Stevensonjr Posted August 27 Share Posted August 27 My seven has a pre crossflow Kent Ford 1500, new rebuild, 244 cam, two DOCE carbs, 4 into one headers, mostly forged internals. I worked with the Webers and got it running quite well, it now has just over 400 miles on it. A couple of days ago on the way to my shop, on a smooth 4 lane, I ran it thru the gears, nothing extreme, shifting at 5000, holding at about 4000 in 4th and 70 mph for a minute or so. I stopped at a light and it started to miss and backfire thru the muffler. I let up and it ran ok at idle but when I tried to accelerate it started shaking, missing and popping thru the exhaust. What I need now is your best guess as to what might have happened to suddenly cause the backfiring and missing. I barely got the car home and need advice on where to start looking for the problem. Plugs and wires are ok and the the solid state distributor has not moved. The fuel pump is electric and +-3psi. Thanks, Bill Stevenson PS( bad dizzy module?) Link to comment Share on other sites More sharing options...
IamScotticus Posted August 27 Share Posted August 27 An exhaust leak can allow oxygen to be pulled up into the hot spots and detonate. Link to comment Share on other sites More sharing options...
Vovchandr Posted August 27 Share Posted August 27 I would start with basic health checks of leak down and compression to get obvious out of the way. Link to comment Share on other sites More sharing options...
Joe Petty Posted August 27 Share Posted August 27 Did you try it later after it cooled down? If it ran OK then, I would suspect hot electronics (module breakdown) or loss of fuel pressure/flow. Good Luck! 1 Link to comment Share on other sites More sharing options...
wdb Posted August 27 Share Posted August 27 Fuel cutting out or spark cutting out are the things that jump into my head. How sharply was it jerking? Sharper = greater likelihood of spark issues. (These are all WAGs, hard to diagnose over the ether...) Link to comment Share on other sites More sharing options...
MV8 Posted August 27 Share Posted August 27 Fuel filter as close as practical to the carbs? I suspect you've picked up some trash in the carbs or have a low fuel pressure condition. Ignition modules and coils typically work or they don't, or they don't work when hot. Since it is both carbs because the plugs were "ok"/all looked the same, I suspect fuel delivery. No new rhythms or new sounds while cranking? Link to comment Share on other sites More sharing options...
Stevensonjr Posted August 27 Author Share Posted August 27 I’ll have to change my statement about the plugs, all looked the same except #4 cylinder. I started to clean the plugs with a small media blast device I use on aircraft plugs. I picked up #4 and as I held it the center rod in the middle electrode disappeared, as in retracted into the middle electrode. I turned the plug upright and the rod slid out and hit the curved side electrode which stopped it. I shook it and the rod slid in and out. The rest of the plug was a bit dark with oil or soot. I quit looking until I run a bore scope tomorrow. I called Champion’s customer service and asked how long the center rod was supposed to be and what it was made of. Trying to find out how much if any of the rod had broken off and was sitting on top of the piston. The rep said the center rod was nickel and wouldn’t tell me how long the rod was supposed to be because it was proprietary information! I was going to break the plug down, let the rod slide out and measure it to see if any of it was left in the engine. I thanked him for his help and will wait on the bore scope. More to follow! Bill 2 Link to comment Share on other sites More sharing options...
7Westfield Posted August 27 Share Posted August 27 If it's just the center electrode moving, I would think the ground electrode would keep it from falling out Link to comment Share on other sites More sharing options...
Stevensonjr Posted August 28 Author Share Posted August 28 I hope you are right, the bore scope should tell me, I don’t want to start it till I know for sure. Bill 1 Link to comment Share on other sites More sharing options...
pethier Posted August 28 Share Posted August 28 Why not just replace the spark plugs? Link to comment Share on other sites More sharing options...
Stevensonjr Posted August 28 Author Share Posted August 28 I’ve already bought new plugs, not going to install them till I’m sure that nothing fell into #4 cylinder from the plug that came apart. Bore scope late this afternoon. Bill Link to comment Share on other sites More sharing options...
wdb Posted August 28 Share Posted August 28 10 hours ago, pethier said: Why not just replace the spark plugs? Because it's possible that a piece of the electrode detached itself and is floating around in the combustion chamber. Or, hopefully, has been spit out the exhaust valve and is safely laying in an exhaust pipe somewhere... Link to comment Share on other sites More sharing options...
pethier Posted August 28 Share Posted August 28 I think I need to go over my reading-comprehension skills again. I'll show myself out. 1 1 Link to comment Share on other sites More sharing options...
Stevensonjr Posted August 29 Author Share Posted August 29 This may get a little long but it’s unusual. The car started backfiring and missing and shaking and sounding like it was coming apart. If it had been just a plug fouling or failing to fire, it would have started to miss and shake while driving and I would have known what to look for. The backfires were shotgun loud and often, being on the left side of the car it got my attention and confused me. What the hell is going on? When I pulled #4 plug out, the center electrode was gone, as in the second photo. When I looked at it closer it suddenly appeared as in the top photo. The electrode would slide in and out when I shook the plug. I’m guessing that the plug never stopped firing, it would fire early or late depending on where the electrode was in it’s in and out cycle. I can’t think of other reasons as to why the backfiring and shaking was so violent. I was concerned that part of the electrode had fallen into the cylinder and had damaged the piston/cylinder so I ran a bore scope. All is well, nothing foreign showed up. I put 4 new plugs in and it ran as before, strong and smooth. Attached is a bore scope photo. Thanks for all the comments, Bill Link to comment Share on other sites More sharing options...
panamericano Posted August 29 Share Posted August 29 Congrats on the scope good fortune. That's a new one as far as I have heard. Too bad Champion wasn't more help, it would have been nice to know the original length to compare with an autopsy of the bad one.. I'm a bit surprised they didn't ask to see it. I wonder how hard the electrode material is. All's well that ends well. Link to comment Share on other sites More sharing options...
IamScotticus Posted September 1 Share Posted September 1 This gives me pause about using plugs with the side electrodes like the NGK BPR6EKN. Then again, has anyone ever had this problem with an NGK plug? Link to comment Share on other sites More sharing options...
jbcollier Posted September 2 Share Posted September 2 Champion racing plugs are top notch! Ordinary, off the shelf, Champion plugs? Not so much. As a shop, we stopped using Champion plugs decades ago. Bosch or NGK, please and thank you. 1 2 Link to comment Share on other sites More sharing options...
NSXguy Posted September 3 Share Posted September 3 The reason, as you have discovered is that the electrode went bad(try to find out why!) and by the photos something caused the center electrode to slide out from within the insulator tip and contact the side electrode. This will undoubtedly cause a misfire(no fire) condition as no gap for the spark and therefore no combustion in cylinder 4 which explains why the plug is black and sutty, the engine was shaking due to imbalanced harmonics and all that unburned fuel being introduced and igniting in the exhaust, thereby causing the loud pops and bangs you heard. I think your setup warrants further investigation to rule out positively the root cause of the issue. Assuming you don’t have an eye on afrs while running, how do the other plugs look? What are jets and carb setting(venturis, idles, emulsions, mains, float heights etc), ignition timing at WOT? With the 4speed boxes on early cats unwell he cruising sometimes on the main circuit at highway speeds so if ignition and afrs are off as the condition is held for prolonged periods something may give. You may not see that otherwise just driving around town or during momentary periods of WOT blasts. just some things to consider. -Dez Link to comment Share on other sites More sharing options...
Stevensonjr Posted September 3 Author Share Posted September 3 Fez, I don’t understand your last paragraph. Could you rephrase it, especially the “cats “ parts. Thanks, Bill Link to comment Share on other sites More sharing options...
pethier Posted September 3 Share Posted September 3 2 minutes ago, Stevensonjr said: [Dez], I don’t understand your last paragraph. Could you rephrase it, especially the “cats “ parts. Thanks, Bill I believe that in this context, "cats" means "Caterham cars" Link to comment Share on other sites More sharing options...
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