure the bracket that holds the lower pressure pipe to the block is attached - this holds the pipe in place to the turbo.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Alex Roy · Posted: Sat Apr 05, 2003 7:46 am Post subject:

I had the same symptoms as you...and it turned out to be that the frequency valve had the ground wire disconnected so it wasn't regulating the fuel pressure properly.

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Lizard · Posted: Sat Apr 05, 2003 9:26 am Post subject:

check this post http://www.924board.org/viewtopic.php?t=6654 it has a pic of how the fuel system works, and do a search on the board be aware though when searching for say fuel mixture it HAS to be typed like this "fuel AND mixture"
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3 928s,

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Smoothie · Posted: Sat Apr 05, 2003 10:55 am Post subject:

That bracket is important because even if the seal (orange o-ring) is good, the pipe still needs to be held down to the turbo. I had this problem a couple months ago and didn't realize what it was 'til I looked up at the joint from below and could see a bit of the o-ring showing. While driving, the joint can be pulled further apart by engine torque and the boost itself. As a quick fix, I wrapped wire around the whole assembly from upper pipe to down around the turbo to pull everything together. Click on "Photos <click>" below. In my case the compressor side of the turbo rotates without having to loosen the bolts on it, so when I'd push down on the pipe from above it rotated together for a tighter fit. If you have a problem with it at idle, just push down on that pipe and see if it clears up.

- I don't think cracking is a common problem with those pipes.

You should find the frequency valve just in front of the throttle. See pics linked to from my post here: http://www.924board.org/viewtopic.php?t=6605
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

mrgtturbo · Joined: 06 Jan 2003 Posts: 526 Location: Skowhegan, ME

Could this really cause the problems I'm having at low RPM's vs high RPM's?

I would think this would cause more of a problem at the higher RPM's when the intake tube is pressurized. I'm sure you know more about this issue then I do, maybe I'm just not noticing it at higher RPM's because of the kick of the turbo. Don't know.

I will give this a shot ASAP, and you may be right on the money. I've given this some thought before, (as in the orange O-ring and allighnment of the turbo vs the tube), but like I said, I just can't see this being a low RPM issue.

Since this apparently could be, would you mind explaining to me why? Just so I may further understand my car. I'm not a mechanic by no means, but I do try to do my own work. I have a healthy knowledge of cars due to asking questions like this. So please don't feel that I'm trying to put you on the spot or trying to tell you your wrong... because I'm not, not at all !!! Just want to understand more.

Thanks. Hopefully this turns out to be the whole problem.
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81' 931

Smoothie · Posted: Sat Apr 05, 2003 11:34 am Post subject:

I had the problem with it only at higher rpms because the joint would pull apart further with boost, but if a gap exists even before the boost comes on, then this could be your problem. It's too easy not to check - just push down on the pipe.

Also have a look at this topic: http://www.924board.org/viewtopic.php?t=5294
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Paul · Posted: Sat Apr 05, 2003 11:34 am Post subject:

If the ring is bad, you'll have a huge vacuum leak until the turbo spools up, then you'll have a huge boost leak.

Alex Roy · Posted: Sat Apr 05, 2003 12:04 pm Post subject:

The frequency valve looks like an EFI injector, except that it has hoses connected to both ends. It is loose, cradled in the inside of the curving intake runners right at the front. When the car is running, it should be buzzing. The frequency valve is what the O2 sensor (lambda) system uses to modify the fuel pressure in the system.

The easiest way to test it that I found, is to unbolt the lambda box from under the steering wheel and unplug the long wire harness so it disables the lambda system and makes the car run like a normal CIS system. You'll have to turn your idle adjustment screw down when you unplug this because your idle should jump up to about 2000 RPM. Then take your car for a short drive and see if the car runs better, if it does, something in your lambda system is the problem.

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

These engines are incredibly sensitive (and unforgiving) to vacuum and air leaks down-stream of the air mixture unit. Since the fuel metering is almost entirely based on the amount of air flowing past the sensor plate, any leaks affect the mixture. If you had dry-rotted rubber boots they may have been leaking air. And, if the PO enriched the mixture to compensate for the extra (un-metered) air, this could/would have substantial consequences.

If you don't have a Haynes manual yet, we all recommend you get one and become familiar with the CIS system. It'll pay for itself in no time! There is a tremendous amount of "institutional knowledge" on this site. Start with the FAQ's. (and test the site's "Search" function for us

- we've had mixed results lately).

Welcome aboard,
Mark
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'79 Eurospec 931