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Loud pop, then tach goes out, then engine shakes like a bitch and has no power
As stated in the title, I was getting up to speed on the highway (2nd gear around 4500 rpm) and I heard/felt a loud pop and my tachometer immediately drops to zero, I'm still moving but I have no power, then at the end of the exit of the highway I stop at a red light and she won't idle. I get it started back up and barely drag along to the nearby parking lot. I popped the hood and was looking for anything wrong with the battery or alternator, but the lights, fan, radio, and all electrical systems were working fine so I ruled that out. I took out all spark plugs and found that the end of the leading plug closest to the front of the car was noticably blacker than the rest. I replaced that one with the cleanest one and ran it for a few minutes. It seemed that the very tip got blacker but not far up the threads. Everything I've read and watched seems to point to a bad leading coil or a blown apex seal. Today I picked up a $12 coil from the parts store and replaced the leading coil. Car idled no different than before. So I put the original coil back in and replaced the other one. No dice. I was able to drive it home but it was still shaking and running like crap and trying to die when I started moving. It smells like fuel. Does anyone know what this is? What step do I need to take next? I'm going to pick up another coil tomorrow to replace both and see if that helps.
79 12a
First off, put the original coil back in. The coils are not the problem. What you seem to describe is a loss of Leading ignition due to loss of Leading Ignitor. This will affect both rotors identically, but you may be seeing (and smelling) overly Rick mixture on the front rotor due to a lack of combustion taking place. The car will run just barely on Trailing ignition only, which is what you seem to describe.
Is your 79 SA a single distributor or dual distributor engine? As stated above, check your Distributor Cap(s), Rotor(s), and the Plug Wires, looking for Leading spark. If none, the Ignitors are mounted to the DS strut tower in a remote moduoe which is easily traced back from the Distributor. There are 2 Ignitors located there, your Leading Ignitor is likely bad. They dont last forever, but shouldnt be too hard to find a replacement.
'Duck, Roxy has a 79, so unless unmentioned, he is running points for ignition, sans ignitors. And single Dizzy.
Feeling/hearing loud 'pop' and power loss sounds exactly what my 74 RX4 did when it threw an apex seal back in the day.
Hope I am wrong.
Compression test will tell everything.
Same thing happened to me in my first SE back in the late 90's. Pulling away from a stop light I heard a pop and lost power. Limped it into a parking lot only to find I lost compression in the rear rotor. Back in 2015 I lost an engine in my RX-8 right in the driveway. Started it up and it soared to a high idle and I heard a pop and the engine stalled and no compression was found on the front rotor. Here's hoping its something a little cheaper and easier to fix for you. I would first run a cold compression test and see where the engine is at. If you can get it started and let it run to normal operating temperature then that would be best to run a compression test with a warm engine.
Odd though that you would lose tach signal. Unless the trailing ignition failed first and compression was lost due to detonation from lack of spark. That's very possible.
UPDATE: just checked sparks and there is no charge coming from the lead coil at all. Since I know it isn't the coil, does that mean its an ignitor? How do I check? There was plenty of spark on both the trailing wires near the plugs but a lot less on the leading plugs. Also I plan to check compression as well to see if the problem has damaged the seals.
Searching here, you will find ways to test in or out of your car. Easy first step is to switch the ignitors to verify, but it sounds like you're on the right track.
To help with diagnosis,swap leading and trailing igniters. Engine will run without or with very weak trailing ignition.This only pertains to electronic ignition,ignition system may have been changed but car originally came with points/condenser ignition.
If you're not sure of which you have,take a closeup pic of distributor so we can see what you have. Post pic of all spark plugs to see condition of firing end and to show what plug you are running.
Oh and the spark plugs. They are NGK and were put in about a month ago. These are the plugs in the order they came out. (So the bottom left dirtiest looking one is the lead plug of the front housing.) This is the top left plug from the first picture after I put it where the dirtiest plug was and ran it for a few minutes. The tips are noticably darker.
Distributor in your engine is original and that is points/condenser ignition.
Take distributor rotor off and take pic of it and inside of distributor cap so terminals can be seen.
Use a small screwdriver on points arm and open and take pic of both contact points so we can see condition of them.
If you can take a video of it running and post it here so we can hear it could help determine what’s going on.
Compression test may need to be done fir definitive answer.
That cap looks ok but its certainly time to replace the points and condenser. I would honestly perform a proper compression test before moving any further and potentially wasting time by on the ignition components. I only say this because I've been there.
The video doesn't do it justice. It sounds pretty choppy in real life and shakes like crazy. Also this is when the engine is warm and had been driving for a good 20mins.
Thanks for posting vid,doesn't sound too bad,but i know what you mean about being different standing beside it. Since it runs,some advice,take it to a shop that has a rotary engine compression tester. If they don't have one,take it to one that does.They may charge $50 or more but results are invaluable,money well spent. Don't beat on it while driving there,you could incur more damage.
A rotary compression tester is different than a piston engine compression tester. The rotary tester will give you results of all 3 faces on each rotor.
just remove all the plugs. pull the fuel pump fuse, and turn the engine over via ignition key with the throttle wide open. if it is a bad apex seal, there will be a distinctive uneven sound. or you can feel it with your hand by the spark plug holes. maybe make a vid of it.
while you have the plugs out, attach the spark plugs to the ignition wires, ground them out, and check the spark. should be a pretty blue arc.
Last edited by midnight mechanic; 01-03-20 at 04:58 PM.
If I have a normal compression tester that I can try tonight, is that worth a shot at all or just wait for the rotary one?
Piston engine compression tester is only giving you an average of all 3 rotor faces not each chamber and why i suggested for time/money spent have it tested at a shop that works on Rotary engines as they should have a rotary engine compression tester that will give printable results and estimate for repair...and if they don't,go somewhere else that does.
If you were thinking about purchasing a rotary compression tester,be advised they're several hundred dollars.
Piston engine compression tester is only giving you an average of all 3 rotor faces not each chamber and why i suggested for time/money spent have it tested at a shop that works on Rotary engines as they should have a rotary engine compression tester that will give printable results and estimate for repair...and if they don't,go somewhere else that does.
If you were thinking about purchasing a rotary compression tester,be advised they're several hundred dollars.
You can remove the schrader valve to get around this.
It won't give a proper set of results like a proper rotary compression tester, but you can have someone turn the engine over while you watch it & it should be fairly obvious if one of the chambers is different from the rest.
01-01-20, 07:00 PM
