Re:[alfa] spark plugs

[George Graves <gmgraves@xxxxxxxxxxx>]

When I had +4s in my GTV-6, the car would 'carbon-up' sitting at 
stoplights and stumble on getaway. Sounds like more or less the same 
symptoms that you are experiencing. When my mechanic fitted Lodges, the 
problem evaporated. Others have told me that the correct heat range and 
tip exposure on a NGK plug will work well too but I have no personal 
experience with them.


George Graves
'86 GTV-6 3.0 'S'




On Jun 17, 2004, at 7:09 AM, alfa-digest wrote:

>
> Date: Thu, 17 Jun 2004 10:08:04 -0400
> From: Ethan Schartman <ethans@domain.elided>
> Subject: Re: [alfa] spark plugs
>
> i've heard people mention their V6s "running like crap" with platinum
> +4s. exactly how crap?
>
> i've been running +4s for almost as long as i've owned my milano gold
> (4 years, 30k miles, or so) - long enough that i can't remember what
> it was like before i put them in. and, since i put them in i've had a
> peculiar acceleration problem (but they went in during my first
> re-valve, so there were too many other variables to eliminate). the
> problem is that below 1500rpm (in first, 2000 rpm in 2nd), if i lay in
> to the accelerator i develop a stumbling with very poor acceleration.
> if this happens, i just pull my foot off the throttle, and slowly roll
> back on. the motor "catches its breath", so to speak, and it goes
> fine. above about 1500 i don't have this problem.
>
> the problem is not engine temperature dependent, but it is erratic -
> some days it is worse, some better. it seems to have a sweet spot when
> the external temp is about 40 degrees F where it is reduced or
> eliminated. above or below and it is back. its been a while since i
> reset the timing to stock, but advancing the ignition timing reduces
> the problem (Fred D suggested this when as a test of proper combustion
> back when i thought it might be an injector mis-spraying).
>
> other data: all grounds are freshly cleaned, coolant temp sensor is
> good, afm is good (also swapped with other afm to double check),
> throttle switch is good, fuel pressure regulator is good (as of 3
> years ago when i replaced it), fuel filter is new, cold start valve
> doesn't leak, injectors were recently swapped with other used ones
> (the V6 they came off of ran fine), intake runners, and injector seals
> are good, intake air hose has no cracks, O2 sensor reads about .6-.7V
> at idle (seems to be within spec according to the "how to tune bosch
> fuel blah blah" book, plug wires, cap and rotor are new, compression
> is fine, valves reasonably within spec (no intake is more than .005"
> out of spec, exhaust are within .001"), cam timing is set properly,
> ignition timing is set to stock, cat is fine. no problems with hot or
> cold starts.
>
> so, some things i am thinking about checking next: fuel pressure under
> load, double check proper functioning of intake air temp sensor,
> voltage at fuel pump (make sure its got 12V), advance the ignition
> timing again to double check original results (not a solution for the
> emissions test, though). other air hoses are way old, but i have seen
> no signs of their leaking (propane check) and false air doesn't seem
> to be consistent with the symptoms (they are on the list of eventual
> replacement, though).
>
> so, should i add the plugs to my (short) list of possible causes? if i
> swap them, what kind should i put in? any other suggestions?
>
> thanks,
> - -ethan schartman
> - -87 milano gold
> - -princeton, NJ
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