Mis-fire when hot.

[daverclasper]

Just a thought. I had misfire after running for a bit and it was running a bit weak on mixture. 

[haggis]

Thanks Pete,  Bfg & Daver, I have looked at coil cooling and devised something (photo to come) to prevent it becoming a heat sink for the engine, it’s right behind the alternator which limits the cold air in that area, which no doubt doesn’t help. In regard to mixture, I have just rebuilt the carbs and adjusted mixture using a series of Colortunes and it appears to be spot on, I even tweaked it slightly in favour of richer mixture too but haven’t checked it again since.
I‘ve read a few more articles and the original fan is looking like my best option, but I think I’ll put a new coil on it somewhere away from the engine as well. 
 

hopefully 🤞, it will be as simple as that. 🤣

thanks hag 
 

[Pete Lewis]

might seem daft but the coil was bolted to the engine to keep it cooled by the  stable block temperature eg  82c 

common practice on many cars , of the day .   dont ask why not on the 4 cyl's   Ha!!

dont forget once you get a duff plug( there are many these days) they dont recover by cleaning 

Pete

[Bfg]

^ Interesting proposition.  I had assumed it was so, during production, the engines could be run up before being dropped into the car. 

[dave.vitesse]

All 2 Litre Vitesse had a 22D6 dizzy. The 25D6 lacked the rev counter drive and was fitted to the 2000 Saloon of the same period. The Mk1 has the number 41168 stamped on the dizzy side. Most Mk2 had 41273. Late Mk2 had a dizzy with less overall advance stamped 41305. All have a vacuum advance.

All Vitesse used a 12 volt coil and no ballast resistor.

I would look at the plugs, plug leads, coil, points and condenser.

Dave

[haggis]

Thanks guys, work has suddenly kicked off, so no time to look until the weekend, still tempted by the 123 dizzy though 🤔 been looking into it and they recommend the 1.2ohm red Bosch coil with no ballast and a 12v supply for the 6 cylinders. 
Doesn’t seem right to me 🤷‍♂️ But my brain doesn’t do electrics. 

hag 

[Pete Lewis]

thats an expensive must have

theres little reason why a dizzy would work cold but fail hot ,    have this feeling you will spend a lot and the gremlin persists 

prove Im wrong  Ha !

Pete

[sulzerman]

Have you tried reverting to points and condensor?

Just had electronic ignitions fail in both my cars, not going to bother with them again.

[haggis]

Hi Guys, A little update on this. So changed coil, took it for a ride in the scorching heat (3 weeks seems a long time go now) and it did its usual, 30 mins in got hot started to misfire, so I pulled over and took a look. It was running rough at this point, but still idling which was a bonus. I looked at the carbs ( I got 3 stromberg set up) luckily they have the little spring on the side to lift the piston, so two of the carbs were as expected when lifted but the middle carb had no affect on the running of the engine at all, in fact I removed the damper and lifted it all the way up and still nothing, let go and the engine idle returned to smooth and I proceeded all the way home without problem. Ive been out since and still have the same problem. I have been thoroughly through these carbs twice now, never found a sliver, the piston runs as smooth as can be and I've rebuilt them with new needles, jets and float needle valves.

Any ideas on what could be going wrong with this particular carb? the only difference I can find is in the 'Screw Bushing' that houses the jet adjusting screw at the bottom, see pic. 

As always any help greatly appreciated. 

Thanks

hag

[Pete Lewis]

 apart from the adjusters seem screwed in further than normal  the middle has a housing i dont recognise ,  not from any i have twiddled over the years

pete

[haggis]

Hi Pete, do you think it might make a difference? the original one leaked as I couldn’t get a seal properly with the bottom cover and replaced it with this one from a pair of 150’s from a mk2 vitesse I Believe. 
 

thanks hag 

[Pete Lewis]

i dont see why it would cause any problems its just a variation in its machined design   or made by an after market supplier 

are all three jets the same diameter    probably  0.9 

Pete

[chrishawley]

Hmmm.

If attention to the ignition side of things isn't giving a good outcome then it might be worth investigating the induction side. 'Misfires only when hot' could fit in with a leak/crack in carbs, manifold or joints thereof which only becomes evident when everything is hot and expanded - a weak mixture results. Crude tests which might provide some evidence would be a 1) WD40 spray test, 2) when the engine is misfiring try the choke and see if more fuel offsets the problem.

I'm assuming you've got CD150s and thus no heat shield. But are the insulating washers present and correct?

If it's just a case of the top engine getting far too hot exploration might have to go beyond rads and fans and consider the internal condition of the water pump and whether a good couple of flushes is need to reduce 50 years of accumulated detritus in the waterways.

For myself I'd be investigating ignition/distributor first but be prepared to focus attention elsewhere as well is nothing shows up.

 

[Pete Lewis]

an old problem of stop restart , get out kick it  cool it and dance about is having the HT coil polarity reversed

 

make sure the coil to dizzy earth lead is on the negative and the white ignition feed is on the positive  coil terminals  ( for a neg earth car) 

Pete

[chrishawley]

I was wondering whether you have been able to get a solution to your misfire problem. Any luck?

It occurred to me that if investigations of the ignition side are not proving fruitful then then there might be some scope for looking at the induction side. Misfiring exclusively when hot could fit in with an air leak on the induction side. Also I'm assuming you have CD150 carbs. These won't have a heatshield but are the insulation washers between the carbs and manifold present and correct?

Other factors which might impinge on cooling capacity are a deteriorated water pump or 50 years of detritus in the internal waterways. Has the engine been rebuilt in living memory?

[haggis]

Hi Chris, thanks for your post. The engine was rebuilt a couple of years back and I’ve recently rebuilt the 150cds to match. It’s a triple carb set up and an extractor manifold and I’ve hand built a heat shield for it along with a bespoke air filter box. I didn’t replace the water pump when I rebuilt it as it seemed to function well without   
too much play. Yes insulation washers installed, new gaskets etc. I took it out at the weekend in cooler weather and it didn’t once play up, so I’m currently trying the original fan to see if permanent flowing air will make a difference, everyone seems to think it’s a good idea. I’ll let you know: 

thanks hag 
 

[chrishawley]

Dear Hag,

I'd best most interested to know the outcome so do please post again.

I had similar problems a while back with my XJ6; 'normal hot' was fine but 'hot on a hot day' was problematic much as you are experiencing. Eventually sorted with a recon rad and sorting out the absence of proper baffling ahead of the rad to direct all the through the rad rather than round the sides. 

Do please post again when you've tried the 'always on' fan.

[Pete Lewis]

Im always a fan of the engine fan 

Pete

[rlubikey]

You've checked the valve gaps?

Cheers, Richard

[haggis]

Chris, I will certainly post again when the fans on, should be this weekend not sure we are going to get the heatwave we had before though to test it. 

Richard, valve gaps are spot on, I do think I have some wear there though, planning on the rimmers uprated shaft and rockers. Can anyone say if they have done this and if it’s worth the extra money? 
 

thanks

hag 

[rlubikey]

Hag, if gaps are good then sounds like it's not the problem. My Gold Seal engine circa 1989 developed a misfire after a few months. Only happened 50mph plus or gradient, when engine really hot and on hot dry days. Of course never when I took it in to BL. Turned out to be one gap was tight and when hot said valve wasn't closing. (Burnt out?)

Cheers, Richard

[haggis]

Hi guys, we’ll I’ve had a busy weekend trying to find the problem and I think 🤞 I’ve found it. 
1, tried mechanical fan - better but still misfired. 

2, found a new set of HT leads - even worse misfire. ( it was hot) 

3, put the old points back on - no misfire so far. (been out today for two hours in the heat.) 
 
so i think it comes down to lumenition electronic unit in the distributor! just goes to show we all think these things are ‘fit & forget’ but that’s not always the case. The only time you realise is when you have replaced everything else. 🤣

fingers crossed for the weekend, gonna do a much bigger ride out. 
 

thanks hag 
 

[Pete Lewis]

if you  swap  back to points you must re time the ignition   theres no telling that the lecy unit triggers in the same position as the mechanical points 

all down to what sits where in relation to the cam .

pete

[haggis]

Thanks Pete, you’re right it didn’t quite run the same, so I’ll check the timing, more likely to get a new module than stick with points. Really didn’t expect a lumenition one to go that quickly, can only be 3 years old. As the dizzy is worn I’ll get mine refurbed with a new module. 
 

thanks 

hag 

[NonMember]

10 hours ago, haggis said:

Really didn’t expect a lumenition one to go that quickly, can only be 3 years old.

There was a Vitesse at the start line of the 2004? Round Britain which had developed "a misfire at higher revs" on the way down. Since the car I was co-driving was in absolutely top fettle, I decided to help the owner diagnose the "fuel problem" he thought he had. After some time, those of us helping finally managed to persuade him to put it back together and demonstrate the issue to us. It took two seconds for all of us to become immediately convinced it wasn't a fuel problem - the car was revving beautifully up to about 3000RPM then cutting out completely and very sharply. That could only be ignition so we asked about the Lumenition unit. "It's only a couple of years old." Well, more persuasion but since he did actually have a set of points with him he agreed to put it back. The problem went away and the car ran nicely all weekend on points.

So no, I'm not surprised if a 3-year-old Lumenition bit fails. But I'm also not surprised if a 25-year-old one (like on my GT6) is still going strong.