matrophy Posted December 29, 2020 Report Share Posted December 29, 2020 (edited) Dealing with rough running carbureted z24 engine that turned out to be a cracked vacuum hose. In the process, I took out the sparkplugs. 1, 3 and 4 on the intake side were a perfect light brown. Number 2 intake had black soot that wiped off. All 4 exhaust plugs were dark brown/black but not oily or sooty. Can anything be interpreted from only the #2 intake plug being sooty black? I imagine that the exhaust plugs are a normal color because they are on the exhaust side but I could be wrong. I had the engine idling for 2-3 hours overall while I was troubleshooting and my ECC was in open loop for quite a long time before I fixed it (and haven't driven it a lot since that repair) so maybe that has something to do with the exhaust side being black but the #2 intake seems odd being sooty all by itself. Edited December 29, 2020 by matrophy added engine type Quote Link to comment
athoose Posted January 15, 2021 Report Share Posted January 15, 2021 When something like this happens to me, I switch the plug with another and see what happens after driving awhile. Quote Link to comment
datzenmike Posted January 15, 2021 Report Share Posted January 15, 2021 ECC in open loop defaults to a 'limp home' mode. Because it's possible that the mixture could range all the way to extremely lean, the ECU defaults to an over rich condition. This won't hurt the engine (in the short term) and is preferable to over lean. It's assumed the owner will notice this and remedy it right away. A properly functioning spark plug will get hot enough to self clean. If the #2 intake is sooty (probably from open loop operation over rich) maybe it isn't firing. Just clean it and try it. Or replace. But confirm the spark is getting to it. Plugs must be BPR6ES intake side and BPR5ES on the exhaust. Quote Link to comment
matrophy Posted January 15, 2021 Author Report Share Posted January 15, 2021 I cleaned it and put it back so once I drive it a while I'll take another look. Quote Link to comment
matrophy Posted January 15, 2021 Author Report Share Posted January 15, 2021 31 minutes ago, athoose said: When something like this happens to me, I switch the plug with another and see what happens after driving awhile. Good idea. Thanks. I can switch #2 and #3 and see Quote Link to comment
matrophy Posted January 16, 2021 Author Report Share Posted January 16, 2021 Follow up. I drove about 50 miles and checked the plugs and they look pretty good now. Both intake and exhaust plugs were a nice tan color. Must have been the combination of the long period of idling and the open circuit condition that occurred earlier. 1 Quote Link to comment
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