TyTheJeepGuy previously posted:
"James, you've probably already seen this but they have a kit for the 72 and newer CJ5 with the 4.2L I6. I'm assuming yours has the 3.8L?
https://howellefi.com/product/tbi-ki...issions-legal/
Not sure why that wouldn't work with a 4.2 in a 1970 CJ, what really changed in those two model years?
"
Huge change...Kaiser sold Jeep to AMC in the spring of 1970, but the 1971 model year was kept the same as the 1970. In 1972, AMC made the changes to their engines (the famous 232/258 inline 6 and 304 v8) and quite a bit of other stuff....1971 is the last of the early cj5 and 72 is the beginning of the intermediate cj5 vintages. The Kaiser era ran a 3.7 v6 that had been bought from buick - its commonly known as the dauntless 225 odd fire. Its history is a bit weird, but Buick basically took their v8 and chopped two cylinders off and rushed it into production using as much of the v8 parts slightly modified as possible. One of its unique features is the cylinder firing is not consistent...thus the 'odd-fire'. Most engines fire a spark plug with a consisent time gap between each spark from one cylinder to the next (assuming constant rpm here). The odd fire fires two consecutive cylinders with a small time gap, and then there is a large time gap to the 3rd cylinder, another short gap to the 4th, large to the 5th and short to the 6th....the 2 large time gaps are basically the missing two cylinders from the v8 design. So basically, even at constant rpm, a tach signal from the ignition is inconsistent...the computer sees 2 quick sparks and then a big gap and thinks the engine rpm is slowing and then it thinks the rpm is increasing again as the quick sparks happen and so on and so forth. At higher cruising rpms, it all kinds of evens out and doesn't cause too much issue, but at lower rpm (say slow wheeling) the computer starts causing all sorts of issues and the engine idle becomes very erractic. This is all assuming that you have replaced the points distributor with HEI (and this is true I think for any TBI conversion such as old sbc's), as points distributors with traditional ignition coils don't put out a sharp enough defined electric signal for the computer to pick-up...Varioius signal filters can be used to help the situation, but HEI usually is the trick, or a crank sensor tach signal is needed. I decided I am happy with my slightly upgraded points distributor to pertronix, but don't want to go full HEI, and fitting a crank sensor has some complications (a friend just finished it within the last couple weeks and his odd fire is apparently awesome with TBI now - but it has been almost a full year of troubleshooting, debugging and fabricating pieces for the crank sensor - which is basically the only solution.) Honestly, after getting the cj5 running so well with carb and basic ignition etc - I don't really care to change it. But I am interested to try out the TBI on something a bit more straight forward, and a sbc would be just about right. Interesting enough, after AMC bought Jeep, they sold the dauntless v6 back to Buick, whom made it a bit bigger (3.8L 231 c.i.) to match the now slightly bigger buick v8 but kept it odd fire for another year or two. They eventually made the needed changes to the internals (crank, camshaft etc) to make the engine an even fire and installed HEI from the factory....This engine became the Buick Grand National and eventually was turbo'd in the 90s or so. Any all of these engine use the same block and can be dropped directly in place of each other....The odd-fire has a distinct low rpm grumble that some love, but if my current 225 (bored 60 over and at its limit for larger pistons rings etc) ever needs replaced, I think an even-fired 231 would be nice.