NP300 D23 - lack of power

[vivasjm]

Hi guys, I'm really frustrated with this situation. My truck is under review since January with an specialist and he can't find the issue. The situation is that in 3rd, 4th, 5th and 6th gear when you push the accelerator to the bottom revs doesn't go over 3800 rpms, some times I get 4000 rpms far from 4500/5000

I replaced both solenoids, cleaned up the MAF, check NPS, the mechanic check the turbo and everything looks fine. Any idea? I'm not sure what else I can check

 

[Old.Tony]

So that we're clear: if the gear lever is in any position on the far left, the engine revs properly and has full power, but in any other gear it has limited power?

If so, it sounds like the NPS might be functioning in those gears but not in higher gears. Could you try driving it with the NPS disconnected? If that improves things, then there may be an issue with the NPS (worn tip?).

 

[vivasjm]

I didn't tried to drive with NPS disconnected but some time ago I removed and test it with a multimeter and was working fine, the CC is also working fine.

Obviously has higher the gear the lower the revs, the weird thing is that if I accelerate progressively sometimes I reach 4000rpms but I push the accelerator to the bottom I barely get 3500/3700. My feeling is that something is limiting the turbo boost

 

[Old.Tony]

I didn't tried to drive with NPS disconnected but some time ago I removed and test it with a multimeter and was working fine, the CC is also working fine.

Obviously has higher the gear the lower the revs, the weird thing is that if I accelerate progressively sometimes I reach 4000rpms but I push the accelerator to the bottom I barely get 3500/3700. My feeling is that something is limiting the turbo boost

Yes, and usually that's the NPS which, while it might test ok on a bench, and is obviously working in the lower gears, perhaps it's just not quite making a full connection in the other gears (it's a possibility, anyway).

The ECU generally controls the boost and won't allow much boost in neutral or reverse. Since the switch is "OFF when NOT in neutral", testing it by disconnecting it is a really easy, quick and cheap way to determine if that's the issue. Because it's cheap to check and it's a common issue in some models, it's always a first go-to for problem solving.

It's also a good place to start if the problem is only happening in certain gears, as in this case with the gear lever only on the left side, not in the middle or right.

However, if it's not the NPS or an issue in the gearbox, there are other things to go and check (intercooler, charge air hoses, EGR and more).

 

[vivasjm]

Yes, and usually that's the NPS which, while it might test ok on a bench, and is obviously working in the lower gears, perhaps it's just not quite making a full connection in the other gears (it's a possibility, anyway).

The ECU generally controls the boost and won't allow much boost in neutral or reverse. Since the switch is "OFF when NOT in neutral", testing it by disconnecting it is a really easy, quick and cheap way to determine if that's the issue. Because it's cheap to check and it's a common issue in some models, it's always a first go-to for problem solving.

It's also a good place to start if the problem is only happening in certain gears, as in this case with the gear lever only on the left side, not in the middle or right.

However, if it's not the NPS or an issue in the gearbox, there are other things to go and check (intercooler, charge air hoses, EGR and more).

I did the NPS test and same results.

Looks like the ECU (or something else) when reads Turbo boost over the standard reduce the RPM to protect the turbo/engine. My mechanic reduced the turbo boost presure and RPMs goes over 5000RPM if he increases the turbo pressure RPM don't reach 4000RPM.

So the question is how do I increase the turbo pressure and remove this "protection" limit? the guy who did the ECU remap told me he raised all limits to the sky but still happening the same. Any clue on how to resolve this?

 

[Old.Tony]

Your guy knows more about the ECU mapping than I do (I don't do any ECU editing). There'll be a routine in the ECU that does this protection, but I'm not sure that needs to be removed unless you're trying to overboost the engine. This can be done - there was one guy on here using about 36psi of boost - but he would have had a completely custom ECU. Under normal operation you should be able to get decent revs with normal boost.

That means there could be something else at play here, like something in the other sensors causing an issue with higher flow rates. I'm thinking of the MAFS particularly - it monitors air flow - and the boost sensor. Neither, to my knowledge, have anything to do with the gear chosen and the only reason why there's any influence from gears is when the vehicle is NOT in gear (hence the original assumption that something must have been wrong with the NPS). Cleaning the MAFS would be my next step here.

However, I am not sure about revving the engine to 5000rpm in top gear. At this speed, a YD25 on stock tyres should be doing around 230km/h (which it probably can't since bricks need a bit more than a 4cyl diesel to go that fast). Stock tyres aren't rated for this speed either - you run the risk of blowing them apart at speed.

Are you using this vehicle on a race track?

 

[vivasjm]

Your guy knows more about the ECU mapping than I do (I don't do any ECU editing). There'll be a routine in the ECU that does this protection, but I'm not sure that needs to be removed unless you're trying to overboost the engine. This can be done - there was one guy on here using about 36psi of boost - but he would have had a completely custom ECU. Under normal operation you should be able to get decent revs with normal boost.

That means there could be something else at play here, like something in the other sensors causing an issue with higher flow rates. I'm thinking of the MAFS particularly - it monitors air flow - and the boost sensor. Neither, to my knowledge, have anything to do with the gear chosen and the only reason why there's any influence from gears is when the vehicle is NOT in gear (hence the original assumption that something must have been wrong with the NPS). Cleaning the MAFS would be my next step here.

However, I am not sure about revving the engine to 5000rpm in top gear. At this speed, a YD25 on stock tyres should be doing around 230km/h (which it probably can't since bricks need a bit more than a 4cyl diesel to go that fast). Stock tyres aren't rated for this speed either - you run the risk of blowing them apart at speed.

Are you using this vehicle on a race track?

actually you are right, today I test to revs up in 2nd, 3rd gear and happen the same, it don't go over 4000rpms. I did a MAF cleanup with a circuit cleaner but still the same, I will resarch on how to test the MAF, not sure if possible.

I have 275/65/18 tyres, but I don't want to get 5000rpm to go fast in highway, I use my NP300 on sand and sometime you need to reach those revs to clim a large dune. Today when I reach 3800/4000rpm the engine just stop of generating enough hp/torque it just keeps the revs but if you are climbing a dune you need to go back and start over.