suddenly a rough running engine

quattro

Well-Known Member
#21
Just an idea, but I had a bearing go on my dizzy once. The the central shaft would wobble around, so the rotor arm would be too far away from the cap at times. Have you tried catching hold of the rotor arm and trying to wiggle it about?

Richard
 

sdibbers

Well-Known Member
#22
Hi there.
today I did more tests regarding the plug leads etc.
eventually found that the cap was not sending a spark to 1and 4 cylinders from the cap end.
So now have to find a cap, Supercheap can order me one for $49 plus postage, so that is my
only way forward. Wins have them for 9 GBP plus post, but going with the local option.
I always use 98 octane , 95 if thats all that is available.
Great news! Sounds like you've got it.
 
#24
hi there,
no it did not work.
The new cap is now working and I have all 8 cylinders now firing, but the exstream rough running is the same.
it wont rev, really does not want to run and splutters to a halt.
Cant imagine what is wrong, it ran perfectly several weeks ago on a club run, came home, parked it.
Went to start it a week later and this happens, giving no indication of the events that now present itself?
totally baffled..
does this mean that I have to remove the heads and see if something is amiss?
it still has good oil pressure of 60 lbs too, and no knocks!
maybe it needs a Mars bar to help it start, run and drive?
Peter
 
#26
One two or three occasions I have had similar problems and has been duff petrol.
Did not accelerate, popping & banging etc. Try replacing it .
thank you for the info.
unfortunately the tank is 3/4 full, so taking in your advice I will buy an octane booster , add to the tank, give the car a good
bump up and down and see what happens....:p
Peter
 

roverp480

Active Member
#28
thank you for the info.
unfortunately the tank is 3/4 full, so taking in your advice I will buy an octane booster , add to the tank, give the car a good
bump up and down and see what happens....:p
Peter
First time it happened I had the whole fuel and ignition system to bits , gradually using up the fuel with testing etc and eventually had to fill up again . Instantly, problem solved . Another time it was on my Land Rover which had two tanks, one filled with the duff fuel, switching tanks would solve it or bring on the poor running, until refuelling.
 
#30
My 2 cents worth. Have you checked the distributor rotor for correct resistance?. I chased rough running down previously which ended in the rotor being open circuit. There was enough spark at idle but once the gas was on it ran very poorly with no power. I think resistance is typically about 5K ohms.
 
#31
hi there,
today I purchased a bottle of Octane booster, poured into the tank, started the car and no difference.
Still the appalling rough running, wont rev.
now wonder if something is wrong with the distributor with the electronic conversion done last year, maybe I should see whats
available in complete electronic distributors for the v8 engines. any recommendations with that regard?
looks like I am running out of options on this problem...
Peter
 
#32
hi there,
today I purchased a bottle of Octane booster, poured into the tank, started the car and no difference.
Still the appalling rough running, wont rev.
now wonder if something is wrong with the distributor with the electronic conversion done last year, maybe I should see whats
available in complete electronic distributors for the v8 engines. any recommendations with that regard?
looks like I am running out of options on this problem...
Peter
If you think the petrol might be the cause then I can't see octane booster making any difference. A fuel problem is more likely to be contamination, than the petrol being of a lower grade. The only solution if it is the fuel would be to drain the tank. You've really nothing to lose, since if fresh fuel doesn't make a difference then you simply put the old stuff back in.
 
#33
I still reckon it's the dizzy. Either a broken spring weight or diaphragm. Just sounds like what happened to me. And they can go in an instant, too. Mine was fine, and then next time I went to use the car it coughed, spluttered, refused to rev and then just wouldn't run. Might not be cheap but I'd get another dizzy. If it's not the problem then you have a spare, or sell it again....
 

sdibbers

Well-Known Member
#34
Have you done a compression check? Just to eliminate the really nasty stuff?

Having said that the symptoms you describe sound more like a vacuum leak or weak ignition spark. Is there any difference between choke out and in? If you do I would suspect fueling issues.

Do you notice a gradually rougher idle if left idling for a while (hard I know when it’s rough in the first place). I’ve found that can indicate a weak spark as the plugs foul due to incomplete combustion.
 
#35
Have you done a compression check? Just to eliminate the really nasty stuff?

Having said that the symptoms you describe sound more like a vacuum leak or weak ignition spark. Is there any difference between choke out and in? If you do I would suspect fueling issues.

Do you notice a gradually rougher idle if left idling for a while (hard I know when it’s rough in the first place). I’ve found that can indicate a weak spark as the plugs foul due to incomplete combustion.
Thank you everyone for your constructive help suggestions.
I have not done a compression test yet, but will do just to satisfy myself that "nothing down below is suspect".
Choke in or out does not make a lot of difference.
On idle, it does seem to get worse and will then stop as the idle is so low.
Will try to source a new complete electronic dizzy , any recommendations?
there seems to be a 35D and a 35D8 , which one is correct for my 1976 model car, V8 P6b?

Peter
 
Last edited:
#36
I think they're the same? What type of dizzy do you have at the moment? Would it be easier to pull it out and have an auto-sparky check it?
 

sdibbers

Well-Known Member
#37
I’d be more inclined to definitely identify the fault before replacing random large parts. I’d confirm spark strength is the issue and not fueling. Also, I’d borrow/acquire a compression gauge to be sure it’s nothing nasty.
 

cobraboy

Well-Known Member
#39
The advance diaphragm can be checked by sucking on the pipe, you can tell if the diaphragm is holed or leaky by sucking and putting your tongue over the pipe end, it should hold vacuum.
The engine will still rev up if the diaphragm is shot so I doubt that is the problem.

BF
In post #6 you say you checked all plugs were sparking with a tester, but in post #20 you say that you are down on cyls 1 and 4 and suspect the cap ? so is this an intermittent result ?
Perhaps go back and check all plugs again.
Do not start pulling cylinder heads !
It may be an ignition problem, and may be related to your electronic ignition. You say the car was upgraded to electronic, well I would put it back on points using the kit that you took off when it last ran on points.
You have had the LH carb looked at, so I think you need to concentrate on sparks now.
For a few bucks you could purchase a temp reader, these are excellent for finding weak or misfiring cylinders without cooking your fingers ;)
Point at exhaust branch by cyl head.
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#40
today I had a look at the dizzy . fiddled a bit with the sensor adjusting the gap minutely, now the car will not start at all.
new electronic dizzy's are very expensive, wins and wadhams need exchange , which postage from and to Australia is prohibitive, so...
looking at new ones from Ignition Bundles - Rover - V8 Engines - Powerspark Ignition
seem to be the way forward?
the tester mentioned showed a light when located anywhere within the lead areas, so unwittingly I had assumed that all were sparking, but that was
not the case. I had to individually remove every lead, isolate it and test.
The tester picked up the signal anywhere within the lead areas, not good.
Peter
 
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