450SE Miss fire
450SE Miss fire
Author
Discussion

1BigBadWedger

Original Poster:

31 posts

170 months

Sunday 7th October 2012
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Hi Guys, my 450SE seems to miss firing on numbers 5 and 6(opposite banks) as when I've taken the leads off those it doesn't seem to make any difference to the engine note. I've tried different leads, dizzy cap and rotor arm which have made no difference.

Any ideas would be great......

Cheers
Nick

MrPicky

1,233 posts

297 months

Sunday 7th October 2012
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Resear the plug into the resistor pack (probably on the inner wing) before spending any more money.

Russ

Danny Hoffman

1,617 posts

292 months

Sunday 7th October 2012
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Have you tried new spark plugs. I had one that looked 100% perfect that wouldn't fire

1BigBadWedger

Original Poster:

31 posts

170 months

Sunday 7th October 2012
quotequote all
Hi MrPicky, not sure what resear is or resistor pack. Would you be able to expand on that?

Thanks

MrPicky

1,233 posts

297 months

Sunday 7th October 2012
quotequote all
BEWARE - this info is based on a 1985 flapper engine, I reckon that there will be something similar on hot-wire systems.

The injectors are specified to work at 6v (a lower voltage than 12v), this allows for cranking etc. when the voltage drops - so there is a resistor in circuit with each of the injectors. The resistor pack contains all 8 resistors and is about the size of a ciggy packet with 9 or 10 wires going into it, in my 390 it is mounted on the inner wing under the bonnet and is marked Lucas.

The connector pins often get a bit corroded and benefit from a disconnect/connect cycle.

The pins carry a fair bit of current so show this problem more than signal wires.

If this works then you need to remove the connector once more and smear the pins with adeline to prevent further corrosion.

Russ

matt-man

2,667 posts

249 months

Sunday 7th October 2012
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Have you checked the three things you need? Fuel, spark and compression?

If you have spark, do you have compression? When I had a misfire it turned out to be a broken valve spring. I spent weeks concentrating on the electrics and it wasn't.

Check the simple things first...good luck!

grahamw48

9,944 posts

268 months

Monday 8th October 2012
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The hotwires don't have that resistor pack...not in that form anyway.

grahamw48

9,944 posts

268 months

Monday 8th October 2012
quotequote all
Assuming you mean this (arrowed)....

.

1BigBadWedger

Original Poster:

31 posts

170 months

Monday 8th October 2012
quotequote all
I haven't got that unit under the bonnet on mine but there's something similar in the drivers side footwell which I've unplugged and cleaned but hasn't altered the miss fire.

Thanks for the ideas though.

grahamw48

9,944 posts

268 months

Monday 8th October 2012
quotequote all
First I'd have a look under the bonnet in the dark to see if there are sparks flying around where there shouldn't be.

Other than that, it's probably best to take it to a someone with Crypton or Suntune machine to see if it's an ignition problem....much cheaper and more accurate than starting on the usual (more expensive)trail of replacing parts which probably aren't needed.

I had a miss-fire on my first TVR...280i, and the machine immediately found the problem...one knackered spark plug. To the naked eye the plug looked perfectly ok, but it was the porcelain insulator that was at fault. Cost - £30 including the diagnostic session.

The next time it was the 400SE. General miss-firing and lack of power. Diagnosis... play in the distributor shaft and timing out (plus a couple of other minor adjustments that I've forgotten the details of).

Cost...£75 for at least an hour of a race mechanic's time setting up timing and other adjustments. Then I was able to go out and buy the CORRECT part.

matt-man

2,667 posts

249 months

Tuesday 9th October 2012
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Have you checked compression?? It's a ten minute job and a 30 pound tool....

1BigBadWedger

Original Poster:

31 posts

170 months

Wednesday 10th October 2012
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Thanks for the tip. I've just done a compression test and everything seems to be normal in that respect. Looks like I'll have to get it put on a rolling road as it doesn't seem to be something straightforward.

Cheers