v8 misfire

S

sharonandmatt

New Member
hey new car as of monday worked solidly last two days to get the car through the MOT which it did (miracle i swear) so have taken it out for a two runs one after filling up with 95 octane (no 99 as they had run out) this afternoon and one this evening the first run was great got up to mid point on the temp gauge and was running smoothly, when at idle waiting for lights and at junctions in drive the oil warning light did flicker on and off but the tiniest bit of throttle sorted that out, got home and adjusted the idle point on the SU's so it idles more smoothly and no more oil light, then took her out for a second run not long ago and suddenly wont warm up at all there is only a kenlowe fan which wasnt on but temp gauge only registered to the very bottom of the green area, and whilst cruising and accelerating the engine would misfire once here then a few times then once etc etc and occasionally misfire out the exhuast was just on one side but now seems to have changed sides or be both not sure yet, pulled over in a petrol station to check things over and the engine did appear to be fairly cool the manifold was quite hot but seemed the temp reading was correct squeezed the water pips to check for air locks etc but no bubbles seemed to come out but not 100% sure there is water in the top pipe as didnt feel quite right but again no bubbles, restarted the car temp went up whilst parked to mid level squeezed the pipes some more seemed fine, stopped engine again to go look for octane booster in cse that may be the problem (no joy as usual nothing to help classics) got back to car adn it wouldnt start tried for a while then sharon suggested choke pulled that, it started run it for a few secs turned it off then tried again no start! turned over but wouldnt fire up tried choke again still no joy waited a bit an she finally started (no idea what caused that) decided not to risk switching off again so headed home again misfiring under acceleration.
sorry for the lengthy description but thought it best to accurately describe the situation, can any one help please is this a combined problem the not heating up/misfiring or totally seperate and what should i do about them both?
help please as don't really want to have to take the heads apart after only one day of driving!
 
Hello sharonandmatt,

With a new Rover or any make of car for that matter, it always pays to carry out some initial maintenance so that you have a known base from which to start should problems crop up and so......I would start by changing all 8 spark plugs,..fit Champion L92YC, gapped to 25 thou. Fit a new fuel filter, new air filters and engine breather fiter. Fit new flame traps and ensure that the hoses linking them are free of any solids. Same goes for the brass pipes off the SU carburettors that accept the hoses.

Drain the engine of all coolant by using each drain tap located on the side of the engine block, same goes for the radiator. Change all hoses including the heater hoses. Flush the system completely and refill with the correct type of anti freeze/anti boil/corrosion inhibitor. Fit a new 15psi radiator cap.

Does the engine still carry the original mechanical fuel pump? If so, remove and fit a new overhaul kit comprising diaphragm, seals and valves.

Change the engine oil and filter.

Is the engine fitted with an electronic ignition system or is it still using points?

An engine misfire at idle can be the result of the idle mixture being too lean, so before adjusting carry out all of the above.

The oil pressure warning light coming on at idle means that the oil pressure has dropped to 8psi or so. This could be due to the engine being filled previously with the wrong grade of oil, or the engine has considerable wear in all bearings, rocker shafts and oil pump.

Ron.
 
Rule no 1- Don't Panic!

Having read you're other posts I have a couple of observations. First off 99 octane, plus a booster, is important for a '68 car as it probably has a 10.5:1 compression engine. Next, if it hasn't run for a while you must regard the petrol in it when you bought it as highly suspect. Don't read anything into it until you've put a couple of tankfulls through. If still persisting then as Ron says do a full service including points and timing to get the basics right. I'd be tempted to jump straight to the carburettors. SU's don't like standing for long periods and the floats in the float chambers have a habit of seizing either shut or open after lack of use. I think I might buy a carb overhaul kit as well and search and read up on here how to deal with twin SU's. If you need more advice after your search just ask. Ron is also right in identifying bushes in the throttle linkage. They have a habit of going walkabout after 40 years and then you don't achieve full throttle at the carbs. The Rover V8 is also known to be extremely sensitive to the quality of ignition leads. Only the best will do - buy a set of Magnecors! Also a new distributor cap. 8 cylinders are a bit of a challenge for bakelite and they are known to break down and track between cylinders much more often than normal cars. If it was running smoothly at idle to start with it doesn't sound as if you have any fundamental engine issues. The low oil pressure we can get to after you've made it run right. Whilst not desirable the Rover V8 is known to tolerate low oil pressure very well.

Chris
 
brilliant thanks very much guys much appreciated, thankfully the car had a new set of leads, plugs, contact points and distributor cap just before going off the road so i know they are all ok, will get a new fuel filter as the old fuel has probably degraded like crazy by now, hoping to convert over to holley carb soon to get away form the Su's so hopefully wont have to fiddle with them before the upgrade, yeah the engine did seem to be running very well before hand so i presume most of the issue will hopefully be just a decent service and clean up we shall see, right sharon of to the shops to get parts and time for me to get dirty again!
 
ok been to our local motor factors and shock horror their new computer system doesnt list our car, helpful keeps saying its a p5 and not parts listed, trying to get some of the bits listed above like flame traps? and a new thermostat etc, they had no idea what a flame trap is so no clue there and the thermostat the only one i could find that might be right is for an sd1 is this going to work or do i need to track down a proper one? are there any parts places that anyone recommends? especially if they are in nottingham or the midlands
 
If this car has been standing for some time , it sounds like the fuel has gone off. I believe it can turn to jelly ? Might be worth blowing back down the fuel pipes
 
having similar issues with my v8 auto. managed one run (short) and on way back was surging slightly. misfire evident. hesitation and trying to add more fuel only made it worse. even idle was rubbish. cut out quietly and without warning.. coasted to kerb . 2 mins later started and revved ok with no load. pulled away and drove at slow speed with engien very unhappy.
took fuel sender out (and drained tank of course). fuel filter on sender unit clogged with fine rust,checked tank around sender, larger rust particles. so suspect fuel starvation main cause . will fit new fuel filter asap. also going to fit electronic ignition so doing away with points and condenser.
coil and leads look brand new.. suspect previous owner replaced. will check after new bits fitted with a road test. hope your issues get sorted soon. hope mine go away too...
 
classicalgreen wrote,...
so doing away with points and condenser.
Click to expand...

A capacitor which is not functioning as it should will certainly have a very negative impact on engine running. Once the capacitor fails completely, the engine won't run at all, so it is my understanding. I was always under the impression that the capacitor was there so as to extend the useable life of the points, through burning prevention, but apparantly that is not the case.

Ron.
 
SydneyRoverP6B said:
classicalgreen wrote,...
so doing away with points and condenser.
Click to expand...

A capacitor which is not functioning as it should will certainly have a very negative impact on engine running. Once the capacitor fails completely, the engine won't run at all, so it is my understanding. I was always under the impression that the capacitor was there so as to extend the useable life of the points, through burning prevention, but apparantly that is not the case.

Ron.
Click to expand...


The idea of the capacitor/condensor is that it inhibits/slow down (to a certain extent) the sudden rise in voltage level when the points open (due to the drop in current - L di/dt - coils [aka inductors] HATE changes in current and will try to keep the same current flowing after the points are opened by generating a huge voltage), which would otherwise result in heavy arcing of the points faces AND also mean electrical energy is wasted in that arcing instead of being sent to the plugs via the HT leads.

However it doesn't inhibit/slow down too much, as otherwise the HT voltage induced would be insufficient!

So while the capacitor/condensor does (to some extent) increase the life of the contact points, that's a side-effect and not the primary reason.
 
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