Dear Ole Mechanic;
I have a real old Jeep from the WW II / Korean War era. Someone in its past had installed a slightly newer GM four-cylinder engine made in the 1960’s. The Jeep ran fine for awhile after I installed a new carburetor. Then it started blowing black smoke out of the exhaust, missing and had no power. It got to the point that it just wouldn’t start. I followed your “fuel, spark and compression” troubleshooting method. I took the air cleaner off to check for fuel, and found that the choke was closed. The choke cable had come loose, so I figured that the choke being closed was causing the black exhaust smoke and had fouled the plugs. I got it hooked back up and checked for fuel squirting into the carburetor when the throttle was opened--and it did. It still wouldn’t start, so I pulled the spark plugs and they were fouled badly, so I got some new ones. Before I installed them, I checked for spark by putting the wires on the new plugs, laying them on some engine metal and had a friend crank the engine. I thought I saw one of them spark,but then nothing. I pulled the distributor cap off and the cap and rotor looked OK. I cleaned the points as best I could without removing them, put things back together and still no spark. Next, I pulled the coil wire and checked for spark. I got some spark, but it seemed to get weaker the longer it cranked. I charged the battery while I went digging in my parts pile and found a old, used coil. With the different coil, the spark seemed better. The engine tried to start but wouldn’t keep running. Thinking that the bad coil might have caused the condenser to go bad, I replaced the condenser. With everything put back together the engine started and would idle, but when I gave it gas it just wouldn’t speed up. I tried setting the timing by ear and it was a little better. I shut it off and then tried to restart it and it would kick back. I reset the timing until it would start, but then it wouldn’t speed up. Finally, it died and now it will not start.
I know this has been a long request for help, but I wanted you to know why I am frustrated and really need HELP.
I am retired and do not normally make house calls, because writing about car problems is usually a lot easier than actually fixing them. In this case I made an exception for a friend of a friend--and a bribe of some German soda-water.
Leaning on the fender of the Jeep, I did a visual inspection of the engine compartment--paying special attention to the wiring of this GM-powered Jeep. I have seen some engine swaps where it was just easier to rip out all of the spliced-together wiring and start all over from scratch. Fortunately, this job was done fairly well and did not require such drastic action. One of the first things that I noticed was an ignition resistor on the firewall that had no wires running to it. On the off chance that someone had installed a resistor wire in the wiring harness, I did some Ohm meter checks. There was no resistor between the ignition switch and the coil. As the old GM coils need a resistor to drop the operating voltage to about 6 Volts, the 12 Volts from the switch was burning out the coils. After tracing some wiring, it was found that the resistor on the firewall had been wired into the wrong wire, making the engine hard to start when cold. With a new coil and the resistor wired in correctly, the engine started just fine. However, it still would not rev up when given gas. A quick reset of the timing helped some, but it still was not right. Also, when the engine was shut off and then cranked to restart it, it would kick back and would not start. With the timing set back to where it would start, I pulled the vacuum line off of the vacuum advance unit on the side of the distributor. No change! The vacuum advance was leaking and therefore not working. A quick search of Frustrated’s parts pile where he found the ‘old’ coil also turned up a six-cylinder distributor that had a good vacuum advance unit on it. After the advance was installed on the four-cylinder distributor, the engine ran like a top. Frustrated was last seen in a cloud of dust headed out in the Jeep to check deer feeders.
Frustrated had done things right as far as trouble shooting. It was the total number of problems that got to him. Just because you fix one problem does not mean that you have solved all of them. Mr. Murphy had struck again. “If anything can go wrong, it will--and at the worst possible time“.
Herr Professor Nuzanbolts