#4 plug keeps going bad

[Tempest455]

Hi all. New to the forum and the world of Fiats.
I have been working on a 1980 spider 2000 for a few months now and for some reason the #4 spark plug works for a while then stops firing. The plug has a nice golden brown color so I know it is not fouled or oil soaked. When I bought the car the plug was dead so I replaced it (and the other 3) with NGKs gaped .30. Five miles later, same issue, dead plug. I know its the plug because the issue will follow if I swap plugs with another cylinder and reconnect. What would cause such an issue?

Thanks Brandon,

1980 Fiat Spider 2000
1970 Pontiac Tempest T-37
1974 Dodge Dart Swinger
2003 Mitsubishi Eclipse GT

[pope]

Check the coil, the wires and distributor cap. Are you carbbed or F.I.?

[Tempest455]

Its an FI car. Here is the time line of events:

1. picked up car, ran rough (engine miss) found bad Cyl 4 plug
2. Replaced plugs, wires, rotor and cap
3. Car ran tops for about 5 miles then started missing again
4. Removed distributor from Cam box to replace a sticking vacuum advance diaphragm
5. while reworking the distributor vacuum advance found trigger wires with missing insulation and had frayed ends
6. Replaced trigger and magnet (IAP parts)
7. Restarted the car and found the miss still present.

I guess I will replace the plug again and see what happens now that the distributor has some new parts...???

Thanks!

[pope]

Are you sure that the fuel injector for cylinder 4 is functioning? Could be blocked.
Did you set the gap in the distributor magnetic pickup when you changed it. (.020 to .024)
Is timing set to 10° BTDC.

Good luck

[Tempest455]

Good point, I will check out the injector too. Thanks for the gap info on the pickup, i didn't know that!. I will set that correctly and throw the trusty light on her. More to come...

Other than that I have been finding it quite easy and fun to work on this car. Can't wait to get her running strong.

[Tempest455]

Okay so i tried tried swapping out plugs, no joy. I then moved to checking the fuel injector. I pulled the connector and probed the contacts while cranking the engine. The volt meter registered current so i feel the ECU is good. I went to the store and picked up some fuel injector cleaner poured in the tank (1/2 tank) and ran the car for about 15 minutes. Trouble remains. Short of replacing the injector... any other advice?

Thanks,
Brandon

[majicwrench]

You need to decide in which area the trouble lies.
So correct me if I am wrong, #4 cylinder dead right?? How did you determine #4??
First things first, does it have compression?? EASY to find out. Pull coil wire and ground so engine won't start. Now crank over engine. Should make nice even sound, rrrrrrrrrrrrrr. If it goes rrruhrrruhrrruh the "uh" is a cylinder with low compression. Obviously that needs to be fixed.
Assuming it is #4, pull plug wire, install a spare plug, lay on head and start engine. Should see nice rythmetic spark, zap zap zap. If that's OK, ignition not a problem. IF no spark, you need to find out why.
Injector.....have you got a stethascope?? Most parts stores have em. If not a long screwdriver will work too, one end on injector hold other end to ear. With engine running, listen to the injectors, the good ones first to get a clue what they should sound like. Should be going click click click. If #1thru #3 are doing the click click thing and #4 is going thud thud or not making any noise, indicates a problem. If no noise, Is not unusual to see the connectors making poor connection at the injector, try wiggling it gently with engine running to see if it starts firing. A injector that is clicking is almost certainly delivering fuel.
So you have three things to check....
Keith

[racydave]

The injectors have power with key on, the ecu pulses ground to the injector which is best tested with a led light.Ive also seen where a vaccum leak at the intake or close to the cyl intake runner will cause a specific miss, but it does sound kinda like a injector. Howbout a compression test???

[Tempest455]

Hi all,

First thanks for all of the great feedback. I determined the issue to be with #4 by running the engine and pulling the #4 plug wire and the listening for a difference in engine operating sound. There was no change in engine operation when i pulled the #4 wire. I did the compression test recommended in a previous entry. The cranking motor goes rrrrrrrrrrrrrrr just as described. I am ruling out ignition since I have replaced everything from the coil forward.

Noticing that the fuel lines to the injectors looked dry rotted and cracked; I decided to pull all of the injectors and will be sending them to http://www.witchhunter.com/ for cleaning and testing. I the mean time I will be getting new lines and clamps for the fuel rail. The tip of the #4 injector was noticeably more dirty than the other three. I check the coil resistance of each injector and each was 3.4 ohms +/- .2. I also did a bench test on the injectors with a 9V battery. Each injector gives a good solid "click" on when energized and off again when de-energized

While taking the fuel rail off I also notice the braided vacuum line connecting the plunem to the fuel regulator was cut due to age and dry rotting. I know these cars hate vacuum leaks. I can't help be wonder if this might have been the simple cause of the strange symptoms being displayed. Either way at $18.00 per injector at the shop I figured why not. Those fuel lines in their condition were a fire hazard and needing replacement. Should have all the parts back by next weekend...

Thanks again!

Brandon

[racydave]

Youll need new seals also! Good luck!

[Tempest455]

Okay, got everything back together and the car fired right up and ran smooth for about a half hour. It started idling rough and then died. The engine would crank fine but would not fire. It now appears that I am getting weak spark. After reading some forum posts about the coil and condenser I decided to disconnect the condenser and try to start the car. I was able to get the engine running with the condenser disconnected but it was running quite rough and would not idle.

Question 1: What is the purpose of a condenser on an electronic ignition equipped car.
Question 2: Why does IAP claim to not carry said condenser for 1980 Spider 2000?

I think this weekend I will pull the coil pack disassemble and clean everything and see where that gets me.

Also, while reassembling the fuel injection (injectors, fuel rail etc) I discovered a vacuum port that I don't remember disconnecting anything from. There is the plenum vacuum port for the fuel pressure regulator line and that is all hooked up fine with fresh line. I found another small port protruding from the bottom of the fitting that supplies break vacuum. Any clue what would have been connected here? I am inclined to cap off if not needed. Strange thing, it is not corroded, looks like something was attached there at some point (PO was good at taking things apart, not so good putting them back together)

[So Cal Mark]

if you lose spark after half an hour, suspect the ignition module. It's mounted under the coil on the heat sink. I believe the vacuum line you're missing is connected to the evap cannister

[Tempest455]

Heat + old electronics, never a good combo!

Canister it was! Can't blame the PO on that one, just me getting old!

[spider2081]

I believe the capacitor you are talking about is a radio filter cap. IF you disconnect it the only side affect is you might have ignition noise in the radio. Particullary on the AM band.

[Tempest455]

Thanks for the follow ups! I got my new control unit today and installed it, no joy. No spark at all. So to date everything has been replaced with the exception of the coil and the EFI brain. I think I will go for the coil next. Do I have to buy anything special or will an off the shelf unit from jegs do the trick?

Thanks!
Brandon