Poor Torque At Lower Revs

[Frank M]

Hi People!

I'm Frank, I'm new to the forum ... in fact never been on any form of forum before .

I've got a 2007 Avensis TR Estate, with the 93kw 2.0 D4D engine. Generally been really happy with the car, its done 115,000 miles and we've had it for 2 years. We don't use it a great deal - probably 5000m a year, and generally for journeys of around 8 miles or less. Summer just gone we loaded it up and drove down to Cornwall covering around 1500miles in 2 weeks. Never missed a beat.

So here's the problem... A few months ago, and possibly unrelated it had a period of being difficult to start; needing a couple of goes before firing properly and then puffing whiteish smoke briefly after start. A while later I noticed it was lacking power at low revs. A mile-long 30mph hill just before home, it would have easily done in 3rd gear now required regular drops to 2nd to keep momentum. On turbo (say over 2000rpm) it picks up and goes great but off the turbo there is a lack of torque and it just feels 'flat'. Pulling out onto roundabouts etc is hard work and requires revs and clutch riding to move smartly. Fuel economy seems fine, motorway cruising is fine, batting up a long fast hill is fine so long as revs are up. Oh, and the starting problem seems to have cured itself.

So here's what I've done:

1, Cleaned EGR valve: this was VERY coked up as was the manifold. The valve seems to be working fine now but it did not alter engine performance.

2, Connected EOBD reader - no codes listed. (Engine management light not on).

3, Ran the engine with the MAF disconnected. This was recognised by the engine management but made NO discernable difference to the running of the engine.

4, Thinking maybe the MAF sensor was out of spec I bought a new one. This new one however threw up the engine management light which would not clear; either it's a faulty sensor or incorrect model. With the old sensor fitted the EOBD reader seems to graph nicely the air flow so maybe there was nothing wrong with it :(

Is there anyone out there got any ideas? Does this sound like a MAF sensor problem (I'm not sure whether to ask for an exchange or a refund)? How about the o2 sensor? I cannot see any air leaks, split pipes etc. The air filter is new and clean. (Were it poor air-flow I'd expect performance to get steadily worse as the engine revs, similarly with blocked exhaust etc).

Pulling my hair out and I've not much of that left ....

[Awebb180]

First try would be fuel filter depending on when that was last changed. Is it using any coolant?

Alex

[Druid Boy]

Yep, fuel filter change is a good thing to do. The other is to treat her like a bad girl and rev the nuts off her for a while, 1, it re-educates the ECU, 2, increased flame propagation through the exhaust ports can clear deposits from places you can't get to.

[Frank M]

Thanks for the replies Alex and Druid.

Someone suggested to me a while ago to check the fuel filter; I dismissed it as an option and never checked it as I assumed this would !Removed! performance at the higher end ... it revs fine and pulls like it ever did on turbo so I dont really understand how that would cause the symptoms I've got .. but I'm not too well up on modern diesels!

Will try revving it more (like a bad girl ) tomorrow and will let you know how I've gone on.

Thanks again guys!

[Frank M]

Oh, sorry Alex, no its not using coolant.

[JAPCAR]

Frank M, my engine is the same and I've got similar symptoms as yours which I've mentioned in other topics... The difference is short knocking under load when low revs (1000-1300). I can simulate/describe it this way:

Accelerate on 2nd gear and take away foot from pedal until revs drop around 1000. Push harder pedal to accelerate- here appears short (1-2sec) sharp knocking which instantly disappears above 1300-1400 revs.

Never ECU errors recorded.

Till now I've done:

-all filters new

-EGR cleaned (tried temporary blank it as well)

-MAFcleaned (can't be sure if it's good working)

-SCV cleane (can't be sure if it's good working)

-BG244 treated + V Power fuel

-"Italian tuning"

No changes, still happens now and again...I missed to mention it happens not always but generally low revs torque is not satisfactorily for me despite this is my first diesel and my criteria may be wrong.

Techstream diagnostic showed 4th injector always is (-0.4 to -0.7), other three around 0 (+/- 0.3) which I think is no so bad...

I don't know what else to check...

Probably is good, somebody else with good engine to make above test and share here results...

[Frank M]

Hi Japcar, no knocking in my case, interesting lines of investigation.

Druid Boy, drove it hard today, revving low gears as hard as I dare (visualising shredded cam belt )

..... no change ... but it did feel good doing it!

Will inspect filter as soon as I get time and report back.

[Awebb180]

Pretty sure its got a timing chain not a belt. You could also try cleaning the MAF as well. make sure hoses are all tight and in good condition ie intake pie/ vac lines etc

Not to derail the thread but JAPCAR yours sounds a bit like your loading the engine too much. does it happen in the gears under lows revs/full throttle. Its sounds like injector knock. If you lightly press the accelerator I take it the noise isnt there?

Alex

[JAPCAR]

jkl

Not to derail the thread but JAPCAR yours sounds a bit like your loading the engine too much. does it happen in the gears under lows revs/full throttle. Its sounds like injector knock. If you lightly press the accelerator I take it the noise isnt there?

Alex

No, I am calm driver and always my manner is the same but it happens not always...Never use full throttle, I drive as I am use to do for years(but this is my first diesel car).

When is cold outside, I can hear injector noise is different then in warm weather, but knocking is different, like detonation knocking of a old petrol engine.

If I am careful and press accelerator lightly I can avoid it ( when it's prone knocking).

Anyway, I think AD engines are prone of this knocking when outside is cold and injectors are slightly worn out...

Today as walking on the street , slowly passed Toyota Verso 07 plate and I heard the same knocking...

BTW when bought the car I thought it is DMF on his way but still I thing it's engine.

[Frank M]

Hi guys, sorry to have left it so long to report back. So, today I finally replaced the fuel filter. The one I removed was a genuine Denso/Toyota, it was a little contaminated but not badly so. While it was off the car I took the opportunity to thoroughly check the pipework in that area for splits etc. but nothing evident. New filter fitted, bled and I went for a drive..... and .... no change

As ever, its fine on turbo but just no torque off turbo. I cleaned the MAF with dedicated cleaning spray a while back but can't help suspecting this sensor is the problem. As you'll all well know though, the cost of a decent replacement is prohibitive unless I can be sure it is this at fault. The alternative I suppose is to take it to Mr T to diagnose.

Any other suggestions, no matter how unlikely, would be really appreciated. Are there any other sensors I should look at? Knock sensor?

Modern engines are just too damn complicated!

[Devon Aygo]

Take your EGR back off make sure it is clean then take a torch and shine through the EGR valve and look for light coming through where the valve actually seats, if you can see any light coming through the valve it is faulty and not fully closing this will cause a lack of low down power

[JAPCAR]

Hi guys, ......................

Any other suggestions, no matter how unlikely, would be really appreciated. Are there any other sensors I should look at? Knock sensor?

I don't think D-4D engines have a knock sensor but let somebody else to confirm.

[Frank M]

Thanks again for the rapid responses guys. The EGR cleaned up well, it had a nice smooth action and yes, it closed completely and seated nicely. (The low torque symptom was completely unchanged from the EGR being completely blocked to cleaned out).

[Frank M]

Update...

Finally bit the bullet and bought another MAF sensor. Genuine Denso this time rather than the much cheaper pattern part I bought originally.

RESULT!

Torque and throttle response restored. Interesting side effect is that the engine warms up within a couple of miles now instead of the previous 5-6 miles. Had put this down to duff 'stat but it would now seem to be the fuelling issue was running it cold.

Thanks again for the advice and interest people!

[JAPCAR]

Update...

Finally bit the bullet and bought another MAF sensor. Genuine Denso this time rather than the much cheaper pattern part I bought originally.

What's the price of genuine MAF?

Interesting, what's the relation MAF- worming up. When I bought this car I noticed wintertime full worming was in 5-6 miles. I thought termostat is faulty but somebody told me it's normal for diesels because of better efficiency then petrol engines. I don't think I can achieve 2 miles full warming up even summer time.

Let other diesel owners share what's normal worming time at cold weather.

[Frank M]

Hi Japcar, MAF bought via eBay from a company in Stoke-on-Trent a2zmotorspares at £75. (eBay item 300667022326)

When I say warm up in a couple of miles I mean decent heat coming through to cabin - this has been a real pain in the colder months as demisting etc has been non-existant for the first 10-15 min of any journey, warm up time is much quicker now. Full engine temperature now reached in probably 3-5 miles - the last few months its struggled to reach normal running temperature at all and putting cabin heating on high you could watch the engine temperature fall away! I can only assume this was some side effect of the incorrect fuelling...

I was told by a2z that the ECU may need reprogramming on fitting a new MAF; its thrown no fault indication and seems to be running great though, any thoughts? Calibration required?

[JAPCAR]

OK, I meant engine warm up, I haven't problem with cabin temperature. Obviously slow warm up of diesels is normal.

Sorry, I don't know if new MAF needs reprogramming, probably you need to get info from Toyota dealer.