R-Series missfire

[mn757]

Hi everyone,
My 1983 1.6 HLS with the R series engine is miss firing at low revs, although the car still seems to pull quite well. I have replaced plugs, leads, distributor cap, rotor arm etc but still have missfire. Have checked timing, tried another carb, still have missfire. All the plugs seems to be sparking ok. The car has been compression tested but seems ok. I have a manual choke and dont have the fuel cut off valve anymore. Does the ecu still play a part in the running of the engine if these components have been taken off? And could the ecu cause a missfire?

Any help appreciated.

Martin N

[H48HPE]

Im not really an expert with ECU cars but Id check that none of the vacuum pipes that come off the inlet manifold are leaking air, this would cause bad slow running. My other thoughts are that the distributer might need to be overhauled, or a new one put in, you need to check the air gap in the electronic ignition and also that the centrifugal (if thats how its spelt) advance mechanism is ok and that the vacuum advance is functioning and not leaking air.

someone else will be able to offer more advice i think?

andy

[G Force]

Hi, if you have a manual choke fitted and the orfco valve disconnected, then in your case the only function of the ecu is to drive the temperature gauge.

You say that the orfco valve is not fitted, I don't know if you just mean disconnected but if you take this valve off then you will get an over lean mixture at part throttle, which would cause a misfire/hesitation. If the valve is still in place but disconnected you should check to make sure it is not stuck in the open position.

If you still have the vacuum switch fitted you should check the diaphragm is not split, as this could give you problems at low speed due to an over rich mixture.

As already mentioned you should check all the hoses for air leaks and check the distributor vacuum unit is functioning, also check the air filter is not blocked. The air filter can become blocked quickly if the exhaust manifold or front pipe joint is blowing.

I notice you have fitted new spark plugs, if the plugs are not gapped at 0.040" you can get a light throttle misfire due to the plug gaps being too narrow.

Cheers Gary

[MaestroMatt]

The Haynes manual that I happen to have on my desk at work (dedicated or sad?) recommends a 0.8mm or 0.031" spark plug gap. Is this bad advice? Is your recommendation of 0.040" borne of experience?

[G Force]

Originally posted by MaestroMatt
The Haynes manual that I happen to have on my desk at work (dedicated or sad?) recommends a 0.8mm or 0.031" spark plug gap. Is this bad advice? Is your recommendation of 0.040" borne of experience?

Haynes or Rover Who would you trust?

Gary ;)

[E_T_V]

Err neither ;) ;)

The rover dealers I've been to have been the most unhelpful, and useless I've had the misfortune to deal with.

The cap shouldn't make too much of a difference in theory as so long as it jumps the gap well it'll ignite the petrol.