Finding the correct spark plugs
Q I’m hoping you can clear up some confusion on the correct model of spark plugs and gap settings for my 2007 Ford Focus MKII 1.6 TI-VCT. On the Bosch website, it lists HR8 MPV as the recommended type, and also HR8MCV – these are gapped at 1.3mm.
A few years ago, I emailed Bosch asking if you could get the Super 4 electrode type plugs, as I found these were great on my old Escort. They said HR78NX were the right ones, even though they didn’t come up when doing a search on the website. However, they have now added them to the list. So are they ideal for this engine?
A good small independent Ford garage I’ve used says the plugs should have HR7, not 8, MPV stamped on them and the gap should be 1.2mm. And looking on various online forums, it seems Ford revised the gap from 1.3mm to 1.0mm as coil packs were failing too quickly. My thought is that 1.2mm is not going to wear the coil pack down as quickly, but should give slightly better performance with a slightly larger gap.
The reason I’m interested in the plugs is because I have just had the core plugs on my Focus replaced for the second time, as they were leaking. I wasn’t getting a misfire, but the car seemed down on power. I took out the plug leads and there was a very tiny amount of coolant around a couple of the plugs. I’m hoping this is just fluid which hadn’t fully dried up from the previous leak. Once I had put the leads back in, I was changing from 5th to 4th gear to overtake while climbing a hill on a motorway and the car juddered. If I pressed down on the accelerator, it would misfire and flash the EML.
Later, I plugged in my scanner and it had a pending misfire on cylinder 4. Do you think I just need to give the plugs a good clean and try and soak up every bit of the coolant or are the new core plugs leaking? Phillip Gwynne A The Bosch HR8 MPV spark plugs have been discontinued and HR8 MCV+ should now be used. The former type had a platinum electrode and the later ones have a nickel electrode. Autodata and Bosch still specify the gap should be 1.3mm and I would continue to set them at this. The technical specifications in the Ford data I have does not specify the gap. Bosch do also list the HR78NX plug as being compatible with your Focus, with a note that the replacement interval should be 20,000 kilometres.
The misfire could be for a couple of different reasons. First, the HT leads may have been damaged by the damp or the coil pack could have been affected by the damp in the cylinderhead. If the garage replaced the core plugs in the centre of the head, they would have had to remove the cam cover and consequently the area should have been thoroughly dried out before the vehicle was returned to you.
The possibilities are that either the replacement core plugs have not been sealed in effectively, or that the water isn’t from the cooling system but is rainwater and has run down from above – I have seen this in the past. The source of any water ingress into the spark plug recess does need to be checked to ensure that no further damage occurs. In extreme cases, spark plugs can corrode in position and shear off upon removal due to sitting in water.
To summarise, I would expect the misfire to be caused by a failure of either the HT leads or the coil. It is difficult to know if the core plugs are leaking again, but a pressure test of the cooling system should be carried out and, if no fault is found, further investigation into where the liquid is coming from should be undertaken.