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| backfiring through intake https://www.slantsix.org/forum/viewtopic.php?t=28491 |
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| Author: | kit [ Sun Apr 20, 2008 7:00 pm ] |
| Post subject: | backfiring through intake |
so for the last year or so my van '79 sportsman(slant 6 one barrel, with 4 speed) has been backfiring through the intake. It was not so bad for a while it was only when it was cold or sometimes under a load. It started getting really bad lately, and I always thought it was my carb, because it had a striped bolt hole witch kept causing it to blow out one of the gaskets. So I replaced the carb with a brand new one and took the van for a test drive and it did not change a thing. Now its gotten so bad, I cant even get the thing started, and before it totally died, it would just crackle and pop through the intake and I could not get it to go over 35 mph. I popped of the valve cover and all the rockers are rising and lowering the same so Im figuring that the cam lobes are still good, timing looks good, compression still in range, and it seems I have spark, coil is pretty new and so is the electronic ignition (the little 4 pin thing that bolts to the firewall). Am I missing something here? What else could I check? I did pull the distributer apart to see if any springs broke or the weights were binding up but they looked good to.. Please Help Me!!! |
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| Author: | SlantSixDan [ Sun Apr 20, 2008 7:25 pm ] |
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Ignition timing may be OK, but have you checked the cam timing? How 'bout timing chain stretch, have you checked for that? Could also be a vacuum leak at the intake-to-head junction, or even a bad (porous) intake manifold casting particularly if yours is made out of aluminum. |
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| Author: | kit [ Sun Apr 20, 2008 7:56 pm ] |
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Yes I forgot to say I replaced the timing chain a while back so its new to. also I should add lately my smog pump froze up and I had a leak in the EGR pipe from the exhaust pipe to the smog pump so I just plugged the exhaust side so I could rule out the chance that it was just an exhaust leak. So do you think that could have anything to do with it? |
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| Author: | Charrlie_S [ Sun Apr 20, 2008 8:26 pm ] |
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Have you checked the valve "lash"? You might have one or more tight valves. |
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| Author: | LUCKY13 [ Sun Apr 20, 2008 8:39 pm ] |
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All the above plus check the distributor cap for cracks. If nothing is found out of all these area's then do a compression test and see if maybe you have a bad intake valve. There is a very good chance you do have a valve that is ajusted to tight, or a bad vacuum leak though. Also a valve spring that has cracked/broken would be something to look for. Have you check firing order incase one of your buddies may have been having fun? Jess |
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| Author: | SlantSixDan [ Sun Apr 20, 2008 9:01 pm ] |
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Quote: Yes I forgot to say I replaced the timing chain a while back so its new to. also I should add lately my smog pump froze up and I had a leak in the EGR pipe from the exhaust pipe to the smog pump so I just plugged the exhaust side so I could rule out the chance that it was just an exhaust leak. So do you think that could have anything to do with it?
Yes, perhaps. The pipe you plugged had nothing to do with the EGR, it was for air injection. If your van still has a catalytic converter, it's probably thoroughly cooked and creating exhaust restriction.
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| Author: | kit [ Mon Apr 21, 2008 7:50 pm ] |
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I was hoping it could have been a exhaust restriction but I pulled the cat off and still I cant even get the thing to fire or even sound like it wants to. Is there any thing else I could check? |
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| Author: | LUCKY13 [ Mon Apr 21, 2008 8:29 pm ] |
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At this piont you need to verify that you do have good fuel and fire. Pull a spark plug wire and have a friend crank it over to see if its putting fire from the plug wire to ground while laying it on metal ( the end of th eplug wire). If it has fuel coming out of the carb ( when you move the throttle), and fire comming out of the plug wire (not the coil wire a plug wire) then try a fresh set of spark plugs even if they are not that old and double check that the firing order is correct. Also make sure your carb choke is open when trying to start it. Jess |
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| Author: | kit [ Mon Apr 21, 2008 10:09 pm ] |
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thanks a bunch I was thinking of trying that, I know the coil good but the plugs sparking themselves Im not positive about. |
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| Author: | Aggressive Ted [ Tue Apr 22, 2008 7:17 am ] |
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Kit, I had a 73 Dodge Sportman van that used to do that. It was embarassing...... after alot of head scratching I found that the ECU was cutting in and out. I through in a points distributor as a test, problem solved. So after replacing the ECU and resistor, all was well. |
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| Author: | 6shotvanner [ Tue Apr 22, 2008 1:00 pm ] |
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Couple other things,you mention pulling the dizzy out/apart did you check the air gap between reluctor and pickup?Was there any side to side movement in the dizzy shaft? Also you replaced the timing chain and both gears so was that before or after all this started? Good Luck 
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| Author: | kit [ Tue Apr 22, 2008 7:33 pm ] |
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I noticed when I pulled it apart there was a little wheel with what seemed to be a magnetic pick up, the wheel seemed to have been rubbing on the pick up at some, it has some chipped teeth. As for the timing chain and gears, the gears were just stripped out and it never had a problem before that. It was not very long after that, that the van started backfiring though. |
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| Author: | 6shotvanner [ Tue Apr 22, 2008 10:52 pm ] |
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Kit,I'm no expert on these puppies but sounds like there is stuff going on in your /6. If the dizzy shaft has moved enough to let the inerds get chipped from hitting I'm thinking the shaft bushings are worn out and you need a different dist.You can get a reman from your local parts house for like 40bucks,just look at it real close before you pay as some of them are just cleaned up junk.You say the timing gears were stripped? That don't sound real good, hopefuly someone here will chime in that knows what caused that and if it might have hurt something like a valve.I've seen timing sets wear out so that it will jump timing and the gear teeth are sharp enuf to cut you but not "stripped".I had a 318 in a van years ago that just running worse an worse until I finally wiggled the the dizzy shaft whilst scratching my head,the thing had like an 8th of an inch back an forth,not good.New dizzy and away we go,just something to check.Good Luck. |
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| Author: | 66aCUDA [ Wed Apr 23, 2008 7:38 am ] |
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Did I here you say the CAM GEARS WERE STRIPPED??? If so I think you had better look at the cam gear, dist gear is chipped too, and the oil pump gear. This is probally a sign of a more major problem than previously thought. My 02. Frank |
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| Author: | kit [ Wed Apr 23, 2008 7:58 am ] |
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yes the timing gears were just so wore out that the chain skipped. I replaced both gears and chain and it was fine. But if I pull my distributer, how do I check the bearings? Also I have the timing set perfect I found a mark on the balancer pulled the valve cover the rockers on #1 are both loose, I crank the motor over and check it with my timing light and its flashing at 8, or to marks below 10 on the little tab. and I did check for spark at the plugs and they all have good spark. So with knowing I have good spark and #1 it sparking when it should do you still think it could be bad bearings in the distributer? |
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