71 replies to this topic

[Steve Scheifler]

Anyone that is a fan of Abba is showing their age too.

As Bench would say…

[Jim Drago]

Well, cautiously optimistic... I ran 45 laps at MIR yesterday in 90-92 degree misery. 11 of the last 15 under my current track record, not too shabby for an old guy if I dont say so myself   )  Never shut off at all.  What I thought was or could have been my issue was proved NOT to be my issue. 

 

So I am down to computer or engine harness.. This is the third of EACH since this started. ( original, second one added before sprints and replaced Monday before this test)  I had concerns with air gap to cam trigger and new Mazda sensors being defective or not as good as the original sensors that came in the cars when new.  Tested several sensors and air gaps and no issues in any direction. I was literally UNABLE to get the car to shut off yesterday in any configuration. ( likely waiting for a real race ) I tested I ran the exact sensor that came out of new Mazda box at the Sprints when car shut off...  It ran 20 laps straight yesterday with no issues. 

 

Further info: 

on previous harness, I ran a new wire from ECU to cam sensor, new wire from ecu to Crank sensor, new connectors on both as well. We ran its own dedicated 12v power and separate ground before Sprints as we have had luck with this in the past with other cars. There are other things like heated o2 on same circuit and slight shorts that don't blow fuses do cut the car off. 

 

The current harness is right out of an 120k parts car that came in last week.   

 

I will test that harness for short somewhere else and the computer when time permits.  It is a time consuming process for sure. Currently talking with Bill Agha on getting VVt harnesses made. 

Jim

[38bfast]

Jim this always seems to be the fix. Replace everything and when it doesn't work do it again and again till it does. It's so time consuming, costly and frustrating as you know. Sure wish we could find the smoking gun. 

 

On our new builds we get the new 99 harness from Mazda just to replace the 20 year old heat aged one that came with the car. I agree it would be nice to have that option on the VVT cars. 

 

 

F ing electrons. 

 

As a mechanic electrical problems are the worst. Especially intermittent ones you can't always reproduce in the shop. 

[LarryKing]

 

 

getting more mature is positive.

Better to be seen than viewed.

[Mike Tesch]

Anyone that is a fan of Abba is showing their age too. 

 

What's wrong with Abba?

[Kenneth Teal]

Well...  I had that issue happened to me at ECR.  Car shut off 4 times on Saturday, pretty much every session.  Here's a video where you can see it (around minute 3:40). 

 

https://youtu.be/41SUUzRdATY

 

I checked timing that evening, was really high, like 17 degrees btc.  I reduced it to about 12 degrees and the car ran without any issues on Sunday, but was down on power...  It wasn't great power before though.  

 

As far as I know the reluctor wheel is unmodified, and the only timing advance we did to the car was from the slotted trigger wheel.  It had ran fine before with no issues for the past 3 or 4 weekends.

Some simple questions...data gathering. Lets assume all cars that have had a shut off problem are running a slotted wheel and nothing else.

 

1. Is the slotted wheel Mazda purchased or home ground(potentially more/less advance)?

2. Has anyone solved the problem by retarding the wheel or removing and putting in the unaltered stock trigger wheel?

3. If #2 is true for you...change in power? 

4. any specific model year popping up more than others?

5. Is the shut off momentary(less than 2 seconds)or longer?

6. Is the shut off predictable(speed, rpm, load, traffic)

 

For anyone who has had the problem and then clocked the reluctor wheel...did it 100% solve the problem? (post under an alias if you are a front runner )

If it did not...any specific thing that did?(Jim has mention timing belt)

[Jim Drago]

Well...  I had that issue happened to me at ECR.  Car shut off 4 times on Saturday, pretty much every session.  Here's a video where you can see it (around minute 3:40). 

 

https://youtu.be/41SUUzRdATY

 

I checked timing that evening, was really high, like 17 degrees btc.  I reduced it to about 12 degrees and the car ran without any issues on Sunday, but was down on power...  It wasn't great power before though.  

 

As far as I know the reluctor wheel is unmodified, and the only timing advance we did to the car was from the slotted trigger wheel.  It had ran fine before with no issues for the past 3 or 4 weekends.

 

ken

If its the engine we did, the reluctor wheel is definitely stock. Backing off the timing seems to help but IMO is not the "fix"  Nor have I personally had any luck with moving the reluctor wheel to fix this issue. 

1-start with new crank position and cam position sensor, from Mazda, no aftermarkets.

2- check connectors at both sensors

3- check timing trigger wheel tits are all present, cut gap to .025 on crank sensor

4- check timing belt tension

5- make sure no paint under cam position sensor

 

If none of that fixes it.. Change engine harness, then computer

Good luck

 

Its a good thing this isn't a safety hazard or anything Nothing worse than waiting for someone to run you over

Jim

[Steve Scheifler]

Jim Drago, as I recall at one point you too temporarily solved the problem by backing off ignition timing but in that same car no tweaking of the reluctor wheel helped. Ultimately the fix seems to have been either harness or ECU, which leaves unanswered why backing off ignition timing also seemed to eliminate it. I think maybe the broad answer is that the NB2 ECU/logic is extremely finicky and any number of different minior hiccups can cause it to shut down the engine.

As it happens I had a ‘95 (early) in the shop last weekend with very similar random shutdown/restarts, frequent and sometimes at idle or even immediately after starting. As an OBD1 car we couldn’t log all the vitals so it was old-fashioned troubleshooting. The owner had already done the basics but we repeated them anyway. We wiggled and cleaned all the wires, connectors, fuses & relays; tested the CAS and swapped with one a friend leant us, and sacrificed a goldfish to the car gremlin gods to no effect. It cut out frequently but never in response to our tests. It seemed to be getting fuel but we didn’t have a gauge available. Tach would always drop out completely when it stalled BUT a timing light would continue to flash as it died. Occasionally the tach would jump up a few hundred RPM for just a blink but the engine didn’t. Fortunately another friend was kind enough to drop off her ‘94 for more parts-swapping. We went first with the ECU and BINGO, problem solved. We ran it for a long time including on the dyno to get some baseline numbers and set ignition timing, and it never missed a beat. Then, almost as if sticking it’s tongue out at us, the tach dropped out several times on the dyno for multiple seconds at a time without the engine even stumbling.

Anyway, FWIW, if your NA8 has similar issues and it isn’t the main fuse or wiring/connectors, borrow a known good ECU.

[Jim Drago]

Jim Drago, as I recall at one point you too temporarily solved the problem by backing off ignition timing but in that same car no tweaking of the reluctor wheel helped. Ultimately the fix seems to have been either harness or ECU, which leaves unanswered why backing off ignition timing also seemed to eliminate it. I think maybe the broad answer is that the NB2 ECU/logic is extremely finicky and any number of different minior hiccups can cause it to shut down the engine.

 

That is correct. I am hoping someone smarter than me can explain why backing the timing back seems to help. It is not that the cam/crank sensors are out of phase and brought back in phase by reducing timing. But there is no denying ,my car( and several others) would run all day when we pulled timing out, but would start shutting off when we added timing. This after years of running the timing advanced to the same number.  I have yet to get a grasp on this.

Jim

[TylerQuance]

Jim, does the ECU count sync loss instances and shut down when it reaches a threshold?

[RWP80000]

That is correct. I am hoping someone smarter than me can explain why backing the timing back seems to help. It is not that the cam/crank sensors are out of phase and brought back in phase by reducing timing. But there is no denying ,my car( and several others) would run all day when we pulled timing out, but would start shutting off when we added timing. This after years of running the timing advanced to the same number.  I have yet to get a grasp on this.

Jim

Jim,

Have not heard anyone discuss what affect the Knock Sensor may be playing in any of this.  Could the higher compression VVT's combined with advanced timing result in the knock sensor calling for a retard in timing play a role? Possibly resulting in the ECU being confused as to where things actually are and contributing to this "loss of sync"?

 

Has anyone evaluated plugging in a stand alone knock sensor in to the engine harness that is grounded to the chassis but isolated from any actual engine vibration inputs to see if this had any affect on a "problem" car?  

 

Rich Powers

[Jamz14]

Or you could just unplug the knock sensor.