So my project car finally started, but it sounds like one of the rotors isn't firing. It sounds like a lawnmower when I try to rev it.

As soon as I have time I will pull the plugs and make sure the rotors have compression. And hopefully see one side simply wasn't firing.

But until then I would like to see if you guys can help me diagnose it.

Here are the conditions.

1. The engine starts relatively easily (at least when warm) and idles (a little low)

2. The exhaust has a staccato sound like it's only firing on one rotor. It's blowing a little bit of black smoke at idle. Raw fuel, perhaps? The car has a straight pipe so some nastiness is to be expected.

3. The boost meter shows -10 kpa vacuum, which is low, but it's steady, all considering. Considering how poorly it's running, I don't think it would idle at all with any serious vacuum leaks.

4. I noticed the leading plug cords (FEED) are really, really lose. Like, they'll pop off with just a little pressure. The plug cords on the trailing plugs (which seem to be NGKs) are as tight as a....tight object. They won't come off without some serious elbow grease and pop on with a solid click.

5. I didn't drain the tank, which I suspect was almost empty, but any gas in there would have been four years old... I added 20 liters (about five gallons) of gas to it. I'm gonna pull the pump so make sure it's not full of rust.


So is it more likely I have a blown rotor (it wasn't blown when the car was last running), stuck seals, bad/insufficient fuel, or a bad coil/plug wire?

 

Why start a car with loose plugs and 4 year old gas?
Why not drain the tank of the bad gas and 4 years of condensate and put some proper plug wires in serviceable condition before going further?

You drain the tank and you see what comes out. If there is a bunch of foreign material or corrosion you save yourself from pumping it into the lines.

The fuel will gum up and could have stuck a seal. Running some ATF straight into the Intake plenum and cranking the motor with the fuse pulled for the fuel pump can allow the ATF due to its high detergent content work out a stuck seal that's carboned or gummed up.

You will want to let the ATF sit for a few hours so it's detergents can work. Then the engine turning over can help free up a stuck seal. I would try this method before assuming the apex seal is broken.

 

I'm thinking there's something wrong with the oil seals, since the plugs were covered in oil.

I was going to drain the tank, but my mechanic friend said it probably wouldn't make a difference. I"m gonna pull the pump and see what's inside.

I tightened the plug wires with pliers and it didn't seem to make much of a difference.

 

i'd make sure the MAP sensor is plugged in, and maybe pull codes, although step one really is a compression check.

it is possible its just grumpy, and i do agree that draining the gas won't matter much

 

It's a Power FC and I don't have a PFC to pull the codes. DOH. There is a pretty good chance that there are wiring issues because the harness isn't in great shape...

I have to think this goes beyond "grumpy" since I'm almost certain it's only firing on one rotor (because of the sound of the exhaust), whether that's because of compression, fuel, or spark.

A friend is going to borrow a Mazda checker and bring it next month.

Yesterday it actually shut off on its own and wouldn't start again. I suspect that's fouled plugs, though.

 

power FC has a sensor check screen....

 

I don't have a commander.

 

I may be doing the spark check wrong but leading seems to have no spark and trailing seems intermittent (couldn't check T1 since the cord was too short.

I had to use my phone to take a videos and couldn't hold it properly against a ground, but I suspect the coil, cord, or wiring may be bad...

 

For what it's worth, this is basically what my car sounds like:


Today I noticed that the #2 rotor's deposits made it look like it had been sparking, but I couldn't get the leading wire to spark with the method I was using. Also, it looked like neither of the #1 plugs were firing today (they were basically clean and slightly wet) and the #2 plugs looked like they were firing (albeit a bit soiled). Which is weird because it's the opposite of what happened yesterday.

 

Turns out it was running only on the rear rotor.

I borrowed some cords, coils, and an ignition harness, and it didn't change. So me and a friend tried starting with only one rotor hooked up at a time, and it would only start with the rear (and ran the same way).

Since the engine clearly has compression (just from the sound) and almost certainly has spark (assuming there's nothing wrong with the ECU or main harness), we're thinking it's probably the #1 primary injector being gummed up with old gas. So I'm going to borrow some stock injectors and give them a try.