bizarre ignition problem

[troycalm]

i just finished with a total rebuild on my wifes 78 spider 1800.rebuilt engine with .005 overisze pistons 9.5-1 ,cams from international auto,weber 40 dcnf carb.the problem started when I started losing spark in my secondary ignition,spark at the points but no spark to the plugs,i just bought a crane xr 700 electronic ignition hooked it up and Bam running great.After running about 15-20 mins and shutting off the car NO START good spark to the dist from the coil but none or very weak to the plugs,replaced a already new cap rotor plugs and wires same problem.Here is what is very very bizarre,in the no start condition it will crank the battery dead trying,but if you bump the ignition just enought to get about 2 full revolutions it will start or if you let off the key real fast like a snap release it will start.It will also have a hard start condition if it is running hot,I have the recomended coil and ballast res installed and 9.3 volts to the coil.
Any Ideas from you folks,I have been a wrench bender for 25 years and have never seen anything like this.

Thanks in advance Troy

[ventura ace]

Check to be sure that the cap and rotor are correct. I had a similar issue to yours and eventually discovered that the cap was incorrect. Even though it looked identical to the correct cap from the outside, the contacts on the inside were about 1/4 - 1/2" too deep, leaving a big gap to the rotor. Changed the cap, and everything was OK. You may need to do some measuerments with a set of calipers to determine if the rotor is going down deep enough inside the cap.

Alvon

[troycalm]

thank you,what I have done is raise the rotor a little just enouigh to know that the dist button is in good contact with the rotor, I have not checked the rotor tip to to dist cap gap i will do that.
Thanks again

[So Cal Mark]

some of the Fiat rotors have a resistor built into them. I'd check the rotor with an ohmmeter

[troycalm]

No resistance in either rotor.its got me Boggled

[So Cal Mark]

can you crank the engine with the dist cap off? Use a test light to see how the spark is from the center button on the inside of the cap. It that's ok, lay the rotor in the cap and crank the engine using a test light to see how spark is from the rotor tip.
That's the best way if you don't have a scope to hook up to it

[troycalm]

Thinking out loud,when I installed the xr 700 electronic ign how would that effect the mech advance,should that have been disabled? also if my plug wires are sitting on a hot valve cover would that cause them to thermally break down,what is the best brand of cap and rotor for my fiat.
Thinking out loud...
PS is there some type of ign kill system on this car .

Thanks Troy

[So Cal Mark]

you still need the adv mechinism, Plug wires can arc if they're in poor condition, the heat factor isn't a problem until the outer casing is damaged from excess heat. No ign kill from the factory. The best brand of cap and rotor IMHO is the oem Marelli stuff

[troycalm]

Thank you Mark its appreciated

Troy

[ventura ace]

Still sounds to me like a problem with the rotor / cap. I have the same setup as yours, I believe. Crane 700 ignition, 1.8L engine, cam mounted dizzy. Mine is only mechanical advance, no vacuum.

When I was first setting up the engine, I saw signs of the problem, but it didn't register. I was checking for spark, with 1 spark plug out of the hole, connnected to the spark plug wire and grounded so that it would spark. Well, it did spark, but the spark looked weak, and it sparked for every time the engine was at TDC and BDC, rather than 1 out of every 4 times as it should be. It was 3 very weak sparks, then 1 stronger spark, over and over. In hindsight, I know now that the spark event was arcing to all 4 spark splugs simultaneously because the gap from the rotor to the top of the cap was so large. In fact, whenever I would try to adjust the timing, I had to wear a big thick glove to keep from getting shocked because the darned thing was trying to jump to whatever ground it could find. I drove it that way for a couple hundred miles, though it sort of coughed and sputtered some until it warmed up good, and then it ran great, until one day it just carboned up so bad from all the arcing that it just quit on me 30 miles from home, and that was that. I could not get it started, and had to tow it home. Troubleshooting was the same as you. Fuel . . . yes. Battery . . . good. Coil . . . good. Alternator . . . good. Electronic ignition event . . . good (strong spark from the coil wire). No sparks at the plugs.

I was completely puzzled over the same things that you are describing until I discovered that the inside of the cap had a gap that was much larger than the rotor could reach. If you have a pair of calipers, I'd be glad to compare dimensions over the telephone with you. Let me know. 805-335-1767.

Alvon

[troycalm]

thank you for the info,I may have found the problem doing some research I found out that the plug wires Im using (carbon silicone) are not recomended on this car, with the resistor plugs its just too many ohms.the local speed shop (in this town there is only one)is telling me due to the high energy needs of my engine I need a spiral wound copper wire I forget the name brand.He says that the carbon plug wires will cause all kinds of problems from erratic idle to fouling plugs to burning the spring out of the button in the dist cap. he ordered me a set for my car and we will see how they work out ,hell 40 bux is worth it.I will post what happens this weekend.
Thanks again guys ,this is a great board

Troy

[So Cal Mark]

unless your wires have unusually high resistance they should work fine, can you measure the wire resistance with an ohmmeter?

[troycalm]

Problem found ,My xr 700 is not getting enough voltage when the cooling fan comes on,the voltage to the ballast resistor drops to 11.5 volts and the voltage to the coil is only 7.0 volts.On the nostart conditon If I jump the ballast resistor the car will start but wont run long with the voltage drop.i guess i need a bigger alternator than 55 amps,can I change the voltaGE reg or a whole new alternator..

[So Cal Mark]

what is the alt output? It should have enough output to keep the car running with the fan on. Most points-type cars bypassed the ballast resistor when cranking, then switched to the lower voltage when running. Does your xr system require a ballast resistor? Most electronic systems don't use a ballast; that was a method to keep points from arcing.

[troycalm]

the alt output while the car is running without any accessories is 14.7 ,and 9.5 at the coil.when the fan comes on the alt output is about 11 volts and 6.7 at the coil.The xr 700 claims it needs a ballast resistor in line or it will overheat.
The ign relay that changes the points has been bypassed.does this car have a system that runs the starting voltage high then drop during running? so I may not need a inline ballast resistor.