Going to change the plugs and COP on our 1999 E450 RV which also has an LPG conversion due to the high gas prices here in the UK. It has only done 75k miles but it has had a minor intermittent misfire lately an being an RV I dont want it spoiling family holidays so would rather get it sorted. The help I need is:

1. Are standard plugs fine for running with LPG?
2. What parts will I need other than the plugs and COP's, if any?
3. Will I need anything other than standard tools to get to the awkward plugs?
4. What is the correct torque for the plugs? I have read previous threads and there seems to be some contradiction.
5. Last time out we had a vac leak but fortunately it was at the end of a line so I was able to cut it back and refit. Looking at the rest of them they are all starting to crack so need changing. Is there a diagram anywhere with sizes to save me measuring them?

Being UK based I need to get the parts imported so would prefer to put a shopping list together and have everything here before I start so any help would be much appreciated.

Oh and what is the easiest way to access the engine? Just climb up and lie across it?!!

 

I don't know anything about the LP specific parts, but it is recommended to replace the plug boots as well. Order the Denso COPs as they are the OEM manufacturer and are much cheaper than the Motorcraft branded part.

Mid 20 ft/lbs is the recommended torque around here, with the big debate being whether to use anti-seize or not.

 

When you say lay on the engine, if it's an E450, doesn't it have a "dog house" that you remove from inside the cab?

1) Unknown. LPG burns hotter than petrol, and may or may not require a "colder" plug usually one step down. What I would do is, pull a plug NOW, post a picture of it, and we'll decide if it's been running too hot. The misfire could be a spark plug that's been overheated. This will also tell us what plugs are in it now.
2) Make sure the COPs come with the boot and spring, and if not, get them. Don't reuse the old ones.
3) Not really. Standard extensions should be fine.
4) Go to 21ft/lbs with nickel-based anti-seize.
5) There should be a decal under the hood with the vacuum diagram, but there will be no sizes. You should have standard sizes of rubber lines in the UK.

Out of curiosity, the LPG conversion is basically a bolted-on throttle body conversion?

 

By the way, Ford actually did offer LPG and Natural Gas "bi-fuel" options around 2000-2001 - my service manual for 2001 has all the maintenance procedures in it.

There is no specific spark plug for LPG or Natural Gas, it's the same one for gasoline (petrol). So the V10 running LPG seems to be OK with the standard plugs. I'd still like to take a look at one before going any further.

 

Ok so vac lines I will figure out. Yes we have standard sizes over here so once I have measured them I will replace them all with silicone like I have done on our cars.

Having read up some more I agree with you that standard plugs will be fine for running LPG. NGK do specific LPG plugs which are iridium as they apparently cope with the additional heat better. These plugs are mega bucks so probably just go with the standard iridiums from NGK which I know will be readily available over here.

Time and weather permitting I will pull a plug to check and post a pic on here.

Thanks for your help.

 

I used a set of Bosch plugs in my V10, because they were given to me to do a review - they've been flawless. Your Mileage May Vary

 

If I recall the lp motors that ford produces have harden valve seats in the heads.

the non-lp motors do not.

I assume softer seats will erode, and cause issues.

​​​I would never suggest new plugs and COPS are not a good starting point but wanted the OP to be aware of LP issues with non-harded valve seats.

 

It's an aluminum head, and no-lead gas, so they all have hardened seats. But there might be something different in the valves themselves. But good point