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backfire out the tail pipe question

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  • backfire out the tail pipe question

    Hi all, I'm trying to start a 1967 390 motor that has a lot of unknowns. The guy I bought it from said it had NO spark at the plugs a couple of years ago when he last tried to start it. Well he was wrong, it does have spark at the plugs. However he had the wires on the wrong plugs. I compared them to my 1959 352 motor and wired them to the distributor the same way. From what I found online that is supposed to be correct. If anyone can confirm that I would greatly appreciate it.
    When I tried to start it (using some starting fluid) it wouldn't fire at all. After a few attempts, and a few more shots of starter fluid it backfired out the exhaust. The neighbors loved it! Can anyone tell me what this might mean? Could it be a timing issue? Like I said, it didn't fire at all while cranking the starter. I think the fuel pump is working because I pulled the hose off the carb and it was wet.
    I didn't want to run gas through the old lines and rusty gas tank so I used a gas can as a fuel source. I ran a line from the fuel pump into a gas can as my fuel source.
    Any ideas or procedures that you guys have would be greatly appreciated.
    thx, Dave J

  • #2
    The firing order is the same; 1-5-4-2-6-3-7-8. I would start with the basics. Bring the #1 piston to TDC and check the rotor position. It sounds like a timing issue to me. Verify that the points are set correctly also. You can rotate the distributor one way and then the other a little and see if it starts.
    John Pizzi - Squarebirds Administrator

    Thunderbird Registry #36223 856-779-9695


    • #3
      Your distributor cap should have a "1" on the top (and no other numbers). This is #1 spark plug tower.

      Just to verify, crank the engine to TDC then pull the distributor cap off. The rotor should be pointing at either #6 or #1. If it is on #6, you can rotate the crank one more turn, and the rotor will be pointed at #1. If it points to any other tower, your wires are off.

      If your rotor is pointed between two towers, your distributor may be off by one tooth.

      So, to directly answer your question... it sounds like your wires are firing on the exhaust stroke instead of the power stroke. If you follow the above directions and it still won't fire, you can pull the rocker cover off the driver's side and check your lifters (in case your timing chain is off).

      Let us know what you found. - Dave
      My latest project:
      CLICK HERE to see my custom hydraulic roller 390 FE build.

      "We've got to pause and ask ourselves: How much clean air do we need?"
      --Lee Iacocca


      • #4
        Thx gents, I'll check it out tomorrow in between turkey, football, beer, and naps.
        Have a great holiday!



        • #5
          No start ...

          Sounds like the dist. could be 180 deg out. When bringing it up to tdc on #1, make sure you are on the compression stroke. often when they have been "worked on" this is a common error. Mike


          • #6
            Hm, maybe I did do it 180 out - I got turned around the first time I tried so I just went by my 352. Here's what I found online;
            When I read that the engines were all the same I just went by my T-birds 352 cuz I knew it was correct.
            I'll check it out today one more time - I was in a bit of a hurry yesterday.
            thx, Dave J
            Attached Files


            • #7
              Alrighty then, I did as SimplyConnectd said. First I corrected the plug wires. Got it to top dead center and the rotor was in between number 1 and number 5 - it was closer to number 5. I compared that with my 352 at top dead center. I noticed the 352's distributor was advanced (or retarded) more than the 390 so I adjusted the 390 distributor to match my 352 - that caused the rotor to point to number 1 (like it should). Thinking all was well I tried to start it, now it back fires out the carburator. It doesn't backfire flames, it just pops and spurts gas.
              Any ideas on what to try from here?

              thx, Dave J


              • #8
                David, I would normally start by verifying the timing chain is set right. For now, I will shoot from the hip and assume it is***.

                At TDC your rotor should point directly at #1 (not half way to another plug tower). While pointing to #1, your points should have just cracked opened.

                What could be wrong? Simply turning the cap will NOT correct the situation because of a few reasons:
                There are 8 towers but your distributor has 11 gear teeth. That means each tooth represents 32-degrees but each tower represents 45-degrees. Notice they do not match.

                If your distributor is one tooth off, it is impossible for the rotor to point at #1 tower when the points open. Being off one tooth puts the rotor inbetween spark plug towers (like yours is) causing the spark to 'jump' to the wrong plug wire at the rotor.

                Set the crank damper at TDC and pull the distributor out. Turn the rotor so that it does point at #1 when you slip the distributor back down in the hole. If the distributor doesn't go all the way down, leave it there while you slowly turn the crank either way about 1/3 turn and it will drop in place.

                Now, put the timing marks on 6-degrees BTDC. The rotor should still be pointed at #1. Rotate the distributor slightly until the points just open, and tighten the distributor hold-down bolt. Your engine should start and run smoothly. If it doesn't, your timing chain has jumped a tooth and it must be replaced. - Dave

                To verify cam/crank timing is correct:

                Pull the valve cover off of the driver's side and 'bump' the engine. Pay attention to #6 pair of rocker arms (second set back from the front). First the exhaust rocker will open and close. Immediately after, the intake rocker will open and close. Then a long pause before the next cycle.

                Why #6? Because in the firing order (1-5-4-3-6-2-7-8), #1 is opposite #6. So, at TDC, both #1 AND #6 are BOTH at top dead center at the exact same time. When #1 is on its power stroke, #6 is on its exhaust stroke.

                If you watch #6 rocker arms and stop the crank just at the point where the exhaust is closing and intake is just starting to open... when these two rocker arms are dead level (use a straight edge), your timing marks should be exactly at TDC. If it is not, the timing chain is off at least one tooth and must be corrected.
                Last edited by simplyconnected; November 24th, 2011, 09:14 PM.
                My latest project:
                CLICK HERE to see my custom hydraulic roller 390 FE build.

                "We've got to pause and ask ourselves: How much clean air do we need?"
                --Lee Iacocca


                • #9
                  Thanks Dave!
                  I understand how the engine and parts work, but I had no idea how to troubleshoot things. Your instructions are perfect - just what I needed. Hopefully I'll have some time tomorrow to go through them and see just what's up.
                  Thx a ton!
                  Dave J


                  • #10
                    Very good, David. Those instructions pertain to ALL V8 engines, even though the firing order may change. For example, a Chevy uses 1-8-4-3-6-5-7-2 firing order. Notice that #1 and #6 are opposite? All the rules still apply.

                    Also, if you have a hot cam, the exhaust and intake valves overlap (for scavenging). No matter... when the rocker arms are dead level, the piston should be at TDC.

                    I am big on cam timing. It costs nothing to do and you would be surprised at how many engines are far off from the factory. I caught 460's off by 15-degrees. Later, I discovered Ford set them that way from the factory for emissions. That's why these engines were DOGS! Correcting the cam and crank timing properly, unleashes big HP.

                    Stretched timing chains retards the cam by ~2-degrees which puts in a 'gas pedal lag' at the light. It also lowers manifold vacuum. Whenever I change timing sets I use a 4-degree cam key to advance the cam. That brings the torque curve closer to 'street' performance, raises vacuum, and it 'builds-in' compensation for later on, when the new chain stretches.

                    Good luck in your findings. - Dave
                    My latest project:
                    CLICK HERE to see my custom hydraulic roller 390 FE build.

                    "We've got to pause and ask ourselves: How much clean air do we need?"
                    --Lee Iacocca


                    • #11
                      To all who read this post - WE should all print out Dave's instructions and keep them with our manuals for reference. Sooner or later we will need this info!!

                      Great explaination on setting the distributor which is often an intimidating job.


                      • #12
                        Indeed Joe, I have a 1992 F-250 with a 460 that has always pinged at low RPM, and seems under powered. It'll be next after I work on this 390 I'm trying to get running.
                        Thanks again Mr. Dare.


                        • #13
                          Originally posted by simplyconnected View Post
                          I caught 460's off by 15-degrees. Later, I discovered Ford set them that way from the factory for emissions. That's why these engines were DOGS! Correcting the cam and crank timing properly, unleashes big HP.
                          I'll be checking my 460 at some point before next Spring. Apparently '73 and up 460's had a timing set that was 8 degrees retarded. Earlier 460's were "straight up". My motor is a '73 and was freshly-rebuilt when I got it, but the seller had alot of cars and just couldnt recall exactly what timing set was put in there.


                          • #14
                            Joe Johnston & Davidmij, thanks for the kind words, but i am honored to help our restorers. This is practical knowledge that's hidden in the shop manuals, but the info is there if you think about it.

                            Let's back up a bit. Before setting anything to the crank marks, let's make sure they are right. I use three basic tools that cost very little or could be made:
                            * Go online, print a degree wheel, and glue it to a shirtboard.
                            * Spare the threads but smash the porcelain out of an old spark plug and weld-in a piece of mild steel round stock that sticks out ~1-1/4". (I call this a 'slug'.)
                            * Use a small wire made from a hanger, bolted under any engine screw, and point it to the degree wheel edge.

                            Disconnect the battery and unscrew #1 (or #6) spark plug. Replace it with the new steel slug you just made. With the degree wheel bolted to the crank, slowly turn the crank with a wrench until it stops. Make a mark on the wheel at the pointer with a pencil.
                            Slowly turn the crank in the opposite direction until it stops, and make another mark on the wheel at the pointer. TDC is exactly between those two marks you made. Turn the crank in between those marks.
                            Now turn just the paper degree wheel until 'zero' is at the pointer.

                            REMOVE THE SPARK PLUG SLUG and store it away. Now, you are ready to check your cam timing against true TDC.

                            Originally posted by Dakota Boy View Post
                            ...'73 and up 460's had a timing set that was 8 degrees retarded...
                            One caution is in order; when talking about 'degrees of offset' the 'standard' is in crank degrees (there are 720- crank degrees in one cam rotation). Not to confuse anyone but, 8 cam degrees are 16 crank degrees. Cam companies use 'crank degrees' on their spec cards. (Advancing the cam, retards the crank.)

                            I am guilty of using 'cam degrees' because I tell folks to advance the cam by four degrees. Think of the chain as having no keys. If you turned either sprocket clockwise, you would advance the cam. There are three choices for Squarebird FE's to accomplish this; retard the crank by using an offset crank key, advance the cam by using an offset bushing, or buy a timing set with multiple slots in the crank sprocket (and you choose your offset).

                            Dakota Boy is correct in his report of "8 degrees retarded". He is talking about 'cam degrees'. That puts the torque curve peak way up around 7,000-rpm (which de-tunes the engine), but after timing set stretch and wear, it gets even worse.

                            I get physically sick when I see a Police Interceptor 460 that only produces 260-hp, but that's exactly what Ford produced. Check this out:
                            I don't expect anyone to run a compression ratio at 14:1 on the street, but that same 460 puts out 800-hp. I would expect a 460 with aluminum heads and 9.5:1 compression ratio and a mild street cam to output around 500-hp.
                            - Dave
                            Last edited by simplyconnected; November 25th, 2011, 10:45 PM.
                            My latest project:
                            CLICK HERE to see my custom hydraulic roller 390 FE build.

                            "We've got to pause and ask ourselves: How much clean air do we need?"
                            --Lee Iacocca


                            • #15
                              OK, here's the latest. Per Dave's excellent step by step instructions I found the distributor to be one tooth off. However, when I put in on what feels to be the correct tooth it won't drop down into place - it sits about 1/4 inch too high. If I go either way one tooth it drops down perfectly - just can't get it to go on the tooth I need. I tried what you said Dave about turning the crank 1/3 of a turn either way but it still won't drop in. Any suggestions on how to work this out?
                              thx, Dave J.