Perculiar engine behaviour when warm

ghce

ghce

Well-Known Member
Registered and warrented my P6B last week to get it legal, first time since 2002/2003, not that I havent driven it in the intervening years, now that I have engine operation back to a reliable state I have noticed that once the engine is up to temp (on the gauge), after about 2 to 3 Km's of running the engine develops an erratic miss, it has always done this for the last 20 odd years after about a kilometer more it dissapears (not the car, just the miss :LOL: ) as you might note in my signature the car is fitted with a Weber 500 prior to this with the SU's it did exactly the same, also have fitted the pertronix unit, did it before.....still does it, have swapped between electric and mechanical fuel pumps still does it, timing is bang on and the car runs with out miss or roll at any other time..... all in all I am scratching my head over this, any one elses P6B do the same? is it a perculiatrity of temp and camshaft or some other thing....any suggestions gladly welcomed.
PS now that the car is all legal again I have used it every day and covered a few hundred K's already, all done with a big smile. :mrgreen:

Graeme
 
Never thought of that, there is plenty of oil pressure and lots of liquid running about under the rocker cover

When in the missing state it will conk out when doing things near idle, ie slow manouvering in a car park or pulling up at the lights but this state only lasts about 2 or 3 minutes then its all 100% till the next day after the car is started again.

Graeme
 
My bet would be either coil or plug leads (or a bit of both!). Did you change the coil when the Pertronix went on? If you haven't already, it is also time to discover the revelation of fitting Magnecor plug leads!

Chris
 
Hello Graeme,

What is the compression ratio of your engine? What brand of spark plugs and ignition leads are you using? The carbon contact in the distributor cap,..it is free to move with a nice amount of spring pressure behind it?

Misfire is typically electrical I suspect hence the reason for the questions.

Ron.
 
Replaced the coil with a new pertronix flame thower II coil, checked the distributer cap and carbon brush when I fitted the ignitor module all looked excelent, The plugs are newish (about 2000kms on them) from memory I put one up in the heat range as I was having trouble with plug fouling back in 2002 with the new unleaded fuel. Plug leads are 8mm Silicon leads that have been in a while (still look new) I put them in in 1989 from memory but when checked at night in my dark garage with the engine running there are no flashes at all.

Engine compression I think is the 9.25:1 option

Graeme
 
I had a 2.0 Manta that behaved a bit like this - half warm it would start to sound like it had a slight misfire then when was up to temperature it would disappear again.... Turned out to be the valve. Sounds like you've already done the electrics, it's regular so shouldnt be fuel.....
 
Hope it's not a valve, dont want to take the head off :LOL: Its had this odd behaviour for a long time now and it has not got worse so i guess I can live with it as its only happening for a short period of running time in any one trip from cold. and now that the engine seems to just be just run in (225,000 KMs) it would be a shame to strip it down for a minor complaint :p Was thinking of roller rockers as the next bit of engine work and like a bit of string, if I have to take the heads off I would not know where to stop, rings, bearings, pistons and bores........I could see a good NZ$1500 to NZ$1800 in parts dissapearing into the motor.

Graeme
 
My grandfather had a P5b when it was new... He used to change and grind the valves every 6000 miles apparently!

Taking the head off and putting it back on itself isnt the hard bit. The hard bit is whatever bolt decides to be seized in or rusted badly and snap are the problem!

Certainly though i think you have to explore every other avenue first.

If it works and doesnt affect power/economy too much I'd leave it as is... Then do the proper all out recon job when you're well and truly ready and have built up the funds to pay for it to the standard which will give you satisfaction....
 
My V8 auto does the same most times I drive it but not every time. It is also hesitant and pulls back when accelerating firmly from 6omph plus although it will still get to a decent speed. It was suggested yesterday at the Harrow meet that if I clean all the contacts on the coil and dizzy and re route the HT leads so they do not cross over I may get rid of both the problems. What do you think? I will try this at the weekend .
Can anyone tell me which magnacor leads to use in case mine require replacing (product code?). I would want them to be black and to fit under the clips which separate the leads.

Thanks
Julian
 
Carburretor icing ? Just a guess
Click to expand...

I was going to say! Sounds like what many of my carburetter-fed cars have done in cool weather; hesitate during warm-up on applying light throttle, threatening to stall near idle. With an engine and carb/manifold that've been run in ... that would be typical of many a car. I assume it's "winter" in NZ now? A good splash of anti-condensation agent in the fuel should help you tell if that's what's going on.
 
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