Thread: 92 Classic 3.9 Running Rough under load

For moisture problems, remove the distributor cap and dry it out either in a sunny location for 1-2 hours or use a hair dryer.

More advance won't hurt. 6 to 10 degrees BTDC for a healthy engine.

If it is running rich and blowing black smoke there's no point replacing plugs etc until you have fixed it. Possibles are temp sender for the EFI, air flow meter, fuel pressure regulator. Search on those for test procedures.

Have you checked the aircleaner for rat's or bird's nests??
Regards Philip A

Now there's a thought......to be honest no.....I will do that tonight
(first rule....check the bleedin' obvious first !)

I Didn't think of that as I had it apart before I went away.

Originally Posted by bee utey

For moisture problems, remove the distributor cap and dry it out either in a sunny location for 1-2 hours or use a hair dryer.

More advance won't hurt. 6 to 10 degrees BTDC for a healthy engine.

If it is running rich and blowing black smoke there's no point replacing plugs etc until you have fixed it. Possibles are temp sender for the EFI, air flow meter, fuel pressure regulator. Search on those for test procedures.

Stripped it all down, cleaned and dried it at the time. No change.
No black smoke. More grey/white ?
I am replacing Plugs and leads anyway. I'm sure this will only help the diagnosis rather than hinder it. Dizzy cap pickups are pitted.

Originally Posted by PhilipA

Have you checked the aircleaner for rat's or bird's nests??
Regards Philip A

OK....No rat's or birds nests !

so back to my original question, what affect will the lack of vacuum advance have on the performance as I have read conflicting views on this ?

Is the greatest vacuum at lower or higher revs ?

Originally Posted by bigdog

OK....No rat's or birds nests !

so back to my original question, what affect will the lack of vacuum advance have on the performance as I have read conflicting views on this ?

Is the greatest vacuum at lower or higher revs ?

Vacuum advance makes no difference to operation at more than say 70% throttle. It is there to improve economy at light throttle settings as the speed of combustion slows down.

Thanks - new vacuum unit is on its way but based on the feedback I am not expecting this to make a great difference to performance under load.
Does anyone know of anyone in the Hornsby area with Rover diagnostics kit (or someone who owns a Volt/amp/ohm/multimeter and knows how to use it)?
Cheers

Sure enough it gradually improved until I am up to what feels like 7 cylinders. Now it starts and idles well, steps through the 1200rpm to 900 and then ticks over at approx 650rpm, slighly lumpy but not bad. However under load there is no power. Struggles up the smallest hills. Petrol only, no gas.

The stepper motor will raise the idle to a target amount even if it is only going on 6 or 7.

Checked plugs & leads. Spark is good. As I pull each lead the revs drop so it is firing on all 8. Purchased a strobe light to set the timing, 1-2 deg BTDC by the book, but it is off the scale and I cannot rotate the dizzy (clockwise) as it hits the thermostat housing.

Huh? this would suggest that maybe the timing chain has slipped a tooth or so, unless the timing was out before you bought the light. Did you have the sensor on 1 which is the LH (passenger In OZ) side front plug lead?
If the chain has slipped the only way to tell AFAIK is to pull the timing case off and have a look.
I would check teh timing again , and if it comes out "off the scale" again, then you are faced with pulling the timing cover.
BTW, you didn't pull all the wires on the dizzy out when replacing the cap by any chance? If you did , set the engine to No1 TDC firing and check that the rotor points to No 1 wire in the cap. You can tell firing by sticking you thumb or suitable appendage in the plug hole and turning the engine by hand towards TDC. Pressure=correct .

There is a smell of unburnt fuel from the exhaust so it is running rich, and I can suck through the vacuum advance and there is no resistance suggesting the diapragm is gone.

The vacuum advance being inoperative would have nothing to do with your symptoms.
Regards Philip A

Another cause of 3.9s missing under load is sticking exhaust valves, butr yours appears to miss all the time from your input.