Loss of Revs and Power on Acceleration...

I was hoping someone here may be able share some insight into the current problem I am having with my Navara. It is a 2007 D40 YD25 126kW Manual 140 000K. EGR blocked 15000K, catch can fitted 5000K, 1 injector replaced 10000k ago with new fuel filter, new air filter and it has just been serviced 2000k ago with no issues until the past week.

Initially I thought it was a little down on power but had put that down to driving the Mrs' car around for the week proceeding and leaving the Nav in garage. We went out camping over the long weekend and a little bit of easy off road work which wasn't too challenging on the car and once again felt like it was down on power particularly when the revs were down low. However I really noticed that something was a miss today on the way when accelerating in 2nd, 3rd 4th and 5th was down on power but when I reached about 2400RPM (+/- 200rpm) and it may drop back on the tachometer to 2000RPM (+/- 200RPM) on flats and hills. It is worse in 3rd and 4th and seems to be more of a flat spot in 2nd. I went to over take a few occasions and when climbing some of the hills and noticed it wasn't taking off like it usually does. Brother in law was behind and said he didn't see any real amount of smoke from the exhaust during acceleration.

I have run the OBD2 bluetooth and Torque App and I have no error codes.

I have tried the loose fuel cap for the SCV.

Previous injector problem was smoke on start up and rough idle. It might be a little rough on cold idle at the moment but nothing compared to what it was previously.

I have had a quick look around the turbo hoses and actuator and it all appears normal there but plan to have a better look tomorrow when the sun is shining.

So I am pretty stumped with this one if anyone has anything to contribute please do.

Thanks in advance!

I would try a ECU rest to start with. This should be done on every fuel filter change anyway. If it's still there after that you will have to eliminate other possible causes like type of filter, genuine / non genuine, are all the o rings in place on the filter housing etc.
cheers, Brad

Thanks Navmania I have since tried the ECU reset with no change to performance.

The ecu reset will not change your issue why was one injector replaced and not the rest?, Just a guess before I get grilled (not by you) you "may" have a weeping injector ie not firing the correct amount of fuel in one or more cylinders.
HJ

I had a loss of power. Some of the others on here suggested the neutral balance sensor for my issue, mine was fine but maybe that could be your problem?

her.d22 said:

I had a loss of power. Some of the others on here suggested the neutral balance sensor for my issue, mine was fine but maybe that could be your problem?

Click to expand...

That'd be the "nuetral position switch"

Rumpig said:

That'd be the "nuetral position switch"

Click to expand...

Yeah, that's the one!

Nps hasn't really appeared to be an issue on d40s..

I'd give the turbo actuator a good look. Try some contact cleaner on the maf sensor, just to make sure thats nice and clean.

Was the fuel filter genuine or aftermarket? Scv could still be at fault too, I am pretty sure people have done a how to on pulling it apart and cleaning it, so that's still worth a look...

Thanks for the suggestions guys.

I have tried the loose fuel cap and that didn't make a change to performance either so I believe that can rule out the SCV.

I did the MAF sensor clean about the same time the last injector was replaced. I only had one replaced because Diesel Australia Tested them and only found 1 was faulty. The fuel filter was then replaced at the same time by them with a Ryco filter (Z711).

Funnily enough I also had the neutral position switch go in January this was 2 days after getting the car from the Father in law and driving from Perth to Brisbane. The side effect was no cruise control for the trip but it was a quick and inexpensive fix when I got back thanks to Nizzbits.

Thursday afternoon I plan to have a real good look under the bonnet and see what is happening and I will try to get some footage of what the tacho is doing and put up a link. It actually looks and feels like the car is shifting up a gear which is a pity because it is a manual...

It sounds like either a unreported (no error code) limp mode. If it were a turbo problem you'd get a considerable amount of smoke. Turbo issues are usually an actuator failure which is more often the vacuum hoses or the vac solenoid, on two occasions users reported a faulty brake booster. If your brakes are spongy check that, if the actuator arm during engine idle isn't moving 3-5 mm then it's vac hoses or solenoid.

I'm still wondering about the SCV because of the lack of smoke. The fuel cap trick doesn't always work and the problem came back in Beergutz's car where we tried that (it worked for a little while).

The SCV could be dirty, restricting flow. Try a bottle of Liqui Moly Injector Cleaner - it's under $30 from Supercheap and it works miracles. If that doesn't work, we've had a couple of people remove their SCV to find actual debris in it, cleaning it fixed the problem.

As above, Old Tony is right. I tried the fuel cap trick and well...it didn't work...not even once!

In the end it was still the SCV. Go get it looked at. Skip all the BS dealerships and find someone with extensive experience in diesel engines. I found out these can be serviced/cleaned and not always requiring replacement, mine was fixed an hour or so after dropping it in and it hasn't skipped a beat since! Total cost..like $200

Drove like a new car after that. was amazed at the change

Thanks for the further input.

I am going to explore the SCV in more detail and report back with the findings. Given that they are a substantially cheaper fix than an injector I am hoping we are on the right track...

Cleaning it is next to free. That's what I'd do first.

Sorry Old Tony I only just read your reply. I have already installed a new one and done an ECU reset it has seemed to improve the engine idle however the problem on acceleration still persists.

After doing some more reading on the topic and driving around trying to describe the problem could be perhaps be better labelled as a surge from 2000rpm until about 2500rpm. At 2500rpm it is accompanied by a flat spot in 2nd and a loss of revs in 3rd, 4th, 5th and 6th. This loss of revs from 3rd up is in the vicinity of 400-500rpm so down around 2000rpm (+/- 200rpm). After this first loss of revs the car then builds again but is sluggish.

So I think I can now rule out the SCV however I am at a loss about what to look at next. The OBD2 still isn't reporting anything but this ECU didn't report anything to Nissan when the Cruise control was stuck on and was unable to be engaged with steering wheel controls or the brake....

This sounds like a possible Neutral position switch issue. (NPS). Next time it happened try puling/pushing the gear lever across the gate to see if things improve.

If it was a D22 I'd agree with the NPS. There haven't been many reports of faulty NPS in the D40s, but there's always a first time eh!

By all means try moving the gear lever around to see if it makes things steady up. If it works, you may be up for a new NPS.

Only other thing I can think of is a fault in either the turbocharger or its control system (actuator, vac hose or vac solenoid). You won't get any codes if there's a vac leak in either the hose or the brake booster (shares the vacuum from the pump on the right hand side of the motor near the oil filter).

Thanks again for everyone's input on this thread. As I haven't had much exposure on mechanical things in the past I have learnt a great deal and I am willing to give some things a shot...

I did have my Neutral Position switch fail in Jan this year and it was replaced in Feb the symptoms then was only that I didn't have cruise control but no loss of revs then. Just went for a drive then to try and move the gear stick around and there isn't any difference when I push it to the passenger side (the side I used to determine that as the cruise control fault) also nothing when pulling to the driver's side.

I will have a look at the actuators again and double check all my turbo hoses. I have just redone the MAF clean to see if that does anything.

Have done a few nps on d40s here but Scv are more common. Can you log / see boost/fuel/tps?

Thanks for the question I have the OBD2 Bluetooth adapter and the Torque App for android. I can see boost and a few other parameters.

check your vacuum lines, the lines in my 2007 where getting the age cracks and were leaving black residue on my fingers when i touched them, in the end i replaced the entire lot for less then 15 bucks, fixed my problem

when i replaced them they where hard and brittle and one had a circumferential split, it would have definetely been leaking,

also definetely recommend at least draining the fuel filter into a bucket, and seeing what comes out, mine was full of sand 15k after replacement, its will only cost time