1991 Pontiac Sunfire 2.0 Ohc Backfiring

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Old 08-15-08, 07:14 AM
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Angry 1991 Pontiac Sunfire 2.0 Ohc Backfiring

Had Motor Rebuilt, Checked Timing About 3 Times. Still Backfires Through Throttle Body. Cannot Figure It Out......
 
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Old 08-15-08, 08:12 PM
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As far as I know, if spark timing is ok then valve timing must be off (unless you've spark plug wires out of sequence?).
 
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Old 08-16-08, 09:55 AM
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You never said if it runs!

(To all posters, please give as many vital details as possible.)
 
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Old 08-20-08, 07:29 AM
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Cannot Get It To Run. We Got Fuel And Fire. New Coil, Plugs, Wires, Distributor, And Still Not Running.
 
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Old 08-20-08, 08:07 AM
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autozone repair info says this model/engine does not have a distributor. I assume you have one since you said you've a new one. How did you test for spark?
 
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Old 08-20-08, 09:17 AM
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All The Plug Have A Spark. How Do You Test Them?
 
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Old 08-20-08, 12:02 PM
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You are probably 180 degrees off on the insertion of the distributor. Common mistake. Some people forget that crankshaft comes to top center TWICE, for only ONE revolution of the distributor.

The solution to this is to take off the distributor cap. Rotate engine with coil wire(s) removed, so that not only is the engine at top center according to your timing mark on your engine, but also that your distributor is pointing to where #1 distributor tower was.

Now, rotate the engine exactly one more revolution so that the engine comes to top dead center timing mark again. NOW your distributor rotor will be pointing the opposite direction it was before (180 degrees different).

Now you remove the distributor and reinsert it so the rotor is pointing once again to #1.

But before you go through all this work, you can cheat first. I am going to presume your valve-to-crankshaft timing is okay and you simply have the firing orientation off, that I spoke of. So all you have to do is remove all your plug wires from your coil. But before doing this, label all of them with tape and the number to which cylinder each of them go. Now reinstall them in the same rotation direction, only start by putting #1 plug wire in the tower hole that is 180 degrees opposite of where you pulled it out of. And then put each of the other plug wires back in following the firing order and correct rotation.

Technically, you could just leave it this way, and run the car, without pulling the distributor as mentioned. However someone else in the future, working on the car might be confused.

...........................................

Disclaimer: If your valve-to-cranskaft orientation is correct (i.e, timingbelt or chain is on correctly), that means the swapping around I suggested will not do any major harm. For example, it can't cause the valves to bend. BUT - without you actually removing the valve cover to confirm that when the crankshaft reads top center and rotor is pointing to #1 tower, and then confirming that both the #1 cylinder's intake and exhaust valves are NOT fully closed (meaning that indeed your firing order is off by 180 degrees) - I cannot be responsible what may happen in regard to backfires or actual fire around the throttle body area, if I am wrong in this assumption (even though I don't think I am, based on the fact it is backfiring on you NOW, and that is the symptom of the very 180 degree off thing I have been talking about. So I leave it up to you and YOUR responsibility if you just want to swap those distributor wires around as I mentioned, or to be doubly sure and check the valves as I just mentioned. I'd keep a fire extinguisher by you that is rated for things like grease fires, and also have wet towels by you, to smother with, just in case.
 

Last edited by ecman51; 08-20-08 at 12:23 PM. Reason: added disclaimer
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Old 08-21-08, 11:22 AM
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Tried That.... Still Doesnt Run. Is There Any Sensors Or Any Else That Could Tell The Car Not To Run. It Is About To Be Scrap Metal....
 
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Old 08-21-08, 02:39 PM
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You shifted all the plug wires to the otherside, and kept the rotation of the firing order the same?

But did it still backfire? The key here is with that backfiring. Your firing order or timing is not right. Unless you have something really odd like gas is just pouring into the intake, or some intake valve(s) are not closing.

Who did the engine rebuild?: A pro shop or you?

Have you tried a timing light on it yet? Do that. Get one. [Came back here to add that at the stage you are at - not knowing what is going on - this is actually a must.]

Also you can try doing a compression test.

If this was my car, this would not get the best of me, I guarantee. Junk er, and it has beat you!
 

Last edited by ecman51; 08-21-08 at 03:57 PM. Reason: added an emphasis
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Old 08-21-08, 02:41 PM
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Does it even try to run (hear combustion) or do does the engine just turn over? Is this fuel injected (throttle body or multiport?)? Can you spray some starter fluid in and see if it catches? Spark could be tested by holding spark plug with the cable end on it to an engine ground and see if you're getting a healthy blue spark across the plug gap. Engines are simple: air, fuel, ignition. Something(s) aren't there otherwise it would do something. Trick is to find out what is missing and why. Don't give up. I had a similar problem on a head gasket replacement and it wouldn't start. Ended up I had reversed fuel line supply with return line and engine never got fuel (I could hear the pump running). Switched lines and started right away. Look for stupid stuff like that.
 
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