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Cranking/starting time
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Sat, 24 May 2008 21:33:54 Share Post by Email
In Reply to: Long cranking: VOLTAGE DROP to ignition or brain?, RayF, Sat, 24 May 2008 15:14:34
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There are sooo many things that go into the time it takes for an engine to start. Yes, fuel pressure is one of them. Compression, which is a function of cranking speed and battery voltage, and timing, which is a function of timing, is the other.

So the first question is about cranking - is the issue how many times the engine turns over before starting, or how fast it turns over? If the engine turns over slowly, that's a voltage problem. But a voltage problem with the battery or the wiring to the starter. If the engine turns over slowly, it's hard to get enough compression to get the right air-fuel mixture to get ignition.

Simple test - listen for how quickly the engine turns over - revs per whatever unit of time you like. Then try it again with the throttle all the way open. Yes, be prepared to get your foot off the gas when the engine starts. If the cranking speed is much faster with the throttle open, you've got an issue with the battery or the wire from the battery to the starter. Why? It takes a lot of power to crank an engine. And believe it or not, it takes more power to crank an engine with the throttle closed. Think of the engine as an air pump. With the throttle closed, that pump is pulling against a vacuum. If the battery is tired or you have a voltage drop in the wiring to the starter, it'll show up when you reduce the load on the engine. This is a trick to get an engine to start on a cold day when the battery is really weak.

A common issue with older cars is the battery cable corrodes. Peek into the insulation at the battery end - do you see a lot of greenish or whitish powder in the strands? Then replace the cable. It's tired. Pull the clamps off the posts, and polish the inside of the clamps and outside of the posts with some sandpaper. If the battery is over 3 years old, it is probably getting tired.

IF the engine cranks fast, but just isn't catching as fast as you want, two things. First, give it a break. It's a 20 year old car - that's 87.3 in people years. I don't start as fast as I used to. It starts - that would satisfy most of us. Second - what's the timing set to? If your timing is too advanced, it's harder for the car to start. At a minimum, make sure the ignition system is in good shape - new plugs gapped per spec, new cap and rotor, timing set spot-on. If the spark plug wires are over 3 years old, replace them.

If that doesn't do it, do a compression check. Specifically, notice how many turns it takes to get up to full compression. You'll see the needle go up on the first engine turn, then up some more on the second turn, and after a few, won't go up any more. If it gets up to as high as it'll go in two or three cranks, that's a good sign compression builds fast. If it takes 5 or 6, the rings are probably a little tired. Do a dry test first, then a wet test. (In a wet test, you drop a teaspoon of motor oil into the cylinder through the spark plug hole, then crank). If you get a substantially higher (10-15 psi) reading wet, then your rings are probably weak, and the compression is low.

The LH system supplies fuel to the pump, and I'm pretty sure it keeps the fuel on for a couple of seconds even if it isn't seeing cranking. So voltage to the pump probably isn't the issue. My guess is that the starter is just cranking slowly due to a weak battery or poor battery-to-starter connection, or just slightly low compression.

Again, 7 turns of the engine before starting isn't shameful, or a sign of any manly dysfunction. It's a 20 year old car. It starts. Be happy.

posted by 76.202.162...
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