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Rough running 4.6l
Posted: Wed Feb 23, 2022 3:10 pm
by Stagrover
Hi,
Recently had a rebuilt 4.6l Rover engine fitted to replace a smooth idling and running but tired 3.9l, both fitted with a piper 270 cam.
The 4.6 has the non serpentine front cover.
I transferred over the distributor and edelbrock 1404 but cannot get the new engine to idle smoothly or cruise without stumbling and kangarooing.
I’ve checked the fuel pressure is around 6psi when running.
I’ve tried 3 different distributors and a new earth and live feed but no difference. Can’t put a figure to the timing but it’s smoothest (relative term) engine speed at an indicated 1000 rpm.
I transferred the entire ignition system including plugs from my other 3.5 which is running fine but no difference so put it back to the 3.5.
Currently using sidecars settings of 86 primary and 67/55 needles with the Lucas distributor vac disconnected and blocked on the carb.
There’s no discernible difference between having the vac connected or not.
I’ve spent so much time swapping things over and revving the engine that an anonymous neighbour has now written to complain - all constructive ideas welcomed.
Can anyone suggest a specialist (ideally in the SW) who has the knowledge to help to keep the peace in the neighbourhood?
Re: Rough running 4.6l
Posted: Wed Feb 23, 2022 7:11 pm
by Ian Anderson
Poor earthing, engine / chassis/ or battery
Ian
Re: Rough running 4.6l
Posted: Wed Feb 23, 2022 8:00 pm
by ChrisJC
Sounds like some science is needed! Can you get a gas analyser on the exhaust?
Chris.
Re: Rough running 4.6l
Posted: Wed Feb 23, 2022 8:31 pm
by Stagrover
Thanks Ian/Chris
I’ll try using the jump leads for extra earthing not something I thought of as the braided earth from battery to engine looks to be in good condition.
If I knew a garage that would do more than twiddle the idle screws I would book in for a reading. Asked the local American cruisers for a recommendation - the garage owner who has a corvette tried to convince me that I had the carb at right angle to normal as he obviously hadn’t seen an offy dual plane manifold that is split front to back not side to side.
I have been adjusting the idle screws as a pair not one at a time.
John
Re: Rough running 4.6l
Posted: Wed Feb 23, 2022 10:11 pm
by Richard P6
Is there any way that you can measure your AFR?
Also, have you tried the primaries and needles from when you had the carb on the 3.9?
Re: Rough running 4.6l
Posted: Wed Feb 23, 2022 10:30 pm
by Stagrover
Hi Richard
Haven’t got any Lambda (?) sensors fitted to measure afr.
Started with the 3.9 settings, which I believe are the base 1404 I ran for 15 years, went up and down on the needles and springs but didn’t stumble on a better setting.
Real steel and rpi both say base settings for 1404 ok for 4.6l starting basis.
Only switched to Sidecar needles and springs and no vac connections today without success after reading more posts on the forum over the weekend.
The problem seems to be lots of people seem to have got good results from different settings due to the different characteristics of each engine.
Re: Rough running 4.6l
Posted: Fri Feb 25, 2022 9:38 am
by SuperV8
Stagrover wrote: ↑Wed Feb 23, 2022 3:10 pm
Hi,
Recently had a rebuilt 4.6l Rover engine fitted to replace a smooth idling and running but tired 3.9l, both fitted with a piper 270 cam.
The 4.6 has the non serpentine front cover.
I transferred over the distributor and edelbrock 1404 but cannot get the new engine to idle smoothly or cruise without stumbling and kangarooing.
I’ve checked the fuel pressure is around 6psi when running.
I’ve tried 3 different distributors and a new earth and live feed but no difference. Can’t put a figure to the timing but it’s smoothest (relative term) engine speed at an indicated 1000 rpm.
I transferred the entire ignition system including plugs from my other 3.5 which is running fine but no difference so put it back to the 3.5.
Currently using sidecars settings of 86 primary and 67/55 needles with the Lucas distributor vac disconnected and blocked on the carb.
There’s no discernible difference between having the vac connected or not.
I’ve spent so much time swapping things over and revving the engine that an anonymous neighbour has now written to complain - all constructive ideas welcomed.
Can anyone suggest a specialist (ideally in the SW) who has the knowledge to help to keep the peace in the neighbourhood?
What idle advance value are you using? I think the 4.6 will prefer a different value to the 3.9.
I would also double check your crank pulley pointer is accurately pointing to TDC when the engine is at TDC - using either a piston stop tool in number 1 spark plug hole or dial indicator on the rocker.
My pointer wasn't accurately pointing to TDC - so I 'calibrated' my crank pulley advance/retard marks - I made a piston stop tool from an old spark plug and cap head bolt - put two marks on the crank pulley where the engine stops - and the centre of these marks is 100% TDC.
Re: Rough running 4.6l
Posted: Fri Feb 25, 2022 4:01 pm
by Stagrover
Thanks for the suggestion, as I said I can’t put a figure to the btdc that I’m using, just the best speed I could achieve when adjusting the distributor.
I’m going to start a new post in the engine section as I’ve taken the carb off and found that the right hand rear barrel appears to be flooding as it is wet when I have just come back from a slowish drive to see if adjusting the float settings made a difference - no such luck.
Thanks again.