Misfiring Sprint Engine

Beans · Postby **Beans** » 12 Oct 2014 16:50

Checked a few more things today.

Using the strobe light with the trigger lead connected to #3, the light flickers rather randomly.
It is missing out about half the time, so it looks like the ignition module is on the way out.
So back to basics, putting the points back in the dizzy ::)

Also did a quick check on #3 venturi but nothing visibly wrong there.

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

Stag76 · Postby **Stag76** » 12 Oct 2014 19:49

Do all cylinders except 3 have a steady spark? If the module was failing, you would expect all sparks it generated to be weak, not a single cylinder. The only part you haven't changed that is cylinder specific is the chopper disc.
You could re-phase the distributor 90 or 180 degrees and see if the problem moves to cylinder 2 or 4.

TR7 Convertible
Sprint Motor
MegaSquirt EFI

dursleyman · Postby **dursleyman** » 12 Oct 2014 21:56

We don't have a "like" button on here but I like Stag76 suggestion. It seems odd if it's a misfire on 3 only caused by the electronics. The chopper/rotor part could be a culprit?

Russ

1981 TR7 Sprint DHC
Dursley
UK

http://tr7russ.blogspot.co.uk/

jeffremj · Postby **jeffremj** » 12 Oct 2014 22:10

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dursleyman

We don't have a "like" button on here but I like Stag76 suggestion. It seems odd if it's a misfire on 3 only caused by the electronics. <hr height="1" noshade id="quote"></blockquote id="quote">Without the spark guard, the spark could short through parts of the ignition kit - consistently failing at one rotor position. Simples.

Stag76 · Postby **Stag76** » 13 Oct 2014 08:44

If the spark is leaking it shouldn't be hard to find...30,000 volts will leave a trail.

TR7 Convertible
Sprint Motor
MegaSquirt EFI

alc59 · Postby **alc59** » 13 Oct 2014 14:59

To check if the spark is leaking, turn the lights off in the garage and it's generally very visible.

[img]/Users/alistaircaie/Documents/tr7/Grinnall/IMG_3398.jpg[/img]

Beans · Postby **Beans** » 13 Oct 2014 16:55

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jeffremj

Without the spark guard, the spark could short through parts of the ignition kit - consistently failing at one rotor position. Simples ... <hr height="1" noshade id="quote"></blockquote id="quote">
Sounds plausible as the contact inside the dizzy cap closest to the ignition sensor is from #3 spark plug ...

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

Beans · Postby **Beans** » 22 Oct 2014 18:57

Short update, took of the carburettors for inspection, but nothing wrong there. Completely clean inside
But the flange holes on number three barrel were badly worn out due to a collapsed rubber spacer.
Sadly that wasn't the cause for the problem
So I borrowed a Sprint dizzy with points today for the final check. Hopefully will be able to put that in this Saturday.
Fingers crossed [8)]

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

dursleyman · Postby **dursleyman** » 22 Oct 2014 22:03

Good work Beans, its amazing what you can find sometimes but still not solve the problem. The mystery continues.

Russ

1981 TR7 Sprint DHC
Dursley
UK

http://tr7russ.blogspot.co.uk/

Beans · Postby **Beans** » 25 Oct 2014 16:19

Wanted to swap the dizzy today but decided against it.
I first replaced the rotor only ... result. I knew it had to be something simple.

Though I can't figure out why the rotor only misfires on #3.
Remains the slightly lower compression on #1. Will see how that develops after next weeks "Nachtrit".

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

FI Spyder · Postby **FI Spyder** » 25 Oct 2014 21:08

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Beans

Wanted to swap the dizzy today but decided against it.
I first replaced the rotor only ... result. I knew it had to be something simple.

Though I can't figure out why the rotor only misfires on #3.
<hr height="1" noshade id="quote"></blockquote id="quote">

There are bad rotors out there. They can fail within 50 miles of new. Jag Mechanic that is a club member brought a good new one and a bad new one to a meeting a few years ago. You could see the different construction between the two but I wouldn't be able to tell the difference between a good one and bad one today. I guess they are still out there and we will run into this from time to time whether it be because the problem has never been fixed or it's bad ones out in the supply chain.

- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

dursleyman · Postby **dursleyman** » 25 Oct 2014 21:17

Beans, well done to get to the bottom of the problem.
Questions:-
Was it a new or old rotor?
Can you see anything wrong with it?
Is it something we can avoid?

Russ

1981 TR7 Sprint DHC
Dursley
UK

http://tr7russ.blogspot.co.uk/

Beans · Postby **Beans** » 25 Oct 2014 22:35

It was an old rotor (original Lucas) which I fitted in 1997, and it didn't have any real signs of damage ...

Swapped it with another fairly old one I borrowed through a friend.

Problems will be pretty difficult to avoid. As another friend warned me that modern rotors can be pretty unreliable.

But bear in mind that I wasn't in a hurry and didn't want to buy loads of new stuff. As a result I went "shopping" locally, and it paid of ... actually very well. More on that later [:)]

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

john 215 · Postby **john 215** » 26 Oct 2014 05:07

Hi Beans,

Well found, they tend to loose there resistance and short to earth down the middle. Rover had terrible problems with there's on the K series, you tested by holding the coil king lead with insulated pliers, spin the engine over with the cap off and holding the lead 1/4" inch away and see if there was a spark if so the rotor was duff [xx(]

Read report on other forums that there are lot of poor quality rotors out there.

Poss why no3 only effected was that is was running weaker due to the carb fault you found and needed a bigger spark to jump the plug gap to earth ?? These faults can be a combination of things when you sit down and work it out [^]

Cheers John

LIVE LIFE A QUARTER OF A MILE AT A TIME!

1976 Speke FHC Beauty Now with an overdrive conversion

1979 3.5 FHC(STATUS PENDING!!)

1982 2.0 DHC NOW A 4.6, BUILT NOT BROUGHT !!!!

Beans · Postby **Beans** » 26 Oct 2014 06:46

Thought I had found the fault earlier in the search ...

#3 spark plug after I ran the engine with the fuel supply shut off to empty the carburettors.
The thin cracks in the insulator tip were pretty easy to spot with some deposit on them.

<center>

1976 TR7 FHC (needs some TLC ...)
1980 TR7 DHC (my first car, a.k.a. Kermette)
1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
[url="http://www.tr7beans.blogspot.com/"]My full Blog[/url]</center>

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Misfiring Sprint Engine

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