Xantia HDi 2.0 (90) - Misfiring, juddering issues

[RoadkillUK]

I'm having trouble with my Xantia HDi 2.0.

About 4 months ago the car was misfiring on cylinder 4 (right hand side looking at the front of the engine), I replaced the injector with a second hand unit from a scrap car, this sorted the problem out but it has returned. I have again replaced the no 4 injector which has improved the performance but still I can feel that when I start the car it's rough, also it's juddery when braking.

Feels like a misfire, but doesn't lose power.
Sounds rattley below approx. 3000 rpm.
Car judders a little when braking hard.
When I unplug the injectors one at a time, it runs when I unplug no. 4, but if I unplug any of the others, the car stalls which leads me to believe that whatever the problem is, it's to do with cylinder no.4.
I have used Bio-diesel in the past.

Can anyone point me to a fix?

Thanks, Lee.

[oscar]

hi are you getting diesel up to it? crack nut a turn or so while running see if good flow at pipe if so must be injector or head/piston problem if not a pump problem also whip it out and take to a diesel place they check for spray pattern they also should be matched really
Try some Forte diesel treatment gear fill filter housing when engines warm pref! put another in tank and take for a drive on an open road so gets a constant run good speed

[RoadkillUK]

Thanks for the reply, I'm going to get a fuel filter at lunchtime and change that this evening. I'll 'crack a nut' and see if we have pressure there, also I have a couple of old spare injectors now, I'll try one of those out again.

[RichardW]

DON'T crack a nut on a common rail on an HDi!! It runs at at least 300 bar and is liable to inject diesel into your skin if you get your hand in the way. If it will run, there is plenty of pressure there (the ECU monitors and controls the rail pressure, and all injectors see the same pressure).

Sounds like a coincident fault with the 'new' injector, but you could swap a couple of the injectors over to see if the fault moves.

[RoadkillUK]

Ok then, I'll give that a go instead

[RoadkillUK]

OK,so this is what happened after work last night.

I changed the fuel filter, it was quite dirty inside, then proceeded to swap the 'problem' injector for another one, the same was happening, running rough etc. I then swapped 2 injectors over and found that the problem was still with cylinder no.4. So either it is some mechanical fault, or it's an electrical fault to the injector. Is there an easy way of finding out? Would a lexia help at all?

Lee

[Mandrake]

I would start by using a small test light on the injector connector (try both a good and a bad injector) to see if the injector is being fired by the ECU.

[thorter]

Be very careful. If running properly, the pressure at the injectors is 1350 bar. Keep well away when the engine is running!

If I remember correctly, the voltage on the injector coil starts off at 80 volts, though only for a short time. I am not sure what kind of test light would be suitable - perhaps a neon if you can still lay hands on one.

Fred

[Mandrake]

If I remember correctly, the voltage on the injector coil starts off at 80 volts, though only for a short time. I am not sure what kind of test light would be suitable - perhaps a neon if you can still lay hands on one.

A small automotive incandescent (not LED) "test light" of the probe and coiled return wire type should be fine.

If its supplied the same way as a petrol injector it is supplied switched 12 volts by the ECU but there is a very brief turn off spike of about 50-80 volts as the coil is switched off and the field collapses.

This will not hurt an incandescent bulb as they respond to RMS voltage and the spike is very brief so has no real effect on the RMS voltage.

[thorter]

The HDI injectors definitely run off more than 12 volts. The Peugeot document I have says initial phase is 80 volts at 20 amps for 300 micro seconds, then a holding phase of 50 volts at 12 amps, no time stated. It also warns that applying 12 Volts DC will burn out the coil. The ECU has inverters to derive these voltages.

You might get away with a filament lamp depending on RMS value of the composite pulse.

Fred

[Mandrake]

The HDI injectors definitely run off more than 12 volts. The Peugeot document I have says initial phase is 80 volts at 20 amps for 300 micro seconds, then a holding phase of 50 volts at 12 amps, no time stated.

Madness! I stand corrected then, HDi's are very strange beasts indeed. I would guess the 50 volt phase would be a few milliseconds in length and would be the remainder of the injection pulse time, thus variable with throttle.

It also warns that applying 12 Volts DC will burn out the coil. The ECU has inverters to derive these voltages.

You might get away with a filament lamp depending on RMS value of the composite pulse.

If they're warning about burning out the injector with 12v DC applied the RMS value must still be well below 12 volts, so a few watt bulb should be fine. I would still try it - the worst thing that can happen is you blow a bulb worth pennies!

The alternative is to go all high tech with a scope etc, which I'm guessing the OP doesn't have.

Edit: another way actually would be an LED with a 5K 5 watt resistor in series, but it could be hard to see in daylight and then you have to get the polarity right too.

[thorter]

Actually, a cheap digital voltmeter would do to compare all 4 injector drive voltages. Just go down in range till you get a measurable voltage. However, I would advise adding test leads somehow to avoid poking on the injector connectors of a running engine. Unfortunately, the pins on the ECU are not readily accessible either, but in case it helps, the pins are 2 and 30 injector 1, 5 and 6 injector 2, 3 and 31 for injector 3, 4 and 32 injector 4. Only one or other of these will have the "signal" on it, but unfortunately I have no indication as to which, nor whether it is switched live (unlikely) or switched earth return (probable).

Fred

[RoadkillUK]

Thanks chaps, I'll check all that out when I get the time.

Lee.

[oscar]

DON'T crack a nut on a common rail on an HDi!! It runs at at least 300 bar and is liable to inject diesel into your skin if you get your hand in the way. If it will run, there is plenty of pressure there (the ECU monitors and controls the rail pressure, and all injectors see the same pressure).

Sounds like a coincident fault with the 'new' injector, but you could swap a couple of the injectors over to see if the fault moves.

Hi didnt see HDi as was in between doing a few other things

[RoadkillUK]

Thanks for all the replies, after much research I'm thinking it could be as simple as the seating of the injector, I'm just waiting on the delivery of a seat cutter. I keep you updated.