timing/ backfire issue

st8pipe350 · #1 09-09-2009, 11:40 PM

well i was driving one day and heard a pop. (backfire) ever since my truck hasent ran right. so i pulled the front motor apart as i suspected the timing chain was worn. about 1 1/2 slop. replaced timing chain and sprockets. put it all back together. its starts and idles fine.. sometimes.. if i ease the gas its fine. but as soon as i punch it it backfires like crazy. i put a timing light on it. ( unpluged the spout connector of course) put it at 0 degrees. turned it off pluged connector back in. turned it on checked timing if was about 4 inches to the left of the timing mark.. my guess 20 degrees advanced.. i now have the motor torn apart again. just align the timing chain.. can i get step by step instructions on how and what to do? replaced cap,button,plugs,wires,ignition module,and knock sensor. any ideas?

st8pipe350 · #2 09-09-2009, 11:45 PM

88 1500 305 by the way

2000CAYukon · #3 09-10-2009, 01:55 AM

With the EST connector connected, timing should be at 20 degrees BTDC.

It sounds to me like you are going lean when you punch it. Need to check fuel pressure specs. Should be 9 - 13 PSI. Also need to check MAP and TPS sensors.

//2000CAYukon

jdmccright · #4 09-10-2009, 12:39 PM

Is there play in the distributor gear? Slop between the distributor and the camshaft will obviously play havoc with the timing.

st8pipe350 · #5 09-10-2009, 07:06 PM

ok well i tore it apart again today. align the sprockets again. had everything perfect. cranked it... wouldnt start... backfired through intake.. pulled dist cap off.. dist was 180 degrees out... could my cam be bad?

777stickman · #6 09-10-2009, 07:14 PM

Did you match up the dots on the crank and cam gears? With the motor at TDC on the timing mark crank dot should be straight up and cam dot should be straight down. Use a straight edge, cam centerline to crank centerline to be sure the dots are lined up right.

Keep in mind that the cam rotates only once for two rotations of the crank. So it's possible for the cam dot to be straight up at TDC. Just turn the crank 180 degs more to get the cam dot on the bottom.

Ok just read your 2nd post. With the cam dot down this is #6 TDC firing position. If your setting dist for #1 it's 180 out. Best to pull #1 plug and feel the compression come up to TDC and set the dist for #1.

st8pipe350 · #7 09-11-2009, 10:44 AM

Quote:

Originally Posted by 777stickman

Did you match up the dots on the crank and cam gears? With the motor at TDC on the timing mark crank dot should be straight up and cam dot should be straight down. Use a straight edge, cam centerline to crank centerline to be sure the dots are lined up right.

Keep in mind that the cam rotates only once for two rotations of the crank. So it's possible for the cam dot to be straight up at TDC. Just turn the crank 180 degs more to get the cam dot on the bottom.

Ok just read your 2nd post. With the cam dot down this is #6 TDC firing position. If your setting dist for #1 it's 180 out. Best to pull #1 plug and feel the compression come up to TDC and set the dist for #1.

me and my brother tore it apart. we aligned crank dot up and cam dot down. so they were mere cm from each other..before we put the chain on we pulled cyl 1 plug rotated crank till we felt piston come up. made sure dots were crank up cam down. installed chain set dist at cyl 1. put it all together when i turned key it wouldnt fire. pulled cap off dist was 180 out AGAIN!!

777stickman · #8 09-11-2009, 11:04 AM

The chain needs to be put on with the cam dot down crank dot up and then motor rotated for #1 TDC compression stroke.

st8pipe350 · #9 09-11-2009, 02:14 PM

done so. im just completely lost. ive timed 350's a few times and never had a problem. but my 305 is hell!

ronaldk · #10 09-11-2009, 06:41 PM

Stickmans advice is spot on. And 4.3,5.0,5.7, and 7.4L are all the same as far as this procedure. Try putting crank on TDC compression making sure your exact then line up as stickman says crank up cam sprocket down as you install chain,then with cap off make sure you rotor button is facing #1 cap wire.If not pull distr and line it up before you crank, then lock down snug put back cap and try to fire up.P/S if oil pump doesnt let case down all the way make sure you compensate for more rotor button motion You can press down on case as soneone cranks it will align with pump and drop you may want to disable ablity to start as you do this, like leave cap off till done. Good luck take your time

777stickman · #11 09-12-2009, 11:32 AM

Pull the distributor up far enough to turn the rotor 180 degs and go from there.

ronaldk: Just to clarify one thing. With crank dot up and cam dot down the motor is at #6 firing position.

ronaldk · #12 09-12-2009, 07:47 PM

I never touch the distr when changing timing gears.But when I time distr I always use TDC and #1 cyl.(OLD SCHOOL,just me) I stated he should put to TDC and then follow your(STICKMAN) timing of crank and cam which the way I stated is backwards. Those marks would need to be lined up first on cam & crank and rule of thumb crank should be turned twice to make sure they continue to line up. At that point your done there and I would button up, put balancer back etc. then I would put to TDC (if I had removed distr)and then I would put distr to #1 plug. I apologize for not being clear, you do things one way all your life and it works you dont change.

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