Can you solve this puzzle?

[gm3mtm]

I have made some improvements to the problem but here is the issue. The engine runs a bit rough for the first 20 to 30 seconds. So far i have replaced the following, some of which have helped improve the situation.....

new Pre cat O2 sensors
new mass air flow sensor
oil changed
fuel additive (barhdohls) ....seems to have helped
new fuel filter
new plugs
new cam positioning sensor


Of all of the above the oil change and the fuel additive seem to have helped the most.

Any other thoughts??

[slyhog-22056]

I would be happy if mine only ran rough for a few seconds... I have to wait 2 to 3 minutes while heat builds in the engine before mine smooths out........

[Wiseguy]

Bad intake mainfold seals/gaskets aka "oil separator plate".

Common on M60s and M62s

[Merlin4SC]

Exactly Wiseguy!

The puzzle is solved...

As heat build the intake mainfold blocks expand and seal off the leaks. Also, when the GT1 is reading out the fault codes from the OBDII, I bet it is always the same cylinders misfiring..

But you will get misfires until it does. To verify this take off the maifold cover and spray some Wurth silicone around the edges of the manifold - intake port connections and see if it doesnt smoothen out. This proves that you need to replace these manifold blocks which will only get worse over time.

If it were injectors, it would not get better when warm. And I assume that you have no other symptoms with your misfire that would point to a head gasket. But if you see white smoke or a "milkshake" in the oil galeries, then it IS likely a head gasket blowing though, which seals off when warm enough. This also deteriorates over time to become totally unserviceable.

Good news is that those other parts wont fail for a long time now. On a V-12 that can be like a giraff with a sore neck! More good news, on your car it is cheap to accomplish.

[Bear]

Originally posted by gm3mtm@Aug 25 2004, 05:44 AM
I have made some improvements to the problem but here is the issue. The engine runs a bit rough for the first 20 to 30 seconds. So far i have replaced the following, some of which have helped improve the situation.....

new Pre cat O2 sensors
new mass air flow sensor
oil changed
fuel additive (barhdohls) ....seems to have helped
new fuel filter
new plugs
new cam positioning sensor


Of all of the above the oil change and the fuel additive seem to have helped the most.

Any other thoughts??


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Or the Idle Control Valve, also a common complaint on these engines.

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