Evening all. 

I've been experiencing juddering/hiccuping while accelerating in my 1.8tdci Connect. So far I've replaced egr actuator which was knackered, maf sensor and fuel pressure regulator - all to no avail. I've recently run a cylinder balance test in Forscan and they're all all over the place but seem to even out and match over 1.2k rpm. I've read on Forscan forum that this is based on the knock sensor interpretation so I'm not sure how accurate it really is. Could someone shine some light and let me know what they think? I will be doing a leak off test this weekend, but just thinking if all the injectors are knackered I will have no reference really. The van's done 96k miles. Thank in advance, Dave

On 11/9/2023 at 7:11 PM, chipsngravy said:

I've recently run a cylinder balance test in Forscan and they're all all over the place but seem to even out and match over 1.2k rpm.

I have only looked at the cylinder balance a couple of times on my car, and not logged them - They all read the same number very close to 1.

I would assume that the ECU injector pulsewidths are used for this test, the VDO system has no pre-set calibrations and the ECU must be able to tune itself to even out any small variations between injectors.

The symptom of juddering or hesitation at certain speeds is certainly consistent with injector problems. But check the main earths first, body to battery -ve & battery to engine. I have been having hesitation at pull-away, and intermittent starting problems, which seem, at the moment to be due to a poor body to battery earth. A multimeter on ohms is no use at all on these, the resistance should be below 1 milli-ohm. The best test is to pass a known current from battery to body (an old filament type headlamp bulb would do), and measure the voltage change as the load is repeatedly connected and disconnected. Use a DMM on mV range, with entirely separate probes direct to battery & body. 1 milli-ohm would read as 4mv for a 4A load (48W bulb at 12v.)

I assume no DTCs have been seen. Often injector problems do show up as DTCs.

A leak-off test is a good idea if there is any suspicion. Bear in mind the term "leak" is misleading, there is a fixed volume of fuel sent to the leak off port on each actuation, due to the way the injectors work. So an abnormally low reading would be as bad as an abnormally high one. I would change the most out of line (low or high) injector first, and see if that made it worse or better, before doing any more.

You're a gentleman and a scholar Peter. I will certainly check the earth connection. I've never had any problems starting the van, however my interior light as well as headlights do flicker very slightly when ticking over so I'm just wondering whether it might have something to do with bad earth.

I'm very close to getting a set of refurbed injectors but I'm gonna get just one second hand I think for now and replace the most obvious culprit.

Thanks again Peter, you've been a great help as always.