General Multijet problems at low RPM

[varesecrazy]

To fully answer clockworks

Glowplugs..
Similar to RC nitro engines:

The plugs glow cherry red for a few seconds.. under electrical power.

Then the heat of combustion should also keep them warm enough.
However there are 2 main differences.

By design Diesel engines are 'Compression Ignition'
As long as there is enough latent heat in a cylinder the action of compression should be enough to burn the fuel mix
(Thats how you can get it running on EasyStart spray )

But. Instead of a needle in carb primitively controlling fuelling..

You have an array of sensors giving live feedbsck.. and making adjustments accordingly

The other BIG consideration..
You have 4 x individual cylinders.. if one is COLD by nature .. the good 3 have to drag it along until HOT

I have 2 old mj puntos.

One has bad glow plugs.. not happy this weather

The other flashes the warning symbol after starting.. and is a bit lumpy for 1st couple of minutes..
After an hour at 2400 rpm it runs REALLY strongly.

Start with the basics.. heat in cylinders

Then the basic sensors.

Unfortunately.. the engine management will work hard.. masking a lot of the obvious signs..

 

[clockworks]

Short drive today, didn't seem as bad on hills as it was last week. It did stall when I dipped the clutch pulling off my driveway. Very cold this morning, and I pulled away as soon as I started the car, so it had only been running for a few seconds. Restarted OK.

Could it be the glow plugs? Do they come out easily? Heard plenty of horror stories of stripped head or snapped plugs on other engines.


Is there a decent guide on removing the EGR anywhere? Looks to be tricky to get at.

 

[DaveMcT]

Glow plugs sometimes come on while a very cold engine is running but normally they should operate only on startup.

Slightly off topic - I found this on the DPF subject. He talks about how upstream issues can kill the DPF. But the same issues can cause many of the problems in this thread.

 

[Wee Smurf]

We don't need to worry about DPFs. Our cars don't have them fitted.

 

[clockworks]

Car died pulling off the driveway again yesterday - engine just stopped as I dipped the clutch while turning to get around my opposite neighbour's car. No shuddering or anything, just stopped running. Restarted straight away, and was fine for the rest of the journey. It was fine when I drove back from the shops.

Next time I go out, I'll start the engine before I put my seatbelt on, leave it idling for 30 seconds before pulling away. See if that makes any difference.

It is looking like a temperature-related problem.

 

[DaveMcT]

We don't need to worry about DPFs. Our cars don't have them fitted.

Yes. I did say that.

BUT he explains the upstream issues that will kill a DPF. Those very same and common issues will cause problems on "normal" engines. (air leaks, oil leaks, EGR, etc)


The random stopping just could be the crank position sensor. Normally they are worse when hot, but it could be a bad wiring connection. It will not show as a fault on the ECU.

 

[madalinV]

Hi Guys,

I am also interested in this topic. I have a Punto mk2.5, mk year 2004, 1.3 multijet 70Hp, Robotised gearbox.

I have a similar issue, which went away for a while, then came back.
The car has a new"ish"(one year old) MAP sensor. The glow plugs are new (6 months).
Had this "no power at lower RPMs" issue for a year now, but did go away at a certain point for 1 month for example.
Changed in November 2019 the MAF also, and the issue seemed to go away, but in all honesty I don't know if it was from changing the MAF or not.

Anyway, the issue is back, and is more noticeable with the cold engine. From 1000 to 2000/2200 rpm no power at all, pedal to the metal and nothing happens, then at 2200 RPMs or higher, "rocket mode" is on, the car just feels like having 200HP.

Some small observations on MultiECUscan: with the car not moving, engine at 2000 RPMs, constantly for 2-3minutes or more: I have "Boost pressure" 1004 mbar(so atmospheric value) and "desired EGR position"= 99.97% with "EGR duty cycle" = 66.67% .

Any ideas?

Thank you!

 

[DaveMcT]

You need to read the actual boost pressure. Then you can work out when and how much the turbo is delivering.