scaleless Posted July 4, 2021 Share Posted July 4, 2021 Right, finally got to the first real big problem of my build. New engine, new electricals, new everything for the most part. I've only run the engine for seconds at a time as I do not have the cooling system installed yet, but it starts right up faster than I've ever seen a Renix start and idles great. As soon as the throttle is opened even a little bit, however, it starts missing on multiple cylinders with an even cadence and randomly backfiring out the exhaust. An inspection of the plugs shows it's running very, very rich. The plugs are dripping with fuel. All vacuum ports are plugged for testing. It is currently running remanufactured 746 injectors which I expect is the problem even though I randomized the injectors twice and the cadence of the misfire did not change. I checked the MAP sensor with a meter and a vacuum pump and it is reading as expected. The MAP line holds a vacuum and if I pull the line, the engine sputters and dies. I tested the IAT and CTS and they are both reading expected values. If I unplug either, there is a slight change in the idle but the symptoms do not change. I swapped them anyways since I had extras on hand and nothing changed. The grounds are new and fresh, and also test fine. The fuel pressure is pegged at 40. I ran the engine with an inline spark tester on every plug and I'm getting spark as expected. I previously performed a compression test and each cylinder put out exactly 150psi within a few cranks with no deviation. 20210703_223346-small.mp4 Anyways, I was going to swap to some known working stock injectors to isolate that as an issue, and wanted some input from the forums. Just spit out some ideas. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 4, 2021 Share Posted July 4, 2021 Dizzy properly indexed? Link to comment Share on other sites More sharing options...
Jeep Driver Posted July 4, 2021 Share Posted July 4, 2021 7 minutes ago, cruiser54 said: Dizzy properly indexed? He's got a timing issue for certain but I didn't want to be the first to say. He needs to resolve his problem, those short idles are going to ruin his camshaft. Link to comment Share on other sites More sharing options...
scaleless Posted July 4, 2021 Author Share Posted July 4, 2021 The distributor is properly indexed, and I already put a timing light on to see if there was a timing issue and it's idling at 20 btdc. Can't really see how much it increases with throttle because of all the sputtering. I would love to break in the engine before playing around so much, but it won't get above 1200 RPM or so. As another note, I also verified all injectors are connected in the correct order. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 4, 2021 Share Posted July 4, 2021 with a timing light, they usually show 12 at idle FWIW. Link to comment Share on other sites More sharing options...
scaleless Posted July 4, 2021 Author Share Posted July 4, 2021 I've also got a high altitude CPS. Link to comment Share on other sites More sharing options...
Jeep Driver Posted July 4, 2021 Share Posted July 4, 2021 Which flywheel or flex plate? Link to comment Share on other sites More sharing options...
Ωhm Posted July 4, 2021 Share Posted July 4, 2021 Your video sure does sound like cross-firing. You mentioned 40psi as fuel rail pressure. Does that drop down to 31psi when engine is at IDLE? Link to comment Share on other sites More sharing options...
scaleless Posted July 4, 2021 Author Share Posted July 4, 2021 It does drop to 30 or so at idle, yes. My flywheel is a Luk LFW194. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 4, 2021 Share Posted July 4, 2021 so, this is a new to you flywheel? Link to comment Share on other sites More sharing options...
scaleless Posted July 4, 2021 Author Share Posted July 4, 2021 Yes. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 4, 2021 Share Posted July 4, 2021 That's not comforting.....If they're anything like the Renix flexplates that are off. Link to comment Share on other sites More sharing options...
scaleless Posted July 4, 2021 Author Share Posted July 4, 2021 I found a few threads on CC and other jeep forums describing my issue, and in those cases it was fixed by replacing the flywheel and/or slotting and adjusting the CPS, so that may be the issue. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 4, 2021 Share Posted July 4, 2021 Those are 2 different things. Slotting the CPS so it is closer to the flywheel increases it's output. The flywheel teeth or flexplate teeth being off is of those teeth being out of whack rotationally. Link to comment Share on other sites More sharing options...
scaleless Posted July 6, 2021 Author Share Posted July 6, 2021 Hahaha I believe I get the honor of being inducted into the league of extraordinary dunces today! After not having the time to diagnose the truck for a few days, I returned to first principles and very rapidly found the issue - I apparently don't know which way the distributor spins lmao. Not really, perhaps, but I definitely had a very long brain fart. My distributor was perfectly indexed out of the box (don't know where it came from or if it was oem - it was in a box in the truck when I bought it) so I did not need to cut the tab off. I double checked the index again after priming the engine with oil, but the truck sat a week or so before I started it so I primed the engine again and replaced the distributor. When I did this, I apparently put it in one tooth off, and now the leading edge of the rotor was nearly perfectly aligned with #1 at TDC. When I was visually inspecting the distributor, I was not paying enough attention to notice that it was, in fact, not actually the trailing edge of the rotor. This was just enough for the spark to jump the gap at idle, but miss or fire on the last plug when advanced any further. After the first start, I checked the distributor indexing at least twice and failed to spot this. Anyways, despite feeling slightly dumb, I'm glad I was able to solve the issue somewhat quickly, without tearing everything apart, and most importantly without spending a buttload of money on random parts that I don't need! After moving the distributor back a tooth, the engine runs fantastically and I'm finally ready to move on with the truck. Thanks everyone for the help, especially @cruiser54 for naming the issue immediately despite my inability to quickly follow up on it! I'm updating the title to better reflect the issue in case someone searches their issue and could be helped by this thread. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 6, 2021 Share Posted July 6, 2021 What a guy!! It takes cajones to admit this. LOL. Glad to hear this is solved. Now, I have to ask a question. Did you use my Tip 13 to index the dizzy? This is the first time I've seen this happen. Is there something in Tip 13 that should be clarified? Link to comment Share on other sites More sharing options...
scaleless Posted July 7, 2021 Author Share Posted July 7, 2021 Yes, I used tip 13 and no, it wasn't ambiguous at all - it is clear and well-written. I think what happened was I indexed it correctly first before removing the distributor again to prime the oil pump, and after that I had too much confidence and wasn't paying nearly enough attention since it was something I had done before. I definitely recall that I was listening to podcasts at the time. Although maybe if you arranged it like a picture book for ages 3-5 I would have gotten it right LOL jk jk Link to comment Share on other sites More sharing options...
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