2002 Nissan Altima 2.5 S review from North America

2002 Nissan Altima 2.5 starting problem.

I purchased a 2002 Altima with 2.5 DOHC (variable valve timing engine) new and now have over 65,000 miles on the car. It has a very annoying intermittent cold start problem the dealer could not define under warranty, further more the dealer states that all the 2.5 DOHC engines have this problem and the only fix Nissan offers is to hold the gas pedal to the floor and crank the engine over until it starts. When the engine finally starts there is a lot of black smoke from the exhaust a result of unburnt fuel, the E.P.A. should decertify the car for this. The official explanation from Nissan for this no start in cold weather is that the vehicle floods, and if the customer writes to Nissan he is assured there will be NO written response.

I have researched this problem and found the flooding is a result and not a cause of the no start condition! The real failure has more to do with variable valve timing.

What really happens:

1 During a cold start in cold weather the oil is very thick.

2 The E.C.M. (engine control module) tests all the components - this happens every start cycle, but this problem only occurs intermittently during cold weather cold starts.

3 The I.V.T. (intake valve timing control solenoid) receives its test pulse, but due to the thick cold oil can drive the intake cam to an over advanced condition.

4 With the intake cam advanced for operation beyond 2,000 RPM and the starter motor cranking the engine below 500 RPM the near static compression is nil compared to the dynamic compression of a high revving motor with an advanced cam.

5 Cold cranking an engine with low compression while injecting fuel results in a flooded engine.

6 Holding the gas pedal down while starting from this failed condition causes more fuel to be injected, more air to flow through the engine and the throttle position sensor to tell the E.C.M. that the throttle is wide open. The E.C.M. senses the RPM of the engine is at cranking speed (too low for an advanced cam), The PHASE (camshaft position sensor) signals the E.C.M. that the cam is advanced and the E.C.M. commands the I.V.T. to retard the cam, however since the oil is still cold and thick this takes several cycles to work - resulting in more flooding until the engine finally starts.

Proof - for those who are not technically lost yet.

1 With the engine in the cold no start position (and not flooded yet)

a. Remove the spark plugs.

B. Bring pistons 1 & 4 to top dead center.

C. Put 5 psi of compressed air in cylinder 1 and feel it exhaust out cylinder 3.

D. Put 5 psi of compressed air in cylinder 4 and feel it exhaust out cylinder 2.

A tech could reasonably expect either steps c OR d to occur because ONE of the cylinders 1 or 4 will be on overlap a condition where both intake and exhaust valves are slightly open, however the other cylinder in this static condition should be on compression and the valves should be closed! If the same leak down test is performed after the failed engine finally starts and runs there will be no leakage at one of the last two steps.