12a misfire?
02-12-13, 01:18 PM
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12a misfire?
Ever since i got my 84 rx7 in july it has idled rough, and was extremely slow compared to other stock first gens. I hated being the slowest thing on the road, so i purchased an RB header and deleted my catylitic converter and replaced the stock muffler with a glasspack (i know, it will probably melt). But my car was still slow, so i bought the racing beat intake manifold and racing beat holley carb, and deleted every emissions related component as well as the a/c (the pump was bad anyway). The car got a considerable power gain but not as much as i was hoping. the idle is very bad, it will stay running for a while, once it is warm, but it sputters and seems like it is going to die, and it is impossible to hold steady rpm under 3000 rpm, and i need to feather it up between idle and 3000 in order to actually drive it. or else it will stall out. this could be caused my carb tuning. but the part that really worries me is that we hooked it up to our emmisions sniffer at school and it spiked to 17000ppm HC in my area where i have no power; 1000 to 3000 rpm and then dropped to like 7000ppm HC around 4500rpm. if you are not familiar with HC, it is the unburnt fuel coming out of the exhaust, the legal limit to pass an emissions test (in utah) is 220 ppm and anything over 600ppm is usually a missfire. Does anyone have any suggestions as to where to start? i have replaced plugs and wires, but it didnt change anything
02-12-13, 01:54 PM
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Any special notes for performing the compression test? What readings should i expect? And the rb bolt-ons were the plan before i even bought the car, haha, i was just hoping that the problem was vacuum or something. And i actually got lucky and found some awesome deals and did everything rb for under 500.
02-12-13, 02:01 PM
#4
warm the car up
attach a battery charger to your battery and turn it on full
grab a piston compression tester
remove the schrader valve from the line between the tester and the spark plug port
disable the ignition by unplugging both of the distributor pickups
remove both leading(lower) spark plugs
install the compression tester into either plug port
have an assistant hold the throttle wide open and crank the engine over
watch the needle peak and take each reading consecutively for 3 bounces in order.
repeat for the other spark plug port
minimum should be 85psi for any single bounce.
each bounce should be no more than 7% from the highest or lowest bounce for a particular chamber
difference between one rotor, peak to other chamber lowest should be no more than a 10% difference
if the engine is the culprit, it should stand out like a sore thumb during these tests.
(yes i made these figures up but they are about as fair as one should expect, cranking speed plays a big role so be sure the engine is cranking to at minimum 200RPMs if possible)
attach a battery charger to your battery and turn it on full
grab a piston compression tester
remove the schrader valve from the line between the tester and the spark plug port
disable the ignition by unplugging both of the distributor pickups
remove both leading(lower) spark plugs
install the compression tester into either plug port
have an assistant hold the throttle wide open and crank the engine over
watch the needle peak and take each reading consecutively for 3 bounces in order.
repeat for the other spark plug port
minimum should be 85psi for any single bounce.
each bounce should be no more than 7% from the highest or lowest bounce for a particular chamber
difference between one rotor, peak to other chamber lowest should be no more than a 10% difference
if the engine is the culprit, it should stand out like a sore thumb during these tests.
(yes i made these figures up but they are about as fair as one should expect, cranking speed plays a big role so be sure the engine is cranking to at minimum 200RPMs if possible)
Last edited by RotaryEvolution; 02-12-13 at 02:05 PM.
02-12-13, 08:05 PM
#7
Sin City Rotary
Ever since i got my 84 rx7 in july it has idled rough, and was extremely slow compared to other stock first gens. I hated being the slowest thing on the road, so i purchased an RB header and deleted my catylitic converter and replaced the stock muffler with a glasspack (i know, it will probably melt). But my car was still slow, so i bought the racing beat intake manifold and racing beat holley carb, and deleted every emissions related component as well as the a/c (the pump was bad anyway). The car got a considerable power gain but not as much as i was hoping. the idle is very bad, it will stay running for a while, once it is warm, but it sputters and seems like it is going to die, and it is impossible to hold steady rpm under 3000 rpm, and i need to feather it up between idle and 3000 in order to actually drive it. or else it will stall out. this could be caused my carb tuning. but the part that really worries me is that we hooked it up to our emmisions sniffer at school and it spiked to 17000ppm HC in my area where i have no power; 1000 to 3000 rpm and then dropped to like 7000ppm HC around 4500rpm. if you are not familiar with HC, it is the unburnt fuel coming out of the exhaust, the legal limit to pass an emissions test (in utah) is 220 ppm and anything over 600ppm is usually a missfire. Does anyone have any suggestions as to where to start? i have replaced plugs and wires, but it didnt change anything
Below is a vid I've meant to post as I've seen the question 3 times in teh last two days ... 3 even pulses if what you want to see
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02-12-13, 09:35 PM
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The Holley is a 550 vac secondaries, which i believe was meant for a streetport 13b. But i don't think the extra 80cfm would cause such a major problem, we have a 650 double pumper with mechanical secondaries on our stock port 12a Volkswagon and it runs awesome all through the rpm range, 10.9 in the quarter
Pistons...WTF?
Pistons...WTF?
02-13-13, 11:21 AM
#9
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I just performed the compression test, and after 3 puffs it settled at about 90psi, and after about 6 puffs it maxed out around 110 for one side then 120 for the other. And no matter where i stopped it, it would hold pressure.
Pistons...WTF?
Pistons...WTF?
02-13-13, 11:28 AM
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Shouldn't hold pressure if you took out the schrader valve from the compression tester as RotaryEvolution instructed 
you want to know the PSI on each face of the rotor individually, not the highest for the three faces....
you want to know the PSI on each face of the rotor individually, not the highest for the three faces....
02-13-13, 02:17 PM
#14
then the engine sounds fine.
now i would check your ignition and timing. first hook the timing light up to each of your 4 spark plug wire leads and make sure the timing light is pulsing off each wire. if not then you may have a fouled plug, burnt wire or faulty ignitor.
if that is fine hook the light up to L1 plug, disconnect and plug your vacuum lines, idle the engine down as far as you can go without stalling it and see if it is close to the pointer on the front pulley.
now i would check your ignition and timing. first hook the timing light up to each of your 4 spark plug wire leads and make sure the timing light is pulsing off each wire. if not then you may have a fouled plug, burnt wire or faulty ignitor.
if that is fine hook the light up to L1 plug, disconnect and plug your vacuum lines, idle the engine down as far as you can go without stalling it and see if it is close to the pointer on the front pulley.
02-14-13, 12:18 AM
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I can do that probably tomorrow, but my only vacuum is going to my brake booster, no vacuum advance, should the advance diaphragm nipples be plugged? Or just left open?
Pistons...WTF?
Pistons...WTF?
02-15-13, 05:39 PM
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i swapped the distributor and cap and rotor and it actually runs a little better, i can open it up at lower rpms without it stalling out, but still doesnt run smooth, Im thinking about replacing the power valve in the holley and seeing what happens (it had a power valve block-off when i got the carb)
02-17-13, 05:00 PM
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much the same as adjusting ignition points just have a look you will see . The one cas that I have the reluctor was actually very loose and moving a bit on its mounting plate might want to give it a wiggle and make sure it is firm
Last edited by gerald m; 02-17-13 at 05:03 PM.
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