Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy | Technical matters | Back Room Forum

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Fri 8 Apr 2016 01:32

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Peter.N.

I recently bought this car in very good condition and very well maintained, it drives like a dream but is only averaging 37.7 mpg, the one I replaced it with was doing 50-60mpg and my C5 with the same engine is doing around 50 mpg.

I have disconnected the EGR, fitted a replacement MAF, the one off the other car, and fitted a new thermostat to no avail.

I was hoping I would find that the cam belt was a tooth out as it has recently been replaced but according to my PP2000 reader shows 'camshaft and crankshaft synchronised - yes' is this a guarantee that there is no error?

I have done a leak off test on the injectors and they are all pretty well matched. The car is slightly down on power but does not smoke.

I have run out of ideas, can anyone help?

Thanks

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Fri 8 Apr 2016 09:38

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - hardway

Injector correction value figures from the PP?

And a compression test wouldn't be a bad idea.

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Fri 8 Apr 2016 13:57

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Railroad.

There could be any number of reasons for poor fuel comsumption, but if the engine runs well it's difficult to see what might be wrong with it. It doesn't smoke excessively you say, well that should tell you that there's not much wrong with combustion, and so the engine is drawing air and injecting fuel in more or less the correct proportions and at the correct time. You did say it's slightly down on power. A small valve timing issue could be the fault and as Hardway says, a compression test should pick that up.

Can you use PP2000 to measure expected airflow against actual airflow, and the same for turbo boost pressure? I'm not familiar with the Peugeot system, but you can with VCDS for VAG vehicles.

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Fri 8 Apr 2016 15:13

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Gibbo_Wirral

I have a similar car Peter. I've had a few Pug 307s, 2L 90bhp diesels, all Mk1 (2001, 2003, 2005). All bar the current one could easily get 550 miles out of a full tank. But this one will barely do 500.

And its the first one which won't drive smoothly at 30mph in 4th gear, it must be in third.

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Fri 8 Apr 2016 16:40

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Peter.N.

This isn't even a small loss of consumption it only doing about 60% of the other one and the C5 with the same engine.

Boost pressure showning about 1400 mb on the PP2000 and I have taken the inlet hose off and felt the pressure and it nearly blows your hand off.

Injectors read at 803rpm: 0.59, -0.67, -0.98 and 0.98

At 1960 rpm: 0.27, -0.98, 0.27, 0.98.

I don't know what these figures mean, can anyone help. Thanks

It does say that the crankshaft and camshaft are synchronised, would it know if it was one tooth out?

Edited by Peter.N. on 08/04/2016 at 16:41

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Fri 8 Apr 2016 17:07

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Railroad.

If the valve timing was as far as one tooth out the drop in performance would be very noticeable. One tooth is a long way out. Valve timing is all about the correct respective positions of the crankshaft and camshaft, or more accurately the piston and the valves. The valve timing could be less than one tooth out because on most diesels the shafts are not keyed to the pulleys. The shafts must be locked in their correct positions relative to each other whilst the belt is tensioned correctly, and then the locking devices removed. Any other method could mean the engine is not correctly timed.

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Fri 8 Apr 2016 19:56

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Peter.N.

The shafts are keyed although there is an adjustment on the camshaft pully to make sure the belt is correctly tensioned but I doubt that it would ammount to one tooth.

The difference in performance is mainly noticable on hills, the other car would pull up the Axminster bypass at 60 mph but would then accelerate a little if you floored it, this will just hold 60 with your foot on the floor.

The most noticable difference in fuel consumption is on fairly flat roads at a steady speed, where the other cars mpg would slowly creep up this one stays the same and drops very quickly if you really floor it. On a gentle hill that the others would maintain about 30 mpg up this one can be less than 20mpg.

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Fri 8 Apr 2016 20:18

Peugeot 406 2.0. Hdi 2001 - Peugeot 406 poor fuel economy - Railroad.

Have you tried cleaning the Mass Airflow Sensor hot blade? Dust and dirt build up will prevent the sensor from accurately measuring airflow, leading to underfuelling and a lack of power.

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