S70 T5 Overboost

[Saxo Boy]

I have a 1996 S70 T5 that is overboosting very briefly on gearchanges to 15psi. The rest of the time it runs around 10-11psi which, I believe, is standard.

The overboost is only for a half second and it quickly settles back to 10-11psi. My questions are:

1) How big a problem is this? Is my engine likely to grenade?
2) If this is a problem that needs fixing, where do I start?

Thanks

[acshortt5]

If the car is an auto then that is normal as the boost spikes on gearchanges. Nothing to worry about.

If it's a manual then yes something is wrong.

[Saxo Boy]

Originally Posted by acshortt5

If the car is an auto then that is normal as the boost spikes on gearchanges. Nothing to worry about.

If it's a manual then yes something is wrong.

It's an auto

Why does it spike on the auto? What is going on that causes or necessitates it?

[960kg]

Originally Posted by Saxo Boy

It's an auto

Why does it spike on the auto? What is going on that causes or necessitates it?

You have a leak!

[Saxo Boy]

Originally Posted by 960kg

You have a leak!

The previous poster seemed to think this was normal for an auto

Does anyone have a diagram/photo of where I should be looking for such a leak? How do I test for such a think given that I can't create boost with my head in the bonnet to see where air is coming out!

[960kg]

Originally Posted by Saxo Boy

The previous poster seemed to think this was normal for an auto

Does anyone have a diagram/photo of where I should be looking for such a leak? How do I test for such a think given that I can't create boost with my head in the bonnet to see where air is coming out!

Why do you bring it to attention if you may think it is normal? You must be concerned.
If you think it`s normal then leave it.

You can check the hoses marked for leaks or just replace with Volvo ones £9 per metre which is sufficient.

[acshortt5]

You don't have a leak, this is completely normal for an AUTOMATIC transmission car.

Think about it, you don't lift off the throttle when it changes gear like you would in a manual on gear changes. That's the basic reason but I'm sure there will be a better, more technical explanation either somewhere else on the forum or on another site.

Edit: if you do replace the small diameter vac hoses then use Goodyear fuel hose as it's better and cheaper than getting the Volvo ones ;-)

[960kg]

Originally Posted by Saxo Boy

I have a 1996 S70 T5 that is overboosting very briefly on gearchanges to 15psi. The rest of the time it runs around 10-11psi which, I believe, is standard.

The overboost is only for a half second and it quickly settles back to 10-11psi. My questions are:

1) How big a problem is this? Is my engine likely to grenade?
2) If this is a problem that needs fixing, where do I start?

Thanks

I would worry about it as spikes can be dangerous.

I had this before i had a re-map and you must have a hose leak from somewhere around the compressor of the turbo to the BCS or back to the actuator diaphragm.

Because it leaks the boost will be high then the ECU corrects the boost back to the normal, not really ideal!!

[ColoradoSoul03]

Ok, I know I’m bringing up an old topic again, but my 1995 850 T5 is doing the same thing. I don’t have actual boost numbers because I’m going by the factory gauge that does not have numerical values. When under full or near full throttle, there is a momentary spike in boost when the car shifts. It is an Automatic Transmission car. There is a slight but very noticeable pop in the exhaust when it happens as well. Now, my understanding as the difference between a manual and an automatic car when it comes to shifting with a turbo is that when you shift a manual, you let off the gas obviously. This causes a cut in air, fuel, and also opens the CBV, BOV, DV, whichever you like to call it which releases the boost to prevent a lean condition when the throttle is reopened after the shift and also prevents damage to the throttle body and intercooler piping due to the sharp increase in boost when the throttle is suddenly shut and the turbo is still spooled. Now, with an automatic transmission, obviously you do not lift the throttle when the car shifts. As the engine’s RPM increases, so does the turbo’s RPM because the faster the engine is turning, the quicker it uses the air so the turbo has to spin faster to maintain the boost level at whatever setting it is. Now, when the transmission shifts and the engine’s RPM suddenly decreases, the turbo is still spinning fast enough to maintain say 11 psi at 5,500 RPM but now the engine is only turning 4,000 RPM. There is a spike in boost before the turbo slows back down to the necessary RPM to maintain 11psi at 4,000 RPM. This is a normal thing to happen but, if I was the manufacturer and I was programming the ECU (The Bosch Motronic ECU is a VERY GOOD ECU), I would program it to open the TCV right at the shift to fling the wastegate wide open to drop the turbo’s RPM at the same time the transmission shifts. The ECU and TCU communicate constantly so the ECU HAS to know when the transmission is going to shift so it can react properly. It’s either I would program for the TCV to fully open (basically run straight mechanical wastegate instead of holding the boost out of the wastegate’s reference hose and bleeding the excess into the inlet pipe before the turbo) or I would do what VW does on their DSG cars and I would cut the ignition and fuel right at the shift. Now, on my car, all of the hoses to do with the wastegate and TCV are brand new and I’ve recently replaced the turbo as well. This condition has stayed throughout the hose and turbo changes. To me, this is either a normal operation which has been compensated for in the ECU to add more fuel and drop timing right after the shift, poor programming of the ECU if there is not a compensation, or a lagging TCV. The latter seems the most likely. So, does anyone have any experience with the Heavy Duty TCV from IPD? I am getting ready to have the ECU flashed with IPD’s software and I would like to know if this is something that needs to be corrected before I have to flash done. Obviously the flash is going to raise the requested boost in the ECU so this spike is going to be exaggerated after the flash and I really don’t want to cause damage or blow the engine because of it. Or, does IPD’s software compensate for this issue? If they have addressed this issue and the problem doesn’t happen on their software, there may not be anything to worry about. Another note: this really seems to be most significant when the car is in “Sport” mode, probably because the shift logic is different and the ECU and TCU are running a more aggressive map for everything. Sorry for the novel you all had to read and I hope I wasn’t ambiguous with anything.

[acshortt5]

It shouldn't be popping in the exhaust on gear changes. I'd have a look and see if you have an exhaust leak first of all - my mx5 (miata) popped and sounded like a rally car with antilag, especially on overrun, when I had a small leak at a joint in the exhaust. I've never had any popping in the exhaust on the volvo.

Personally I don't think it's poor mapping at all on the factory ecu, I find the shifts and power delivery to be extremely smooth, certainly on a par with other younger autos I've driven.
Time has moved on of course and there may well be better ways of mapping the gear changes now but this is only because other aspects of engine management have advanced such as coil on plug with individual cylinder monitoring and VVT as opposed to what we have which is cylinder firing driven directly off the end of the camshaft (via the rotor arm/dizzy cap) with a single coil providing power to the plugs - they did the best with what they had at the time.

I run the IPD TCV, it has not made a difference to me but I have not had a remap.

I've not noticed any difference in boost levels in sport mode. It just makes the gearbox hold a lower gear for longer (and burns more in fuel) so when you put your foot down it does "feel" more aggressive.

If you have queries on the IPD map you really ought to direct those to IPD to get the best answers and have a look on the american volvo forums as there should be some reviews out there.