Replaced spark plugs and now the car wont start.

[worldwalker]

Hey guys, I've tried posting this elsewhere but the responses are coming through slow and I figure the tech savvy guys here would probably have the best idea anyway.

I just replaced the old denso plugs on my Mrs MX5 with new NGK BKR5E-11, went to start it up and nothing. Assuming it couldn't be plugs, I went through all the online advice, checked pump, relay etc and all ok (I don't own a fuel pressure tester but will look at this during the week). So I gave up and put the old plugs in, fired first time after one rotation. I let it warm up and did a comp check, came in well within spec. The car seems to run ok, idles smooth and free revs fine though it does seem pretty weak compared to my 4AGZE AW11.

What are the chances of all 4 new plugs being faulty? My only other guess is that there is a weak spark and the old plugs have a slightly lower resistance giving enough spark to keep it running. It's a factory ignition of DLI with 2 coil over plugs and secondary lead to plug. Plugs are all identical, gaps all the same. I ran them dry and the first spark seemed fine but the subsequent sparks seemed a little weaker. The engine has a good earth.

I can't understand why old plugs work "fine" but new ones wont even get the engine to fire up once!

I know it's not a Toyota but I thought it's more a generic question anyway, any advice or ideas would be appreciated.


Cheers,

[nathanshnoz]

very weird. new plugs have less resistance/wear which theoretically should mean they work better than the old ones. are the plugs the same model/make etc? i assume so since you say they are identical. maybe try half new and half old first and see if it will start? if it starts and is miss-firing on the cylinders with the new plugs then it is obvious they have issues. did you get the plugs from a shop that has high turnover? i would take the plugs back and say they are faulty and get a new set to try and narrow it down.

[worldwalker]

That was another strange part, I ran it with 2 old and 2 new and it still wouldn't start, as soon as the other two old ones went in (without any other changes) and it fired first time. I spent a good few hours trying different things including push starting, to no avail. I got the plugs from supercheap and they were grouped together so I guess there is a chance they're dodgy, just strange to get 4.

["Z" UTE]

The calibre of the average joe working at SupaCrap almost guarantees that you will get dodgy plugs. Shit man all they have to do is toss a blister pack across the floor and the ceramics will crack. In future buy your spark plugs from a reputable parts shop.

cheers Chuck.

[worldwalker]

What's reputable now? They're all supercheap or repco now and they're as crap as eachother.

[lexsmaz]

Certainly strange, but as has been said sounds like they have cracked insulators .. I think Repco or Bursons are better than super cheap, they are / were aimed at the trade more so than super cheap

["Z" UTE]

What's reputable now? They're all supercheap or repco now and they're as crap as eachother.

I get my NGK plugs from my local Toyota parts manager, (at the right price)

When the Crown gets some new plugs and points, the old corona gets a set of pre loved ones, got to love Toyota common use articles!

[worldwalker]

I tried as hard as I could to convince her we needed another MR2 but 2's enough... apparently .

[jondee86]

Just thinking out loud... do the Denso plugs have an "R" in the model
number ? Not familiar with the ignition system you describe, but if you
replaced non-resistor plugs with resistor plugs that might upset things.

Cheers... jondee86

[worldwalker]

Nah both are resistor type. They're the identical NGK version of the Denso.