Misfire after Spark Plug Change

[Spinal]

A query...

Last night, I changed 3 of the 6 plugs on one of my cars. I didn't do the remaining 3 as to get to those I need to take the alternator, inlet manifold and wiper motor out... and will need to wait until next weekend.

Anyhow, after changing the plugs (one at the time, so I didn't confuse the wires), and coating the threads evenly with copper grease, I thought I was done.

I don't have a gap-measuring device, so stupidly just though "it'll be fine". That said, the car seems to have developed a very slight misfire when in neutral.

Any ideas?

I'm thinking:
- lead not fitted tightly enough
- too much grease? could this impair a good connection?
- I fitted bosch plugs, which looking online (now) seem to have a bad reputation, any thoughts?
- gaps...

Anything else I should check?

M.

 

[grober]

Which MODEL of car please?

 

[Spinal]

It's a Chrysler Voyager, 3.3l V6 petrol (1998 iirc). It's old, but essentially a van that's perfect for driving demijohns of wine, skis and a dog across Europe

Worth adding that there was no misfire before the change...

 

[Ted]

Just my opinion

The gap - especially on a new plug is not THAT critical - sure that the default gap would be ok.
I don't believe the grease would impair the connection (especially if it is copper grease) - there is only a minute amount of current flow.

FWIW, I think the fault is that you have disturbed/moved something - maybe a HT lead is now shorting to earth - easy to see, just look under the bonnet in the dark (standard disclaimer about rotating parts applies) - could be one of the leads that you haven't touched.

If a plug is suspected, I would be tempted to remove the HT lead from each of the plugs, (plug in one of the old plugs and earth it to prevent a possible high voltage in that circuit with no plug connected) and see if it misfires. It (obviously won't be smooth, but a misfire should be evident).
If it still has a misfire when you do this, that is NOT the guilty cylinder!

 

[grober]

Plug leads almost certainly the culprit as has been said---- possibly damaged when removed . Is the engine layout like this?

 

[Spinal]

Very similar... here's a picture stolen from pistonheads (not my car, but the same engine - though this one looks quite rough!).
M.

 

[grober]

You probably have CARBON (SUPPRESSION) CONDUCTORS Probably best to renew them

Carbon conductors are used in original equipment ignition wires by most vehicle manufacturers, and in the majority of stock replacement wires. This style of ignition wire is cheap to manufacture and generally provides good suppression for both RFI (radio frequency interference) and EMI (electromagnetic interference). Conductor usually consists of a substrate of fiberglass and/or Kevlar over which high-resistance conductive latex or silicone is coated, and functions by reducing spark current (by resistance) to provide suppression — a job it does well while the conductor lasts. Vehicle manufacturers treat ignition wires as service items to be replaced regularly, and limited life is never an issue.

 

[Spinal]

Interesting... how does that differ from other HT leads? Could moving them to remove the sparks have damaged them? (curious as I've never had this issue before - and keen not to have it again!)

I did notice that the ends of the leads were aluminum which I found interesting (with rubber inside) - I presumes a Faraday cage of sorts... something like the image attached...

I think I may need to stop by ECP on the way home (well I definitely do, they still owe me a spark plug!) so may pick up a set of leads... they aren't that expensive, so may as well change them.

M.

 

[Deleted member 65149]

I'd go for Ted's advice of swapping the new plugs one at a time for an old one. Very many years ago I did a complete rebuild of a single pot motorbike engine. I tried for ages to start it without success. After many hours of wondering what I'd done wrong and out of total desperation I tried the old spark plug - it fired immediately. The new plug was faulty!

 

[Spinal]

Thanks - sadly (and stupidly) the old spark plugs are sitting at the bottom of my bin. May have to do some dumpster diving tonight...

 

[Spinal]

Right, took out the spark plugs (one at a time) and tested. Typically, it was the last spark plug that I tried that was the issue; turns out, the gap was quite a bit smaller than all the other plugs (so much I could see it immediately upon removing).

Did I somehow bend it fitting it, or did I get it bent? I'll never know - but I know that getting spark plugs from ECP has proved to be an interesting experience (so much that I may post a different thread here... somehow I've ended up paying for 7 spark plugs - but at under £2 I don't care too much)

Picture of the offending plug attached (the gunk is copper grease). Plug replaced and all it ticking over smoothly again. When I get the HT leads (had to order them for delivery) I may change them anyhow, it's a pain to get to the rear plugs, so may as well...)

M

 

[grober]

Glad you got it sorted---Occams razor---- You changed the plugs and then had a misfire so that's the first thing to check. I have given up on Bosch plugs who evidently subcontract a lot of their manufacturing now. NGK still make their own
ps very unlikely you bent it fitting unless you dropped it from a height- probably like that from factory.

 

[Spinal]

I may as well post here... was going to start a new thread - but this seems easier. Hopefully ECP read it.

I ordered 6 plugs from ECP click&collect last week (under £2 each). I went to collect them, and after much rummaging, they found 5 plugs - two which were out of their boxes. I didn't give this much thought. I was told to return the day after to collect the 6th as they couldn't find it. The day after I forgot my receipt, which wasn't an issue. Also they still couldn't find it - so I said I would come back on Monday (Friday I was working from home so didn't try).

Yesterday, I went down to collect my plug and (stupidly) forgot to bring my receipt stating 6 plugs; didn't think this would be an issue as I had the click&collect email on my phone; and it wasn't needed the week before. I was wrong, and they wouldn't give me the last plug (which I had paid for). I (kind of) understood this, and for the sake of £2 bought another plug (without mbclub's discount as it was only £2).

After more than 30 minutes waiting (seriously guys - you need to sort out your stock management system!) they gave me a back with 4 spark plugs. I queried this saying I only bought one, and was told they are sold in packs of 4; for £2.16.

Confused, but a little tired, I shrugged my shoulders and walked out with 4 plugs.

Now I have 9 spark plugs (of which one is faulty), I paid for 7 (of which one was at a higher price) and somehow have ended with an an extra working spark plug from the deal.

That is, assuming the mistake was made on the second day - and they don't really sell 4 plugs for £2.16... otherwise I should have had 24 plugs on the first order (6x4).

So now, my conscience is telling me to return two plugs... but how do I return two plugs without a receipt, and without asking for a refund? Similarly, the faulty plug, I'm tempted to return to get the £2.16 back from the second order... but that order is for "4 plugs" apparently.

I'm not fussed (or upset) by this whole thing, just feel that ECP may be losing some money somewhere due to some clear stock management issues. May just take the two extra plugs and pop them in the mail to ECP...

M.

 

[Major774]

Company error... keep it as spares for next time

 

[Paparazi]

Their mistake

They definitely got their nickers in a twist...there isn't a retailer on the planet selling 4 Bosch spark plugs for £2.16...infact that's bloody cheap for just one.

Obviously you have found your fault but as a heads up, the plug just needed re-gapping, probably closed down if it was dropped down the spark plug hole?
Also...not telling you how to suck eggs but for the benefit of others, never pull the leads to remove the cap...this is a sure fire way of breaking the carbon impregnated string within the lead, always remove by pulling the cap itself.
This type of lead became the norm (pre-coil pack era) and as pointed out, are often the first port of call with misfire faults.

Martin

 

[markjay]

You say two of 5 plugs in the first batch were out of their boxes... the electrode can get bent easily if the unboxed plug got toss around in the warehouse or accidentally dropped by ECP staff.

 

[Spinal]

You say two of 5 plugs in the first batch were out of their boxes... the electrode can get bent easily if the unboxed plug got toss around in the warehouse or accidentally dropped by ECP staff.

I thought that - but tbh I really didn't think of it when I bought them; and as such, I didn't check them. Unless I'm sure of it, I didn't feel like "accusing" ecp, they're usually pretty good. At the end of the day, it's less than £2 a plug... I'm not going to lose any sleep over it. Just happy that it is sorted

Now I'm waiting for the leads, and then I get to spend a weekend swearing while I try to put the manifold and alternator back on before calling a mobile mechanic

M.

 

[grumpyoldgit]

Just read through your post Spinal and glad you've got it sorted. As already advised, it's also worth replacing the leads if they are the carbon fibre type. I always check the gap of new plugs against vehicle manufacturers advised settings before installing them and no doubt you will be doing so yourself in future.

Just out of curiosity, I checked on the price of plugs for my previous motor, a Volvo V70 T5 (current Merc is diesel) and I think you've had a bargain with plugs at £2.00 each. I have to agree with you about ECP's somewhat confusing pricing as you will see from the following screen shot. It makes no sense whatsoever. The V70 is a 5 pot engine, but the price for 5 plugs only amounts to £39.00. Note the List Price - Something isn't quite right!