Engine miss firing (90) miata
 

Just purchased car and engine has a constant missfire. It's not a dead skip, but rather like the timing is retarded or something of the sort. I had to mash the throttle slightly to get it to start. I advanced the timing manually and it seemed to help but still has the same symptoms but it'll idle without periodically tapping the throttle to get it to start. Sounds like a cylinder in coming in and out. It's out the exhaust not the intake. I've drained and refilled the tank and cleaned the fuel system. Replaced plugs,wires, and fuel filter. There is no check engine light on.If you floor it, it stumbles like it's starving for fuel. If you go about 3/4 throttle, it'll rev to 6000 rpm but still doesn't have any torque. At that same point if I floor it, it falls back to 4500 rpms and stumbles like it's starving for fuel or timing of the spark is off. Help Help.... I need to resolve these issues before I install my turbo kit.

What is base timing per timing light?

About 8 degress. I've move the timing all around and still have the same results.

stupid suggestion but have you checked plugs wires and spark strength? then if all good check fuel press if up to spec could be something as simple as a pluged cat had a vehicle in at work doing approx the same thing turned oout the cat broke up and was totally plugging the exhaust...

good luck
Kris.

New plugs and wires. You can feel the exhaust is flowing well, can be felt over 10 feet from the pipe. I have not checked the spark energy. I stuck a plug in the wire while car was running, the spark was orange/yellow..I can remove a plug wire at a time and there's a noticeble difference when I pull the plug and reinstall it.This is my first setup with 4 cylinder engines. Generally run bigblocks with alot of spray. Was thinking of taking it to the dealership to have it diagnosed to keep from throwing parts at. I'am leaning towards the cam sensor, but I don't have enought experience with these engine.Will the check engine light appear if any of the sensors fail, or are some of them passive and need to be diagnosed?

Could be a dying fuel pump or a bad AFM.

Also check for crank pulley wobble/worn-out key way.

Crank pulley is not wobbling.... How much fuel pressure should I have at wide open & Idle??? Also, how do I go about checking the AFM??? And what should my reading be? Remember I don't have a check engine light on.....Also when I got the car, the tank was half filled with water...

To check the AFM you basically have to replace it with another one and see if that fixes it.

Just a thought. Have you checked the timming belt? When was it last run before you bought it? Wh was it not run? Why did it have so much water in the tank?

Have a great day,
Jared

Checked timing belt, and changed the coils with the same result....I checked fuel pressure and it's 38 @idle and 43 wide open .I pinched off return line and pressure went up to 78 psi. Does this mean the regulater is bad? When I pinched off the return line, the problem still existed. I was thinking that if it were fuel pressure issue, it should have started running better but it still had the same result. The manuel said it should have62 to 74 psi at wide open. It doesn't.But squeezing the return should have corrected the problem, but it didn't.Someone has to have had this problem before out there. Still no check engine light on. Checked code by jumping ground to b+ in diagnostic port, no codes. I keep thinking it's the cas sensor. Shoulden this set a code if it's loosing its ability to keep the ignition and injector timing?

Have you checked compression just out of curiosity?

I haven't check compression on cylinders, I will tomorrow..If we could jump forward to eliminating that as an issue, what would be your next resolution to the problem?

Compression on all 4 cylinders are really close and not much difference on the average.

I have a really funny story for you. I replaced my plugs and wires and a little later, (i thought) my car developed a miss. I changed wires, coil, tps, maf, checked timing. Then i figured what the hell, lets check my new spark plugs again. If you just drop them down the holes, apparently the spark plug can hit just right to close up the gap all the way. FYI I spent a pretty chunk of change being too lazy/stubborn to recheck plugs, lesson learned. I hope thats all it is for you, and if not, sorry i made you pull your plugs bro.

Rechecked plugs and they are fine.Does anyone know what the fuel pressure should be a wide open throttle? Igot 38 and idle now and 43 wide open.

Not to get back on the subject of the plugs and wires, but are the wires in the correct order? I had a similar issue and a member on here suggested I re-check the wires (I assumed they were correct, seeing I just did a ton more technical wrenching over the past couple weeks), and sure enough I had 2 wires mixed up.

No, the wires are correct. I've been building cars for the last 25 years but, they've be carb styled and I didn't need a laptop to diagnos they. I'am computer literate but this things doesn't have a check engine light on. I don't want to throw parts at it. I'am in the process of trying to get a donor car for parts to stay away from the dealership. That way I can throw parts for a lower price than full price or taking the chance on buying a used part and it doesn't work or something like that.Everything so far is by the book. I've checked and rechecked everything I've done. GHranted, there a few more checks I could do, I'll get to them later when I can get back to it. Still , any help will be appreciated. I need a good used turbo kit also with all the bells and whistles with at least 12psi boost.

I've been searching for clogged converter symptoms and haven't had any luck. Has anyone had this problem and what were the symptoms?

It seems to me a clogged converter would cause extreme lack of power. I have seen 1 actual bad convertor in my life, it was on a fd rx7. Go figure. Make sure your injectors are clipped on all the way. I spent 300 dollars trying to find a miss on a stanza i had, guess what it was. Loose injector clip.