The old 12-valve Cummins can teach you something new every time you work on one

I got into this trade back in '98 when everything was mechanical injection pumps and no computers. Now I mostly work on common rail stuff with all the sensors and wiring harnesses. But last month I had an '89 Dodge with a 12-valve that needed a P-pump rebuild. That truck had over 400k miles on it and the pump was still original. Made me realize how much simpler things were back then, even if they were harder to diagnose without a scan tool. Anybody else find themselves getting rusty on the old mechanical stuff?

3 comments

3 Comments

dixon.james1mo agoMost Upvoted

Man I gotta disagree with you on the "simpler" part. Those old mechanical pumps had their own kind of complicated, just different. You ever spend a day chasing a fuel timing issue on a 12-valve where the pump is off by a few degrees and you're messing with shims and timing pins? No scan tool but you still need a bunch of special tools and feeler gauges. Plus the fuel leaks were a nightmare on those old rotary pumps. I'll take a modern common rail with a wiring diagram any day over having to pull a 80lb injection pump off just to check the delivery valves.

phoenix5731mo ago

You really think the wiring diagrams on these common rails are actually easier to follow? Had a buddy with a 6.7 Powerstroke that had a wiring harness issue and it took him a week just to find which wire was grounding out in the loom.

martin.riley1mo ago

Ask him how many times he's had a common rail injector stick open and melt a piston...