Technical Frustrating: 1978 with no spark on #3

[U404S]

Recently, I noticed that #3 quit firing at the distributor cap. Using a wire I could not get a spark against a ground, however with a voltmeter I see I have 12.XX volts at the cap at number 3, just no blue spark.

I assumed it was a bad cap or rotor so I ordered those items and installed them tonight. Unfortunately, there is still no spark at #3, yet tons of spark on 1, 2, and 4.

The wires, points, condensers, plugs are new in the past thousand miles. Points are also gapped right. I thought maybe I had the cap on crooked, but confirmed it is sitting flat.

Can't find anything in the Forum similar or on the net.

I know I must be missing something simple, but what? Everything has always made sense with this car until now. What's worse is this is my wife's car and she is grumpy because my Unimog is running, but her Fiat isn't and is convinced I have brought this problem on just to aggravate her.

So, any advice would certainly be appreciated.

Cheers,

Jerry

 

[GeorgeT]

Try swapping wires with another cylinder. Also look closely at the lobes on the distributor shaft and verify that are all the same; have someone crank the carwith the cap off and observe the points opening and closing on each lobe.

 

[spannerdude]

Jerry,
it should all be pretty simple really. If the points are opening it should generate a spark. They are opening for the other 3 cylinders but due to bush wear or a bent spindle they might not be opening for number 3.

Check the points gap on each lobe and make sure they are opening. Check the spindle for play at each lobe too.

I've never seen this problem with a FIAT twin cam but on other engines where the oil pump is driven by the dizzy shaft I've seen the resistance of the oil pump pull the dizzy spindle to one side if there is play in the bushes. Spin the engine over on the starter and check for the spark at the coil lead. If it's skipping number 3 you should see it.

If the coil is sparking then the next thing to check is where it's going, that's where your new cap and rotor will come in.

 

[U404S]

Spannerdude and GeorgeT,
Thank you for your replies. You were right on the points. On one set, the round soft orange/red electrode material had split in two if that makes sense. This substantially increased the gap. I am just guessing, but maybe the car was running off of the starter set?

Regardless, I had ordered a Petronix kit from Auto Ricambi for use on a rainy day. Today qualified, so I went to work on that and finished it up a little while ago. It started right up with spark at all cylinders. I really don't understand how the Petronix thing works, but it does. I still need to time it, but it sounded real good. It has been raining here in Jacksonille, Florida since about 6:00 p.m. So I won't get to try it out on the road until morning. What's more, I am off my wife's list.

Unrelated to the Fiat, I have had drivability problems with my 404 Unimog for some time. Despite replacing or working on points, plugs, wires, timing, carb, fuel pump, filter, fuel pick up, fuel lines, valve adjustment, etc, it has driven poorly for years. Last weekend I tried one more thing and drained the fuel tanks filling them with marine gas (no alcohol mixed in) and after a couple miles, idle speed increased noticeably and the engine became much more responsive. Top speed was always around 76 km/hour; now it hits 94 km/hour. Maybe it's the gas, maybe some crud broke loose, not sure what for sure. It was a nice surprise though. Wish I knew more about mechanicing.

As a side note, marine gas is $4.41 gallon where regular 10% ethanol pump gas is $3.79 gallon.

Regards,

Jerry

 

[s130]

Related to your problem is that on some distributor setups on Fiats fitted with electronic ignitions then the position of the distributor body can be rotated relative to the rotor. If rotated too far the then electrodes in the cap get to far away from the rotor. It can happen that the spark is able to jump from the rotor and to some but not all of the cap electrodes.

 

[U404S]

Thanks S130, that might have been the problem. It certainly makes sense.

Otherwise, We have been driving the Fiat every day and having a great time. This Petronix ignition conversion is quite the ticket. In my next order to my parts supplier, I intend to buy a spare kit just in case.

Next step for the car is a new set of lowered springs. That seems like a nice change and it also is time for new shocks so the two should go hand in hand.

Cheers,

Jerry