VS V8 slightly rich

[VR38]

First of VS so basically same as VN-VR ECU etc.

Short story, fitted foam tune, replaced temp sensor, fuel pump and filter, plugs, cap/rotor, leads tested fine, cleaned throttle body etc etc, ran like cracking mad, best it ever did, two days of driving later I cold start it in the driveway in the morning heading for the strip, it fired to like and seconds later it stumbled, gave it a rev but it didn't clear, exhaust pipe blackened but no smoke.
Idle is now slightly low but never stalls.
Still took it to the track and ran 15.07 (stock auto with CIA and zorst)
Now for the life of me I can not fault it, it just never came good, to be quite honest i probably would not even have picked it beside from the fact that I know how it could be.
Fuel consumption is high around 20l/100km for a few weeks now, was down below 15l/100km before.
Fuel pressure is within spec.
Checked the coil and lead today hoping for a weak coil and even went to buy a new coil but mine tested better than the new ones at the shop so I reinstalled the old one.
It's not the temp sensor either cause that went a few days later (stupid ebay boshc shit) so it did not right the problem here.
Thoughts please?

[creastyle]

Try changing your o2 sensor. They turn "lazy" and wont send the correct voltages, but not enough of a variation to trip a code. They only have a life expectancy of 100, 000 KM. When they fail they make your engine run rich.

[yxyx64]

Base timing?

[VR38]

Well it just came good on me the other day, she went like a rocket again, barely breathing on the throttle to maintain the speed limit... then it started to miss and run sluggish again a couple of hours later

[yxyx64]

has it set any soft fault codes (check engine light does not stay on but the car will remember the fault codes).
your OP says car stumbled on cold start.....you need to be very clear on what you think is a cold start as a number of the cars sensors are not used at all at start (hot or cold) and then kick in anything from a couple of seconds to a couple of minutes after start depending either on time elapsed or on temperature or on vehicle rpm. Some sensors/controllers are only used at idle and others are never used at idle. Many sensors are bypassed when the engine is cold no matter the time or rpm.
for example (for vr and non-roller engine vs), when you cold start the engine it is locked to your base timing number (factory is 10 degrees BTDC) and the computer cannot change this until you hit about 450 RPM the first time and enters open loop. The coolant temperature is checked to set a pulse width for the injectors and the fuel pump runs unless the computer times it out due to no rpm. Everything else is pretty much ignored when you start the car except the throttle sensor (this may put the car into a flood clearing start and reduce injector pulse width). The oxygen sensor is never used at either start or at idle. after you start and it goes into open loop then other sensors are called into use (providing they are supplying figures which make sense otherwise the figures are pulled from a backup table) like the air temp, pressure....etc

My point is to diagnose without seeing the car the quality of information is very important.
a crook oxygen sensor will waste fuel in general diving as already said by creastyle (but be aware it is not in use when the car is subject to rapid throttle changes and the computer goes into Acceleration Mode .... oxygen sensor is used in Run Closed Loop Mode). so if you car stumbles on acceleration or stumbles at idle it is not O2. Quality of information again.............

[VR38]

Cold start means just that, plain English good old fashioned cold start.

There has never been any codes set or stored by the PCM, but just for kicks I put it into diagnostic mode yesterday while I was checking a VR and I noticed my VS condenser fan did not seem to be running fast enough, also the wiring next to the radiator going to the fan seemed hot too.
MAybe there is a bad earth gremlin somewhere.
Is it unusual for the condenser fan to fail in this manner?

[yxyx64]

not convinced the fan is related to your main problem as it is not in use a great deal (but who knows...maybe)....for a VR V8 the fan runs quite fast and makes a fair bit of noise in diag mode before you start engine and noise then gets covered by engine a bit (so it may well be crook). Is VS the same wiring? Hot wires indicate high current flow which may mean an earth problem somewhere (short circuit to earth) as the electricity will race back to battery via the new earth, but normally will blow fuses as well. Or your fan windings are shorted to some extent to each other and offering less resistance to the circuit resulting in higher currents and lower fan speed. Whereas a poor earth connection will reduce the current flow, not make it more. Your fan gets power directly from the battery via the cooling fan fuse. This power is switched via the cooling fan relay. The relay is what does the talking to the ECM and EFI Relay and other stuff but if the relay is energised and the contacts inside it are made to connect (as they must be if your fan is running) then your fan circuit is simply...battery, fuse, relay contacts, fan motor, earth. (so logically your fan motor is getting crook). The ECM in no way monitors the fan running speed or the fan current draw. The ECM tells the fan relay to turn on the fan but has no way of knowing or checking if the fan actually turns on. so the ECM does not and cannot do anything to set codes or to "fix"a crook fan but of course if coolant or MAT temps rise and cannot be stabilised then the ECM will add extra fuel to help cool down the motor. If you are burbling down the highway the fan is unlikely to be suddenly required and so the ECM wont just suddenly add a bucket load of fuel to cool the motor because the fan seems to be doing nothing to help cool..
this may not help with your problem but may help with your fan (read ECM as PCM for ur auto)

[VR38]

Thank you, I doubt too that the fan is directly the problem, I more wanted to eliminate a voltage/connection problem with the motor.

[yxyx64]

by connection problem if you mean a dirty or poor wire connection then current would decrease (not increase) in the wire but the actual joint itself may possibly get hot due to arcing and high resistance.....motor sounds crook....maybe you can find resistance figures for the windings and test them with ohmeter - if low then it is crook.

[chargedvx6]

Have you tried re fitting the original memcal that was being used prior to the issue starting? Common mechanical practice when an issue occurs after changing something is to revert whatever was changed to rule it out

[VR38]

Yeah changing the memcal back to the OEM one will be the last step if nothing else shows up.

Can reprogrammed memcal go out of tune?