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

[MennoS]

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.

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!!

[Boxman]

When you mention rapid on/off of power, that's sounds a bit like misfiring or some other form of incomplete burn. I assume it runs fine on idle?

There could be a number of reasons for that;

• Spark is not igniting your fuel mixture properly
• Fuel mixture is not okay (too rich / too lean) thus not properly burnable
• Major error in engine / ignition timing

Since you essentially did Stage 0 on your ignition with a new distributor cap, rotor etc, a weak spark is probably not the issue. The coils on these cars rarely go bad. Inspect your HT leads (the wires to the spark-plugs and distributor cap) to be sure they are not broken and causing the spark to jump somewhere else.

Regarding fuel mixture, I have had a similar problem once that was down to a bad fuel pump. I would have to baby the car, but at higher throttle the pump couldn't keep up and low fuel pressure meant I was getting a super lean mixture causing un-ignitable conditions. Check your old spark-plugs for a white haze all over - this indicates lean (=very hot) burn. Check your fuel pressure at the rail with a gauge. It should be ~40psi stationary, and should hold that when ignition is off. It should also hold this pressure under load. If the pressure is too low, inspect your fuel pressure valve (the cylindrical device on your fuel rail) as these do go bad from time to time. If this is okay, your pump might not be getting enough power or might straight up be broken. Alternatively, having one or more bad injectors is always a possibility.

Regarding the timing, check if all the timing marks on your distributor belt assembly line up. If you checked all the above and it's all fine, it has to be some sort of sensor failure somewhere making you miss proper timing/fueling.

 

One other point of advice on old-engine care (as yours is probably well on its way to 400k); you should shy away from 'flushing' products. Old engines have carbon deposits built up in places where it actually helps keep the engine sealed. Engine oil flushing products aggressively break down these deposits - while this opens up possibilities to leaks in unforeseen places, the deposits also have to go somewhere and can cause clogs elsewhere, for instance the oil pickup line. If you used an aggressive flushing agent, I would recommend a complete oil+filter change on the earliest convenience.

[BlackBrick]

I would guess either a boost leak on an intercooler hose, or the MAF needs cleaning or replacing.

[Fudge_Brownie]

6 hours ago, MennoS said:

it is supposed to be chip tuned (don't know by who, or what). For the rest it is original.

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.

I fueled it with octane 102 fuel, but this didn't do anything to the problem.

I'm curious about the mystery tune. Is it possible this car was never tuned, and the owner lied? I'd be surprised if the previous owner didn't know who tuned it. Or maybe some failed do it yourself attempt? Try to get a spare original ECU from junkyard / ebay and see how the car runs.

Why do you think 12psi max? Most tunes for these cars were 15-18psi. Stock was about 10psi.

FYI to all: 102 octane is probably RON, where in the US we use AKI, so that's 95 octane in the United States.

[gdog]

All good advice above.. ^^^ 

Are the injectors stock?  If so, subbing in a stock ecu, as FB mentioned, is a great idea.  That will tell you right away if someone foo-barred the "tune".

But IMO a stage0 includes a compression test; did you do one? 

If all that checks out, then start looking at fuel pressure, under load would be best.  If the fuel pump is original then it's due, but don't shotgun it; test it...

BTW: that's a really long first post!  Welcome to VS 

 

17 hours ago, MennoS said:

 I also placed some LEDs on the ignition ...

what the heck is that?

[MennoS]

Thanks for the replies, I really appreciate it!

Fuel pressure: I clammed the fuel line going back to the pump: this didn't do any difference. I will check the fuel pressure with a gauge and check the fuel pressure valve
HT leads checked and look fine - I could swap them temporarily with another 850
Old sparkplugs looked fine, they didn't even needed replacing, but I was on it anyway
Belt timing is perfect

No leaks on the intercooler hoses - checked them multiple times
MAF sensor is cleaned - no difference, and also no codes on that

The guy I bought it from said it was tuned, but by a previous owner. Therefore I now don't know where/when/who about the tune. A spare ECU would be great I guess, but I've heard the ECU's on these cars are matched to the car and won't work with others. It is something I will get into, because maybe the tune is the whole problem, who knows..
I don't know exact numbers on stock boost pressure, but 12 PSI stock was something I read somewhere. My 6,5 PSI is then much less then stock.😏
I haven't done a compression test, but since the car is running supersmooth on idle and acts fine in lower revs, I assume that should be fine. But then: never assume anything, right?

I connected LED lights to the injectors to see if they are cut off or not

I will try and find an ECU that I can borrow and a MAF. If the ECU is the problem, I will try and see if someone can see what is done for tuning and maybe reverse it, or give it a better tune.

 

I'll come back to this, as soon as I have time to work on the car

 

I've added a video, where you can see how it behaves on WOT (incl LEDS on the injectors)

 

_50_full.speed

[Boxman]

 A spare ECU would be great I guess, but I've heard the ECU's on these cars are matched to the car and won't work with others.

Nah, as long as you stick with the right revision (either M4.3 or M4.4) of any other turbo'd car, they're the same. Don't put an NA ecu in a T5 though.

[Fudge_Brownie]

54 minutes ago, Boxman said:

Nah, as long as you stick with the right revision (either M4.3 or M4.4) of any other turbo'd car, they're the same. Don't put an NA ecu in a T5 though.

Correct. He probably needs an M4.3 ECU from an 850 Turbo/T5/R. I believe the newer 'P2' cars (2001+) were bonded to the car and couldn't be swapped without additional steps.

If I remember correctly, some chip-tuners would solder on a different chip to the ECU, while others are flashing them. You could open the ECU's shell to look for evidence of this. It should be obvious. They remove the soldered on chip, install a socket, then put their chip in the socket. The part labeled 'VL' is a chip sitting on top of an installed socket. But it's still possible your problem is elsewhere so this may be effort spent going the wrong direction.

[andyb5]

On 11/17/2016 at 11:05 AM, Fudge_Brownie said:

I believe the newer 'P2' cars (2001+) were bonded to the car and couldn't be swapped without additional steps.

ECUs are VIN-mated starting on the 99 ME7 S/V/C70s.

P2s bring additional complications in with the expansion of the CANBUS system to include most electronic elements of the car

[MennoS]

 opened the CBV and guess what: there was a hole in the diaphragm. 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?

[TryingBe]

How's your TCV vacuum hoses routed?

[MennoS]

From the side with the screw holes: turbo - intake hose - waste gate. This should be the other way around I just saw in a video. Would that matter much?

 

[Boxman]

They are color coded red yellow and blue. Check the colors on the TCV and compare this to the literature (should be easy enough to google), and go with that.