Quote:
Originally Posted by ukvolvo
What is the sensor attached to the yellow pipe on the blow off valve them? just overboost?
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That is your EGR valve. The actuators connected to the other end of the yellow vac line are the control components for the EGR system.
You could disconnect that stuff if you want to. Usually doesn't work properly after 25+ years anyway, and these old engines have no feedback computer diagnostics to catch the malfunctions nor know if you have disabled it. EGR on an old diesel can add to intake manifold carbon deposits also.
You can do elaborate tests with vacuum gauges etc to determine whether the EGR system is still functioning as intended, but easier to eliminate it and head off any potential for problems. These old engines are not the cleanest runners regardless, and the EGR "system" (such as it is) is extremely primitive in its strategy even when working perfectly, so the emissions impact either way is negligible.
At any rate it should not affect performance at all unless the EGR valve is sticking open or being commanded open at the wrong times. To answer your other question, no, none of this is related to control of turbo boost. On these engines the boost regulation is all fully mechanical and integral to the turbocharger. No external solenoids, N75 valve, etc like you were mentioning being familiar with a TDI engine. There are no electronics at all in terms of the turbo except for a switch mounted inside the overboost pressure relief valve on the front of the intake manifold, which gets tripped and lights up the turbo warning light on the dash if an overboost situation occurs (in case of wastegate failure etc).
All of the boost pressure control machinery should be visible on the turbo if you look over there, or post a picture of it and we can help identify. On our early style non-IC D24T engines here in the US, the wastegate actuator is internal so you can't see the vacuum bellows and actuator arm, but I think your D24TIC engine might have a proper external actuator that you would be able to see visually. IIRC they do also run higher boost, non-IC motor here is something like 10psi stock but I thought the D24TIC runs somewhere around 12-13.
Quote:
Originally Posted by ukvolvo
...I think my 940 is literally running no boost. It smokes a little on start but no other time so no tell tale failed turbo signs for such low performance.
Or are they really that slow standard and flat ? It does not feel boost assisted really. Acceleration increases at 3k but no noticeable kick at all or boost noise etc.
Should I run a t piece and test boost? What should it be if so?
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Measuring boost pressure is a good idea certainly, but do note that if you are accustomed to newer direct injection electronically controlled diesels, like VW TDI, Peugeot, Ford, etc. The D24TIC Volvo engine has a very different feel and power curve, even when performing exactly as designed. D24T/IC is more smooth and progressive, and has a wider RPM range, but less absolute power. It runs more like a nice similar-size gasoline engine in terms of its power delivery, and quite unlike today's aggressively tuned diesels. So it may well be working normally, just not quite what you were expecting. This is a big heavy RWD car with an engine that was designed and marketed to achieve a balance of performance and fuel economy, not max performance (for that, Volvo had turbo gas engines available). They are good strong runners, especially at speed on the highway, and can feel peppy in city driving especially with the automatic transmission. But they don't really win drag races, smoke the tires off the line, etc, unless heavily modified.
It is not a "torque monster" type of engine, if that is the type of sensation you have in mind when you say "boost assisted". D24T and others from its era do not push you into the seat with a jolt of boost and torque at 1500 rpm and then run out of breath at 3000 rpm. The power comes on more gradually and is strongest ABOVE 2500 rpm. And they can continue to pull strongly up to 4000 rpm or higher. (And sound great when doing it) Part of what makes them in many ways more fun and involving than the newer direct injection diesels, which have more of an industrial type power characteristic. However, the modern ones obviously are far faster in terms of outright speed, just like today's gasoline cars versus those of the D24's era.
So, for us to be able to say if it's "too slow" or not, we need to know your context. If it feels slow compared to other similar type and age stock turbo diesel cars you have tried (eg large Mercedes turbodiesel from same time period), then there may be an issue. But if it feels slow to accelerate versus a 20 years newer Golf TDI or something like this, then it might just be the nature of the beast.