1998 Chevy Astro Not starting

Have you checked the starter? Or maybe the ignition switch?

Did you find the answer? I have the same van same problem replaced fuel pump and distributor still having problem.

I have the exact same problem in my 1999 Astro!

Starter cranks energetically. Engine hiccups and burps,
but will not start. Keep trying. Hiccup, hiccup, burp, burp. After a few to several minutes of this ( trying to minimize the cranking and maximize the burp-burping )
and it suddenly starts and runs.

Mostly happens when the car has been sitting for a while ( over a few days ). Especially if it is cold and wet outside.

I am troubleshooting this now. Stuck a OBDII interface on it. All sensors look normal during cranking except for the MAP ( Manifold Absolute Pressure ). This is 14.2PSI to 14.4PSI, with just a few spikes down to 13.6PSI. That's not much vacuum.

The factory shop manual says that you can pull the MAP
sensor out and hook it up to a vacuum pump. Slowly pull twenty inches of mercury, you should see about 5 PSI on the OBDII. Actually, 34 kilo-pascals, but what the bleep is a kilo-pascal?

So I did that, the sensor reads normally. Also stuck a vacuum gauge in the hole.

While cranking,

There was no manifold vacuum whatsoever.

Maybe a few little tiny burbles on the gauge needle.

The shop manual has no spec for cranking vacuum, but
this is a 4.3L vacuum pump being cranked at 150 rpm's ( according to the OBDII. There has got to be vacuum.

I then focused on holes or leaks. First the EGR valve. Pulled it off, looks pretty good. The pintle valve (cone that closes the hole ) is reasonably clean. I fashioned a blanking plate out of soft aluminum sheet and put it back together. Still no vacuum.

Other things with valves that plug into the intake manifold include:
* a bypass valve for the throttle.
* The EVAP purge valve.

Checked for loose spark plugs, all tight. If I cannot find any leak among the hoses and valves, I guess I will do a compression test. Hate to do it because the spark plugs are so hard to get at on this car. And in my experience, basic mechanical flaws are usually not "intermittent".

Anybody know what is the proper cranking manifold vacuum for a 1999 Astro?

- Jerry Kaidor

I put my hand on the intake, turned the key, and it made good vacuum. Plopped a big book on top of it, cranked, read five inches of mercury. So I am guessing it is not the vacuum. Thank goodness.

A friend had suggested the crankshaft position sensor. So I popped the CKP out, looked at it ( there was just a bit of oil on the face, but no metal shavings )
and put it back in.

The shop manual states that the CKP must emit pulses of no smaller than 40% duty cycle, and no greater than 60%. And that above 60%, the car will be very difficult to start. How about impossible? My scope was alas too small to give me a decent measurement of the duty cycle. Wait, is Dwell not really the same as duty cycle? Got out my fancy timing light with the dwell function. Crank-crank-crank. 46% on
the four cylinder scale, aka 51% duty cycle. Perfect. Nice clean pulses, too.

Then I stuck my scope on one of the fuel injector outputs of the VCM. Sure enough, no pulses. Wait, there's a pulse once in a while, Exactly when the engine burps. Okay, the problem is that the VCM is not delivering pulses to the fuel injectors.

Unfortunately, that does not narrow it down very far. The VCM looks at a lot of sensors to figure out how and when to pulse the injectors. You can almost consider it the main output of the computer. Fuel injector pulses and spark. By the way, the spark is fine.

Now I just have to figure out which sensor is misbehaving. The crankshaft position sensor is okay because I measured it. The camshaft position sensor must be okay, because without it, there would be no spark. The MAP is okay, because I tested it with a vacuum pump. The MAF (mass air flow) sensor seems to be okay, but it is hard to be sure with the small amount of air motion available.

I am guessing that the oxygen sensors does not need to work to start the car.

- Jerry