I am completing the final stages of the Boxer restoration and have run into a bit of a perplexing issue. At initial startup, all is generally looking good with instant oil pressure upon firing up. I am running it with the headers only for now to facilitate Lambda settings. the issue is frequent "backfiring" seen from the header from #7-9. If I disconnect the plug to #8 it instantly stops. I tested the compression and did a leak down test. compression is 120 PSI all cylinders within 2 psi. leak down is dead on the same across all cylinders @ 4% The fuel distributors have been professionally rebuilt and calibrated although I have not pulled the injectors to confirm a good fuel pattern. Ignition wiring is correct. Any thoughts would be really appreciated. Thanks
change the fuel injector from 8 to 10, 11 or 12 and othersie to eliminate this injector check the ignition wire and the plug
Meaning you've verified the firing order of the spark plug wires around the dist cap? Have you confirmed that the dist rotor -to- reluctor star wheel -to- flywheel phasing is very correct? (Not room for much error on the single-cap 12-cyl design.)
I am going to try swapping the ignition wire and see if perhaps this is causing a misfire-not really a "backfire". As I am considering the possibilities ignition would appear to be the most likely. I did not replace my original spark plug wiring harness as it appeared to be OK. Maybe not the case. I'll try the swap later today. also will swap injectors if this doesn't work. I can't think of any other possibility.
Rotor(advance) is moving freely? Inside the cap is clean on all contacts? Then wires. We're the lines from the fuel distributors to the injectors replated, if so maybe doublecheck there is no blockage on the # 8 cyl. Have you set the ign timing. I had some issues with my car when I first got it and one of the old time fchat mechanics and boxer owners said to me almost all fuel issues on boxers are ignition related. He meant it is rarely fuel, it's really ignition. PS: I have an old set of wires if you want them for pilfering.
Sorry replied inside Steve's quote rebuilt the distributor to include manufacturing brass bushings to replace the nylon for advance. Very smooth and clean. I dont see that there is any adjustability to the star wheel induction trigger. It is all indexed on assembly. Am I missing somethig? I had limited time today for further testing but I did check the wire resistances on a few of the leads including the " suspect" lead 7 and they are at 6.5-6.9 kOhm. Ok? Or perhaps high for electronic ignition. I haven't confimed the injector pattern yet but they had all been thouroughly cleaned tested and calibrated. What is wierd is the behavior where it is "misfiring" and i am getting sputters of unburned fuel igniting out of the header but this stops if i disconnect the wire to #7. As noted excellent compression and normal leak down. I did check the firing order in the cap and I do believe it is correct- tripple checked. The additional thought is that I installed the Pertronix HP mobile "bluetooth" that i bought 1 year ago and now appears to have been discontinued. I have in inquiry to tech support on this pending
Don't really know if it could be mis-assembled, but the figure in your OM indicates that there is a particular desired relationship between the rotor and the star wheel and also the rotor and the flywheel (i.e., there is a positional target shown for the rotor at the cyl #1 firing position of the flywheel). In your first post, you said disconnecting the #8 plug stopped the backfiring, but now you say disconnecting #7 stops it -- has the symptom/behavior changed?
same I wanted to ask just now I once had an equal problem at a 308 4V. there the gap at the sparkplug was too little
Sorry typo #8 is the problem. I did index it to the mark on the distributor with the crank at TDC and timing is OK. I'll look at the plugs again but I think they're good- NGK iridium. I'll do some more diagnosis today.
I know it is a stupid question and it has been asked before; Have you adjusted the ignition timing and checked against the marks on the flywheel at idle (800 - 1000 rpm) and 5000 rpm? Best Peter
Solved! Possibly as dumb as it gets but I had #7 and #8 reversed. Now purrs like a tiger! And I do feel a lot better but a bit foolish. https://www.instagram.com/p/CBO-UpqAPL2/?igshid=1vwxstyf0u0gx
I respect your honesty and it is very important for us to share mistakes as well as good solutions. This may help someone else one day. we all have our own "feel foolish" moments. Thanks for sharing.
I hate and love when I find a simple solution. I hate that it takes me a few times looking at something to see the obvious, but love that feeling of it being resolved at minimal expense and it's not something my mind has congered up as a horror mistake. Then it is best to just chuckle at the human element. You put so much effort into the job, it was hard to believe it could be anything other than a simple solution. Congrats and go enjoy the car.
Thanks, really a great sigh of relief, particularly when the initial thoughts were? leaking valve and having to remove the engine again.
