Post Reply
Alfa GTV6 UK
Silver
Silver
Posts: 5
Joined: Mon Feb 28, 2005 8:54 pm
Location: East of England

Slight Missing at Cruising Speeds

Post by Alfa GTV6 UK »

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. :D

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.
User avatar
MD
Verde
Verde
Posts: 2436
Joined: Mon Nov 22, 2004 2:37 am
Location: Brisbane, Australia
Contact:

Re: Slight Missing at Cruising Speeds

Post by MD »

You could have a faltering alternator delivering various volatges including spikes. Remember that an alternator makes AC unlike a generator that makes DC which is what the car wants. Any problems in the rectification of the AC may induce faltering in the computer.

The second suggestion is that a lot of these symptoms can be appraised in a controlled environment such as during a dyno session. I suggest you try a dyno tuner .
Transaxle Alfas Haul More Arse
kevin
Verde
Verde
Posts: 2762
Joined: Sat Jan 22, 2005 9:09 am
Location: Esher, UK

Re: Slight Missing at Cruising Speeds

Post by kevin »

Following what md said above I had similiar issue long time back and changed rectifier box ,the capacitors and the green wire . Problem was solved however I'm not sure which one it was or if the connections I made were better than before . Ironically this was on a v6 carb GTV so it was a long process after rebuilding carbs etc . The carb GTV6 and injection GTV have same ignition set up next to the coil .
kevin
Verde
Verde
Posts: 2762
Joined: Sat Jan 22, 2005 9:09 am
Location: Esher, UK

Re: Slight Missing at Cruising Speeds

Post by kevin »

If you have not won the battle check for bad fuel or water in tank . Usually when cruising water would settle to a consistent place . Friend just had a problem with van and had it on all the latest diagnostics here in uk as revs were hunting at cruising . After trying everything some one noted he had dodgy fuel from a particular garage and after fuel was changed no more problem .
Alfa GTV6 UK
Silver
Silver
Posts: 5
Joined: Mon Feb 28, 2005 8:54 pm
Location: East of England

Re: Slight Missing at Cruising Speeds

Post by Alfa GTV6 UK »

Thanks for the help folks. The fault has been traced to one fuel injector. It will be attended to in due course. The rest will be checked and cleaned.
User avatar
75evo
Verde
Verde
Posts: 944
Joined: Tue Oct 11, 2005 8:56 am

Re: Slight Missing at Cruising Speeds

Post by 75evo »

You should look into upgrading the injectors to the 3 hole type, and run 164 fuel rails. The barbed type injectors are probably more expensive and even if you clean it, is now more than 30 years old.
Post Reply