Slight Missing at Cruising Speeds
Posted: Sat Oct 04, 2014 12:25 pm
Hi
I have a late 1984 GTV6 in Lincoln UK with a problem.
Here’s the story:
Starts fine when cold or hot
Engine’s revs rise smoothly and quickly.
Car accelerates quickly with no issues. Even hard acceleration is smooth.
No lack of power at all. Accelerates well in fifth gear from low speed.
No hesitancy when quickly lifting above idle to 2000 rpm with gear in neutral.
No hesitancy when revving to 5000 rpm in neutral gear. Happens quickly and smoothly
But when cruising at virtually any fixed speed there appears to be slight missing and I can feel the car slightly jerking.
When car is stationary and I raise the revs and then hold at any rpm I also notice slight missing. No missing as I raise the revs
Engine does miss a little when idling
What I have done:
I can’t find any air leaks in pipes etc.
Changed spark plugs for correct new ones, old ones also correct and were the right colour at the spark point – No difference
Fitted a spare ECU I have – No difference
Checked distributor and rotor, all looks fine
Spark plug leads are good and well connected to plugs
Checked earthing/grounding - all looks fine
Valve clearances are OK
Used fuel injection cleaner - No difference
Auxiliary Air Valve is clean
Throttle switch looks OK
Emission test is OK
It is very strange that the car accelerates smoothly with no hesitancy and then when you cruise it appears to slightly miss at all cruising speeds except that the faster you go with the cruise the less you notice it.
Could it be a fuel injector or AFM that is faulty?
Any thoughts would be much appreciated thanks.
Someone told me the valve seats could be worn. I don’t think so and anyway the engine can use unleaded petrol and the mileage is not high.
Engine does not smoke out the exhaust at all. No oil is burnt.
No black smoke when I raise the revs. Car is not running rich.
Otherwise car is great and in lovely stock condition.
I have a late 1984 GTV6 in Lincoln UK with a problem.
Here’s the story:
Starts fine when cold or hot
Engine’s revs rise smoothly and quickly.
Car accelerates quickly with no issues. Even hard acceleration is smooth.
No lack of power at all. Accelerates well in fifth gear from low speed.
No hesitancy when quickly lifting above idle to 2000 rpm with gear in neutral.
No hesitancy when revving to 5000 rpm in neutral gear. Happens quickly and smoothly
But when cruising at virtually any fixed speed there appears to be slight missing and I can feel the car slightly jerking.
When car is stationary and I raise the revs and then hold at any rpm I also notice slight missing. No missing as I raise the revs
Engine does miss a little when idling
What I have done:
I can’t find any air leaks in pipes etc.
Changed spark plugs for correct new ones, old ones also correct and were the right colour at the spark point – No difference
Fitted a spare ECU I have – No difference
Checked distributor and rotor, all looks fine
Spark plug leads are good and well connected to plugs
Checked earthing/grounding - all looks fine
Valve clearances are OK
Used fuel injection cleaner - No difference
Auxiliary Air Valve is clean
Throttle switch looks OK
Emission test is OK
It is very strange that the car accelerates smoothly with no hesitancy and then when you cruise it appears to slightly miss at all cruising speeds except that the faster you go with the cruise the less you notice it.
Could it be a fuel injector or AFM that is faulty?
Any thoughts would be much appreciated thanks.
Someone told me the valve seats could be worn. I don’t think so and anyway the engine can use unleaded petrol and the mileage is not high.
Engine does not smoke out the exhaust at all. No oil is burnt.
No black smoke when I raise the revs. Car is not running rich.
Otherwise car is great and in lovely stock condition.