Can't Get Correct Timing
#1
06-01-2020, 09:49 PM
Can't Get Correct Timing
I've got a 2000 blazer and I had to put new distributor in it and I've tdc it in put the 6 mark pointing to the #6 cyc as supposed to be and now I'm get backfiring through intake so I tdc it again 180 the distributor and still getting same thing what am I doing wrong
#2
06-02-2020, 06:37 AM
Which year Blazer?
Which engine version?
Backfiring could be an indication of the dizzy being 180 degrees off or a tooth off.
1st step to understanding ignition is to realize, that the distributor turns only at half the speed of the crankshaft.
Determine the "correct" TDC for ignition. Else it will all be off by 180 degrees at the distributor.
Check on the internet on how to find TDC ignition (also called TDC on compression stroke).
As the crank does two full revolutions for one complete 4 stroke cycle this is the first thing that can be off.
2nd check your distributor gear and if possible (endoscope - phone camera - looking down the rabbit hole) the gear on the camshaft. This is visible looking straight down the bore where the distributor sits.
3rd do a test fitting of the distributor. It needs to go down and at some point mesh with the camshaft gears and a bit further down with the slot in the oil pump shaft. Usually it sits fine if the collar of the dizzy rests nicely in the bore on top of the block with the shoulder. If you need a longer bolt vor the V-clamp to hold the distributor down - something is wrong.
4th Properly align the engine turning by hand to: TDC compression and to the 0 (zero) mark on the balancer. Distributor should go in in such a way that the connectors of the ignition module are back where they were when you took it apart. Normally pointing somewhere to the front left. The "finger" (rotor) should point to about the #6 cylinder (right,
Consider hovering above the car and looking at it if it were a clock's dial. Noon being the front of the vehicle, six o'clock aft. Then the rotor should be pointing about to the 2:30 position. Look underneath the distributor and try to figure how the slot for the oil-pump needs to go in. With a long screwdriver you can turn the oil-pump to properly align. Take into account the slight turn imposed to the rotor shaft by the drive gear meshing with the camshaft.
This needs some fumbling. As you mesh the gears it will turn the rotor a bit. This is where it can be off by one tooth. More fumbling with rotor and oil pump shaft.
Why is it the #6 cylinder? Actually it should be the #6 ignition wire or contact in the cap. Simple - the ignition triggers ahead of the TDC. We have the engine set to exact TDC for #1 therefore the rotor should be already past this wire (contact in the cap). The next cylinder to fire will be #6. If it does insert in such a way that it points exactly at the #6 cylinder but does not run at all or backfire, pull the distributor again, turn the oil pump shaft slightly back (about 15 degrees) and insert the dizzy back in, but when the gears start to mesh turn the rotor 1 tooth back. This assumes you do not turn the body of the dizzy. I use a pencil mark on the block and on the collar of the dizzy. (A good idea to place this mark before taking it apart...
). It is even possible to transfer the mark to a new distributor. Makes life a bit easier, and if the engine was placed on TDC compression before taking it apart it's a walk in the park.
Nice picture:
https://www.quora.com/What-is-the-fi...cap%20layouts.
5th When you have it running again you need a strobe light to check if it is correctly aligned. Not sure if the 2nd gens still need to unplug the ECU cable (brown wire) to revert into no ECU advance. Follow the service procedures from the service manual as per your Blazer's engine and year.
Which engine version?
Backfiring could be an indication of the dizzy being 180 degrees off or a tooth off.
1st step to understanding ignition is to realize, that the distributor turns only at half the speed of the crankshaft.
Determine the "correct" TDC for ignition. Else it will all be off by 180 degrees at the distributor.
Check on the internet on how to find TDC ignition (also called TDC on compression stroke).
As the crank does two full revolutions for one complete 4 stroke cycle this is the first thing that can be off.
2nd check your distributor gear and if possible (endoscope - phone camera - looking down the rabbit hole) the gear on the camshaft. This is visible looking straight down the bore where the distributor sits.
3rd do a test fitting of the distributor. It needs to go down and at some point mesh with the camshaft gears and a bit further down with the slot in the oil pump shaft. Usually it sits fine if the collar of the dizzy rests nicely in the bore on top of the block with the shoulder. If you need a longer bolt vor the V-clamp to hold the distributor down - something is wrong.
4th Properly align the engine turning by hand to: TDC compression and to the 0 (zero) mark on the balancer. Distributor should go in in such a way that the connectors of the ignition module are back where they were when you took it apart. Normally pointing somewhere to the front left. The "finger" (rotor) should point to about the #6 cylinder (right,
Consider hovering above the car and looking at it if it were a clock's dial. Noon being the front of the vehicle, six o'clock aft. Then the rotor should be pointing about to the 2:30 position. Look underneath the distributor and try to figure how the slot for the oil-pump needs to go in. With a long screwdriver you can turn the oil-pump to properly align. Take into account the slight turn imposed to the rotor shaft by the drive gear meshing with the camshaft.
This needs some fumbling. As you mesh the gears it will turn the rotor a bit. This is where it can be off by one tooth. More fumbling with rotor and oil pump shaft.
Why is it the #6 cylinder? Actually it should be the #6 ignition wire or contact in the cap. Simple - the ignition triggers ahead of the TDC. We have the engine set to exact TDC for #1 therefore the rotor should be already past this wire (contact in the cap). The next cylinder to fire will be #6. If it does insert in such a way that it points exactly at the #6 cylinder but does not run at all or backfire, pull the distributor again, turn the oil pump shaft slightly back (about 15 degrees) and insert the dizzy back in, but when the gears start to mesh turn the rotor 1 tooth back. This assumes you do not turn the body of the dizzy. I use a pencil mark on the block and on the collar of the dizzy. (A good idea to place this mark before taking it apart...
). It is even possible to transfer the mark to a new distributor. Makes life a bit easier, and if the engine was placed on TDC compression before taking it apart it's a walk in the park. Nice picture:
https://www.quora.com/What-is-the-fi...cap%20layouts.
5th When you have it running again you need a strobe light to check if it is correctly aligned. Not sure if the 2nd gens still need to unplug the ECU cable (brown wire) to revert into no ECU advance. Follow the service procedures from the service manual as per your Blazer's engine and year.
#3
06-02-2020, 03:55 PM
I've got a 2000 blazer and I had to put new distributor in it and I've tdc it in put the 6 mark pointing to the #6 cyc as supposed to be and now I'm get backfiring through intake so I tdc it again 180 the distributor and still getting same thing what am I doing wrong
https://blazerforum.com/forum/tech-a...-timing-24373/
Last edited by LesMyer; 06-02-2020 at 04:53 PM.
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