Alfa Romeo Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
10,929 Posts
Discussion Starter #1
I've got a beautiful 3.2 Gtv with a modified engine (cams, heads, compression, valves, con rods were all done) that develops around 305 bhp. My problem is the car starts easily and will idle like a sewing machine while warning up but once warm it sometimes idles like a v6 with the Maf disconnected. Not always though. It sounds as if it may be "hunting" with the revs cycling once per second from around 650rpm to around 950 and dropping again. It pulls very smoothly and is very responsive from idle. There are no fault codes at present. My question is what will cause the car to behave this way? Could it be throttle or Maf related, or would it be a cam timing issue? What makes me not want to suspect the cam timing is that the car idles perfectly most times and just sometimes acts up like this.:confused:
 

·
Registered
Joined
·
390 Posts
First thing is to see if there are any faults in the ecu, next thing i think best is to relearn the throttle position.
switch on the ignition for 90 sec without starting the engine and do not press the accelerator pedal then switch of ignition again wait 90 sec and your done!
If this doesnt do the job then I think you have to replace the throttle-body, good mod for U would be then an upgrate to Ferrari 360 throttle!
Good Luck,

Tim
Auto Zagato
 

·
Registered
Joined
·
233 Posts
I've got a beautiful 3.2 Gtv with a modified engine (cams, heads, compression, valves, con rods were all done) that develops around 305 bhp. My problem is the car starts easily and will idle like a sewing machine while warning up but once warm it sometimes idles like a v6 with the Maf disconnected. Not always though. It sounds as if it may be "hunting" with the revs cycling once per second from around 650rpm to around 950 and dropping again. It pulls very smoothly and is very responsive from idle. There are no fault codes at present. My question is what will cause the car to behave this way? Could it be throttle or Maf related, or would it be a cam timing issue? What makes me not want to suspect the cam timing is that the car idles perfectly most times and just sometimes acts up like this.:confused:
Give you more information on the engine changes so that we can help you?

what piston with ratio, camshaft, valves....
 

·
Registered
Joined
·
233 Posts
I've got a beautiful 3.2 Gtv with a modified engine (cams, heads, compression, valves, con rods were all done) that develops around 305 bhp. My problem is the car starts easily and will idle like a sewing machine while warning up but once warm it sometimes idles like a v6 with the Maf disconnected. Not always though. It sounds as if it may be "hunting" with the revs cycling once per second from around 650rpm to around 950 and dropping again. It pulls very smoothly and is very responsive from idle. There are no fault codes at present. My question is what will cause the car to behave this way? Could it be throttle or Maf related, or would it be a cam timing issue? What makes me not want to suspect the cam timing is that the car idles perfectly most times and just sometimes acts up like this.:confused:
Hi,

I think your idle is very different because the profile of your camshaft.

do you know the values ​​of the enrichment according to your engine?

you say you have camshafts 305 ° is very important as opening time!

you always have hydraulic lifters?

cheers.
 

·
Registered
Joined
·
10,929 Posts
Discussion Starter #6 (Edited)
It's been remapped, intake cam is timed at 104 degrees. These figures were given to me as the "starting point" by the tuner who then adjusted the cams slightly to get the desired performance so I doubt if it's still at 104 degrees.

I did a throttle reset, and that did work to an extent. It's a bit smoother on the throttle now, and the lumpiness at adle is a bit less.

What I was thinking is to look at the enrichment map for cold starting: The car deffinitely starts and idles smoothly for a minute, then it slowly becomes unstable, and when the engine is warm enough, it stabilises. Could the intermediate warm-up cycle (not the starting enrichment) be enriched slightly to ensure that it idles well? It does seem to me as if the mixture is just not rich enough to keep it idling smoothly?
 

·
Registered
Joined
·
10,929 Posts
Discussion Starter #8
Valve lifters are still hydraulic, lift is around 11.4mm on inlet, intake timing should be 47/77 on 105 lobe centers, duration it seems should then be 304 degrees (not 305 as I said earlier). The engine tuner said he altered the cam timing manually so I do not have exact figures.
 

·
Registered
Joined
·
233 Posts
Valve lifters are still hydraulic, lift is around 11.4mm on inlet, intake timing should be 47/77 on 105 lobe centers, duration it seems should then be 304 degrees (not 305 as I said earlier). The engine tuner said he altered the cam timing manually so I do not have exact figures.
engine tuner to set the camshafts of 304 ° with hydraulic lifters, but it is crazy!
Hydraulic valve lifters will not endure, the opening time is very important!

do you have reinforced valve springs?

the opening time of the camshaft is not for hydraulic valve lifters.

:tut:
 
1 - 9 of 9 Posts
Top