Missfire

[sulzerman]

Hi all

Had the 2500 saloon out the weekend all running very well.

Then there was single missfire, or more like a large jolt! Then a couple seconds later the same again.

The next 40 mile no problems at all just running normally. 

Any ideas what it could be?

I have fitted the following new parts NGK plugs, HT leads, Pertronix electronic ignition, rebuilt distributor, red rotor arm,and dist cap.

[Guest]

Could it have been a bit of dirt in the fuel - a coincidence I agree, having made the changes you stated.

 

Can you recall exact speed and road conditions: incline etc; it may help to narrow down the cause or focus elsewhere.

 

My money would be on the dizzy, as the jolt does not sound like a misfire but a sudden loss of electrics. 

 

Sorry, not much help at the moment.

 

Regards.

 

Richard.

[sulzerman]

Hi Richard

It was going up a hill doing about 40 mph.

A sudden loss of electrics sounds very likely.

 

Thanks for your help

Paul

[Guest]

Paul.

 

Under the circumstances I think it will be prudent to check all the electrical connections first, commencing at the battery posts, thereby eliminating any problems in that sector.

 

Then the fuel connection etc, which then brings you to the recent changes you have made.

 

It's a case of progressive elimination but necessary I feel. Pointless checking your new goodies when the problem MAY be elsewhere - coincidental or otherwise.

 

Regards.

 

Richard.

[dougbgt6]

Paul,

 

Unfortunately the quality of some new parts these days can be poor. I had a brand new condenser fail after a week. I went electronic after that! 

 

When helping with computers, plumbing or cars my first question is always "What was the last thing you changed before it stopped working?"  In your case it seems, almost everything!

 

As Richard says first check all the connections. Do you still have all the old bits? Put them back, easiest first then re-test. From you list of parts I wouldn't be surprised if it were plugs or HT leads. The rest less likely but possible.

[Pete Lewis]

as this is a TC  are you on HS6 carbs or strombergs 

 

what oil do you use in the dash pot damper ??

 

Pete

[sulzerman]

Hi Pete

I use 20/50 engine oil in HS6s

 

Thanks

Paul

[Pete Lewis]

Does it only hicup under load?

Check the rotor top brush is in contact

new plug breaking down under load

mixture on the weak side of Ok.

check theres no green stuff in the coil, head terminal

Do you run on 97+ fuel with near factory timing

is the coil runing a balasted 6v ign feed , is the petronix on 12v feed ?

 

Just few more ideas

pete

[sulzerman]

Hi Pete

Thanks for the ideas. I will check these items at the weekend. I did put £20 worth of 95 unleaded before the jolt it would have been mixed with the super unleaded already in the tank, do you think this could make a difference?

 

Thanks

Paul

[dougbgt6]

Wouldn't have thought so, poor fuel would give you poor running, not a complete cut out.

[Guest]

Paul.

 

I do think your car problem is electrical rather than fuel.

 

Fuel problems give a gentler notification whereas electrical is more severe and with the jolt you described it sounds as though there was a complete loss of electrics briefly.

 

If that is the case then you would be looking at one of the key components such as the battery lead or the main supply wires / components to the ignition set-up. As mentioned it will need a step-by-step elimination examination. 

 

Doug is correct regarding the side effects on fuel - going back to my "gentler" point.

 

Under load is the key factor here and something has been unable to deal with the additional "strain" placed on the electrical requirement.

 

It may have been a spike of some sort that has cleared fully - these things do happen now and again. However, I think you can only check the usual suspects and run the car again in the same environment that you first noted the problem. In addition you may wish to substitute a part at a time to ID the problem, even if it means running your test route many times.

 

I would also say that you need to eliminate any doubt you have about the fuel by using a 97+ octane, then you will know you are dealing with electrics only; which I think we can all agree on to be the case in all honesty.

 

Good luck.

 

Richard.

[Pete Lewis]

You havnt got spark plugs with an R in the suffix ?

 

and on the ballast /non balast coil feeds

balasted runs at 6v and has 1,5ohm coil

non balast runs at 12v and 3 ohm coil

 

problems are some electronic units dont like a 6v feed

if bypassed and you have 12v feeding a 1.5ohm coil you get very excessive HT and high amps through the leccy unit blow rotors etc.

so the high HT can leap about in our old style systems

 

use 6v on a 3 ohm coil and you halve the HT and get a weak spark.

 

add in R sufix plugs that are resistive and you get some interesting hic ups

pete

[sulzerman]

Hi all 

Had a good check on Saturday. I decided fix the slightly dodgy connection to the positive battery clamp.(see picture)Took the car for a good 60 mile run lots of hills ect, no problems at all.

Could this have caused the jolt/missfire?

 

thanks

[dougbgt6]

SLIGHTLY dodgy?!!

 

Go directly  to the naughty step!

 

Don't know if that was the cause, how was the cable clamped, in the clamp, if you follow me? If it was loose, yes, likely.

[Guest]

Paul.

 

I think you may well have identified the problem, the broken strands will reduce the current flowing ability of the wire and also the wire will run hotter in that condition. The reason the wire is that thick with those many strands is to ensure that the correct amperage can be handled by the wire and the wire does not get hot.

 

The fact you have done "up hill & down dale" without a problem seems to suggest a solution found. In time that wire would have broken completely and if you are running an alternator that would probably bugger it.

 

I presume the corresponding earth wire is okay ??

 

Well done.

 

Richard.

[sulzerman]

The wire was moulded in the clamp. Yes earth wire is perfect. The positive lead has been dodgy for a while, probably deterating gradually without me noticing.

Cheers