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Author Topic: 2000 Astro Van misfire  (Read 3560 times)

Offline keith

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2000 Astro Van misfire
« on: November 26, 2009, 03:58:44 PM »
Car came into my shop with a misfire, the owner put new plugs and wires and cap and rotor still misfire.  I checked codes has 304 (misfire # 4) (and another code also something like: lost of class 2 serial data??) ( I figured he unpluged something with the key on while doing the tune up.)

I checked the wires for proper install and made sure the plug was not cracked or dropped and van has good spark.  Then I replaced the injector.  Now van is still missing.  I am thinking the injector is not getting a pulse?  Which is hard to check on these vans?  Anyone have an idea about that, I guess I will have to cut the wires to check for injector signal.  Otherwise could be a bad connection or corosion at PCM or broken wire or no compresson, I will check compresson tommorow.  I doubt this only 90,000 miles.  Anyone have any other idea or have a problem like this.  Anyone see a bad PCM do this before?

Offline Gus

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Re: 2000 Astro Van misfire
« Reply #1 on: November 26, 2009, 07:09:06 PM »
Do you have a scan tool that shows a misfire on cyl #4?

If yes, I would Have replaced or swapped the plug in cyl #4......if you have spark at the end of #4 ignition wire, then I would check injector pulse(don't have to cut wires, either use proper test light or rig a noid light with adapters.....you replaced the injector, so I assume it is ok and an injector coil and flow test is not necessary....only thing left is to check compression of cylinder.....

Offline keith

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Re: 2000 Astro Van misfire
« Reply #2 on: November 26, 2009, 10:43:34 PM »
Yes the scanner shows the misfire on number 4 cylinder, (on the misfire chart) these engine have one big connector that goes to all the injecters which is why I think I have to cut the wires to test for injector signal, unless some else has any idea, let me know.

Offline Gus

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Re: 2000 Astro Van misfire
« Reply #3 on: November 27, 2009, 07:48:14 PM »
You disconnect harness and attach the test light to the two wires that fire injector #4......need schematic to know which wires....

Offline keith

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Re: 2000 Astro Van misfire
« Reply #4 on: November 27, 2009, 10:31:23 PM »
Thanks Gus, I was able to check the injector pulse and it was fine.  I also checked the whole ignition system and it also seems fine.  The compression also is good.  I notice that if you rasie the rpms of the engine the misfire goes away and the engine runs smooth.  At higher (1500 and up) rpms the engine is even smooth under load.  I am thinking vacuum leak, because it is only missing at idle.  I do not hear a vacuum leak, but I dont know what else it could be?? any ideas?

Offline Gus

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Re: 2000 Astro Van misfire
« Reply #5 on: November 28, 2009, 07:57:02 AM »
This is an old trick:

While idling and misfiring, take a piece of paper and hold it at the end of the exhaust pipe....if the paper gets sucked into the pipe, could have a broken valve spring problem...

Offline PC

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Re: 2000 Astro Van misfire
« Reply #6 on: November 28, 2009, 09:36:01 PM »
Had a 2001 Astro throwing a misfire code.  Turned out to be a vaccuum leak, that hard plastic line going from the intake to the HVAC controls by the accumulator.

Offline NickD

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Re: 2000 Astro Van misfire
« Reply #7 on: November 29, 2009, 08:43:30 AM »
Quality control must be going to hell, with plugs, ran into mis-numbered plugs so lay them all in a row first to make sure they all look alike, they all have to be regapped, lucky to find 2 out of eight that are right on.  Also ran into leads between the metal base of the plug and the ceramic that causes blowby that can blow out the spark, so pull out my spark plug tester first.  I know they are brand new name brand plugs and also feel you shouldn't have to do this.  But the extra minutes spend can save hours and even the possibility of going insane trying to find a problem.

Always do a compression check with all the plugs out, and especially if the engine has a miss, if I find a low cylinder, pull out the cylinder leakage tester so I know the cause of the problem.  But the latter is a PITA to use as have to hand turn the crank to the correct position.  Also install a vacuum gauge first before taking stuff apart, with my altitude, expect to see 18"/Hg at idle, but depending on the engine, a vacuum leak can either cause a misfire or simply run the engine at a higher speed, so the tach also comes out.

Todays ignitions system really make me long for the days I only need my eyes to look at a set of points, have to swipe my wife's sewing needles to make contact for test points as they don't give you terminals anymore that were easy to access.  And with DIS, distributorless ignition systems, have either 2,3,4, or even eight coils to test out instead of just one.  Always put a drop of RTV on the pinholes I made or that cheap copper strands will corrode out.  Have to pull out the scope, but have to admit I am guessing as they cannot give the courtesy to show waveforms, but at least know if the pulse is there or whether it's missing beats or not.

Fuel systems are equally maddening, with three instead of one fuel line to worry about, coupled with evaporative control, fuel pumps inside of the tank, pressure regulators with a very thin neoprene diaphragm that can rupture at any time,  I don't like to think about that when driving, nor the millions of transistors in the PCM or BCM plus the countless electrical connections that can go bad.  But do know I am in for a very long day if there is a problem somewhere.

And yes, I have returned electronic modules even though that big sign says you can't telling the counter guy, you sold me a piece of crap, already bench tested my old module and have the experience to make sure the new module is doing the job.  Most of this stuff is put together by kids in China and doesn't even work out of the box.

Thinking about getting a horse.  Good luck in finding your problem.

Offline keith

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Re: 2000 Astro Van misfire
« Reply #8 on: November 29, 2009, 04:41:24 PM »
Thanks everyone for you input here is the lastest.

I took the spider out to double check everything.  I unput the coil and hooked up the fuel lines.  I watched all the injectors spray one at a time as I cranked the car over.  All the injectors were spraying and the patterns and amount all looked good as must as I could tell by only lookings.  For me this eliminates many problems.  The engine is only missing on one cylinder at idle.  The fuel system must be working (because 5 cylinders are fine) the ignition system has been replaces and the coil and module are working on the other 5 cylinders (only one coil) and I checked the spark and tried a different plug.  So the ignition system seem to pass all tests like the fuel system.

I check the compression and it was at 90 psi, I did not compare it to another cylinder ( I know you are suppose to test all for balance) but for now that seems high enought, (90 psi) should not cause a hard miss at idle. 

Because of this I am only left to think internal vacuum leak.  So I pulled the intake and valve cover gaskets (to make should a spring was not broken, I have also have a friend who found a misfire caused by broken value spring)

The valve springs were not broken and the intake gaskets looked good, but I will know more after I put it back together, them I will let you know.

If anyone else has any idea I would much appriate to hear them.  The vacuum line to the hvac alway break on astros, I have seem this to, but in this case it is not leaking.  I also checked the egr to make sure it was on sticking open and it was ok (even though this should cause misfire on many cylinders not one.  Keep in mind the car does not miss if the rpms is over 2000, even if under load.

Any one have reason to believe that the scanner is recording the miss on the wrong cylinder.  ???  Or am I just loosing my mind. 

Offline NickD

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Re: 2000 Astro Van misfire
« Reply #9 on: November 29, 2009, 08:03:34 PM »
90 psi for compression is not good.  Lots of blow by when running, can easily blow out the spark.

Offline Alan

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Re: 2000 Astro Van misfire
« Reply #10 on: November 30, 2009, 03:49:29 PM »
Check for a valve binding in the guide. Pretty common on these engines.  See TSB 1539013 for more info.

Offline NickD

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Re: 2000 Astro Van misfire
« Reply #11 on: December 01, 2009, 08:08:45 AM »
Could also be excessive carbon build up on the intake valve, particularly if that cylinder is misfiring, like a chain reaction as when the plug decides to fire, a very rich mixture.  Had some success with this more expensive fuel injector cleaner, the kind that shows a before and after intake valve.  To my amazement, can even work, as it did bring the compression back up.

But suppose if I was doing this job for somebody else, would tell them they need a valve job.  With PVC and EGR systems, carbon is always a problem.  If an EGR problem warps a valve, no choice but to do a valve job.  I use my cylinder leakage tester to verify if it's the intake, exhaust, or even the rings, but would be nice to have x-ray vision to see the inside of the engine.

Offline keith

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Re: 2000 Astro Van misfire
« Reply #12 on: December 01, 2009, 02:46:34 PM »
thanks for the ideas, I will check in these things and let you know what I find out.

Offline keith

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Re: 2000 Astro Van misfire
« Reply #13 on: December 01, 2009, 10:21:01 PM »
Was preparing to check the valve guides, when I hook up my air hose into the spark plug hole and heard alot of air coming out the intake, I loosened the rocker arms to make sure the valves were not sticking open but this did not help, to make sure I check another cylinder and it was not like this.  This is a poor mans cylinder leak down test I guess.  So the valve could be burned or the guide could be sticking but either way the head has to come off.

By the way when i was working on the car the EGR valve connector (about a 5 wire connector) was all green inside.  So this was likely the cause.
thanks for all the help
keith

 

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