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Originally Posted by Paul Workman
Well, 6 seconds seems a bit on the long side. Mine is about 3-4 seconds AFTER the fuel rail is charged.
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Ya know, when I posted above, I didn't really time that video, but Paul must have and I agree with him, if it's six seconds, that's a bit much. My 95's start time after fuel pump shut off, is about the same as Paul's
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Before rolling the ignition switch over to START, turn the switch to the "ON" position and listen to the fuel pumps. When they stop running, the rail is up to pressure, but it takes maybe a couple seconds before the rail (on my 90) is up to pressure. If I roll to the START position before the rail is charged, I can see how that might invite a backfire (NOT GOOD) at the very least. But, also add a second or two to the normal 3-4 second (cold) start time.
Once it has been started and run that day, the start time is much quicker - sometimes under a second!
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My 95 has always behaved the same way. Couple of points, though...when the pumps stop running, the fuel system may or may not be at the correct pressure. The pump-cut off is not related to fuel pressure. If you've got a pump out, leaking pumps, leaking regulator or leaking injectors, its possible the fuel pressure is not at a nominal level when the cut-off occurs. The cut-off is related to how long (2 sec.) the ECM will allow the pumps to run without an rpm signal, not fuel pressure. When you turn to "run" the ECM turns on the pumps but, if it doesn't see the engine running after two seconds, it turns off the pumps.
Also, if you've got the key in start, the engine is cranking but fuel pressure is not up, the engine will not backfire nor are you inviting it to do so.
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And, if nobody told you, you want to hold the switch in the START position for almost another second after it fires to let the motor rpm start coming up. This avoids backfires which tend to blow hoses off the MAP and the Fuel Pressure Regulator (for starters) at the very least, or rupture diaphrams in said parts (rare, but happens). This trick might avoid a plenum pull to re-connect a vacuum hose. Just sayin...
P.
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Holding the key in "start" after the engine is running is pointless and might not be the best thing for the starter. Intake manifold backfire won't happen once the engine is running.
The infamous backfire occurs if the start cycle is interrupted but the key remains in "run" rather than going to "off". If the engine attains some rotation but not enough run, the ignition is hot and the engine is at a certain position with the right intake valve open, sometimes air-fuel mix in the plenum will ignite. The resulting "bang" sometimes takes out the MAP sensor and/or blows vacuum hoses off the nipples at the front or the rear of the intake manifold.