General Multijet problems at low RPM

[clockworks]

Gradually working through the problems with my 2006 Dynamic Multijet, 105k on the clock

Fixed the earth fault that made the rear wiper come on when braking.

Fixed the blocked scuttle drains and sealed the screw, so the interior is now dry and the ECU doesn't get wet.

New clutch and slave cylinder, now works smoothly and pedal no longer squeaks.

While under the car, the mate who did the clutch checked the turbo actuator.

Just leaves what I hope will be the last problem - lack of power at low RPM. This is particularly noticeable when going up hills in 30 limits. I have to hang onto 2nd gear until the car is revving at over 3k before I change up. There is very little power below 2000rpm.
I noticed it today on a very gentle incline. I slowed down and pulled in between parked cars to give way to a van coming the other way. I changed down into 2nd gear, and tried to accelerate from about 1500 rpm. Took ages to gain speed. As soon as it got to 2000rpm, the car took off. Got some smoke for a couple of seconds as the power came in.

It's almost like it was overfuelling and flooding, then cleared it's throat and worked fine.

The car runs fine on the open road. No smoke, good power, equally happy at illegal speeds on the dual carriageway, or trickling along at 40mph in 5th gear. OBC is showing 69mpg average.
There are no fault codes now, but I did have a MAF error a few weeks ago which meant the car would barely pull away in first gear. Reseating the MAF plug and clearing the code sorted that.

What should I try next?

 

[Ralf S.]

Check for intake leaks, if it's flat and smokey.

I dunno if it's worth cleaning out the EGR valve too, although if yours was actually not working you'd get an engine management light... but my old JTD was full of soot.

If the car has been over-filled with oil, you might also have a load of oil vented into the inlet manifold and that would have polluted the MAP sensor (which measures the inlet manifold pressure). Have a nose around in the manifold and see if it looks tidy or like the inside of an oil tanker. MAP might be cleanable with contact cleaner.


Ralf S.

 

[clockworks]

No EML light, not even a flicker. Hopefully it's not the EGR, as that looks like a right pain to change.

It only smokes for a couple of seconds after I experience the low rpm/low power problem. At all other times the exhaust is clean.

I had the problem when I first bought the car a few months ago, and it still does it after having a full service.

Is the MAP sensor easy to get to?

 

[DaveMcT]

If the turbo wastegate is stuck open you'll get no boost until the engine is really pulling hard. However if the gate is stuck shut, the turbo will be over-boosting, causing the ECU to back off the fuel until the boost has crept back up, only to drop the fuel again when it over boosts yet again.

Both versions can can feel much the same to the driver. You'll need to see what the manifold pressure is to diagnose properly.

 

[Wee Smurf]

Keeping a watch on this as this is exactly the problem that I'm having with mine. 2005 with 150K miles on the clock.

 

[clockworks]

I don't think it's the wastegate, as it's working perfectly over 2000rpm. it's happy to pull well on both a light throttle or if I floor it. No hesitation, no smoke, all the way from 2000 to 5000 rpm.
It's also fine in normal town driving. It'll trickle along in top at 30mph, and pull cleanly up to 60mph when I reach the end of the 30 speed limit without having to change down - as long as I'm not going up hill.

It's just going up hills below 2000rpm, it's totally flat. Throttle position seems to have no effect on speed. Change down a gear and it will pull fine, with a bit of smoke for a couple of seconds.

I will check the wastegate myself though, as soon as I can get it up on ramps.
After that, I'll check the MAP sensor.

 

[DaveMcT]

The wastegate allows turbo to boost correctly at revs which would otherwise over-boost. If its not closing properly, you wont get much boost at low revs. If its not opening properly you could be over boosting with the ECU refusing to add fuel until the engine is spinning faster.

It needs further investigation.

 

[Kronkron]

My MJ only comes on song at about 1800rpm. I have a hill as I leave the house in a 30 zone and it's painful untill the car is warmwd up and 1800rpm is reached, otherwise I have to drop it down a cog to second gear which seems to aggressive for the 30zone. I just put it down to the character of the car and this particular hill not playing well.

 

[Wee Smurf]

For mine, it is only a recent thing having to drop to second to get up the steep hill out of work. It used to do it without any issue in third. Now it struggles most days.

 

[Kronkron]

Is it possible the viscosity of the oil in the cold weather maybe having an impact?

 

[DaveMcT]

It won't be the oil. You could run the oil dry and not notice until the engine is about to seize.

In the 90's I had a VW TDI engined Galaxy. With just 90 bhp on tap, it was slow so I went to have it chipped to 110bhp. It turned out the turbo was over-boosting and causing the ECU to drop turbo pressure. No wonder it was slow. After that was sorted and the revised chip fitted I had a MUCH better car. Fuel consumption went from 33-34 to 37-38mpg and even the kids noticed - asking why the car is not so noisy today. I was changing up at lower revs.

Brother had an Alfa 156 2.4 with variable geometry turbo. That got jammed with carbon (as they did). It would over-boost at low revs and refuse to accelerate then go like stick at the top end. He just lived with it but it was gutless below 2000 revs.

 

[clockworks]

I took the car on a 90 mile round trip yesterday, making 3 stops. Much of the journey was along country lanes, plenty of hills and sharp corners.

Weirdly, the car seems to have fixed itself, at least once it had warmed up. I could hang on to higher gears going up hills, and pressing the pedal actually made the car accelerate rather than die. No smoke at all. It was happy to pull strongly from 1500rpm up hill, rather than just lose power and slow down.

Seems like either the fault has cleared, or it only happens on shorter journeys when it's not fully up to temperature

 

[Wee Smurf]

I took the car on a 90 mile round trip yesterday, making 3 stops. Much of the journey was along country lanes, plenty of hills and sharp corners.

Weirdly, the car seems to have fixed itself, at least once it had warmed up. I could hang on to higher gears going up hills, and pressing the pedal actually made the car accelerate rather than die. No smoke at all. It was happy to pull strongly from 1500rpm up hill, rather than just lose power and slow down.

Seems like either the fault has cleared, or it only happens on shorter journeys when it's not fully up to temperature

With me, it's definitely a cold problem. When I leave the car-park at work, I have a steep hill to climb. Back in the day, I made it up the hill in third without issue, but I'm now struggling and have to drop to second and spew smoke over whoever is behind me to reach the top. I have another steep hill nearer home and by the time I get there, I don't tend to have as much hassle with it.

 

[Kronkron]

Agreed, my car is very sluggish in the cold until it has warmed up.

 

[clockworks]

I wonder what systems in the car could be causing this? Maybe dodgy glow plugs?

I must admit that I don't know much about glow plugs in modern diesels. On small "nitro" engines used in RC cars and planes, an external power source is applied to the glow plugs to get the engine started. Once running, the plugs stay hot and ignite the fuel.
Do the glow plugs in diesels stay "lit" in the same way, so a fouled or degraded plug could be good enough to start the car (and not give a warning light), but not work properly until the engine is fully up to temperature?

It does feel like a misfuelling or misfiring issue in my car. When it is playing up, the engine feels totally flat and lifeless at low RPM.

Or is there a secondary temperature sensor somewhere? The temperature gauge does go up to the middle of the gauge after about 5 miles or so, and it goes up a little more in traffic, down a little on the open road, so I assume that the primary temp. sensor is working.

 

[HP]

Glow plugs only work on cranking and for the first few seconds.


Original posters issue sounds like an EGR valve that's not closing properly.


Overboost would bring up the engine management light.

 

[DaveMcT]

Glow plugs only work on cranking and for the first few seconds.

Original posters issue sounds like an EGR valve that's not closing properly.

Overboost would bring up the engine management light.

My VW TDI never displayed the engine management light and I dont remember seeing it on Bro's Alfa. Agreed they were a good deal older but still fully electronic.

 

[HP]

Neither of which are Pandas or Fiats.

 

[DaveMcT]

The Alfa is a Fiat (by another name) and as already said, both were fully electronic. Turbo is under ECU control to adjust boost pressure and affecting the amount of fuel delivered. If it stays within normal parameters it wont raise a warning light but it will drop power if it keeps having to open the waste gate/vanes.

 

[HP]

The Alfa is a Fiat (by another name) and as already said, both were fully electronic. Turbo is under ECU control to adjust boost pressure and affecting the amount of fuel delivered. If it stays within normal parameters it wont raise a warning light but it will drop power if it keeps having to open the waste gate/vanes.

Smoking and lack of power at low rpm are classic EGR symptoms as can be found anywhere.