Any of you diesel drivers find that your vehicle can perform differently – noticeably differently from day to day and do you know why?

I’ve noticed it with every diesel I’ve ever had, but moreso with the current one (190bhp 2.5l Nissan Navara). Some days it feels really laboured and struggling, yet I can get in it the next day, or even hours later and it zips along. Better throttle response, smoother power delivery – almost feels like 20bhp difference

Every diesel I’ve ever owned (and that’s a few) wanted a good warm up before it felt at its best. “Laboured and struggling” sounds a bit strong but I can appreciate what you’re getting at.

Any of you diesel drivers find that your vehicle can perform differently – noticeably differently from day to day and do you know why?

Nope. Definitely sounds like a fault to me.

Also never had an issue with cold driving. It’s noisier when cold, but still drives the same.

I have no proof or science, but my diesel always feels like it’s down on power (as you say, it feels a bit sluggish) when the weather is cold & damp.
EDIT – Not a massive amount, but just like the edge has been taken off.

Pertty sure the manual says something about full power may not be achieved for several minutes after starting from cold….

Navaras are known to be rattly old tractors but the injector rattle is something to behold on this thing. Goes into limp home mode occassionally too, but as it isn’t throwing up any fault codes Nissan don’t really seem interested in finding the problem.

Years ago I had a company Xantia TD, and that seemed to go through phases just as you describe.

Also my wife’s LR does, but it’s usually connected to whether the engine is warm or not.

I do 500-1000 miles a week so know it’s not a cold engine problem.

Stumpy – does seem worse in cold damp weather

You shouldn’t really be driving hard until the engine oil has warmed up. The oil is very thick and will reduce turbo and other component life drastically.

If its a turbo car there will be a fair difference in power between hot and cold days, the colder denser air should add performance though not reduce it.

Hmm.. replace the MAF?

Also never had an issue with cold driving. It’s noisier when cold, but still drives the same.

This. My diesel always feels the same, even when it’s running on unleaded 🙂

That depends, if it feels laboured and struggling continuously I’d suspect something up but if you mean that you put your foot down and the result doesn’t feel as strong as it sometimes does, then yes my 530d is a bit like this. As were the two Impreza turbos that preceded it. I’d put it down as a turbo thing rather than a diesel thing. I could be wrong but I reckon that it is the combination of three effects. First, the actual turbo only gives it’s best once it’s thoroughly warm and has been worked, this is noticable if you have a tuned turbo petrol car rolling roaded, they usually need at least one full beans blast right through the gears to get the hot side of the turbo properly hot before they give peak power. Big turbos sometimes need more than one. So if you have been driving for a while and the enigine is warmed up but the turbo hasn’t been exercised hard the first blast of full beans may not be as dramatic as you expect.
Second, because turbo engines almost always run rich on full boost they are sensitive to air temperature and density as colder, denser air will contain more oxygen to burn more fuel, this affects N/A engines too but compressing the inlet charge magnifies the effect.
Third, the temperature of the air affects the efficiency of the intercooler, which in turn affects the efficiency of the combustion process.
Diesels are additionally affected by how recently they’ve been worked hard, a good blast will clear soot out of the inlet tract and exhaust and help things along.

cheep diesel?

Never drive it hard with a cold engine

robinlaidlaw – cheers for long reply, some food for thought.

As for cheap diesel, nope – always use premium.

Just had a major service too – actually seemed fine for a fortnight after, but then back to being temperamental.

*Goes off to Google MAF

Mass air flow sensor, im not sure whether the temp affects that though.

There is possibly an inlet temp sensor that could be goosed?

I was thinking intermittent electrical connections on some sensor or other, causing the engine to think conditions are different to what they are randomly. The reason I thought of MAF was that if it had a bad connection somehow and it was over- or under-reading, it would change the throttle response and possibly the maximum power. Damp weather could affect electrical connections, which could also improve when the engine’s warmed through.

I’d suggest keeping a log of when it feels sluggish, what sort of MPG you were getting and what the weather was like. Couple that with a log of when and where you fill up and what driving you do, and you can correlate that with incidence of long journeys and also see if there’s any link to fuel.

<STW level of usefulness>
Sounds dodgy – have you checked the points?
</STW level of usefulness>

But seriously, yes absolutely. My non-blown rattler transit demonstrated it best, because there was just the right hill on the way out the village. Drive straight from home and up the hill and it was embarrassing. If for some reason I hit the same hill with a warm engine it was… Considerably less embarrassing, it could hold third instead of second anyway.

Cold weather makes diesels more powerful as the air is more condensed and warm weather makes it less powerful but more economical. This is what you MAF sensor measures so the ECU can calculate how much fuel to squirt in for the volume of air.
Clean the MAF with some IPA to ensure the wires are free from crud. Have you serviced it recently and was the fuel filter changed as these can make the engine sluggish.

I’ve also got the 190PS 2.5L Navara. Mine def differs depending on the temp. really cold mornings it sounds like the engine’s **** for the first few hundred yrds. Overall compared to the previous 2L Mondeo diesel estate, it sounds like a 1970s diesel.

Navara is 4×4 right?

Feels off and sluggish to start then hours later feels alot faster?

Possibly very cold and viscous fluids in the gearbox and transfer box and the diffs. Combine this with cold bearings in the hubs and cold engine oil then thats one possible explaination.

As you drive the cold and damp airflow will keep temps down , and maybe the thermostat is a little tired as well . when you stop the heat will ‘soak’ some the air cooled bits and bobs through to a better temp .
Try a cover over 1/2 the rad or maybe more ( keep a close eye on the temp guage though )

New fuel filter , and maybe clean out the EGR forward to inlet manifold as milage can gunk up these badly.

Mine used to dislike diesel from certain garages.

The Mighty Vectra has off days as described in the OP. It is happiest when it is cold and dry.

If it’s just a bit of a difference day to day then differences in air density can be noticeable on turbos, if its a new car then imo the accumulation of crap in the dpf and where in its cleaning cycle it is can be felt.

Right – it’s nothing to do with how long it’s been running. Can be horrendous at the end of a long journey.

Today it’s running fine, tomorrow it might not be.

Full 36k service recently with all filters changed.

I’ve only been filling up on Shell V Power lately.

One thing it was doing last week – Sat at 2k revs with foot only slightly resting on accelerator. Gentle pressure on accelerator and feels like a flat spot with not a lot happening. Floor it and it goes but feels laboured. Today, even the slightest change in the accelerator – instant pick up!

Dirty or **** TPS then

’11 plate euro 4 = no dpf

Does seem to like cold dry days i.e. today

What’s a TPS?

What do the fault codes say? On lots of nissans you don’t need a diagnostics reader if you google manual fault code … You might be lucky…

Could possibly by a fuel pump suction valve…. Which are available as a spare part…. Most dealers won’t tell you that and will want to sell a complete pump…..

I’ve reset the ecu as read on a Navara forum. Codes (if any) should come up at the end – nothing. Nissan also saying no fault codes.

Goes into limp home mode occassionally too, but as it isn’t throwing up any fault codes Nissan don’t really seem interested in finding the problem.

mine does this, only 5 months old, has been back into the main dealer 3 times, they’ve tried to fix it with a software upgrade and it’s still a poo bag. Seems to like going into limp mode when on motorway slip roads which is fun to suddenly have cock all power, also does it after a long drive, if it’s switched off and then you start again. It’s back again for a week for a full investigation and re-build I’ll let you know what they come up with.

Thank god it’s a company vehicle so it’s only costing ,me time to cock around taking it back to the dealers etc…

so far I don’t think it’s going last the 4 years I’ve got it for and the sort of use it’s going to get. 😕

TPS = Throttle position sensor

It tells the ECU that you have put your foot down . The ECU then sort of cross references engine speed to load index and airflow via the MAF. This gives a time value for the injector pulse timimg.
The injector is just a solenoid connected to a high pressure fuel rail and a few milliseconds will let some fuel into the engine.

If the TPS is borked then the ECU wont know correctly you have pressed the accelerator pedal and therefore wont squirt in enough fuel. Can be cleanable with trike. .

I should have believed what I read about Navaras. Looks nice, drives nice (sometimes), has every single toy you can think of, is a temperamental piece of poo!

Not 2 years old yet. I bought it 10 months old with 7k on the clock – so far: both folding mirrors failed, limp mode, pop-up headlamp washer failed, sat nav/media display screen goes blank occasionally, 4wd selector switch appears to have now failed – keeps coming up with 4wd lo engaged on dashboard.

Previous Ford Ranger – 5 years old, 85k – never missed a beat!

Every vehicle I’ve ever owned, including the pushbikes, seems to perform differently day to day. It’s because my judgement is erratic.

Could also be linked to wastegate actuator .
Next time its doing its impression of a S1 Land rover turn the radio off. Listen hard for turbo whine / whistle . Should come up from 1500rpm ish , then get louder to around 2000 rpm. Above that the whole assembly is spinning so fast the frequency is too high to hear.

Will sound alot louder driving next to a wall or ina tunnel.

Not sure if the Navara will have a VVT turbo , but if the vanos actuator isnt working properly or has an intermittant fault then it would drive like a bag of plop . Can you see the turbocharger without taking half the engine to bits?

Ford Ranger is a Mazda B2500 btw