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EFV-8 Club Forum / 1940 Ford Discussion / 48 Ford Missing on 2, 5, 8 on crab cap distributor

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Posted By Discussion Topic: 48 Ford Missing on 2, 5, 8 on crab cap distributor -- page: 1 2     dknechtly 05-24-2021 @ 1:55 PM reply profile send p.m. Member Posts: 8 Joined: Mar 2021 Guys, we are stumped. We have new coil, condenser, plugs. New plug wires, new crab cap (replaced dome) and rotor from C & G. Points are great and set at .015. Compression test shows are all around 90. Carb was rebuilt (it was leaky). The engine misses on 2,5,8. We pull the plug wire and it does not pull down the motor. We pulled the plugs and the are all getting great spark. We switched the wire between 7 (good) and 8 (bad) and still made no difference in 8 (7 continued to work great). Any ideas? carcrazy 05-24-2021 @ 8:53 PM reply profile send p.m. Senior Posts: 1680 Joined: Oct 2009 What kind of wires are you using? Are you using the metal core wires? Are the end terminals soldered or securely making contact with the ends of the each wire? Measure the resistance of each wire - each one should measure close to 0 or 1 ohm of resistance. The wire for spark plug # 5 has to cross over from the right (passenger) side of the engine to the left (driver) side. The wire for #3 has to cross over from the left side of the distributor to the right side. Are you using the correct spark plug conduits for the crab type distributor with outlets to allow the wires to crossover the top of the engine? If you are not using the metal core ignition wires, but the carbon core (radio resistance) wires instead, be aware that if bent they can lose continuity and go to infinite resistance especially when hot. 40 Coupe 05-25-2021 @ 5:03 AM reply profile send p.m. Senior Posts: 1683 Joined: Oct 2009 Look at the rotor it may be damaged. The rotor can touch one or more of the cap inner terminals causing the rotor to break. Some caps can be defective and do not have continuity between the inner contact for the rotor and the spark plug wire terminal end. Some have too much plastic molded into the holes for the spark plug wire terminal. dknechtly 05-25-2021 @ 7:49 AM reply profile send p.m. Member Posts: 8 Joined: Mar 2021 Thanks for the replies. These are non-metallic wires. They are what C & G sent with the crab cap and crab rotor. We swapped #7 and #8 wires (at cap and plug). #7 still worked and #8 still did not work. That tells me the wire is good (plus we get strong spark). We will double check the inside of the cap and connections for excess plastic. So I have compression; I have spark; I have gas (since #7 works). Would sticky valves show up in a compression test? TomO 05-25-2021 @ 8:34 PM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 When you pull a plug wire on 2, 5, or 8 and hold it near a head nut, do you get a nice blue spark? When you pull the plug on one of the failing cylinders is the plug wet with fuel? Do you hear any noises that are not normal for a good running engine? Did the engine run without a miss before you installed the crab cap? Do you have t 21A rotor installed? Tom 40 Coupe 05-26-2021 @ 4:54 AM reply profile send p.m. Senior Posts: 1683 Joined: Oct 2009 Early Fords and their original ignition system use copper core spark plug wires with nearly zero ohm resistance from end to end. The more modern resistor type plug wires can cause high RPM missing. dknechtly 05-29-2021 @ 8:15 PM reply profile send p.m. Member Posts: 8 Joined: Mar 2021 The plug wire boot is too long to hold up a head bolt however, we pulled every plug, they all had great spark. When my buddy (this is his 48) changed the plugs, they 2,5,8 were wet. We do hear noises that are not normal for the engine. I know what loose rockers sound like. I know what a rod knocking sounds like but I don't know what sticky valves might sound like in a flathead V8. The engine did not have a miss before the crab cap, rotor, wires where installed. The old spark plug wires would give a shock and the coil wire was intermittent; we'd have to jiggle it (this was all the dome distributor). Yes we have the 21A rotor installed. I put my vacuum gauge on it and amazingly, I only got about 5 pounds. needle going back and forth to zero pounds. It has a new carb to intake gasket. The car missed before the carb rebuild. We changed his oil (it was not pretty) and put new VR1 50W plus a quart of MMO. We also squited some down the carb. carcrazy 05-29-2021 @ 8:40 PM reply profile send p.m. Senior Posts: 1680 Joined: Oct 2009 If you have only 5" of manifold vacuum at idle, you have some serious problem causing this. Is there a tube going to the manifold that is open to atmosphere like the tube to the windshield wiper motor? Are there any leaks between the carburetor and the intake manifold or between the intake manifold and the block? What are the resistance values for each of the ignition (spark plug) wires and the coil wire? I have had carbon core ignition wires test OK when they were at room temperature but would go to infinite resistance when hot. If your resistance values are more than about 1 ohm for each wire, I recommend replacing all of them with solid metal core wires. 40 Coupe 05-31-2021 @ 4:39 AM reply profile send p.m. Senior Posts: 1683 Joined: Oct 2009 Did you install the distributor correctly? in some cases it can be installed 180 degrees off usually the case will crack and break. I suggest you remove the distributor and check. Also check all the plug wires are in the correct spots. TomO 05-31-2021 @ 6:05 PM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 Because you did not have a miss before you installed the new cap and wires, the problem is most likely in the cap or wires. Wet plugs indicate that fuel is getting into the cylinders. Pulling a plug and checking the spark can fool you. The plug can fire in the atmosphere but a weak spark will cause it to fail under compression. I pull the plug wire and insert a screwdriver into the opening of the boot for the spark plug and then hold the screwdriver near a head nut. You can also use a spark tester like this on available at Amazon or an auto parts store. https://www.amazon.com/OEMTOOLS-25069-Adjustable-Ignition-Tester/dp/B0014WDFLY With 3 out of 8 plugs not firing, the reading of 5 inches could be normal, the fluctuating needle is probably due to the miss. A new set of correct wires for the 48 V-8 is probably a very good investment at this point. The resister wires could have enough resistance to cause a miss and are easy to break the core with the tight bends in the Ford's system. A sticking valve gives a ticking or a light knocking sound. The MMO should have given some relief from a valve sticking, so that would be lower down on the trouble list. Tom

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