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Discussion Starter · #1 ·
Hi All,

Hope your all enjoying your weekend.

I've got a small problem, I for sometime knew that the large pipe that goes from my air filter to the turbo had a hole in it. So I finally changed it yesterday with one from a later model, only difference being that the dump valve is now nearer the filter than the turbo.

The car runs a lot smoother, seems to perform better and the dump valve is a lot loader. Only problem I have now is that if I rev the car, when it comes back down it stalls. I've tried increasing the idle speed a touch and it hasn't really helped.

I've taken it on a long run, well 30 miles to see if the system adapted it's self, but no joy. It can be a little embarrasing when pulling up at a junction or traffic lights and the car cuts out.

Any ideas?

Many Thanks in advance.

Oh yeah, my cars a 1993 9000 CSE 2.0 Turbo (LPT) Auto.

Cheers,

Rich
 

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Hi RichW,

Ive had the same problem, I checked the dump valve and found a problem with the small pipe that runs from the intake manifold to the dump valve itself. It goes into the dump valve from below so it might not be easy to spot at first.

I think thats your problem if not check all pipes etc, let us know if it sorts it or not!.

Regards
Michael
 

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Discussion Starter · #4 ·
Hi Again,

I checked the small pipe from the dumpvalve and found it was a bit worse for ware, so I just bought a replacement (£1) and fitted it, but it's not made any difference unfortunately.

Cheers,

Rich
 

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Rich, does your car have an AMM (air mass meter) in the pipe to the turbo on the intake? If so have you now go the dump valve on the other side of the AMM?. This could be the cause of the problem.
 

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Discussion Starter · #6 ·
If I'm honest I have no idea what an AMM (air mass meter) is, but there is near the filter a wire connector block. This is still the same side of the dump valve as before though.

I'll take a pic in a min and post it here as you guys will know more.

Cheers,

Rich
 

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Yes, it has got an AMM (it's the unit you idnetified immediately next to the filter box with the plug on it), but it all looks like it's plumbed in the right way round.

Back to your problem then... if you have been running that way for a while, then you will have been slightly lean as their was unmetered air entering the system, which it will have adapted to. To help the re-adaptation, you can disconnect the battery for half an hour or so, then take it out for a drive.

If you han't changed anything, and said you had the idle problem, I would suspect the AIC valve. If the re-adaptation doesn't cure the problem, the try putting the old hose back on and see if it still stalls. If it does, then it may just have been a coincidental problem with the AIC valve, so cleaning it should help.
 

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Discussion Starter · #10 ·
Hi Again,

Bad news unfortunately, I disconnected the battery and left it over night. Reconnected it this morning and gave it a drive, only to notice that it's still the same.

I've checked all the pipes again and they all seem fine.

Looks like I'll have to try another AIC valve to see if it's that. I'll keep you all posted.

Cheers,

Rich
 

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Are you sure the diaphragm in the dump valve is OK? I know you said that it was "a lot louder" so I guess it must be working some of the time at least, but this was exactly the symptom I had from a faulty dump valve. To check, disconnect the end of the small pipe you replaced (the end furthest from the dump valve) and suck gently. If you can suck air, the valve is faulty. If you go blue, then it's OK Replacements can be had from Elkparts etc.
 

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I wouldn't expect a faulty recirculating dump valve to give the stalling problem as both ends of it are connected after the AMM, thus eliminating the possibility of "incorrect" amounts of air in the system.
 

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The problem is that the small pipe ends up connected to the atmosphere. This does produce a small amount of false air (and loss of boost) but also causes the car to stall when coming off the accelerator at low RPM, due the shockwave from the throttle plate not being "dumped"

Quote from Townsend AMM page :

"On turbos, check the turbo bypass valve (hooter valve). It lives in the intake tube from the air mass meter (air filter) to the turbo. Its vacuum line when disconnected from the intake nipple should hold vacuum. If the valve doesn't hold vacuum, you may also be experiencing stalling when decelerating after being in boost."  [/b]
Certainly this fits with the problem I had.
 

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Ahh... thoughts on another track...

A failing recirc dump valve, even if the diaphragm is perforated, may allow air in via the vacuum tube, but it will still be metered air, to the A/F ratio should still be correct.

Rich- your looks like a Bailey piston type- am I correct?

However, it may be that the valve is not operating properly to relieve boost pressure (and the noise also suggests that to me), thus the engine stalling is caused by the shock wave.
 

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Discussion Starter · #17 ·
Hi Guys,

The dump valves is only about a month old and was purchased from elkparts.

I'm gona go try sucking on that small pipe and see whats what. I might even put my original dump valve on and see whats what.

Cheers for the advise so far, it make me glad I changed to Saabs as everyone who owns a Saab loves them and seem very helpful.

Rich
 

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Nope, hang on, I just re-read your original post- when you say "rev the car" do you mean putting your foot down and accelerating or just blipping the accelerator? If it's the latter then I'm pretty certain it's not the dump valve.

Have another go at checking for leaks (an incense stick is good for this- the smoke will be drawn to any vacuuum leak at idle) and clean the AIC valve.
 

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Discussion Starter · #19 ·
I've just checked the dump valve and it's fine, couldn't suck any air through.

Also checked the pipes again and found a small split in a small pipe, it's about two inches long and near where that small pipe from the dump valve ends. Didn't make any odds though.

The car seems to idle fine, and it's fine when the car slowly comes down the rev range, just seems to be when it comes straight down from about 2500/3000 RPM it seems to stall. I've watched the rev counter and have noticed that it seems to get to about 500 RPM and sometimes recovers, rarely, but occasionally.

Not sure if this helps at all. I also tried my original dump valve, but that didn't seem to make any difference either. I'll keep checking though...

I've spoken to my local Saab breakers and they have an AMM I can try in it. Anything else you think I should ask to try? As they are very good to me and generally let me try before I buy.

Cheers,

Rich
 
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