Fuel/ignition/boost cut off under WOT on 850 T-5R Topic is solved

MennoS · Post by **MennoS** » 17 Nov 2016, 07:45

Hi guys,

Recently I became a proud owner of a '95 black sedan T-5R with automatic transmission in the Netherlands. Like all other 850's the odometer is broken and got stuck at 230,000km (±180,000 miles), probably 7 years ago, so it might have done a few more.. It is fitted with silicone pressure hoses, an aluminium intercooler and it is supposed to be chip tuned (don't know by who, or what). For the rest it is original.

Upon test driving the car, it hesitated on full throttle, around 3000 rpm. Reducing the amount of throttle would reduce the hesitation, but it then wouldn't really accelerate much more. I figured it had been standing still for a long time, so that could be it, but after I bought it and drove it for longer, the problem still exists..

I have seen the problem coming up on this, and other forums, but I never came across the answer to the problem. So hopefully you guys can help me??

I installed an aftermarket boost pressure gauge, which shows an increase in boost pressure up until 0.45 bar/±6.5 PSI (isn't this supposed to be 0.9 bar/12 PSI?), after which the hesitation begins. This is a quite rapid alternation of power on/power off, at which I can see the boost pressure drop a little bit and come right up again. Holding WOT will keep it in this mode, even after it shifts to next gear. I also placed some LEDs on the ignition and it looks like the ignition is slowed down as well, but I have to film that in slow-mo next to the boost gauge to be certain of that.

What I have done and done and tested so far:
full stage 0, incl. distribution, OEM turbo sparkplugs, distributor cap and oil/fuel filter. I also filled it with an injector cleaner and oil cleaner, to clean the insights.
I checked al vacuum lines and they seem allright
I unplugged the MAF, turbo control valve, waste-gate, blow off valve, different vacuum lines to see what that did: all of them had other issues come up, next to the hesitation. Also when I unplugged the waste-gate (the actuator), boost pressure came up easily to 1 bar, but the hesitation would still come in (I didn't let the boost go past 1 bar..

)
All codes checked in the beginning: it gave codes for MAF, auto transmission short-cut, brake-lights short cut, ABS malfunction and TRACS malfunction. Clearing the codes didn't change a thing and the codes didn't come back, so there is no codes now.
I fueled it with octane 102 fuel, but this didn't do anything to the problem.
Blocking the fuel reverse line didn't change anything, so I assume fuel pressure is ok.

Upon testing, the TRACS doesn't work and doesn't show any warning lights when the wheels are spinning and the cruise-control doesn't work. ABS works. I am not sure if this has anything to do with the problem, but I thought it might be of interest.

You see I am hitting a wall now in possibilities.. It seems that the problem is in the engine management, as it doesn't react on any of the hardware taken off. But I figure the ECU gets information from somewhere which isn't right. The question now is: what is giving the false input??

I am hoping somebody here can help me to find the problem. But since I have seen this problem coming up multiple times here, I guess it must be findable and fixable.

Many thanks in advance!!

Post by **matthew1** » 17 Nov 2016, 10:50

Welcome to MVS, MennoS .

From across the Internet, it sounds like a worn CBV that's not holding boost.

You can test the system for vacuum leaks to narrow it down to CBV or other vacuum-related components, and test the ECU by swapping in any 1995/96 850 turbo ECU. I'd test the ECU last. It seems to me it's a mechanical system that's failing.

Yes, correct boost is 10-12psi on a 850 turbo.

You're approaching this correctly. Keep eliminating components and you'll be left with the answer.

ZuluR · Post by **ZuluR** » 17 Nov 2016, 11:49

Hi.

Regarding the factory boost levels.
0.9Bar boost does not exist on the 850 models from the factory.

Then 850R manual B5234t4 has a factory boost of 0.86Bar (250hp), i asked volvo and they will confirmed this figure

The 850R automatic + t-5r (aut +man) B5234t5 (240hp) models have a constant boost of around 0.6bar and during 20-30sec overboosts to about 0.8bar (total).
During overboost the hp is 240 and during constant boost levels the engine makes 225hp

The 2.3l t-5 B5234t boosts 0.65Bar and makes 225hp.

the 2.0 t-5 engine makes ~200hp and has around 0.4bar boost.

So if your t-5r is boosting more than 0.8bar then you need to lengthen the vastegate actuator. And set the "base boost" to factory levels.

This is done by the following procedure.
disconnect the BCS electric connection.
Go for a drive and floor it. the boost is not vastegate controlled and should be 0.4-0.45bar
if more lengthen the VG rod
if less
Shorten the rod.

after this reconnect the BCS, and now the boost should be at factory levels.

I guess your car has had its Vastegate rod shortened by some owner and now the boost rises over the ECU level.

I installed an aftermarket boost pressure gauge, which shows an increase in boost pressure up until 0.45 bar/±6.5 PSI (isn't this supposed to be 0.9 bar/12 PSI?), after which the hesitation begins. This is a quite rapid alternation of power on/power off, at which I can see the boost pressure drop a little bit and come right up again. Holding WOT will keep it in this mode, even after it shifts to next gear. I also placed some LEDs on the ignition and it looks like the ignition is slowed down as well, but I have to film that in slow-mo next to the boost gauge to be certain of that.

This sounds like the stock ECU is trying to limit the boost from rising more since it is over the limits already.

ZuluR · Post by **ZuluR** » 17 Nov 2016, 12:09

Since my prevoius post was post nr 1 in here, i guess i better give some "credentials" so that the numbers i throw can be considered as valid.

I drive a red 855R, i have had it for over 10 years.
this one: https://www.ipdusa.com/blogs/386/custom ... er-jansson

I am a moderator on the NordicR Forum and have a few thousand posts there..

And my latest project is a youtube channel about the 850 t-5
https://www.youtube.com/user/serrorZulu

Here is a video that could help you replace the TCV hoses that will help the ECU manage the boost

MennoS · Post by **MennoS** » 18 Nov 2016, 00:22

Thanks for the quick replies, I really appreciate it!

Current boost is ±0,45 bar, so lower than the 0,65-0,8 stock. Therefore I don't need to adjust the actuator rod.
For the CBV diaphragm: this is something that came to my mind, but when I unplugged the turbo control valve, boost pressure would climb easily to 1 bar, and it still gave the same hesitation. Given the age of the car, I think I am going to replace the valve anyway, to clear that out.
I will see if I can find any vacuum leaks again, but up until now I haven't found any.

This coming week I won't be able to have a look at the car, but I will come back on this.

If anything else comes to mind, please let me know!

Thanks again!

ZuluR · Post by **ZuluR** » 18 Nov 2016, 15:18

MennoS wrote:Thanks for the quick replies, I really appreciate it!

Current boost is ±0,45 bar, so lower than the 0,65-0,8 stock. Therefore I don't need to adjust the actuator rod.
For the CBV diaphragm: this is something that came to my mind, but when I unplugged the turbo control valve, boost pressure would climb easily to 1 bar, and it still gave the same hesitation. Given the age of the car, I think I am going to replace the valve anyway, to clear that out.
I will see if I can find any vacuum leaks again, but up until now I haven't found any.

This coming week I won't be able to have a look at the car, but I will come back on this.

If anything else comes to mind, please let me know!

Thanks again!

Whoah!!!!!
when you unplug the boost control valve you should have .4bar :ish

the BCS the middle hose going to the inlet pipe.
Check that the plastic connector on the air inlet pipe actually is "open".
Like i said in the video, i know of a case where this pipe was replaced where this hole was not drilled open and it got no boost with the BCS connected.
If this hole is blocked the VG actuator is always pushed open when making some boost and it would fit your description.

And then it would seem the the prevoious owner has shortened the VG rod so it always stays closed.

Or the Vg actuator is not the correct one as boost should build wery slowly without the BCS connected.

MennoS · Post by **MennoS** » 27 Nov 2016, 06:43

I opened the CBV and guess what: there was a hole in the diaphragm. (Indeed, what a shitty placed thing that is!) I took one from another turbo (from a b23ft) and tried it, but the hesitation was still there. It did stop fluttering on lifting the throttle though. A new diaphragm is on its way.
Checked if the hole in the inlet hose was open, which was. Replaced a few worn vacuum lines as well.
Then I swapped my spark plug wires with another 850 and tadaaaaa, problem fixed!

But now I can finally floor the car properly, It still only boosts up to 0,5-0,6 bar max, about 3/4 on the inbuilt pressure gauge, as you can see in the photo. Any ideas on what might be causing this? Or is this normal boost on a T-5R?

[img]

[/img]

Post by **pkc303** » 17 Dec 2016, 14:24

Very good video, thank you.

Will check my turbo lines now. Feels a little laggy currently. I have the same issue with the turbo gauge showing only 3/4 at full throttle going about 65-70 mph.