How (and why) to Ramble on your goat sideways
02-28-2013, 12:07 PM
Boost Pope
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And this change was sudden, like someone threw a switch while I was driving. One moment it's all happiness and kittens, and the next, *BAM*- no torque.
Here's a datalog showing when the event happened:
At point A, I'm idling at a light at the bottom of the hill. Idle is rock-steady at ~940 RPM, MAP is steady at 29-30 kPa, AFR is normal (AEM miscalibration, 15.3 = 14.7), spark is steady at ~14° BTDC, fuel PW is steady at ~ 2.7, PWM idle duty is steady at ~ 31.
Then the light turns green and I run through first, second and third, and come to a traffic signal at point B. I *think* that's when it happened (during the space between point A and B), however I hadn't quite come to stop, so I didn't notice anything wrong. Ran through the gears again and came to a full stop at point C.
At point C, everything is wrong. MAP is 60, RPM is unsteady and a tad low, IdleDC is WAY up at 45, fuel is way up at 4.8 and yet AFR is still right where it ought to be. And when I tried to take off again, I almost stalled the engine. Had to slip the clutch to keep it above 2,000 RPM.
Drove it again this morning, and it's exactly the same. No mechanical noises, no smoke, good oil pressure, and above 2,000 RPM it runs just fine.
The VE table:
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02-28-2013, 12:51 PM
Based purely on the map at point B, I think you are correct in assuming that things went south between A and B. Other than that, I have no idea what may be your issue.
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02-28-2013, 12:55 PM
Boost Pope
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That's what I'm assuming.
I know the intake cam is fine, as I verified the ignition timing last night (I'm still using the stock CAS on this engine.) Could well be that the exhaust cam skipped a tooth or two and is now retarded relative to the crank, which from what I understand would cause this exact symptom. Probably won't have time to pull the cover and check it until this weekend.
On the plus side, I already have a full timing belt kit (including water pump, crank bolt and woodruff key) lying on the shelf. Anybody know the correct torque for the main crankbolt on a shortnose engine? The earliest FSM I have is '92.
I know the intake cam is fine, as I verified the ignition timing last night (I'm still using the stock CAS on this engine.) Could well be that the exhaust cam skipped a tooth or two and is now retarded relative to the crank, which from what I understand would cause this exact symptom. Probably won't have time to pull the cover and check it until this weekend.
On the plus side, I already have a full timing belt kit (including water pump, crank bolt and woodruff key) lying on the shelf. Anybody know the correct torque for the main crankbolt on a shortnose engine? The earliest FSM I have is '92.
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02-28-2013, 01:52 PM
mkturbo.com
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That's what I'm assuming.
I know the intake cam is fine, as I verified the ignition timing last night (I'm still using the stock CAS on this engine.) Could well be that the exhaust cam skipped a tooth or two and is now retarded relative to the crank, which from what I understand would cause this exact symptom. Probably won't have time to pull the cover and check it until this weekend.
On the plus side, I already have a full timing belt kit (including water pump, crank bolt and woodruff key) lying on the shelf. Anybody know the correct torque for the main crankbolt on a shortnose engine? The earliest FSM I have is '92.
I know the intake cam is fine, as I verified the ignition timing last night (I'm still using the stock CAS on this engine.) Could well be that the exhaust cam skipped a tooth or two and is now retarded relative to the crank, which from what I understand would cause this exact symptom. Probably won't have time to pull the cover and check it until this weekend.
On the plus side, I already have a full timing belt kit (including water pump, crank bolt and woodruff key) lying on the shelf. Anybody know the correct torque for the main crankbolt on a shortnose engine? The earliest FSM I have is '92.
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02-28-2013, 01:54 PM
Boost Czar
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In 1990, the correct torque is 80 - 87 foot pounds. For 1992 and later, the larger crankshaft uses 116 - 123 foot pounds.¹
¹ Miata Crankshafts
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02-28-2013, 03:05 PM
2 Props,3 Dildos,& 1 Cat
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With the valve cover doffed
And a few beers quaffed
Joe Perez will try to discover
the woes of his red miata lover
He'll tug on her bolts
and measure her volts
And compress her valve springs
until her pipe sings
Wearing his homage to Hawai'i
while he's aligning her I and E
The belts will be tight
The shafts will be right
With a spark in his eye and her high tension lead
Joe'll eventually get her back up to speed.
And a few beers quaffed
Joe Perez will try to discover
the woes of his red miata lover
He'll tug on her bolts
and measure her volts
And compress her valve springs
until her pipe sings
Wearing his homage to Hawai'i
while he's aligning her I and E
The belts will be tight
The shafts will be right
With a spark in his eye and her high tension lead
Joe'll eventually get her back up to speed.
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