Nothing but trouble with the new engine - midrange misfire...
09-13-2011, 08:48 AM
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Nothing but trouble with the new engine - midrange misfire...
Right, hoping you guys spot something silly that I haven't before I tear what's left of my hair out...
-Mis-fires badly from 3.5k to 7k.
-After 7k it clears and goes like **** off a shovel.
-Engine starts just fine, no excessive cranking, idles smooth as butter.
-All injectors are working and staging okay, coils are working, variable valves are working, there's nothing stuck in the intake tracts, the earths are all good and clean.
-Leads are relatively new Magnecors, no apparent arcing/corona from them, new set of spark plugs.
- Swapped two coils for brand new spares that made a small improvement but not much.
-Fuel pressure is fine, fuel lines are clear.
-Throttle pot checks out okay, new throttle pot makes no difference. Same for the shaft sensor - Oscilloscope on that shows it's reading the teeth perfectly well.
-Our rudimentary coil tester (patent pending) - otherwise known as a trailing plug with the bar snapped off - shows a consistant spark across all 4 coils - albeit a relatively weak sounding orange spark, but with no difference between 'em that would mean we'd have to have got 2 duff new coils too...
-Winding the coil dwell up just to check makes no difference either.
-Only change between this engine and the old one is the timing (S1 > S2 timing is different), double/triple checked with a timing light and it's right, tried it 20 degrees retarded and no difference bar a lack of power.
-Aux ports are locked open, but locking them closed makes reduced the misfires to the 4.5-6k region, and allows the car to drive through it (but then it starts to run out of power @ 7krpm...)
Ideas?
BSE thinks it could perhaps be a seal allowing blowby at max combustion pressures, but I would have thought it'd be a bitch to start too?
I'm thinking perhaps a poor/blocked spray pattern on an injector but I would think it'd run like a dog up top too
-Mis-fires badly from 3.5k to 7k.
-After 7k it clears and goes like **** off a shovel.
-Engine starts just fine, no excessive cranking, idles smooth as butter.
-All injectors are working and staging okay, coils are working, variable valves are working, there's nothing stuck in the intake tracts, the earths are all good and clean.
-Leads are relatively new Magnecors, no apparent arcing/corona from them, new set of spark plugs.
- Swapped two coils for brand new spares that made a small improvement but not much.
-Fuel pressure is fine, fuel lines are clear.
-Throttle pot checks out okay, new throttle pot makes no difference. Same for the shaft sensor - Oscilloscope on that shows it's reading the teeth perfectly well.
-Our rudimentary coil tester (patent pending) - otherwise known as a trailing plug with the bar snapped off - shows a consistant spark across all 4 coils - albeit a relatively weak sounding orange spark, but with no difference between 'em that would mean we'd have to have got 2 duff new coils too...
-Winding the coil dwell up just to check makes no difference either.
-Only change between this engine and the old one is the timing (S1 > S2 timing is different), double/triple checked with a timing light and it's right, tried it 20 degrees retarded and no difference bar a lack of power.
-Aux ports are locked open, but locking them closed makes reduced the misfires to the 4.5-6k region, and allows the car to drive through it (but then it starts to run out of power @ 7krpm...)
Ideas?
BSE thinks it could perhaps be a seal allowing blowby at max combustion pressures, but I would have thought it'd be a bitch to start too?
I'm thinking perhaps a poor/blocked spray pattern on an injector but I would think it'd run like a dog up top too
Last edited by PhillipM; 09-13-2011 at 08:56 AM.
09-13-2011, 01:15 PM
#4
you really need an HEI spark tester rather than a modified spark plug to get the correct coil fail/pass loading
http://www.amazon.com/KD-Tools-2756-...bxgy_hi_text_b
maybe try a different MAF sensor
http://www.amazon.com/KD-Tools-2756-...bxgy_hi_text_b
maybe try a different MAF sensor
09-13-2011, 01:24 PM
#5
I'm not sure if he has a MAF based system. The previous engine didn't has this problem, this one has (not "new", bought used in working conditions i guess).
Scaling the MAF perhaps might help but after 4\5 engines he would have noticed scaling problems i guess!
Scaling the MAF perhaps might help but after 4\5 engines he would have noticed scaling problems i guess!
09-13-2011, 01:40 PM
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Yeah, probably, just rudimentary methods atm.
Expected to see/hear some difference between the new and old coils though.
It's mapped as Alpha-N, so no MAF/MAP sensors.
Pulled the plugs after another run with some timing and fuel pulled to lessen the extend of the misfire, no appreciable variation between leading and trailing or rotor-to-rotor.
I'm wondering if we've got 2 duff new coils now...
Previous engine was running on the same map, same injectors, coils, leads, wiring, etc - however, the old engine killed a side seal, and we had to make it run to the end of an event by bumpstarting it before every stage and just making it work hard (was seriously down on power), so that probably gave the coils a hard time trying to light the mixture off.
Expected to see/hear some difference between the new and old coils though.
It's mapped as Alpha-N, so no MAF/MAP sensors.
Pulled the plugs after another run with some timing and fuel pulled to lessen the extend of the misfire, no appreciable variation between leading and trailing or rotor-to-rotor.
I'm wondering if we've got 2 duff new coils now...
Previous engine was running on the same map, same injectors, coils, leads, wiring, etc - however, the old engine killed a side seal, and we had to make it run to the end of an event by bumpstarting it before every stage and just making it work hard (was seriously down on power), so that probably gave the coils a hard time trying to light the mixture off.
Last edited by PhillipM; 09-13-2011 at 01:47 PM.
09-18-2011, 04:29 PM
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09-18-2011, 09:44 PM
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well you've got it figured out before i could even chime in but just in case- you mentioned checking the timing but i wonder if you physically checked the trigger wheel and hall sensor?
09-19-2011, 06:19 AM
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Yeah, first thing I checked having changed timing/trigger wheel from one engine to the other.
ECU I use has a built in oscilloscope to check the sensor anyway which also shows no problems.
Lesson learnt, just because you swap coils for new ones, doesn't mean the coils aren't at fault, especially when all the symptoms point that way!
ECU I use has a built in oscilloscope to check the sensor anyway which also shows no problems.
Lesson learnt, just because you swap coils for new ones, doesn't mean the coils aren't at fault, especially when all the symptoms point that way!
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