Won't Start

[aj81spider]

1974 Spider, freshly rebuilt engine. Mark's Computronix electronic ignition system. The Computronix is a couple of years old, but I was restoring the car most of that time, so it probably has less than 1000 miles on it.

I drove the car to work on Monday. After work it started fine and I drove to run an errand. I came back to the car and it wouldn't start. The car cranks over, but it would not catch. It got towed home.

The timing belt was a little loose between the cam pulleys, so my working assumption was that it had slipped some teeth. Yesterday I installed a new timing belt (good and tight now) and it still wouldn't start.

It turns over, and occasionally if you give it a lot of gas it will try to catch. Once it started when I gave it almost full throttle, but was barely running - maybe 400 RPM. I locked the throttle on pretty high (my car has the throttle knob in addition to the choke knob) and went to check the timing. Before I could, it briefly revved up like it was running right, then died. It would not catch again.

Today I went out and checked the fuel - disconnected the line from the carb and get a nice steady high volume flow.

Then I used a spark tester and connected the plug wires with the tester set at about 35,000 volts. When I crank I get intermittent spark on 1, a little better on 2, and really intermittent spark on 3 (didn't check 4).

So a couple of questions:

1.) With the Computronix is that indicative of a problem?

2.) Would a Computronix unit fail like that? (running fine - then turn car off and won't start any more).

Before I put in the work to change out the Computronix for my old distributor I'd like some opinions on whether I'm barking up the wrong tree.

Thanks for your help.

[seabeelt]

It's unlikely that the four coils would all fail. Check the wiring to make sure all the connections are tight an clean. Check the plug harness going from the distrib part to the coil pack to make sure all of those wires are in good condition. Otherwise I'm out of quick check options.
R/

[azruss]

just because you have fuel flow to the carb doesn't mean you arent starved for fuel. Have you looked down the carb to see what the flow looks like. You may want to splash a little fuel down the venturi to see if it springs to life.

[aj81spider]

Thanks both for your suggestions. I checked the connections and they look good.

I dribbled fuel into the carb tonight and it had no effect. The motor sounds like dry heaving and doesn't catch.

When I get a little bit of time I'll have to put the distributor back in and see if that works....sigh - this car spends a lot more time down than up!

[aj81spider]

So good news and bad news.

Good: My Computronix unit is not the problem. This is very good news as I love the unit but was not going to spend that much to get another if it went bad.

Bad: I pulled it out and put the distributor back in and the car still won't start.

It cranks fine and you can smell gas (see earlier post - I also dribbled some directly into the carb), so I don't think it is lack of fuel. Given that neither the distributor or the Computronix will make it catch I suspect it is not a spark issue.

Any other thoughts?

[azruss]

If you are smelling fuel, you may be flooded. I know the FI cars have a couple of extra ignition grounds besides the main engine to chassis ground. How did you test the computronix unit to determine it was ok. Did you verify actual spark by taking a spare plug, connecting one of the spark plug wires to it and grounding the threads on a known good ground and look at the spark.

[aj81spider]

Hi Russ,

It may have become flooded, but I've tried to start it at varying times over the past week with the same symptom (cranks strongly, won't catch at all), so I'm pretty sure being flooded isn't the issue.

The reason I say the Computronix is OK is that I have removed it from the car and replaced it with the distributor and coil that were originally in the car and they have the exact same symptoms. What made me replace the Computronix in the first place was that I had a spark tester that only seemed to spark irregularly. I need to (but won't get to it for a day or two) do the same test with the coil and distributor - but after spending the evening reinstalling them yesterday I was so disappointed that the symptoms didn't change that I simply tossed it in for the night.

[azruss]

You might want to pull all your plugs and give them a thorough clean. I have had non starts where the plugs got so dirty, the car wouldn't start even when the spark and fuel were ok.

[seabeelt]

Just a thought.... If the Computronics spark looked weak. Perhaps a ground issue that neither the high voltage of the Computronics nor the regular distributor can overcome. How is the chassis to engine ground?

[aj81spider]

Thanks for the suggestions.

> Plugs are about 100 miles old (I just changed my head). I pulled them to do the timing belt and they were clean and looked like a reasonable brown color. Car hasn't started since I changed the timing belt (I did that after the tow home because I thought it had slipped a few teeth).

> I have the heavy braid from the transmission to the body, and I have a supplemental ground that I wired from the base of the distributor to the body. I think the engine is well grounded.

What is odd to me is that the car was running fine. I stopped it, then it wouldn't restart and hasn't since. I'm very confused as to what might cause this kind of behavior.

[seabeelt]

AJ I was thinking either broken or loose ground. Wouldn't hurt just to check. Next I would look at the power to the distrib connections all the way back to the fuse box/ignition.

I went through this kind of thing with the new(now old 95 amp alternator). In my mind it just had to be something else because it was " new". New being less than 5000 miles on it. I traced wires, measured voltages, changed the regulator, replaced the belt. In the end even though it produced voltage, the triode section had failed internally and made the alt light come on. Guess what I am saying is just because it's new ( whatever the new item is) doesn't mean it's attached well ( not slamming your work here) or something hasn't been overlooked because it was "assumed " to be in good working order. We have all been there done that and brought home the T-shirt

Take a breath, start fresh, basic checks first.... You know the drill.

[aj81spider]

Thanks Michael - I will do that. You're right - back to basics - start tracing the wires.

At least I don't have to wonder what I'll be doing this weekend!

[76was124]

Car hasn't started since I changed the timing belt (I did that after the tow home because I thought it had slipped a few teeth).

If you have fuel and spark, it is either no compression or timing is way off.

I would double check all your static timing marks, cam wheels on their mark crank at TDC. Plug wires going to the correct spots. Also, I know when I pull the distributor on mine, it takes some playing to get it set close enough for the engine to fire before I can dial it in.

[Kevin1]

So far you have confirmed that there is spark, and fuel is getting to the carb, correct? Before taking things apart again I would give the carb a squirt of starter fluid to see if the engine will fire up. If it does, you may be getting fuel to the carb but not through the carb.

I ran into this on a different car, but the same symptoms and diagnostic steps as you describe taking so far. Mine turned out to be a stuck float holding the needle valve closed. Good luck!

[aj81spider]

Good news, bad news, and more help needed.

Bad news: I'm making progress with the distributor, so I think my Computronix is toast.

Good news: The reason the distributor would not start the car was that I forgot to hook the points wire up. I did that and the car will now start...but

The car only starts if I floor the gas pedal and then keep the RPM above 2500 or 3000. I have a throttle knob I can use to set the throttle, so if I set it so it stays running, then go try to set the timing I find that the engine runs best (but not great) at about 35 degrees at 3000 RPM. I know this because I have a 35 degree mark on my crank pulley from setting the timing on my Computronix.

However once I set the timing at 3000 and then try to drop the throttle so I can set the timing at idle the engine will not stay running.

Making progress, but not there yet.

Any insight or suggestions appreciated.