CEL, code P0340, cuts out at 5K rpms. Bad crank sensor?

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12-02-2009, 01:41 PM
TR6

CEL, code P0340, cuts out at 5K rpms. Bad crank sensor?

Wanted to toss this out for a sanity check. Sorry for the long post but want to give all pertinent information (I also posted this on miata.net).

The car is a 2002 spec miata race car (not street legal). I had it at the track last week running some fun laps when it suddenly started cutting out somewhere around 5K rpms. It was as if someone turned the key off. As soon as you took your foot out of the throttle and the rpms dropped, full power returned. However, as soon as the rpms got somewhere between 4K-5K, it would repeat the same thing. CEL came on. Brought the car into the hot pit and then it wouldn't start. After a bit, it started again and I put it back on the trailer and took it to my mechanic. It still had the intermittant no-start problem and continued to cut out above 4.5K rpms. Mechanic pulled the code. P0340 (cam position sensor circuit). Doing some searching on this site and others, it appears it could be anything from the CPS itself to anything in that circuit including the crank sensor.

Now some background. About two weeks ago at a track event, I lost the fan belt. It shredded when it self destructed. No harm was done in terms of overheating because I shut it down and coasted into the pits before the temp got too hot. Replaced the belt and continued running the rest of the weekend with no issues at all. No power loss or hesitation at all.
However, when my mechanic was looking over the car this morning, he told me that it looks like the CRANK sensor may have been damaged when the belt let go. Said it looked scarred up. He is guessing that is the source of my problem and the P0340 code. As a side note, he pulled the cam sensor and said it didn't appear to be dirty. (I read some threads where a dirty CPS can cause a problem). He said he also checked wiring/grounds and all looked good.

My dilemma is that I am running another event this coming weekend and am wondering if I roll the dice and have him replace ONLY the crank sensor or bite the bullet and spend another $90 on a cam sensor (it takes a day to order these parts, AutoZone, etc doesn't keep them in stock). Obviously, if he replaces the crank sensor and the motor is still cutting out and it is still throwing a code, then we'll know it wasn't the crank sensor and we'll move on to the cam sensor. My concern is that this has been intermittant and I don't want to have it seem to be fine tomorrow and then have it crap out again at TWS this weekend where I won't have access to a cam sensor replacement part. Since the car isn't street legal and is ear splittingly loud, I don't have the luxury of a thorough road test.

Appreciate any input on this.
12-02-2009, 02:18 PM
ken o

Replace. What will you lose if it craps out at the track? Your time, weekend, cost to haul there, etc. In the big picture it is only $90.
12-02-2009, 02:20 PM
POS Racing

Wife's 2002 has similar issues but it decided to strand her on the side of the road....

Mazdaspeed FTW!

p/n BP4W-18-230* sensor,camshaft fixed it up and it hasn't been a problem since!
12-02-2009, 02:31 PM
Majik

I replaced this part several years ago with issues similar to what you have. It fixed it, and mine didnt look dirty either. I think I even sold it in the classifieds here... ;-)
12-02-2009, 03:00 PM
TR6

Quote:

Originally Posted by ken o

Replace. What will you lose if it craps out at the track? Your time, weekend, cost to haul there, etc. In the big picture it is only $90.

Good point. I was thinking along similar lines. Either just take it with me as a spare or replace it in advance. But the analytical side of me wants to only replace one variable at a time. If I do replace both (crank and cam), I won't know which one fixed the problem. But I could go ahead and buy the cam sensor and carry it along as a spare just in case. It is a quick replacement as long as I have the part with me.
12-02-2009, 08:41 PM
Mark52

I have a crank sensor (BP4W-18-221B) and a cam sensor (BP4W-18-230) that I pulled from my 2000 engine. I believe these same sensors were used on the 2002 engine, also. $45 each, if interested.
12-03-2009, 11:10 AM
TR6

Quote:

Originally Posted by Mark52

I have a crank sensor (BP4W-18-221B) and a cam sensor (BP4W-18-230) that I pulled from my 2000 engine. I believe these same sensors were used on the 2002 engine, also. $45 each, if interested.

Thanks for the offer but I already bought both of them yesterday. I decided to go ahead and buy the Cam sensor to have with me even if I don't install it right away.
01-06-2010, 10:47 PM
TR6

Update and renewed request for advice: I replaced the cam sensor and the crank sensor. However the intermittant problems have continued. Most recently at a track day, it started cutting out again somewhere between 4-5K rpms and threw a code of P0335 (crank position sensor circuit). Then after a while, the CEL cleared on its own and the car started running fine. That's what is so frustrating. When I got the car home, I checked the air gap on the crank sensor and it is in tolerance. I also made sure the connector was tight.

Any other suggestions? The only thing I can think of to try next is to replace the plug wires and/or the coil packs. But coil packs are expensive and I hate to just throw money at it without being sure. I've thought about trailering it down to MER to have them look at it. But I'm afraid that if it isn't messing up when I take it to the shop, they won't be able to identify the problem. And I've got a track weekend at TWS coming up soon.