Guys, can anyone tell me a way to test if a specific cylinder or the entire bank is firing? I know I could hold a plug wire against the engine and see if it sparks but I seem to remember a way, using a timing light, that one can positively see if a cylinder/bank is getting voltage from the coil(s). I have an 84 308GTS QV US. Thanks very much.
Archer, You mean like this to test the wires: Doesn’t eliminate/identify a bad plug. Plenty similar of test with ignition connected and engine running. Obviously could require plug test, but narrows it down. Sent from my iPhone using Tapatalk
I bought one of these, but haven't tried it yet. I don't know how well it will work with shielded wires. https://www.aliexpress.com/item/Universal-Auto-Car-Electrical-Tester-Ignition-Test-Pen-Indicator-Spark-Plug-Testers-Wire-Coil-Diagnostic-Tool/32840886275.html Doesn't involve removing the spark plug and zapping the engine (or yourself).
Don't ever remove a wire because it often results in overloading the coil. You can put a timing light on each spark-plug wire, but like StuR said, it does not tell you if a plug is bad. I use an oscilloscope. If you don;t have one, you can but a scope emulator for your PC. Tape a ~ 14-gage wire about 6" long to the center spark-plug wire in the distributor cap; this will be the scope input. You can run a similar wire off spark plug #1 to act as the scope trigger. You'll get a blip for each ignition. No blip = no spark. Low blip can mean bad spark plug, weak wire, etc.
A friend with a 166s used to test for a dead cylinder by licking his finger and touching it to each exhaust header pipe as it exited the cylinder. A dead cylinder would leave a mark, live ones vaporize the saliva immediately. The Top Fuel dragster engine I worked on had EGT thermocouples on each header pipe, the output of which was logged to the onboard computer. Looking at the data I could immediately identify a dead cylinder. Which gives me an idea: get one of those cheap laser thermometers at Harbor Freight and point it at each cylinder's header pipe, The temperature difference between live and dead cylinders should be immediately apparent..
Great idea (I do it too) but you cannot access the front header of a 84 QV engine so no help there. simple idea is to use a timing light, hook it up to the wire in question and pull the trigger. If there are flashes, at the right frequency, then there is spark.
About $10 or less at any auto store. Just lie it on the ignition wire and it will flash if there is spark. Check one wire at a time or place on coil wire to see if the coil is firing. Image Unavailable, Please Login
FYI, the 308 ignition ecu is pretty simple. Here is the wiring to each pin. This is from my 85 QV. Would assume an 84 is similar. Image Unavailable, Please Login
Very welcome. It’s all good motivation for me to get my restoration going again!! Sent from my iPhone using Tapatalk
308 Update: Runs great. Drove it for nearly two hours today, through miserable stop and go traffic as well as at speed on the highway. Didn't miss a single beat. Rewind 2 weeks ago: After installing the rebuilt FD and WUR it still didn't run right so I took it to Tony Ferrari of Autohaus Boston in Braintree, MA. Tony called me the next day and said the problem was a leaking seal on the distributor shaft. The oil collected in the cap would would splash around and interfere with the the electrical contacts causing the back bank to misfire. He said once he wiped out the oil and put the cap back on the car ran great. Rewind almost 2 years: When I got the car back from a major service (NOT Tony) It left me stranded twice. I found that the reason was 2 cracked distributors and a leaking distributor shaft seal on the back bank. The coil wires had also been compromised and the extenders had holes. I changed both shaft seals, put on new distributors, wires, etc, and the car ran great...until this Spring when the misfires started (the leak had resulted in enough oil collecting in the cap). In hindsight I should have opened up both caps and looked for oil. I was lazy and thought since there was no oil leaking from the caps there was no problem there. I was wrong and could have saved myself a lot of grief had I been more thorough. The good news is I found an honest, highly skilled Ferrari Master Tech. While the car was at AutoHaus I asked Tony to replace all the suspension bushings and a few other items. I couldn't be happier with the work and would recommend Tony to any of you guys. Thanks for the advice you all gave me on trying to fix my car. In the end I replaced many failed components in the engine compartment and updated many others. I learned more about my 308 than I ever thought possible. Necessity is a great motivator. Image Unavailable, Please Login
