Ignition Timing & New Distributor Questions

Ignition Timing & New Distributor Questions

Postby JeffZ [OP] » January 4th 2012, 8:43pm

I'm working on my daughter's 2001 Astro van with a 4.3L V6 in it. It's RWD, if that matters. The van has gone through 4 distributor caps and rotors in the last 3 years, with some even "blowing apart" on the car. I have the van for a whole week, so I replaced the entire distributor, cap and rotor, and also installed new spark plugs.

I am now getting a "cam and crank" error code after installing the new distributor, and the engine also does not want to start consistently. The engine seems like it is "kicking back" or locking up sometimes when you turn it over, which would seem to indicate that the timing is advanced too much and firing before the pistons reach TDC. I am somewhat confused by this however, because when I replaced the distributor I thought that both the rotor and distributor housing were in the same positions as the old distributor I just removed.

What further confuses me is that there is a slot in the bottom of the distributor shaft that mates to the oil pump, which would indicate that it could only go in either correctly or be 180 degrees off. Given those facts and the fact that the distributor hold down is designed so that the distributor can not be turned to adjust the timing I'm guessing that the computer completely controls this and that there is no other way to control timing. That leads me to believe that the crank sensor might be to blame.

I am going to replace crank sensor tonight and clear the codes. I'm also going to hook up a timing light to see what it has to say about where the timing is, but I have a couple of questions on that, such as: Do I have to disable any timing advance mechanisms? If so, where are they and how do I disable them? What should timing be at specific RPMs? The timing label under the hood says the computer handles all timing and idle adjustments, so I'm a little lost here.

Also, if the crank sensor and code clearing does no resolve this, should I remove the distributor and use the "square one" approach? That is, find TDC and cylinder 1 and reinstall the distributor with the rotor pointing to the distributor tower for cylinder #1? This car has had starting issues for some time now, including the tell-tale kick back when starting, and even though it has never had a cam-crank correlation error in the codes I'm wondering if somehow it hasn't been out of synch for some time. Maybe due to jumping a tooth on the timing chain, or improper installation of the distributor by someone else, or a bad crank sensor. Some distributor have an advance mechanism built in and I'm wondering if that could allow it to be 1 tooth off during installation. If anyone is knowledgeable in this, please enlighten me!
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JeffZ
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Re: Ignition Timing & New Distributor Questions

Postby chevymaher » January 13th 2012, 2:55am

The slot in the bottom of the distributor drives the oil pump.You probably just got the distributor a tooth off.The oil pump will turn and engage in the distributor slot, if it is off.If the distributor is off far enough it simply will not drop down into place untill you crank the engine a little.But it will go in any way you put it.Not just 180 out, or correctly.
I would start from square one find TDC number one and then reset the distributor.
The code your getting indicates the cam sensor and distributor setting are not in sync.
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Re: Ignition Timing & New Distributor Questions

Postby JeffZ [OP] » January 17th 2012, 5:14pm

Thank you. I got it figured out finally. I was under the illusion that it would only go in either correct, or 180 degrees off, but that is not the case. I was having a brain fart and thinking that the oil pump is physically connected to the cam and crank. That's not correct. It is DRIVEN by the distributor slot, and therefor is free to spin independently. As long as the distributor gear is meshed correctly with the cam gear that drives it, you can crank the engine or turn it over manually (preferred option), until the slot in the distributor aligns with the oil pump drive slot. Only after the oil pump slot is aligned with the slot on the distributor will the distributor go down all the way.

On another note, there is a vertical web on the distributor shaft that is under the plate where that the cap bolts to. The rotor and roll pin on the distributor gear should align with that web before insertion into the engine. That places the rotor approximately 42 degrees before rotor the aligns with cylinder #1 when it is at TDC. When you drop the distributor in, the rotor turns as the gears mesh and will end up pointing at cylinder #1 when it's at TDC. Apparently there are several different descriptions for this procedure of distributor insertion using the cylinder #1 TDC method, and they are different based on the year and distributor you have. Mine was an after market distributor, so the standard Haynes manual description didn't work for. Besides, they try to cover every Astro from 1985 forward, which also doesn't help. Anyway, look for the vertical web on the shaft under the distributor if you're using the "engine was turned over" method.
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Extra Info: LT 4.3L V6 RWD


 
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