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D24Tic 940 Turbo testing and intercooler questions
Hi Everyone,
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. That said, it is very dirty around the turbo area and caked. So could the turbo be kaput but smoke free? It has years of grime on it to wash off. 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? The car has done 256k miles so far on standard everything major i suspect. Its got good service history but its soldiered on it seems beyond a water pump, thermostat and small bits. The previous long term owner told me he had not cleaned the engine bay in 19 years and it shows Also on the intercooler piping etc front and cooler itself, are they the same as petrol turbo units? Thanks Mick |
#2
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Best to test it with a boost gauge as discussed below.
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Yes, good idea, and not hard to implement. Tee it into the small tubing running from the rear of the intake manifold to the boost diaphragm (the "flying saucer") on top of the injection pump. IIRC, D24T stock boost should be around 10 - 13 PSI, D24TIC may be higher. Quote:
Sorry, IDK, not so familiar with the IC as unfortunately we didn't get the IC version here.
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1985 744 gle d24t 1985 745 gle d24t |
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I have noticed the yellow pipe on the boost diaphragm goes to a sensor, is that a regulatory sensor like a n95 valve on other vw engines or mere boost low or high warning? Mick |
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Not sure, can you post a photo?
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1985 744 gle d24t 1985 745 gle d24t |
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As requested, pics of sensor
I should have took some more later, I really went at the engine bay today with some cleaner and it looks alot better. I can actually see hose ends and jubilee clips again haha Last edited by ukvolvo; 02-21-2021 at 09:54 AM. |
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The boost compensator is the very tiptop of the injection pump. To measure turbo boost, you want to tee your gauge into the black tubing that I have circled in red.
With a long enough tube, you should be able to run it into the cabin so you can view it while driving. The engine will not generate much boost when not under load. bay-resized.JPG
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1985 744 gle d24t 1985 745 gle d24t |
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What is the sensor attached to the yellow pipe on the blow off valve them? just overboost? Mick |
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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:
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.
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86 745 D24T/ZF 345k lifted 2.5" 83 764 D24T/M46 155k |
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Oh BTW, in your second picture, the large rectangular relay very close to the EGR control solenoids is your glow plug relay. The one with "VOLVO" and "80A" and "12V" labeling on it.
Don't disconnect or remove that one, or the engine will no longer start. Only the stuff above it, if you choose to.
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86 745 D24T/ZF 345k lifted 2.5" 83 764 D24T/M46 155k |
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