2000 Chevy S10 wont start when it's warm

2000 Chevy S10 4x4 automatic 6cyl Fuel Injected engine
This truck has a weird problem. It seems to start just fine when it's cold, but if I shut it off and try to start it again when it's still
warm, many times it will not start. I hear the fuel pump running. The engine turns over, it often pops as if it's getting a spark, but just will not stay running. Leaving it sit for 10 to 30 minutes generally solves the problem and it will start. However, on occasion, right after it starts, sometimes it kills when I come to a stop, and then the whole ordeal starts over again. Once it's in motion and has been driven for a few minnutes, it seems to work just fine.
What the heck is causing this?
Note: The fuel pump was replaced about 8 months ago because the old one died. I plan to replace the fuel filter this week, just in case it's clogged, but since the truck runs fine once it's been started and driven for a few minutes, I doubt it's the fuel filter.
Anyone have any thoughts on this????
Thanks
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wrote in message

Sounds like vapor lock. Had it on a Ford LTD II.
John
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On 4/4/2012 11:32 PM, John wrote:

Or a leaking injector that is flooding the engine...
The op needs to do some diagnostics. Does he see a cloud of black (over rich) smoke when it eventually starts? Can he open the hood and cool off and start faster or not? (If yes, then vapor lock may be it, if no flooding may be it.) When it starts is it missing? Could be electrical.
Has the OP scanned for DTCs? Where there any? Live data, is it correct or is something off? I can't imagine that there are no codes being set.
--
I'm never going to grow up.

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snipped-for-privacy@myplace.com wrote:

Check the ignition module and crankshaft sensor. They both go bad over time due to heat.
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On Wed, 04 Apr 2012 23:50:16 -0500, Paul in Houston TX

The ignition module is something I have suspected. Aside from replacing them, is there a way to test them?
What is the crankshaft sensor, what does it do, and where is it located? This is one thing I have never heard of.
Thanks
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snipped-for-privacy@myplace.com wrote:

There is no easy way to check the ign.mod. The crankshaft sensor can be tested... sort of. The crankshaft sensor is a hall effect device that senses a magnet on the crank front. It sends the signal to the ecu which then sends a signal to the ign.mod which then sends a signal to the coil. GM has always had trouble with them. Concerning the vapor lock... it does not happen with your vehicle since you have a STP in the tank. You do not have an old style suction pump. They went away with the advent of FI. http://dezertdimes.com/2010/11/the-complete-guide-to-the-4-3-liter-gm-v6 / http://troubleshootmyvehicle.com/gm_ckp_4.3L_5.0L_5.7L/troubleshoot_ckp_sensor_1.php My guess is crank sensor.
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On Thu, 05 Apr 2012 19:01:20 -0500, Paul in Houston TX

I changed the fuel filter and the truck has more power. The inside of the filter was loose and rattling around. But this did not stop the hard to start crap. After changing the filter, I drove it a few blocks, shut it off for 5 min. and tried to restart. Same shit. Tried it at least 10 times and it would not start. I removed the coil wire and put a piece of bare wire in coil and held it near the block with a wooden stick. I got a spark.
According to the *excellent* articles you posted on the web, it seems that the problem is not electrical, but fuel related. When the key is turned to the on position, the fuel pump runs for a few seconds, then stops. I believe that is normal, since it only needs to pump the lines up to the specified pressure. I had someone tap on the fuel pump relay when I tried to start, but no change.
"genius" said to check the fuel pressure regulator. I guess that's the next test, but where the heck is that? And whaty does it look like?
I used to be pretty good at fixing the old carburator engines, but these fuel injected ones are a real challenge. Especially when I dont know what parts look like.....
I just googled photos for "chevy fuel pressure regulator". I found this:
http://ebay.alldiscountautoparts.com/prodimages/10705396.jpg
and this http://tinyurl.com/c3bm6lf
Is this the type of thing I need to look for? Where might it be?
(They look like the vacuum breakers/dashpots in the old cars)
Thanks
--
PS. Thank God I still have one car that has a carburetor. Most
troublesome vehicle I own, and it's 23 years old.
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On Apr 5, 10:19pm, snipped-for-privacy@myplace.com wrote:

Yes, that's what it looks like. Assuming you have the 4.3l I believe that's the same as the 5.3l with 2 cylinders missing. On my 5.3l it was on drivers side fuel rail near the firewall. Pull the vacuum line off and check for fuel. I had very similar symptoms but my truck started and would run really rough and idle about 250rpms. Changed FPR, problem solved.
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You say the ONLY problem is that it shuts down? What kind of mileage were you getting before this started and did it change. When the pump was changed did the pump electrical connector also get changed out? If not start there. The connection on the pump will heat up when the pump starts to fail because it draws more current, plus they corrode a bit. This starts a cycle where the contacts heat up and lose tension makes it worse until they don't connect up.
Next:
The 4.3 pressure regulator is INSIDE the intake manifold, mounted to the back of the injector. Easy way to test it would be to first run a pressure test using a gauge. Connect it to the shrader test port on the fuel rail. You want to see 55 - 65 psi with the key on engine off. Minimum of 55 psi with the engine running. When you turn the key ON you should see the pressure jump up to it's highest reading within a second. any slower and you might have a pump problem. Pressure lower than 55 psi is also a pump problem.
Next turn the key OFF, the pressure should hold at for at least a few minutes. If it doesn't then you can do a few tests to isolate where the leak is.
First connect the pressure gauge to the inlet side of the fuel filter and check the dead-head pressure from the pump. You can power the pump directly using a jumper wire from the battery to the fuel pump power feed. You should see around 60-70 psi on a good pump. Shut off the pump and it should hold pressure for a while. If it drops fast the check valve in the pump is failing. Not a big problem as long as it is constant (IE if you test it 5 times it leaks down the same every time, not once real slow and the next real fast).
Next to test the regulator. Connect the filter back up using a small valve so you can trap pressure. Disconnect the return line from the back of the manifold. Block the outlet side on the manifold. Connect the pressure gauge to the shrader test port on the fuel line. Power up the pump. You should see the same pressure that you saw on the KOEO test. Now shut off the valve on the line and power off the pump. The pressure should hold basically forever if there are no leaks. If the pressure drops VERY slow the regulator or injector is leaking down. If it drops fast the regulator is probably bad OR you have an injector or fuel line problem.
The fuel lines inside the manifold get a lot of thermal cycling and then they leak. However this usually doesn't cause engine shut down just VERY poor mileage and more often than not the converter burn up from the extra fuel.
Regulator leaking will usually cause a no start all the time not intermittent.
The usual problem with hot start is ignition module, CPS or ECM related.
To find out if it's a sensor go get a couple of cans of canned air, or component cooler. Start the engine, let it warm up and shut it off. Then spray each item one at a time. Start with the easy ones like the ECM, the TPS, and such and work your way through them. You will know you have found the problem when you can start it up right after cooling that item.
If you have access to a good scan tool that can read live sensor data you could use it as well. You can watch the sensor data and see what is happening in real time.
Oh and you may also want to check the fuel pump relay AND the oil pressure switches. The fuel pump relay comes on for two seconds to prime the system then shuts off. When you start cranking the engine the fuel pressure in the lines enables the engine to start. The cranking also turns the oil pump which in turn creates oil pressure. Once the oil pressure hits about 7 PSi that switch turns on and activates the fuel pump. If that switch is getting bad/rusty/leaking it could also cause a problem since it is the item that actually runs the pump NOT the relay.
--
Steve W.

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On Apr 4, 7:54pm, snipped-for-privacy@myplace.com wrote:

Fuel pressure regulator? Easy to check, take off vacuum line and if there's fuel in the line, it's shot.
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