35 replies to this topic

[Keith Andrews]

Same thing for a 99, not as much detail but similar thought process.  Just based on the detail of the 2001 procedure, it makes me think this was known problem by the Mazda engineers in the 99-00 (NB) cars.

 

 

Cam sensor is failing or has failed.

Cam sensor circuit/wiring/connector/terminal issue

Cam sensor is dirty.

Open circuit between main relay terminal D and cam sensor terminal A

Open circuit between cam sensor terminal B and PCM terminal 2H

Open circuit between cam sensor terminal C and body ground

Short to ground circuit between main relay terminal D and CMP sensor terminal A

Short to ground circuit between CMP sensor terminal B and PCM terminal 2H

Crank sensor issue in addition to cam sensor malfunction

[Paul Watts]

Keith,

 

 

 

I have a copy of the 2001 OEM repair manual and went through the diagnostics for P1345  (P0340 is not in the manual).  I am convinced there are errors in the manual and will point them out for others to save them the head scratching. 

 

For example, #7 says to measure the terminal B voltage to be B+ (which stands for battery voltage or +12V), when I measure this I get 5V which makes sense to me based on the circuitry and the fact that most ECU / CPU signals are 5V.  Also, when the 2 pickups at the end of the camshaft spin in front of the sensor the transistor switches and pulls the B pin to ground. 

 

In addition, #5 says to check terminal C and body GND for B+ voltage when terminal C in the diagram is clearly attached to ground and terminal A is attached to the main relay (12V).  When I measured, I had 12V on “A” pin and ~0V on “C” pin according to the diagram, which is correct IMO.  The manual should read “Measure voltage between CMP sensor terminal A and body GND.”

 

To me the big take away from the manual is this though, if you are having this code the recommended fixes are:

 

1. Replace CMP Sensor

2. Replace Crank Senor

3. Repair or Replace damaged Crank Pulley

4. Repair or Replace wire harness

 

It is important to note, the solution most often recommended by the manual is to make some type of repair to or outright replace the wire harness.  For me, Items 1 and 2 are new, item 3 has been inspected and is good.  Item 4 is still suspect as it is a total pain to remove and check.  The continuity checks seem fine, but it is hard to replicate engine vibration and and g-forces of a real racing situation. 

[Adax]

Here is another example, this was taken from another forum that is talking about the Miata birthday party at MRLS

 

The usual VVT hickup - cam sensor went out.

Car started cutting bad at part throttle all of a sudden, limped it around until I got back to the garage, instructed my passenger to stay strapped in, jumped out, put a new sensor in 30 seconds and drove right back out with a healthy car.

 

 

I recently had this problem as well in my '01 vintage. Started as occasional part throttle, low (4K) RPM stumble. Over the next 30 minutes it became more frequent and higher up in the RPM range so I had to retire from an enduro. New cam sensor seems to have fixed it.

[Keith Andrews]

Paul great info and thank you.  

 

I've been battling this issue for quite a few months.  My car is a 99 though.  Unfortunately I've been unsuccessful at making it go away.  

 

I've done 1-4 on your list and covered the majority of the diagnostic checks.  I've spent many hours on a dyno "fixing the problem" (sarcasm), only to have it reoccur.  A new cam sensor is good for 1 hour.  Once the car starts backfiring, you can disconnect the cam sensor plug, then reconnect and it goes away momentarily but only lasts for 15 minutes.  Putting a new cam sensor on resets the clock for 1 hour.  Rinse and repeat.  

 

I'd like to understand why a new cam sensor goes from being good for 1 hour to only being good for 15 minutes.     

 

I've had it reoccur on the dyno with the hood open and bigass fans blowing ambient air (less than 90F) at the car.  For my car heat doesn't seem to be an issue.

 

FWIW the other items I've swapped and continued to have the problem are, but not limited to:

 

Plug wires

Coil

ECU

ALL harnesses on the car (including all relays and fuses in different boxes)

Engine

Alternator

Starter

Cam sensor

Crank Sensor

ALL grounds checked and cleaned

Factory gauge cluster

 

Can you tell I want to figure this out

 

I'm going to do some more work on it this week and if I find anything concrete I'll report back.  I've ordered the Airtex Cam and Crank sensors to see if they make any difference.

[Keith Andrews]

 

Keith,

 

 

 

I have a copy of the 2001 OEM repair manual and went through the diagnostics for P1345  (P0340 is not in the manual).  I am convinced there are errors in the manual and will point them out for others to save them the head scratching. 

 

For example, #7 says to measure the terminal B voltage to be B+ (which stands for battery voltage or +12V), when I measure this I get 5V which makes sense to me based on the circuitry and the fact that most ECU / CPU signals are 5V.  Also, when the 2 pickups at the end of the camshaft spin in front of the sensor the transistor switches and pulls the B pin to ground. 

 

In addition, #5 says to check terminal C and body GND for B+ voltage when terminal C in the diagram is clearly attached to ground and terminal A is attached to the main relay (12V).  When I measured, I had 12V on “A” pin and ~0V on “C” pin according to the diagram, which is correct IMO.  The manual should read “Measure voltage between CMP sensor terminal A and body GND.”

 

To me the big take away from the manual is this though, if you are having this code the recommended fixes are:

 

1. Replace CMP Sensor

2. Replace Crank Senor

3. Repair or Replace damaged Crank Pulley

4. Repair or Replace wire harness

 

It is important to note, the solution most often recommended by the manual is to make some type of repair to or outright replace the wire harness.  For me, Items 1 and 2 are new, item 3 has been inspected and is good.  Item 4 is still suspect as it is a total pain to remove and check.  The continuity checks seem fine, but it is hard to replicate engine vibration and and g-forces of a real racing situation. 

 

 

FWIW we verified a 99 does the same thing, PCM uses a 5volt reference signal for the Cam position Sensor.  Which makes sense.  Same sensor same system.

[Keith Andrews]

I just opened the package with my "Airtex" Cam Position Sensor with great anticipation.  It is the exact same part I've been purchasing from Mazda Motorsports.  Which is a Mitsubishi mfg. part.  

[Adax]

Maybe it's already been heat cycled. 😨

[Paul Watts]

Alan,

 

Just a couple quick questions out of curiosity did you get a DTC code along with this? 

 

Also, about how many weekends are you getting from a new sensor? 

 

Oh and side note:……your car is SICK! 

[Joe (dad) Jordan]

I just opened the package with my "Airtex" Cam Position Sensor with great anticipation.  It is the exact same part I've been purchasing from Mazda Motorsports.  Which is a Mitsubishi mfg. part.  

That may be my fault sorry if it is.  This was not the case 3 months ago.  Maybe mazda has made the switch??

[Keith Andrews]

That may be my fault sorry if it is.  This was not the case 3 months ago.  Maybe mazda has made the switch??

 

No problem.  I'm willing to try anything to fix this issue.  I really don't think this is a cam sensor issue anyways.  

[Brandon]

The "1 hour, then 15 minutes" state of the CAM sensor, to me, implies a wear condition with the connectors.

 

Has anyone measured voltage or resistance values across the pins of a new one vs. one that's now only lasting 15 minutes?

I'm not sure what numbers you'd be looking for but if the fact this vehicle has exhibited the same behavior multiple times after replacing the sensor perhaps noting those values beforehand would be helpful.

 

Thinking further on it, could there be something upstream of the sensor that's in-turn causing it to go bad (outside of the environmental options; heat & vibration)?

IOW, the sensor fault is merely the visible symptom of a different part/connector that's failing?  Where do its wires go/route to?

[RazerX]

Paul great info and thank you.  

 

I've been battling this issue for quite a few months.  My car is a 99 though.  Unfortunately I've been unsuccessful at making it go away.  

 

I've done 1-4 on your list and covered the majority of the diagnostic checks.  I've spent many hours on a dyno "fixing the problem" (sarcasm), only to have it reoccur.  A new cam sensor is good for 1 hour.  Once the car starts backfiring, you can disconnect the cam sensor plug, then reconnect and it goes away momentarily but only lasts for 15 minutes.  Putting a new cam sensor on resets the clock for 1 hour.  Rinse and repeat.  

 

I'd like to understand why a new cam sensor goes from being good for 1 hour to only being good for 15 minutes.     

 

I've had it reoccur on the dyno with the hood open and bigass fans blowing ambient air (less than 90F) at the car.  For my car heat doesn't seem to be an issue.

 

FWIW the other items I've swapped and continued to have the problem are, but not limited to:

 

Plug wires

Coil

ECU

ALL harnesses on the car (including all relays and fuses in different boxes)

Engine

Alternator

Starter

Cam sensor

Crank Sensor

ALL grounds checked and cleaned

Factory gauge cluster

 

Can you tell I want to figure this out

 

I'm going to do some more work on it this week and if I find anything concrete I'll report back.  I've ordered the Airtex Cam and Crank sensors to see if they make any difference.

 

Keith, did you replace the main harness?  I know it says all harnesses but i wanted to check.  Also did you say you swapped an engine and it still does this?  

 

Given all that you have done I agree with Brandon's logic that the sensor failure is a symptom and not the cause.  For it to fail that fast, and certainly heat and vibration could do it but that seems highly unlikely given we all are racing these things in similar conditions.  Not knowing your accessory wiring I have witnessed this causing problems, the harness gets cut into to support a gauge, cool suit, AMB, radio, data acquisition system, camera, beer cooler, etc.  The load and/or noise introduced (cool suit pump) and cause transient voltages that does weird stuff.  You logically look at and think "no way" my digital temp gauge can do that but..  So i suggest in your endeavors to remove possible culprits you run a home run wire for the critical stuff and leave the rest off to see if makes a difference.  

[Keith Andrews]

Keith, did you replace the main harness?  I know it says all harnesses but i wanted to check.  Also did you say you swapped an engine and it still does this?  

 

Given all that you have done I agree with Brandon's logic that the sensor failure is a symptom and not the cause.  For it to fail that fast, and certainly heat and vibration could do it but that seems highly unlikely given we all are racing these things in similar conditions.  Not knowing your accessory wiring I have witnessed this causing problems, the harness gets cut into to support a gauge, cool suit, AMB, radio, data acquisition system, camera, beer cooler, etc.  The load and/or noise introduced (cool suit pump) and cause transient voltages that does weird stuff.  You logically look at and think "no way" my digital temp gauge can do that but..  So i suggest in your endeavors to remove possible culprits you run a home run wire for the critical stuff and leave the rest off to see if makes a difference.  

 

Yes the main harness was replaced.  I have replaced every wire from bumper to bumper.

 

I agree on the accessory idea.  So when I replaced the wire harnesses I added nothing to them.  The only thing I wired to power was a transponder.  Nothing.  No kill switch.  No gauges.  Nothing.  

 

Brandon-

 

I've been on the dyno again and able to duplicate the problem regularly.  After the car started backfiring I installed a new sensor and within 20 minutes the car was backfiring again.  I agree the sensor is a symptom.

 

I hope to have some more diagnostic information in a few weeks.  

[Paul Watts]

Best Answer

Was able to confirm the exact issue at the track.  My issue was resolved by a new Crank Sensor. 

[Adax]

 

Alan,

 

Just a couple quick questions out of curiosity did you get a DTC code along with this? 

 

Also, about how many weekends are you getting from a new sensor? 

 

Oh and side note:……your car is SICK! 

 

 

Yes

 

Thanks

[jondimellow]

How did you know to change the crankshaft position sensor (sensor pointed at the front of the engine) instead of the camshaft ( sensor on the rear of the valve cover)? P0340 suggests a camshaft problem.

I had a p0340 at the track too On my 2001.

Thanks