Miata hard starts, runs good, sputters, dies. Help.

So wife and I get in the car, cranks forever, but starts.

We drive about 10 miles, car running fine, all of the sudden bucks a few times, intermittent for a mile, dies.

Now stuck in Tucson heat at about 109 degrees.

What is it?

Did it feel like running out of gas? Fuel pump or fuel pump relay is my hip shot.

Ugh. Turns out we pulled car off next to a shop, they put a reader on it, Cam Position Sensor - cleared code, got down to the dealer to pick up a part, drove a CX5 (still like those), went to leave, another CEL. Same problem, CPS. So dealer clears the code (they couldn't fix it right there on the spot, or I'd have had it done...), and we start driving home. about 5-7 miles, same problem, car dies. Call son, he brings his scanner, clear the code, except this time, it also showed a Crank Position Sensor code (Codes P1345 for cam, P0339 for crank).

Cleared codes, drove the next 15 or so miles home, no issues.

So, might I have some grounding issues, or is it pretty likely its a bad cam sensor, and that's that? I will say, that my hot weather hard start issues went away after clearing two of the three bad codes - leads me to believe that the cam sensor is most likely.

To me, completely coincidental is that I hit a gnarly arse pot hole, car bottomed badly, right before the acute issues popped up (warm hard start has been around a while...).

Thoughts?

Why are you clearing codes? Sometimes codes come one after another and then you can figure out what is really wrong. Clearing codes won't fix a problem, it just erases the log of that problem and has the system retest.

I don't know Mazda but on some Fords the cam sensor is used just for spark, but if it fails the crank sensor is used but it isn't as accurate.

Bad grounds can cause all sorts of codes. heat can cause a sensor to fail after a heat soak. The best way to test for that is to turn on the cooling fan for a while then try to restart.

pjbgravely wrote: Why are you clearing codes?

Because it beat hanging out in 109 degree heat waiting for tow trucks, and got the car home and us back inside AC!

The car wouldn't start until you cleared the code? That is something I have not run into. I have seen Subarus not run well unless the battery was disconnected every week. I am out of my league here.

Isn't the cam sensor a know failure point at least on older Miatas?

When I read the first post, cam position sensor was my first guess, mainly because the CPS in my Sentra has been flaky for the past 2 months. It bucked and stalled on me at a light this morning, but fortunately restarted immediately. Both that and my valve cover gasket are due for immediate replacement.

BoxheadTim wrote: Isn't the cam sensor a know failure point at least on older Miatas?

NB cam sensors do NOT like heat.

pjbgravely wrote: I don't know Mazda but on some Fords the cam sensor is used just for spark, but if it fails the crank sensor is used but it isn't as accurate.

Without VCT, the cam sensor is first used for sequential fuel, and IF there are coil on-plug, sequential spark. And all the cam sensor does is tell you which cylinder is coming up for top dead center. One node running at half engine speed. Vs. the crank that has 36-1 teeth running at engine speed. Crank is quite a bit more accurate.

With VCT, same as the above, but there are 4 more lobes added to know where the cam is so that it can be positioned. Still- those 4+1 lobes are spinning at half engine speed, vs the now 100-2 teeth on the crank spinning at engine speed.

Anyway, OldGray- as posted- I've also read that the cam sensors are a known issue. While there may be a loose wire in the harness, it's almost more likely that there's a partial connection IN the sensor, so when you hit a bump, it gets all screwed up. The sensor is a lot of copper wire spun around an iron core. A break in the wire internally will cause problems.

Could be cam timing.

Common problem on Zetecs.

alfadriver wrote:

pjbgravely wrote: I don't know Mazda but on some Fords the cam sensor is used just for spark, but if it fails the crank sensor is used but it isn't as accurate.

Without VCT, the cam sensor is first used for sequential fuel, and IF there are coil on-plug, sequential spark. And all the cam sensor does is tell you which cylinder is coming up for top dead center. One node running at half engine speed. Vs. the crank that has 36-1 teeth running at engine speed. Crank is quite a bit more accurate. With VCT, same as the above, but there are 4 more lobes added to know where the cam is so that it can be positioned. Still- those 4+1 lobes are spinning at half engine speed, vs the now 100-2 teeth on the crank spinning at engine speed. Anyway, OldGray- as posted- I've also read that the cam sensors are a known issue. While there may be a loose wire in the harness, it's almost more likely that there's a partial connection IN the sensor, so when you hit a bump, it gets all screwed up. The sensor is a lot of copper wire spun around an iron core. A break in the wire internally will cause problems.

I was reading on Miata.net that some have had the warm start issues solved with a replacement sensor.

And, when the code pops, it reads sequential cylinder something or other CMP blah blah, sounds like what you described above.

I'd had the warm hard start for a while, and that it seems to have outright failed coincidental to gnarly bottoming certainly lends additional credence to your prose.

Replaced the cam sensor this morning, but also cleaned and painted the gas tank spout in preparation for the hose replacement, so it'll be a day or so before final report.

In reply to alfadriver:

This is what I learned.

The Camshaft Position Sensor is GENERALLY used in all modern Sequentially Fuel Injected engines to fine tune ignition timing and fuel injection timing after the vehicle has started.

Just a quick example.

The newest system I have worked on is a waste spark coil pack system. Maybe things have changed since then.

In reply to pjbgravely:

That is kind of a large statement for a sensor that give you information once every 720 crank angles. Vs. crank sensor that gives you information either every 6 or 10 deg (depending on the tone wheel) of the crank.

All it really does is tell you where firing TDC of #1 is over a 720 deg cycle. Which is very important for sequential fueling. But that's all it does for waste spark systems that do not run VCT. Not at all important for a waste spark system- since fires once cycle on and off (on one fire) all the time. Matters a lot for coil on plug- since it's just like sequential fueling.

The systems we developed would determine once, and remember it, just in case the cam sensor was lost. And being that the missing tooth on the crank always lead to just 2 different choices, getting it right was a 50/50 shot when there was a fault.

Quick update on this, no issues since replacing the cam sensor, in limited driving, and the car actually runs better by a fair amount after replacing it than it did before (to be expected, I suppose).
The warm hard start problem also seems to have gone away, but we'll have some really hot days coming up, ample test cases available soon.

In reply to OldGray320i:i hope this thread isn't too old to post on - after driving it for awhile, was it the sensor?