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[QUOTE=h2oplr11;4668880]
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Originally Posted by mark houghton View Post
Violent and hard jolt shutdown is not just a stutter or hard miss. Can't miss this overboost protection symptom. Did your boost gauge show you as overboosting? If you were overboosting, then find the reason: look at the wastgate for malfunctioning....either a stuck valve, ruptured diaphram, or disconnected air pressure feed hose. If you weren't over boosting, then most likely it's the boost sensor going bad.
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Mark, I'm having a similar issue to Richard. Definitely the dashboard in the face experience. The background is:

Recent engine overhaul
Replaced fuel filter / accumulator
Electrical - fuel pump regulator replaced

The funny thing is that it happens at 1.1 bar and it has also happened (although less frequently) at .5 to .6 bar. I had an issue this weekend with a squealy fan belt. I tightened it and took it out for a spin. A previous owner had installed a VDO boost pressure guage where the clock originally went. The guage has a historical peak line. Well, it always sat at 1.1 bar. After a little fooling around on the autobahn tonight I noticed that the bar now sits at 1.22 bar. Hope I didn't screw anything up. I definately didn't notice anything wrong on the drive home.

So, I'm wondering 1. if I'm overboosting, 2. if it's a wasgetate issue that you mention above or 3. a combination of both?

Any ideas here? I'm really hoping for an easy, inexpensive fix. Still trying to ease the wife after the overhaul price . . .

Thanks in advance for your help,

Matt

Matt, you need to put specifics for what you're driving in your signature. That helps with the first part of diagnosis.

Did the previous owner set your car up for higher than stock boost? If you're seeing 1.1 bar, then I suspect it may be running with a 1.0 bar spring in the wastegate. Hopefully it also has the necessary modifications to support that high boost. If it's shutting down at 1.1+ bar, then I would say the system is doing as it's designed to do.

If it's shutting down at .6 bar, then either the gauge is faulty and you're actually boosting more than that, or something with the fuel delivery (overboost protection sensor, OB relay, or maybe simply the fuel pump fuse and/or relays up front). Pull the two relays and the single fuse, clean all contacts and look for signs of overheating, etc. These cars won't run on a single fuel pump, so even just one of the relays could be jiggling loose/loosing contact.

If your car wasn't intentionally modified for higher boost, then you do need to look at the wastegate because you shouldn't be able to reach 1.1 or 1.2 bar. Make sure the pressure hose from the intercooler to the WG is in good condition and tightly connected. If everything is stock and you're still overboosting, then I would suspect the WG diaphram is torn.
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Old 05-17-2009, 04:52 PM
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You mention an aftermarket pressure gage. Does this gage get it's signal before or after the throttle body?
Pressure measured before the throttle body will register spikes upon ubrupt throttle lift. If this is the case then 1.2bar is typical for 1.0bar waste gate setting and not harmful to the engine as it does not see that spike.
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Old 05-17-2009, 05:38 PM
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Matt:

1. Overboost switch will typically trip at 1.1 bar.
2. 1.1 bar is a too high to run on non-modified engine and it will shatter the piston rings sooner or later.
3. Even if you have modified CIS to support fueling at that boost, 1.1 bar on 3DLZ is "lots of hot air and little extra power". The fact that boost gauge goes higher doesn't necessarily mean that you have extra power.

Check if wastegate membrane ruptured (by blowing air trough boost line and noticing if it seeps trough).

If you are getting steady 1.1 bar on Autobahn then you either have very stiff spring or there is a malfunction on wastegate side. If you only get spikes to 1.1 bar when shifting then recirculation valve might be stuck.
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Old 05-18-2009, 01:38 AM
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Aftermarket B&B style headers and HF turbos often create over-boost.
Old 05-18-2009, 06:39 AM
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Well, that sucks; nearly done with my reply and lost the whole thing.

Sorry it took me a while to write you guys back. The movers came today. Autobahn time is now limited . . .

Didn't mean to take over Richards post but maybe some of this discussion will help him figure out his problem too. . .

Mark, should have solved your first issue (see below). Not sure if the car was set up for driving higher than stock boost, but I'm ASSUMING it was. Again, before the overhaul I would consistently take it to 1.1 bar and not get the dashboard in the face (DITF). I'm assuming this was because the wastegate would regulate the pressure correctly??? I'm aware of the requirement for both of the fuel pump relays. Just had the one for the rear pump replaced (electrical gremlin) and the one for the front pump checked, so I'm assuming this isn't an issue, but I'll check that first thing in the morning. I don't think this is a faulty gauge. It's a VDO boost guage, and from what I've gathered here and there, they're fairly reliable. This is the one: Can anyone confirm their reliability?

Also, there's an overboost protection sensor somewhere? Where the heck is that thing??? I thought it was integrated somehow into the fuel pump relay to shut the fuel pump off. I definitely need a class on early turbo control / management.

RarlyL8, I'm not sure if the gauge signal is coming from before or after the throttle body. Could you tell from the one I have installed? (see above). Where would I look to figure this out?

beepbeep, where am I blowing this air? Through the line connecting the intercooler with the turbo? I'm not getting spikes to 1.1 bar, the needle pins at 1.1 to 1.2 bar, but this is now where I'm also getting the DITF, but again, it OCCASIONALLY happens sooner, but only when I'm going fairly fast. When it does, it comes around .5-.6 bar. If I go easy, I can sometimes take it further up to 1.1 before it happens again.

It really seems like the entire engine is momentarily shutting down and then coming back when this happens at speed. NOT something that's pleasant, especially when some BMW or Audi is trying to keep up behind me and I loose speed without showing break lights.
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Old 05-18-2009, 12:04 PM
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Well, if you've been boosting to 1.1 bar all along with no problems, then hopefully it's safe to assume that somebody did proper modifications to support it. Personally, without knowing exactly what has been done I wouldn't boost beyond .9bar. Perhaps you have a modified fuel head or adjustable WUR...just a couple starting points for adding more fuel when boosting beyond the stock .8 bar maximum. There is a huge thread on the whole topic of CIS performance tuning if you care to read it. Advanced CIS Turbo Tuning Discussion Thread. Ultimate?

What seems weird to me is that you can "baby her" up to 1.1 bar and not experience overboost shutdown, but sometimes can't make it past .6 bar at WOT. Sounds like a loose connection somewhere, becoming more pronounced with speed/vibration when you're driving like a maniac vs. a old lady :-)

There is a pressure sensor mounted to the front end of the boost recirculation valve assembly, with a single wire going to it. That little jewel is a simple switch that is normally closed and keeps the wire grounded. If you were to pull that wire, the engine (pumps) wouldn't run. When boost pressure exceeds around 1.2, that switch will interrupt the ground...same thing as pulling it. It (the sensor) is linked to the overboost relay (left rear engine compartment) which controls the fuel pumps shutdown in response to the sensor tripping. Either component or connection if faulty could cause your problem.
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Old 05-18-2009, 01:53 PM
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Quote:
Originally Posted by h2oplr11 View Post
beepbeep, where am I blowing this air? Through the line connecting the intercooler with the turbo?

There is a hose going from intercooler to lower part of wastegate bell. Detach this line and blow air trough it with your mouth. If lot's of air is flowing trough, you have ruptured membrane. (observe: some air might escape trough valve stem, nut not much).

Other way to do this is to connect a short piece of rubber hose to vent pipe from the top of the wastegate. This short piece of brass tubing is not connected to anything. If you can blow trough this pipe, then membrane is ruptured.
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Last edited by beepbeep; 05-19-2009 at 02:53 AM..
Old 05-19-2009, 02:50 AM
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Quote:
Originally Posted by beepbeep View Post
There is a hose going from intercooler to lower part of wastegate bell. Detach this line and blow air trough it with your mouth. If lot's of air is flowing trough, you have ruptured membrane. (observe: some air might escape trough valve stem, nut not much).

Other way to do this is to connect a short piece of rubber hose to vent pipe from the top of the wastegate. This short piece of brass tubing is not connected to anything. If you can blow trough this pipe, then membrane is ruptured.
beepbeep, car just arrived back from Germany (no more autobahn ) and I attempted your test. I blew through the hose from the intercooler to the wastegate. It seemed like air did go through. I didn't have any pressure sensitive tools, but about a mouthfull of air would pass through after about 3-4 seconds if I really put pressure on it.

After driving more I have noticed several things. The dashboard in the face doesn't come when I'm pushing the accelerator any more; only when I let up on the accelerator (even if I just think about it), this is usually when the turbo is at max boost. It's almost as if the fuel completely shuts off right when I pull off the accelerator, and I completely loose power and speed MUCH faster than normal.

I believe there is a fueling issue. I say this because I have a second problem. It is most noticeable when I'm accelerating from a stand still. It's a sudden cut out. Seems like it cuts out and then comes back a split second later. It seems like the engine almost stalls several times until it comes up to 3000 RPM. This is more pronounced AFTER the car has warmed up (if I'm driving around town and make several stops at different places). Could this signify a WUR issue?

I'm considering studying up on the CIS system, what would you guys recommend for reading? I've got the 101 projects and the accompanying Modifying Porsche 911 Engines, but neither really got into the weeds on the CIS system. Is there anything I can read that would help me understand the early turbo engine as a whole (fuel, turbo, electrical)?

Thanks for your help guys.
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Old 07-19-2009, 07:24 PM
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Scroll down to the bottom of this page for Bosche CIS manuals: http://www.cannell.co.uk/Manuals.htm
Old 07-19-2009, 08:05 PM
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A930Rocket, thanks for the quick reply. Haven't read through the whole KJetronic manual yet, but it seems VERY informative. Thanks for this helpful link!
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Old 07-20-2009, 06:55 PM
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Hi there. I see the original thread has resurfaced so I should tell you that we found the answer to my original cutout problem. we checked to see if the car was overboosting and the rev .limiter was cutting in but the engine would drop out at anything from .3 to .6 bar. and 5-6000 revs. Eventually tracked the problem to the Boost switch which was faulty and is being replaced. Would all be done by now but unfortunately we stuffed the clutch. So now we are doing a clutch upgrade from the old rubber job to a spring set up and a bit of a tidy up while the engine is down. This forum has been a big help. Thanks
Old 07-21-2009, 12:38 AM
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I got this exact problem. Just when i get some boost (about .5-.6 bar) i get the "dash in my face". Really feels brutal and i got scared at first. Any conclusion on this? Mine is set to 0.8 bar.
Old 10-28-2009, 12:19 PM
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Quote:
Originally Posted by Oheggem View Post
I got this exact problem. Just when i get some boost (about .5-.6 bar) i get the "dash in my face". Really feels brutal and i got scared at first. Any conclusion on this? Mine is set to 0.8 bar.
Feeling lucky today? Disconnect the single wire from the overboost switch located on the boost recirculation piston assembly, and ground that wire. If you are confident that your wastegate has been and is working properly - and that you have not experienced any overboost situations in the past - then take her out and run up some boost. If the switch is the culprit, your boost should now go as high as your wastegate spring allows. Watch the boost gauge very closely, since disconnecting that switch will inactivate your overboost protection. You must be sure that your gauge reading of .5-.6 isn't really something much higher. If gauge accuracy is suspect, don't try this approach!

Alternatively, take the overboost switch off the car, attach an ohm meter to it, and apply gradual pressure to the small hole. It should produce an open circuit at around 1.2 bar.
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Last edited by mark houghton; 10-28-2009 at 01:03 PM..
Old 10-28-2009, 12:57 PM
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Mark, thanks again for your suggestions. I'll have to look into that a little more. It turns out that I may have more than one problem.

A couple of weekends ago I finally decided to adjust the timing myself and found that the ignition wire from the voltage regulator to the distributor would arc against my hand while I was making my adjustments. Looks like it's time for a new wiring harness I would guess since all the wires are likely the same age. Anyone have any good ideas where to get an entire set that don't cost as much as a diamond ring??

I think this ignition problem may have added to my issue. I'm not so sure now that the problem was with my wastegate or overboost sensor.

Matt
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Old 10-29-2009, 04:02 AM
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All the replies here are excellent.
I'll add that a new overboost sensor opens the circut at 1.3-1.35 bar, but as they age the rubber diaphram inside ages and gets soft so they start opening inconsistantly and at lower boost pressures.

Mine would open at .9 bar and sometimes would take up to 30 seconds while I sat on the side of the road.
I mounted a male spade teminal on a metal intercooler bracket next to the overboost switch so I could could get out and move the overboost wire over to it and continue on.
Then I bought a new overboost sensor from pelican. It was a special order and cost around $60.

Another possibilty to your engine cutting out is if you are using the origonal metal braided/sheilded spark plug wires, and if there is no plastic cap over the tower of the upside down fan housing mounted igniton coil then those grounded, braided spark plug wires might be routed right next to the primary terminals on the ignition coil and under decel or accel the g force might be just enough to move the spark plug wires enough to touch a primary terminal on the coil and short it to ground killing the motor.

It's unlikely but distantly possible....
Old 10-29-2009, 10:41 AM
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Great answers on this thread, thanks guys.
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Old 10-16-2011, 01:27 PM
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