What causes an engine to do this? (PROBLEM SOLVED)

[lemming303]

It's on my mom's car. A 76 Ford Elite 351 2 bbl. When trying to start it will crank but it won't fire. After you turn the key off though it sounds and acts like it fires on the last cylinder it stopped on. I don't know if that makes sense or if you understand what I am saying. As soon as you turn the key off after unsuccessful starting the engine turns over on its on. It has a very short pause before doing this. I'm not sure if that is a delayed ignition, or if it is just pushing whatever cylinder was closest to TDC away from the combustion chamber.

We thought it was the battery so we charged the battery. That didn't help. So then we took the battery out of my f150 and tried it, and it still does the same thing. Her battery is a 550 CCA and my truck battery is a 590 cca. I don't know a whole lot about engines so I don't know how to go about diagnosing this issue. The plugs are fairly new, I would guess less than 5000 miles on them. They are Bosch Platinum plugs. The distributor doesn't look corroded or worn, but I have a new cap I'm gonna put on there anyway. The wires are all fairly new as well, Borg Warner wires. It's getting fuel because it floods if you crank it too much, you can feel gas on the inside of the carb. Thanks for the help yall.

[Ornamental]

Back in the day when I was driving a moped, I would check if the spark plug fired by taking it out, putting the cap back on, and hold it to the cylinder head (ground) to see if it fired.

Googled that to see if it would be ok on engines with more than one cylinder, and found this:

Take out the spark plug, place wire back on plug. Hold wire/plug by wire's boot, so firing end of plug is close to (1/4" away from) a ground like the engine block, exhaust manifold, etc.

Have some one turn the key so engine turns over.

If you have good spark you will have a bright blue spark from plug to exhaust manifold. Also will hear a loud pop as it fires.

If spark color is real light blue, orange, or yellow you have weak spark

 http://answers.yahoo.com/question/index?qid=20081208053052AAgO4Ev

If it gets gas, have a good spark, then it would seem like it's a problem with air.
Check if the air filter is really clogged in that case, and try without it.

Hope it helps you!

[dutch]

firing up when you let the key go, sound like a bad ballast resistor to me...

[Changin Gears]

Sounds likea bad ignition switch/switch circuit.  You can test this be runnning a test wire from the battery (12v) to the + side of the coil(aka hot wire) then try and start it.  Just remember that the ignition switch will not shut off the engine, you have to remove the wire.

[HP2]

An engine requires air, fuel, compression, and ignition, in the right amounts and at the right times, to properly run. Checking for the presence of each of those will lead you to the missing piece of the puzzle. Once you know what piece is missing, you can start tracking down component issues.

[ntstlgl1970]

  w/HP2
seems like you have fuel, and if it sounds "normal" when it cranks over, then maybe ignition.
If this is a duraspark system (small 3x3" aluminum box connected to the distributor wiring and coil wiring), let me know what color the box strain relief is (brown, blue where wiring goes into the ignition box) and I can look up some testing for it tonight.

Here is a sample duraspark wiring diagram, it's not very complicated.

Do you have a test light? it's about all you need to diagnose the ignition system on this car.

[lemming303]

Thanks yall. I won't be able to work it again for a couple days. I'll let yall know if I figure anything out.

Ntstlgl, I'll have to go look at it to see about the ignition box. Like I said though it's gonna be a couple days first.

[Moparal]

Bet it's the ignition box.  Fords famus for that.  I believe auto zone can check it, but what matters is the color chip on it and number of wires on the plug   It's the square box that you should check on the firewall. Maybe 4x4 in size or a bit bigger

[71chally416]

   We had a big Ford box truck where I used to work that went through a bunch of those boxes. You always knew when it would backfire going down the road and die. 

[lemming303]

So if it is the ignition box, what is a good brand to replace it with? I don't want her to spend money on a cheap one just to have it go out down the road.

[hooD]

My 1981 F150 would shut down at 70 mph then come back to life again.  After replacing the ignition module (box) problem solved.  I'm not sure if your problem is the same, but that module can heat up and act funny.  Autozone has them for $25 with a limited lifetime warranty.  If it goes bad you get a new one.

[arcticmopar]

 Odds are it's the ign box like eveyone says...but I had the same symptoms with my 4x4 once (BB Mopar) it turned out to be the pickup coil in the distributor. I didnt run the extra balast resistor when running an Acell super coil. NO spark until I let go of the key then it would spark once just as it stopped turning over...very frustrating!

[lemming303]

OK yall, I went back to my Mom's house today to check the ignition module like yall said. Well, it's getting no spark whatsoever. I tried 2 different plug (on the same side of the engine) and put them close to a bunch of different spots on the heads, corner of the block and exhaust manifold. No spark at all. This means the ignition box is shot right? Can I get a new box and replace it or should I be doing more tests first? Thanks again for the help.

[Moparal]

Take the box off and take it to some place like auto zone. They can test it right there. If bad, replace it

[lemming303]

Thanks for all the help yall. It was the ignition. Bought a new box at Autozone and now it works great! It even fired up almost immediately. Runs smoother now too. Only problem now is the trans won't shift into overdrive, but I'm gonna post about that in the trans section. Thanks again for the help yall, I love it when my Mom is happy.