Misfire after a service

[lawler999]

Hi all , Lexus sc430 car has been running fine , untill I had it serviced , new oil filters and plugs. I have run the car on petrol alone for a couple of days as I have been running some cataclean through the system . So a couple of days after the service I switch back to gas and the car is running terrible , really bad misfire . Engine light starts to flicker and then come on , I switch it back to petrol and the light goes back off and car runs fine .
The mechanic said he gapped the plugs down a little due to it being on lpg .
What's the ideal gap for me to try ? I have asked him for one of the old plugs so I can check the gaps .

[lawler999]

So I spoke the the mechanic today and he said his mate gapped the plugs down a little as they knew it was on lpg . So I asked him for the old plugs back today so I could check the make and the gap . He said he would try and find them out the skip . While he was doing this I removed the easiest plug to get to and the gap was just over 1 mm , so that one had not been reduced unless it ha by .1 mm
He found 2 of my old plugs and dropped them round , the gaps on the 2 plugs he gave me were so different 1 was 1mm the other was .8 mm
The old plugs were denso Sk20r11 iridium , the new ones were ngk ifr6t11 iridium , I think the mech may have opened the gaps on the old plugs before he gave them back to me as he didn't want to remove them and re gap them .
When I asked why the gap was still 1mm in the new plugs he had fitted , he said maybe they opened slightly when he put them in .
At this point he lost all credibility with me because that is just plain stupid .
So should I regal them to .6 or . 7 ?

[LPGC]

Or maybe it isn't different plugs / gaps that's caused the problem at all... maybe they accidentally/unknowingly did something to the LPG system while changing the plugs.

Your best bet regards plugs would have been to refit the same make and model plugs (iridium after all) that were removed. Don't often heasr about mechs knowing to gap plugs differently for LPG use. Usually the Lexus engines are quite forgiving when it comes to plugs anyway.

[lawler999]

I am a little upset as i have spent a lot of money with this mechanic over the last few years and i think hes not telling the truth , the only way i will know is if i take the plugs out and check the gaps my self .
Which is something i didnt want to do as thats why i paid him for a service .
Just drove to work 1 minute on lpg running rough so i switched to petrol, and the car is still running @!## , its seems to be missing a bit especially on idle , after 4 miles its gave a P0301 code misfire on cylinder 1 .
I thought i would have a service oil ,plugs ,and filters to keep the car running nice and am totally regretting it now .

[LPGC]

Next time you get the misfire try restarting the engine and running only on petrol. Does it continue to run ok on petrol?

[lawler999]

I am currently running it only on petrol and there is a misfire every so often , it does not idle very good and it hesitates at low rpms , it has gone to cut out a few times when waiting in traffic . No codes showing up on petrol . I'm going to get the plugs out the weekend and take a look at the gaps . Will check all the pipework and wiring around the top of the engine ,in case something has been knocked. It runs a 100 times worse on gas so I'm sticking to petrol for now .

[Brian_H]

There were some counterfeit ngk plugs about a while back, any idea where the plugs were supplied from?

[lawler999]

They were brought from a shop so I'm guessing they are genuine .
I will take them out and gap them down to .7 mm or even .6 , and see what that does .
Will also look around to make sure all hoses and leads are connected ok .

[Brian_H]

Worth ruling it out while your there as your pulling the plugs out anyway, theres some info here
http://www.ngk-sparkplugs.jp/english/techinfo/fake/

If its worse on gas, are the gas injectors or their cabling in the way of the plugs? If so check the wiring is connected to the right injector (might be obvious if its wrong and labelled, but if not, then a photo of the wiring, or summary of the connectors and order they are in might give a clue as to whats going on, though without knowing what channel has been used on the injector cuts impossible to tell for sure).

if its consistently throwing misfires codes for cylinder 1, is it possible to swap the coil pack from that cylinder to another one (don't know what the setup on the specific engine you have is) and see if the fault follows the coil pack?

[lawler999]

So basically I've been had over by a mechanic I been using for years .
I took out some of the more difficult to access plugs only to find they as not changed by the mechanic , he only changed the 2 at the front . Phoned him and gave him what for , he's tried to blame a young yts lad . Replaced the 2 rogue " new " plugs with the old ones so all 8 plugs were the same , still a terrible misfire , getting worse and worse .
Under closer scrutiny and swapping coil packs round ( thanks for the tip Brian) I found one of the coil packs had a great big crack down it .
Must have been done by the idiot who changed that plug .
Further call to mechanic to complain .
Mechanic has replaced the coil pack with some cheap shite ,and the car is now running sweet on petrol and lpg . My only worry now is did they change the timing belt ,pulleys and tensioner and water pump like requested

[Brian_H]

Sounds like progress, I guess you won't be using him again though.

If any of those bits are easy to access (belt, pump etc) it would be worth having a look to make sure they look like new bits - If not I'd suggest you return to him and demand your money back, and take it elsewhere to get it done. Take photos of anything you find before taking it back to him though just in case he tries to wiggle out of it. I take it you've checked the oil and filter you paid for appear to be new ones? (and the air filter assuming that was changed?)

[lawler999]

Simon was right spark plug gaps made no difference and they had knocked or damaged something during plug change , well done Simon .
Car is running great again now , no misfire .
I had new plugs oil filters and belt as part of service / prvebtative maintenance , nomway did I expect the car to be running rubbish when the jobs had been complete .
I can confirm the oil and filters have been changed but I am not convinced about the belt ,water pump,and pulleys.
I can take one of the cam covers of and look at the timing belt ,to see if it looks new , but I won't be able to see the water pump or the tensioner , I think I will have to pre warn him I will be taking it somewhere to have it investigated .
I mean if they are not going to change spark plugs why the hell would they do the other stuff .
I'm totally disgusted in them .
I don't think there is any way of checking the water pump without taking a lot of the front off .
Thanks for your help bri and si .

[Brian_H]

No probably not on the water pump, but if you can see the timing belt hasn't been done I'd suggest it probably hasn't been done as I'd assume its driven off the timing belt from what you've said on your engine. It may be after breaking the coil pack that they didn't want to mess with the rest of the plugs, but if that's the case a phone call to you should have been the next step really.

[lawler999]

So looking back over phone call history ,it appears he carried out this job in less than 4 hours , I know a Lexus guy in glouster who does these blindfolded and it takes him nearly 4 hours .
I pointed this out to the mechanic , for want of a better word , and showed him a load of photos which I had taken clearly showing a lot of the bolts and pipe clips had not been removed in the last 10 years , let alone the last 10 days .
He has agreed to give me my money back , it's a sad day when you cannot trust people any more . Once again thanks .

[Gilbertd]

At least you found out now rather than when the belt snapped or the water pump started to leak. In a way, he's done you a favour by causing the misfire or you would never have investigated the work.

[LPGC]

The garage have clearly tried to do you over... But old coil packs can crack and/or fall to bits on removal without it necessarily being the mechanics fault. Years ago I converted a Shogun for a judge, fitted iridium plugs while I was at it but some of the coil packs fell to bits on removal due to oil damage from failing cam cover gaskets. I showed him the oil damaged packs and he was fine about it, I've since converted other vehicles for him.

[TNT]

It's a shame you continually hear about Garages that pull fast ones these days. If i'm getting work done because i cannot be bothered to do it myself, I stick a mark on the part I want replacing. if it's still there when it's done. I got the knack of doing my own spark plugs and the right tools to do it in a pretty awkward spot now.

It's a slippery road D.I.Y car repairs. You start getting deeper and deeper Then before you know it your mechanic goes out of business and you don't even notice and you realize that's because you don't need them.