My 1986 5000CS turbo has only recently been capable of boost in excess of 1.3 bars - don’t know how this happened other than the turbo coolant pipe was replaced. Anyway I can now get 1.4, 1.5, going to 1.6 bars when ignition cutoff occurs, lasting a fraction of a second. Not a problem around town, but a problem at highway speeds since this boost can occur almost instantly on acceleration.

My understanding at this time is that Audi engineered all turbo intake components to withstand at least 2.0 bars, and further that Audi set the ECU for ignition cutoff at 1.7 bars, over the boost pressure I am experiencing cutoff. Was also told that “weak” ignition components will (may) cause premature cutoff.

Does anyone have any knowledge about this?

The boost pressure now experienced (1.4, 1.5 bars) seems indeed real in terms of acceleration. In other words, I don’t think the in-dash boost pressure indicator is wrong.

Have taken no action on this problem yet.

Help/advice greatly appreciated!

 

Welcome to the forum DickM!

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I'm not sure what I'm reading. Are you getting spikes of boost up to 1.6 or is it sustained boost? Spikes are OK.
Are you getting cut-off when accelerating allthe time?

 

When accelerating, and boost increases,progressing 1.3, 1.4, 1.5 and then about 1.6 bars I get interrupt, which I now know is fuel pump interrupt - not ignition interrupt. It happens whenever the boost pressure increases to 1.5-1.6 bars. And lasts for a fraction of a second. After which everything is again normal, as long as the boost remains below 1.6. It is not a spike, but seems to be over boost. Normal operation maximum boost pressure has never exceeded 1.4 bars. But now, suddenly I am experiencing over boost pressures rising past the historical norm for this 18 year old car that I have owned since new. Whether or not the real boost pressure is greater than the dash gauge is debatable, since I have been told that the dash gauge lags real instantaneous pressure, and to use your term may spike higher then what I read. And I don’t know exactly at what pressure the ECU will command the fuel pump to shut down. My dash gauge says about 1.5/1.6 bars, but the real pressure may be higher. I just don’t know that ECU specification.

Scott Mockry <http://www.sjmautotechnik.com/troubl...boost.html> has made some suggestions to me how to troubleshoot over boost on this particular car and ECU, and has a detailed website on all Audi turbos, by model and year, including detailed information on upgrading turbo boost, and checkout procedures involved - for those interested.

Thanks for commenting, and for any add-ons to the above.

 

That web site's advice is very good! I am surprised that, although he says, "Inspect vacuum/boost hoses on the Waste Gate Solenoid and on the Waste Gate", he fails to mention that the wastegate (commonly known as the DV) may be at fault, too. This is one of the first things we (Audiphiles) consider as a troublemaker. Some times a sticky valve can be the culprit.

 

Suppose this is a wastegate sticking problem.

What is the procedure for checking out a wastegate to see if it is sticking?, And

How hard a problem is it to fix it? Or, can it be fixed, or do you have to replace it? I am trying to get a fix on degree of difficulty and hours ($) of technician time to confirm wastegate sticking and then repair or replace.

Have any opinions on this?

I don’t have a clear picture in my mind as to what a wastegate is other than it must be a valve on the turbo exhaust and is spring loaded to open and discharge excess pressure. I presume that a weak spring will result in under boost, and a sticking wastegate (valve) will result in over boost. I can imagine a situation where the wastegate doesn’t open at all (which might be my situation since a sticking valve might resist opening some of the time, but not all of the time).

 

You're on the right track...
The wastegate is commonly called a DV (Diverter Valve) or a recirculating BPV (By Pass Valve).
If it is a typical Audi part, it can't be serviced. It is simply replaced, but it isn't expensive. The labor to acces the DV and replace it might be time consuming, but, all in all, it is an easy job that you can do with basic tools. Your best bet is to get an aftermarket (upgraded) DV - like a Bailey - these valves last longer and they can be serviced.

 

1.4+ bar is a hell of a lotta boost. More power to ya. you get 10 DK points

 

thats no true at all. a wastegate is like a BOV it release pressure in the event of a boost spike. it also tell you computer how fast to spin the turbo.

 

True... I meant to imply that it is mistakenly called the DV. I was trying to suggest that it could be the culprit regardless of name.

 

Right on