348 Misfire can anyone help???
Discussion
Hi, my 348 has developed a really nasty misfire, it only happens under load and is clear by around 2600 - 3000 rpm, the garage that looks after it have replaced both cat control units with no improvements, new spark plugs made it go away for about 100miles. It is booked in at Scuderia systems to have exhaust and de-cat next week,as i am told the cats and lambdas give trouble on 348's but im still worried this may not be the magic cure...i hope with all the collective knowledge out there one of you may be able to help...
A LOT of 348s have trouble with the Slow Down lights when they have had the cats removed. So get those cats of sharpish, then simply disconnect the heat sensor and it seems to run fine. Undo it at the small junction box which is attached near the rear of the suspension pillar (from memory).
Sorry, no direct experience of this engine but if replacing plugs brought temporary relief even for 100 miles, then the answer could be either overfuelling sooting up plugs relatively quickly or probs with the HT circuitry basis clean plugs having a lower voltage requirement than dirty ones. That said, a diagnostic check should show up either problem immediately.
hope this helps
hope this helps
I had the same problem on my 348. You can test a lot of components yourself using a multimeter to find the cause.
Air flow sensors are the main suspects. You should measure about 383ohms resistance between pins 1 and 6, otherwise it faulty.
Thermocouples in the exhaust only activate the slow down lights. If the temp gets too hot the whole bank of cylinders shuts down. Keep the thermocouples fitted with the cats off and check the resistance is between 800 - 350ohms.
O2 sensors is the final suspect area, I can't remember what the resistance should be on them. You can try swapping left to right and see it the misfire changes banks. Replacements are cheap, universal O2 sensors on ebay are £18.
I replaced the Air flow sensors and leads before discovering the above. My problem was simply bad electrical connection. I cleaned them all with an electrical solvent cleaner and the problem was solved instantly.
Air flow sensors are the main suspects. You should measure about 383ohms resistance between pins 1 and 6, otherwise it faulty.
Thermocouples in the exhaust only activate the slow down lights. If the temp gets too hot the whole bank of cylinders shuts down. Keep the thermocouples fitted with the cats off and check the resistance is between 800 - 350ohms.
O2 sensors is the final suspect area, I can't remember what the resistance should be on them. You can try swapping left to right and see it the misfire changes banks. Replacements are cheap, universal O2 sensors on ebay are £18.
I replaced the Air flow sensors and leads before discovering the above. My problem was simply bad electrical connection. I cleaned them all with an electrical solvent cleaner and the problem was solved instantly.
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