vetzrul1

The simple question: Can bad fuel cause backfiring?

The story behind it (for those that are bored and want to know):

I recently had to repair an oil leak in the back of the manifold so I pulled everything apart, fixed it, and put it back together. The car had been sitting for awhile before hand because I just didn't have the time to mess with it. At some point I had put stabilizer in the fuel although it may have already been too late. Once everything was back together, I tried firing it up and I got backfiring.

Now, I've taken this engine apart many times before and put it back just as many successfully and had no trouble. I thought maybe I had a stupid moment and put the distributor in backwards so I pulled it out and turned it around. Even worse. Turned it back around to how I had it. Pulled the cap and looked to see which spark plug wire the rotor was pointing at. Pulled the corresponding plug, and sure enough the piston was pretty much at the top ready to fire or at least close enough to run even if rough.

Went back through EVERYTHING and made sure I hadn't missed plugging something in somewhere along the way. All is how it should be. Replaced the cap, rotor, and plugs because it had been awhile since I had anyway and they had signs of some wear. Had the ignition control module tested and it tested good. Also had a spare that I tried first with the same results.

So now I'm stuck. I'm pretty sure the gas is bad or at least gone down hill quite a bit. What has me puzzled is that I am still getting some firing out of everything for it to backfire so some fuel has to be igniting. Is it possible for the fuel to go bad and cause the backfiring? Typically when it backfires, it will sound like it's trying to start but not getting much of a spark and then I'll get some small bursts where it backfires. Then when I let it sit for a second and try to start it again, I get one hell of a loud backfire. I've tried using starting fluid as well to no avail. Although sometimes when it backfires with the starting fluid in, there will be a small puff of smoke come out as well.

I'm pretty sure I've talked myself into draining the tank but I've got about 7-10 gallons in there and just really don't want to do that. Does anyone have any suggestions on anything else it could be or things to try? Thanks for any help in advance.

BTW: The car is an '85 that is pretty much still stock.

John A. Marker

Recheck the wires to be sure that you have not taken one out of the firing order. That is what it sounds like. If you put then in the wrong firing order you could get the back fire. There are a couple of wires that you could trade and it would start and then backfire a little because the firing order is so close.

vetzrul1

1-8-4-3-6-5-7-2

That's the firing order I've always set it to and double checked the manual and should be correct. I've rechecked that each time I pulled the wires off because I have made that mistake before. Just out if curiosity, which wires can be swapped that would still let it run even though it would t be quite right?

C409

..... What is the timing set at ? ............

John A. Marker

4 - 3 , 6 - 5 and 2 - 1.

I would triple check wires to be sure of the order. Also make sure that all the boots are tightly on the plugs and the wire is firmly in the cap. You might try and start the car at night with the underhood lights unplugged to see if any of the wires are arching.

Did you check the cap to see if there was any sigh of arching between terminals?

Bad gas should not cause back firing.

Did you touch the valves?

Have you pulled the plugs to see if they are wet from fuel. If you are flowing excess fuel into the cylinder and it is being forced out the exhaust valves into the exhaust manifold....this could result in backfire also.

Frizlefrak

Run a compression test to ensure no valves are hanging open and it hasn't jumped time. Triple check plug wires, correspond with firing order, and in the correct rotational direction. Double check all wiring to the distributor. Check EGR. Check for grounded injector(s) pouring fuel into the engine, as well as fuel pressure. Check voltage at TPS.

Bad fuel will cause poor performance and missing. It won't cause backfiring.

Maybe I missed it somewhere in your original post....is the backfiring out of the intake or the exhaust?

WW7

This might make it easier for you to check firing order.......WW

xrav22

I you have 1 and 3 switched it will backfire and run . I put them back and no more backfiring. Fyi

Cliff Harris

The only time I've had backfiring was when I got the distributor off by one tooth.

Well, that's not really true. I had backfiring when the timing chain jumped a tooth or two on my old Dodge mini motor home.

I did manage to swap a couple of plug wires once. In that case the engine ran on 6 cylinders because the spark came at the wrong time on the swapped cylinders.

vetzrul1

The car is back firing primarily through the exhaust although it did go through the intake once or twice. I finally got a minute to work on it today though and just played around with some things.

So I checked the wires to make sure they were in the correct firing order once again and they definitely are. I tried changing a couple of the wires around that a couple of people said could be swapped and it would run but would be rough. Sure enough the car fired right up but definitely wasnt right so I knew the timing is off for sure. I changed them back to how they should be and turned the distributor as far as I could counter clockwise and got a little better sound like something was trying to fire. So I changed all the wires in order one post counter clockwise and tried again. Almost started. Turned the distributor farther counter clockwise and the car fired right up. After fine tuning the distributor, I got the car to run pretty smoothly.

I don't really want to leave the distributor like that because I know that's not how it should be. Does that mean the timing has jumped or the distributor is installed wrong or what? From the way the car sounds, I think it would be perfectly fine as far as running once I change the old gas out.

John A. Marker

It means that when you installed the distributor the first and second time the rotor was not pointing to the number 1 plug wire. You have now moved the wires so they line up with the rotor. It may not be in the "exact position" as shown on a diagram....but it works.

You have two options:
1) leave it alone.
2) Put wires back where they were. Pull the distributor and rotate it back a tooth (may have to turn the oil pump shaft) and drop the distributor back in to match diagrams of the #1 plug wire position on the cap.

vetzrul1

Ok, great. I've never had that happen to where the teeth got off when I reinstalled the distributor. I was under the impression that the distributor only fit in two different ways. One being the correct way and the second 180 degrees off. Any idea on how the teeth could have gotten off to prevent it in the future?

John A. Marker

It is really a matter of the position of the oil pump shaft. If that turned a small amount when you pulled the distributor then when you re-installed it could have been off a tooth. It really is not a big deal. If it happens again, just take a long screwdriver and stick it down the distributor shaft hole and turn the oil shaft.

If you turned the oil pump shaft 90, the distributor would drop into a different position from standard. If you then re-positioned the wires to match the position of the rotor...it would run.

corvetteronw

Review this video and the next one in the series. Good stuff:

red89c4

bad fuel should not cause a backfire, it would cause a miss or sputtering from not burning or igniting. it sure sounds as if you have the dist out of time. like you stated you have done this many times, and if you are like me sometimes we get in our own way when doing things. i would take a deep breath and start over. rotate the engine until the timing mark on the balancer is pointing at TDC. at this point the rotor button should be pointing at either 1 or 6. it will either fire emmediately or it will be 180 out. if 180 out simply remove dist and rotate 180.