V8 Missfire - Back Again!

dmcsweeney

dmcsweeney

Active Member
Hi all,
finally got round to collecting my white V8 from our RO, Tony, at the weekend. She had been in storeage in a farm building across from his house since he cured her missfire last Novemember due to the prolonged spell of ice on the roads. Tony met me about 10 miles from where the I'd planned to keep the car and all seemed well, and it had no problems keeping up with my modern car as we drove back. However, he disappeared from view about 1/2 mile from my storeage. The car had lost power and died. After cooling for a few minutes she fired straight up and got about another 500m. After a few stops she made it back. He reakoned it was fuel vapourisation and all would be well once she cooled. However, when I fire her up from cold, she is perfect at first, fires instantly and runs well, then after about 3-4min won't rev, and misfires badly. If i bring her up to around 1500rpm, the engine speed remains constant but the rev counter can deflect up and down by up to 1000RPM, and generally behaves irratically. As the coil is fed from the rev counter (with a standard copper cable - ballast by-passed) I assume this is down to failing condensor or coil? Or an intermittant short to earth in the dizzy? As I say it will fire and run perfectly for the first few minutes, and the rev counter behaves. Didn't get a chance to investigate properly as the other half had lost her patients at that stage!Any thoughts?
 
Hello Dave,

Sorry to hear that the problem is still there.

Hmm,...when you say that the coil is fed from the tachometer with the ballast resistor bypassed,..I am assuming that the original way in which these components connect has been totally changed? Is that correct?
I am also therefore assuming that the original 16C6 ignition coil which must run with a ballast resistor has been replaced with a 12volt coil?

The modern day condensors are a load of rubbish by all accounts so it is entirely possible that it may fail as soon as you use it.

I am a firm advocate for replacing the points and condensor with an electronic ignition system for a whole host of reasons,..not least of all...reliability!

With the coil...measure the primary resistance and voltage when cold and then again when the problem starts and see if the values differ markedly.

Ron.
 
Ron,
thanks for the reply. Luckily she missfires on 8 cylinders this time! I'd have cried if it dropped down to 4 cylinders again! The live feed to the ignition coil on my car consists of a 12V feed from the starter solinoid to energize it during cranking, and a 'running' supply from the rear of the rev counter (originally 8V?), which was a resistive cable, now copper at 12V. I fitted a 12V high performance dry coil and new condensor at the time. I'm away all week again but will try swapping the coil and condensor with spares at the weekend. I removed the instrument panel a few months ago to replace the voltage stabilizer and have had a few issues since - no temp gauge and no warning lights - seems to be a lose multipin connection at the back. Also have intermittant headlights and wipers so i'll be going through the entire electrical system when i get a chance. Can't remember if the supply for the rev counter is seperate or runs through this multi pin connection as my problem may be power loss.
Regards,
Dave
 
Graeme,
thanks for the suggestion but I don't think the conditions are right for it to be a tracking issue. The car starts first touch and runs well for a few minutes. The first time it happened was after a long run. From my experience of HT problems they normally start when the car is cold, but someone please correct me if I'm wrong about this. I feel that the erratic rev counter also points to an LV fault. Has anyone experienced the rev counter problem with the missfire?
Regards,
Dave
 
This does sound exactly like coil or condensor problems, suspect the condensor first. Recommendation of an electronic system is certainly worth considering, especially if you want to use a more powerful coil.
 
Thanks Richard, what kills me is that the car was fitted with a luminition kit when the previous owner had the car and he removed it because he felt it would leave him stranded if it went wrong! He converted the car back to points on reliability and ease of repair grounds. Wish he hadn't :( . Must call him and see if he still has the kit. I have a kit from an SD1 (complete with dizzy - which i know won't fit) and wounder if this could possibly work on the P6 dizzy. By the way, is there any difference between the coil used with electronic ignition and points? I was told years ago that a coil from a points setup couldn't be used with electronic ignition.
Regards,
Dave
 
Maplins make an electronic ignition kit ,about £10 which retains the points , does away with the condensor , and the rev counter still works .I think it uses the points to switch a power transistor . Easy to make up and fit .

In my garage I've got an old Mobelec capacitive discharge ignition kit which works but the rev counter then doesn't and a Lumenition kit removed from a Mk4 Cortina in 1984 . I either need the 8 cylinder kit to fit a P6 dizzy or to sell the unit as it is . I've no idea whether the rev counter works with the Lumenition fitted
 
Points coils are generally ballasted, to prevent excessive current flow, which would kill the points very quickly, and stop them burning out if you sit with the ignition on and the points closed.

Electronic ignition coils can have much higher current ratings, as there are no points to burn out, plus they are generally fed the full battery voltage rather than through a ballast. All this means you can have a much more powerful spark with the electronic systems. I've seen modern cars do 60-70k on a set of spark plugs without cleaning, even thought the plugs were knackered the coil produced enough spark to run the engine fine.

Whether or not you can use a points coil with an electronic system pretty much depends on the system, I've had cheap Maplin kits before that work fine with the points coil.

Assuming you fit a system that still uses the distributor, there's nothing to stop you carrying a set of points, condensor and coil in the boot if you're worried about failure, although (touch wood) personally I've never had an electronic system fail on me, even ones I've made myself ! :LOL:
 
DaveHerns said:
Maplins make an electronic ignition kit ,about £10 which retains the points , does away with the condensor , and the rev counter still works .I think it uses the points to switch a power transistor . Easy to make up and fit .
Click to expand...

That's one I've used on an old Chevette, worked fine, never gave me any trouble, although you've still got the problem of points triggering, but they run so much less current that they last indefinately.
 
Hello Dave,

The standard Lumenition system uses a points coil, so in the case of our Rovers, the Lucas 16C6 or equivilent.

Ron.
 
HI Dave

Have a read of my recemt post on experiences with "Lucky". After them I'd put a huge amount of money on it being condensor, but I wouldn't rule out completely that it is LV loss from some other cause.

As you'll see I finished up fitting an ignition amp, because of a combination of time pressure and the fact that there will ultimately be a Mallory Twin Point over a 4.6 where the standard dizzy and 3.5 are now. I would have thought you ought to be going for an in distributor electronic?

Chris
 
Gents,
many thanks for all your replies. I had a look at the amplifier in maplins and will order one today to see how it works. I'll also try to get the electronic system that was on the car back. Even if i fit this later i can always use the amp on one of the other cars. At the moment I've very little time with the cars as I'm away all week so it could serve as a stop gap measure at the very least, and be more reliable that the pile of useless new condensors I have!At least if the unit failed on the road the system could be reversed in minutes. Ultimately full electronic with a back up set of parts in the boot is the way to go. By the way, does the rev counter work with luminition?
Thanks again lads.
Regards,
Dave
 
Hi Dave,

What a frustrating problem for you! :evil: I'm in the process of moving to electronic and received my Pertronix Ignitor in the post today. I've copied the email exchanges that I've had with Pertronix below (most recent first) - there's some useful info on installation and coils/tachos.

Cheers for now - keep at it! :)

==========================
Stan,

Thanks for the diagram. The Ignitor should work with your tachometer with no problems. If you have problem installing a 10K ½ watt resister in line with the tachometer wire and coil negative should fix any problems.

If you have any further questions feel free to contact me.

Marvin Grebow Jr.

PerTronix Inc.

Technical Department Ext. 1030

marving@pertronix.com

From: Stan [mailto:vaultsman@ntlworld.com]
Sent: Monday, April 13, 2009 10:36 AM
To: 'Marvin Grebow'
Subject: RE: Ignitor set-up for Rover V8

Hi Marvin,

Circuit diagrams attached, vehicle is negative ground. Tachometer (#37) hooks up to the negative terminal on the coil (#44).

Regards,
Stan

From: Marvin Grebow [mailto:marving@pertronix.com]
Sent: 13 April 2009 16:10
To: 'Stan'
Subject: RE: Ignitor set-up for Rover V8

Stan,

How does your tachometer hook to the coil, the positive terminal or negative coil?

Marvin Grebow Jr.
PerTronix Inc.
Technical Department Ext. 1030

marving@pertronix.com


From: Stan [mailto:vaultsman@ntlworld.com]
Sent: Friday, April 10, 2009 8:39 AM
To: marving@pertronix.com
Subject: FW: Ignitor set-up for Rover V8

Hi Marvin,

Carl suggests I mail you regarding whether the Ignitor setup will affect the tacho on my 1973 Rover V8? (Car details below)

Regards,
Stan

From: carl dudash [mailto:retrorockets@snet.net]
Sent: 10 April 2009 16:07
To: Stan
Subject: Re: Ignitor set-up for Rover V8

Stan,

The Ignitors are compatible with most factory tachs but I'm not certain about you Rover. Please email Marvin at the PerTronix Tech Dept with your question at marving@pertronix.com

Thank you.

Carl
Retro Rockets

Stan wrote:
>
> Many thanks for your email Carl,
>
> Just one more question if I may: Are you aware any issues with the tacho after fitting?
>
> Regards,
>
> Stan
>
> From: carl dudash [mailto:retrorockets@snet.net]
>

Sent: 10 April 2009 13:57
To: Stan
Subject: Re: Ignitor set-up for Rover V8

Stan,

I assume you looked at out Lucas page to determine that your 35D8 takes the LU-181. There are two versions of the 35D8 that take different Ignitors as shown on the page below:

http://www.vintageperformance.com/retro ... /lucas.htm

If you haven't already done so, please check the 35D8 pictures on this page to compare with what you have.

8 cylinder Ignitors are designed for 1.5 ohm coils. If yours is newer and in good condition there would be no reason to replace it. If you need a replacement the 1.5 coils are listed on the page above.
It is permissible to remove the resistor wire when running a 1.5 ohm coil with the 8 cylinder Ignitor. However, on a stock engine there would be no advantage. With a stock engine the best setup would be to leave the resistor in the coil circuit but to run a full 12 V line from the ignition switch to the red Ignitor wire. The source must go through the ignition switch so that there is no power to the Ignitor when the key is off. This would automatically avoid any possibility of low voltage to the Ignitor. Leaving the resistor in the coil circuit would allow the coil to run cooler. With the Ignitor in place you would still have significantly more spark energy available than with points if your engine needed it.
Your instructions will show a wiring diagram for this setup.

Thanks for your email.

Carl
Retro Rockets

>>Stan wrote:
>>
>> Hi,
>>
>> I’m planning to change from points to electronic ignition, and am considering the Pertronix Ignitor.
>>
>> The car is a 1973 Rover P6B 3500 V8 with a Lucas 35D8 distributor (circular baseplate), 1.5 ohm coil, and a resistor wire in the loom which is by-passed when cranking.
>>
>> As far as I can see I need an LU-181 Ignitor, but what coil? And would I need to bypass the resistor wire and re-feed the coil with a new 12V ignition-switched supply?
>>
>> Kind regards,
>>
>> Stan Barnes
>>Leicester, UK
 
Stan,
thanks very much for the information. One thing I've noticed in the correspondance is that the wiring in my car is slightly different to yours. My car is '72 (can't remember if my '73s are different) and the cable from the tacho connects to the positive side of the coil (as apposed to negative on yours), via the (now bypassed) resistive wire, accompanied by the 12V cranking by pass. I've left the original cable in the loom, so I could go back to the resistive feed and original type 1.5 ohm coil in minutes. Will keep this option in mind. Let me know how it goes once fitted.
Regards,
Dave
 
Hi all,
made the most of the other half being away and got out to the cars on Saturday. Fired up the '72 S, which hadn't been touched since it's last breakdown due to other commitments, got about 500m and she stopped. After a few minutes I got another few hundred meters and died in front of a speed trap! I fitted a new condenser, got about 5 min from it. Found an ancient lucas one at the bottom of the toolbox and fitted it. Took her out for a long run. All well!! These new condenser are such rubbish! Must get to maplins next weekend and buy that ignition module.
Regards,
Dave
 
Surely there must be companies manufacturing quality condensers still ? Even if they have to be fitted externally as long as the capacitance is the same it should be OK
 
Hi all,
problem returned on saturday after a run of about 18 miles, accompanied by smoke from my nearside calliper! Looks like the old lucas condensor is now failing. Car runs perfectly for a few minutes, then dies with little warning, no missfire, just one cough and stalls. Starts after about 2min with no hesitation (at least the brakes could cool!). Could the fact that I'm running my coil (high performance dry coil) at 12V? Or is it just telling me to sort out the sticking piston :D . Never had this issue on my other converted car. Day off thurs so going to maplins for the amplifier at long last!!
Regards,
Dave
 
Hello Dave,

If you are running a high performance coil directly from 12 volts as it would be designed, then the condensor and points won't last as you expected. When using points, you need to keep a ballasted system else no reliability.

Why not give the points et al the flick and install an electronic ignition system?

Ron.
 
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