Engine cutting out, hesitating, missing

[Dudley Dawson]

I'm tempted to douse this damn car in gasoline and set it on fire.

About three weeks ago, it started acting up. I'd be driving along at a steady speed, and all of a sudden it was like the rev limiter was kicking in. The car would bog momentarily, then go back to running as usual. It deteriorated rapidly, and started cutting completely out under moderate acceleration, even stalled a couple of times at idle.

I had the fuel filter replaced, and that seemed to fix it. The old filter was partially clogged. It ran perfectly again for six days. Then it started feeling like the rev limiter was kicking in at the wrong times. I replaced the plugs and wires. Ran perfectly again for a day, then started doing the same thing. I noticed the tach needle going all wonky this time, jumping up erratically here and there.

Took it back to the shop. Had them check the grounds, check for vacuum leaks. They pulled a code and found a dirty connection to the CAS, and cleaned it. Car ran perfectly again for two days. Today it started cutting out again, as in the engine completely not firing for a split second, then catching again. Bogging again too. Mostly under acceleration. Didn't notice any tach weirdness this time, though.

So far, it sounds like it could still be several things. Bad AFM, TPS, CAS, O2, ECU, injector, fuel pump, the list goes on. I can't afford to just keep throwing parts at it and hope that fixes it. Can anyone here narrow it down for me?

Car is a '90 NA with a stock B6. 177,000 miles. When it's not doing this, it runs very strong.

[mtrx804]

Spark plug wires in correct order? I know a couple people who had them in the 1.8 setup on accident and it "worked" but not well. Clean injectors would be my next check.

[Dudley Dawson]

Yes. Out of order wires would cause the car to run poorly all the time. This is an intermittent problem, but one that is occurring pretty regularly. When it isn't happening, the car runs very well.

[Walsted]

Have you looked at and/or cleaned your fuel pump electrical connections?

[goofygrin]

Cas goes out with heat. If you're paying to diagnose this will get expensive... Get some tools, this stuff is easy.

Fuel, air, spark. Fuel pump, filter, injectors. Filter, tb. Coils, wires, plugs.

Any codes being thrown?

[OZMDD]

Best bet is to sell me the car cheap and find another. :)

[Dudley Dawson]

I've been working on cars since before I got my driver's license in 1991. Problem is, no matter how much practice I had, it was something I never, ever got better at. So I quit altogether recently. Intellectually, yeah, I know what to do, but in practice, it never works out. There's always a problem, always a rounded bolt, a stripped fastener, something that won't come apart, or won't go back together the right way, or something else gets damaged in the course of fixing the original problem. I want my car to be nice, and I am simply incapable of performing the quality of work I desire on it. And after a couple of decades of trying, I despair of ever being able to do the kind of work my car needs without making a mess of the job. I really hope I don't have to do this myself.

However, that is interesting about the CAS and heat. The problem never occurs when the engine is cold. Doesn't have to be warmed up for very long, but it does seem to only happen once the engine is at normal operating temperature.

As for codes, the shop I brought it to pulled a code, which led them to check the CAS connection. I don't remember what that code was, though.

Not ever selling this car. There's no way I could ever sell it for even 1/3 of what I've got into it.

[IMG] IMG_1511 by awesomeOrson, on Flickr[/IMG]

[goofygrin]

Cas always goes out and it feels like a bad spark wire and then the car dies and you can't restart until it cools down a bit.

But a new one, its cheap and easy to swap.

[EricJ]

Does a '90 have a Crank Angle Sensor, or just a Cam Sensor? Sound like the behavior I had when I failed to get the right gap on the Crank Angle Sensor.

[Dudley Dawson]

The 1.6 Miatas have just the one sensor, driven from the back of the intake camshaft. It goes by many names, but it essentially functions as a crank position sensor.

[channelmaniac]

If your plug wires are good, swap out the CAS first as it's a 10 minute job at most.

After that, my $$$ is on fuel pump.

[Flyin96M]

Two things: 1. Coils also can cut out when they get hot. Had this on and old Honduh and it drove me nuts trying to figure it out. 2. I had another car that had some crap in the tank and every once in awhile it would clog the fuel pump inlet. Slamming on the brakes usually dislodged the clog and I would drive on. So if it feels like it is loosing power my guess is fuel, if it acts like a rev limiter with plenty of power until a certain rpm my guess is spark. You could rig up a fuel pressure gauge that you can see from the drivers seat and it should tell you if you are experiencing low fuel pressure when the symptom returns.

[Dudley Dawson]

Thank you, all.

My father is planning to fly out here for a weekend and help me out with some work on this thing. More than anything, it's an excuse for us to spend some time together, but I'd be lying if I said working on a car with him looking over my shoulder didn't make me feel a whole lot more confident in tackling the work. We're planning on replacing the CAS and the fuel pump, checking and cleaning as many connections as we can find, and replacing all the caps in the ECU. Probably take a good look at the battery cables, and take a multimeter to the whole damn thing if we have to. Dad is particularly good with electronics, which is great, since electronics are probably the surest thing to drive me insane.

This has turned out to be a good thing in a way. He hasn't been out since I moved out here. Hell, I don't think he's been here since we lived here in the early '80s. So in a way, I'm almost glad the car is giving me trouble now.