Sluggish no power

[Bradda]

Hi . I need some help with a Nissan navara d40 Spanish 2007.

Went off road got stuck in the mud and that's when my vehicle changed. Took alot of effort to get unstuck.

When I got back on the road vehicle was very unresponsive, felt like I lost boost power, when I got to 100km/h it surged boost then no boost . I changed the vacuum control valve and still no boost . Changed all my vacuum lines done a pressure test to check for any leaks in the intake system. No faults or dtcs and still no boost. Checked live data and my boost was spiking straight to 150 kpi then drop to 6 and 8kpi so changed my map sensor. Still giving same problem. Pulled my exhaust off knocked my CAT out completely. Still had the same issue. Tried towing my boat and could hear a loud vibrating sound coming from the turbo area when trying to get to speed, car maxed out at 100km/h. Checked turbo shaft play. It seemed excessive. So changed turbo with a new one. Vehicle doesn't surge any more. But still very Sluggish. Have good boost pressure but still slow off the mark. Any ideas of what else it could be would be much appreciated.

 

[Old.Tony]

Is the radiator clear of all debris? Did anything snag the boost pressure sensor wires? Have you plugged in a OBD connector and asked the ECU about boost pressure, or read any codes that might be stored in the car? Is the connector on the SCV (attached to the fuel pump) still in good condition? How about the BCS, is it still connected and providing control to the turbocharger?

This last one is tricky, sometimes at idle you can't tell if the turbocharger is being controlled so a couple of basic checks should sort it. Usually I'd get you to start the engine and look at the arm underneath the actuator (the round gold part on the turbo that the vac hose connects to). The arm should move a little in response to fluctuations in the control signal from the BCS but this isn't always the case.

If there's no movement here, since it's a new turbo, I'd suspect the BCS or its cabling. You should check the boost pressure while driving (bluetooth OBD adapter and an app like Android's Torque, or borrow a mechanic's analyser), if there's little to no boost you have the answer - it's probably the BCS, but try disconnecting and reconnecting it and retesting it before throwing it out.

To make sure it's the BCS, do this (carefully). Remove the vac line that comes across the top of the motor from the BCS and connect it directly to the turbocharger. Take the car for a drive but do NOT take your foot off the accelerator quickly - ease it off. When accelerating, your turbocharger should get full boost at all times and overpressuring the intake manifold is very easy to do. If you got good boost when accelerating, the BCS isn't working properly. Reconnect things the way they were (to be safe) and consider the BCS replacement.

There are 2 ways to replace the BCS.

1) Buy another. Second hand is risky, they seem to fail a bit, but if a wrecker has one really cheap it's worth trying, a car is unlikely to be written off because of a failed BCS. New ones vary in price from about $300 (Nissan) to about $50 on eBay (example here).

2) Replace it entirely with either a Dawes or Tillix valve. I bought a Tillix valve for mine and while it's not as responsive as the BCS (I don't get as much boost early on), it's not failed at all since I installed it. It's a very simple device and works a treat. The Dawes valve is (I'm told) quite similar.

 

[Bradda]

Hi Tony . Thanks for the response. Sorry I called the boost control valve a vacuum control valve. But I have changed it with a new one. It was the first thing I done as I have experienced a problem with one before. I have done the basics like air filter, fuel filter vacuum lines etc. Removed intercooler inspected couldn't fault it. When I had my old turbo fitted I could see the boost actuator on the turbo flutter at idle. Don't see that happening with my new turbo fitted ? If I pull the vac line off the turbo actuator the arm drops put the line back on the arm lifts. So I know I have good movement on the actuator. I have had a good play about with the car to try figure the fault out, with no luck. I will try and test a known good boost control valve to confirm its not the issue. Do you have any other thoughts or ideas? Thanks

 

[Bradda]

Sorry forgot to say didn't get any fault codes. Also couldn't see any problems with scv valve. I have replaced the scv valve about a year ago . Do you think the symptoms im getting now could be the scv valve?

 

[Old.Tony]

It sounds like the BCS is doing the right thing, so I don't think we need to worry about boost issues. It's gotta be something else.

The SCV is the next likely culprit, although given you've replaced it recently it's unlikely to be a problem now unless you've had particularly dirty fuel. It's worth a shot, adding a bottle of injector cleaner to the tank and driving it around, see if there's any improvement. If your engine is hunting at low RPM (idle varies, or seems to surge and relax repeatedly) it's probably your SCV.

It's also worth grabbing your primer bulb and squeezing it a few times (count the number of squeezes). After a run it should be only a couple of squeezes to make it firm, but up to 4-5 squeezes is fine. Keep squeezing after it gets firm and look around the fuel filter for leaks. Normally this part of the fuel system is very low pressure so diesel won't come out (but air will get in, and that's the problem) but if you over-squeeze the primer bulb you'll pressurise this area and spot the leaks. Mine did this because the mechanic failed to tighten the water sensor properly in my fuel filter, all it took was aligning the electrical connector with the knurled knob on the front which they hadn't done.

 

[[email protected]]

probably not the issue , but i managed to partially block the tail pipe with mud

 

[Bradda]

Should have said, I have replaced the fuel filter and bulb because I also suspected that could be the issue. I don't have any hunting or idle issues, the vehicle always starts first time, no problem there. It also doesn't go into limp mode. I will disconnect the exhaust from the Cat and give it a little drive to see if its blocked further down the exhaust but don't think it is. Also I don't get any black smoke but since removing the CAT I get a little bit of white or light blue smoke on start up but otherwise don't ever notice any when driving about. I havnt replaced the maf sensor but when doing live data on the vehicle I can see the figures and the seem realistic. The fuel pressure also climbs rapidly on demand and drops as you would expect. Im not sure if the figures are where they are supposed to be because I don't have any references to run off. My MAP sensor is the the one that has made pursue the boost area because at idle I would sit at about 110 kpi and shoot up to 250kpi on acceleration then drop out and I could feel the lag and surge when the figures where changing on the live data readings.

 

[Old.Tony]

Ok, the boost sensor should be on the intercooler piping (cold side). Add an earth to that pipe (just a wire from the battery negative to the pipe) and make sure the sensor's electrical plug is clean.

 

[Bradda]

Sorry Tony but do want me to to put a ground to the intercooler or to the sensor?

 

[Old.Tony]

The pipe that the sensor is on. It has to have a ground to work, it receives a positive signal from the ECU and returns a reduced positive signal to the ECU. The reduction is proportional to the pressure. My assumption is that the sensor won't function if it doesn't have a viable ground on its thread/pipe connection. I'm simply trying to determine if some debris may have interrupted the normal negative electrical path from battery negative -> chassis -> intercooler pipe -> sensor.

 

[Ukracer]

How did the issue get resolved?