Limp mode no EML

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Alpha242

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Hi guys I’m really stuck! 3.0 V6, as soon as you try to accelerate hard and go over 2500-3000 RPM It drops into limp mode with no engine light come up.
When you turn the engine off and back on again it is back to normal until you try to put your foot down again. Although the light does not come up it does store code P0235 which is to do with turbo boost but when you clear that it doesn’t come back on straight away which would suggest it’s not the boost sensor.
Anyone had this? No luck on UK forums unfortunately.
 
Welcome to the forum.


It could very well be a turbocharger that has a faulty actuator circuit. This may result in the turbocharger vanes not opening as expected, with a substantial power reduction.


It's easy to determine if this is the case. Normally your turbocharger will produce upwards of 18psi of boost, and under hard acceleration it should be boosting in the low 20s. Put a OBD reader on and watch the boost pressure while you drive. This is also easy: bluetooth ELM327 OBDII adapter and a free OBD reader app from Android/iStore.


You should also check whether or not your engine bay has been pressure-cleaned. Using high pressure water may result in some debris entering the plugs that connect things like the turbocharger actuator, boost sensor etc and these can give false readins to the ECU even when the components themselves are functioning properly. They may be erratic. They are usually fixed by unplugging and replugging the items, perhaps giving them a quick spray inside with electrical contact cleaner.



You might also pay attention (while you're monitoring boost) to the fuel rail pressure. If the SCV (Suction Control Valve, it's on the fuel pump) has a fault, your fuel pressure won't rise as expected. The V9X engine is capable of 1800BAR (over 26,000psi) and under hard acceleration should be pumping at least over 20,000psi. Normal cruising at 100km/h should see it delivering between 10,000psi and 15,000psi (roughly). An SCV fault may not present any codes at all.
 
Thank you very much for your detailed response, unfortunately it was not what I wanted to hear......turbo OUCH! My concern with watching live data on the turbo is- say the fault is something else (not turbo) this something may cause the car to go into limp mode before the turbo can reach higher boost, does that make sense?

Also if it is the veins in the turbo is the only option replacement? Engine out etc 🙁. Is there any fix in situ?
 
We really need a few more details. How old are air and fuel filters? I find it hard to believe the turbo is on its way out if it drives normally otherwise. Could be bad connections between the connectors as mentioned above. It won't hurt to either get one of those obd2 scanners yourself or if you know anyone with one ask them to give you a hand with it.

My d22 had an issue a few times when using cruise control. For no reason when set at around 100km/h a few times the car went into limp mode when it was accelerating uphill with no engine light or codes at all. I checked the stats out with torque and one of those bluetooth obd2 adaptors and everything looked ok. Fuel rail pressure spiked a bit over 20k psi which it did using the accelerator too without issue. The only thing I tried was replacing the fuel filter and it hasn't done it since.

I hope you get yours sorted out, but start with the small stuff first.
 
Thank you too for your reply. Well the air filter has not been replaced but it does need to be and was on the list but I will do that ASAP. The fuel filter was replaced recently by the previous owner but is not a genuine filter, perhaps I should change it for one to eliminate it?

What more can I tell you, well it revs out fully whilst in park, it only goes into limp when under load it seems.

I just don't get why it's not putting the light on! I mean maybe it could be the boost sensor but surely if it was faulty the code would come straight back up rather than only showing when the car goes back to limp.

If I stay in low revs and build up speed gradually as not to put it under too much load, it drive so perfectly, I really don't understand it.
 
That's normally what points to a restriction somewhere. If it was throwing the code all the time then you'd suspect a failing component. I'd start by replacing the air filter, do an ecu reset, then see how it goes. If still no luck, then look at the fuel filter too.
 
The typical reason for loss of power under load is the SCV, but because of the turbocharger error I am thinking actuator. Not the turbocharger - just the actuator. Or the electrical connections to it (or the boost sensor).


To get full revs in neutral you don't need a lot of boost. The car knows when it's in neutral and won't fire the turbocharger much in neutral (no need to). It will still rev freely, but if that actuator has a problem or isn't being communicated with properly, it's easily the source of your troubles.
 
Hi again, I know it takes up a lot of your time replying and I am thankful for the help so far but if anyone could help with the below questions I would appreciate it hugely!
I’m not being lazy, I have spent hours trawling through the internet and on forums but just am a little unsure of some things or find some information contradictory.

So update so far, I have now replaced the intercooler (because it had a leak anyway) and the boost sensor, on the side of the intercooler-are there anymore in the system?

So my questions are as follows;

Does the V6 have a SCV? Some say it does others it doesn’t.

Are the exhaust pressure sensor and temperature sensor the same thing?

The boost control solenoid on the rubber bracket to the left of the turbo, does this have any function over the turbo or is it purely cruise control?

If It turns out I have a blocked/ sticky vein or actuator, is this something anyone has managed to rectify without removing the engine/ turbo?
 
Wait, wait, wait. Your V9X has a BCS? I thought they were electronically controlled turbochargers. Ok. That changes the picture a little.


The BCS is probably the one component in my engine bay that I hate the most. Sure, I've replaced a couple of turbos, but that BCS is a painful little bugger. I've had 3, and now have a Tilix valve (like a Dawes valve). I also replaced all of the vacuum hosing (3mm rubber fuel-grade hose).


There is a way to test the BCS. It will have 3 hoses coming from it, one of these hoses will connect to something on the engine itself (not the turbocharger or the air intake). Find this hose that connects the BCS to the engine ("primary hose" ), get a new piece of hose and connect it to where the primary hose connected to the engine. Now connect the other end to the turbocharger actuator and take the car for a GENTLE drive.


I can't stress that "gentle" too much. If the turbocharger is working properly, connecting the vac pump directly to the actuator will pull the vanes open from the word go, which means max boost all the time. Your car will feel really powerful, but you don't want to be hitting the throttle hard and then stopping suddenly. Bring the revs up fine, but do it where you have loads of room to back off slowly.


If that's what you experience, then you should connect this new piece of hose back onto the BCS, reconnect the actuator and take the car for a drive again. If you now experience a lack of power, your BCS is POSSIBLY at fault. Replace the other vac hoses too, and drive the car again. If it's still weaker than normal, it's the BCS.


Nissan will sell replacements (about $240 or so in AUD) or you can go the alternative way. I have, and while my fuel economy isn't the same because the ECU isn't able to fine-control the turbocharger's boost, it's now 100% reliable.
 
s-l300.jpg


Thanks for the reply Old Tony, mine is the one in the link above and only has 2 hoses! Hopefully I haven’t got my parts mixed up describing it to you!
 
Same thing, just a slightly different variation. One of the hoses from that will go to the vacuum pump on the engine, the other will go to the turbocharger actuator.
 
Update...
Fitted new boost control solenoid, no difference :(
Got live data now and tc boost reached 50psi!!! Before going into limp.
On Tickover it’s reading 15psi. What could cause such a severe overboost? Veins stuck open? Could it be the actuator?

I have one last sensor to try which is exhaust pressure sensor then on to the turbo replacement I suppose.
 
You replaced the BCS without testing it?



50psi is a bit high, and at idle you should be reading 0, so the first thing I'd do is subtract 15psi (14.7 really, but 15 is close enough) from the figures.


So at idle you're getting 0, and at full noise 35psi. That's a little on the high side. Now try this: disconnect the vac line from the turbo actuator and take the car for a drive. Performance should suck, but if it doesn't - if your car still goes like a scalded cat - your vanes are stuck or the actuator is jammed. You should (with everything connected, engine idling) see some movement of the actuator arm beneath the actuator (this arm leads into the centre area of the turbo). If the car performed poorly with the actuator disconnected, the turbo is probably fine, leave it alone.



It might still be overboosting, or sensing an overboost, but it's probably an electrical issue (either a loose/bad sensor or a poor earth). Until you've checked the connections it's probably not worth spending more money just yet.
 
I did do because over here they’re not too expensive fortunately.

And thanks very much for the advice I will try that tomorrow and let you know.
 
Sooo I disconnected it, no real difference apart from it went in to limp mode as before, however it did rev out more at least 1500 RPM more than it did before and for longer before it cut out.
After I reset it, it didn’t go into limp mode again it just went flat around 2000 RPM then pulled through it and accelerated ok apart from a bit of a judder.

I’m really confused now!
 
I don't have access to a STX550 so I can't try that myself, but in the YD25 D40 if you pull the vac hose off the actuator, it's so gutless you can't beat a Shoprider at the lights.


It does sound like the vanes of the turbocharger aren't behaving properly. There's another free test to do first, requires two people for method 1, or just you and a new piece of hose for method 2.



Method 1: get your assistant in the driver's seat, engine OFF. Find yourself a convenient perch where you can see the arm under the turbocharger actuator that doesn't place you in danger of the fans or exhaust etc. Have them start the car while you're watching that little arm, and give it a couple of revs to about 2000rpm plus a few taps on the throttle from idle so the engine just starts to wind up a couple of hundred RPM ('tap' means literally that, a very quick jab on the pedal).


Method 2: get a new piece of hose, connect one end to the top of the actuator and suck on the other while watching the arm underneath.



If there's NO movement in that arm, either the actuator is damaged or the vanes are jammed. The actuator has a diaphragm that the vacuum works on and pulls the arm up, if you can suck and there's no resistance, the diaphragm is damaged and that's your problem. If you can suck hard and there's no movement, try blowing into the pipe, if there's still no movement then the turbocharger needs to come out and be cleaned at the very least (plus have a seal and gasket kit to replace the old ones).


It still sounds like control, rather than function that's an issue.
 
If you can see live data, can you tell us what the fuel rail pressure and maf rate (it measures air flow in grams/sec) are doing? This will give a bit more of an indication of what the ecu is seeing, rather than just guessing what is going on. It could be another sensor playing up or bad earth as Tony mentioned, but if you can tell us the above info it will help paint a bigger picture...
 
Hi all, so for some reason I can’t copy pictures into here anymore but the values I found are below.

Intake manifold absolute pressure at idle is 30.6 inHg. It did increase as the revs increased but only to 50 or so before limp mode again.

The other values are at 3267rpm boost pressure was 34.08 psi. Fuel rail pressure was 14307.97 psi this was just before it cut into limp mode.

Straight after that the readings were boost pressure 10.88 psi. Fuel rail 4249.60 psi.

I am getting a few consistent codes these are;
P0235 turbo boost sensor
P0470 exhaust gas pressure sensor
P1525 ASCD function

Occasionally I get P2263 TC system.

And today for the first time I got P2002 DPF, this was after I tried some higher grade fuel, not sure if it related or not though.

Most strangely of all I have not once has the EML on just the limp mode alerting me to faults and then plugging obd in to see the codes. I’m very confused with it all!
 
It sounds like the earth on your ECU could be erratic. ASCD is cruise control, nothing to do with boost pressure or exhaust gas pressure that you can't create with your foot, so it makes me wonder if the entire problem isn't created by a poor electrical connection. On quite a few occasions this has been the answer for odd, seemingly random DTCs. Cleaning the earth points (and both battery terminals) is another free thing to try.


Your stated pressures seem normal. 30.6 inHg is about 15psi which is about atmospheric pressure (so you need to subtract 14.7psi from all readings to get actual figures). That means at 50 inHg - 34psi - your boost is actually 20psi, quite normal for a D40. Fuel rail pressure of 14,300psi is a bit low for driving at those revs, so it's well within acceptable range - the V9X can produce 26,000psi, so it's barely half way.


So we're either back to a faulty SCV or it's an erratic electrical fault - worst case could be that it's both. Personally I'd try cleaning as many electrical connections (including battery terminals) first in order to eliminate them as a possible source of trouble.
 
Thank you Tony, I will try the earths next. So you don’t think the turbo could be failing and causing the codes as a byproduct I.e. they were in use at the exact point the turbo discovered a problem?

Have you heard of other such substantial problems not throwing up an EML?
 

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