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Multiple sensor errors - ref, sync, air temp

PostPosted: Mon Jun 21, 2021 3:21 am
by stownsen914
I have an older M4 setup on a Porsche 968 racecar, and I've started seeing multiple sensor errors in the logs. Mostly ref and sync errors, but also air temp sensor errors. There isn't much storage in my M4, so I get less than 10 mins of logs at 5x / sec. In my most recent log, I'm seeing almost 3 minutes of errors on sync and ref in ~9 minutes of logs. Surprisingly the car seemed to run OK most of the session, but it was misfiring at times. Some observations after spending some time looking over the logs and also examining the car:
- The errors seem to come in clusters of 2-5 seconds, with sync and ref errors almost always at the same time.
- The errors seem to happen in all RPM ranges, but may be more frequent at higher RPM/load
- The air temp sensor, which is located in the airbox, is mostly giving readings all over the place, ranging from 0 deg C to 25 degrees (the actual air temp). Or giving an error in the logs (about 1 minute worth). The errors for this sensor are sometimes at the same time as the sync and ref, but not always.
- System voltage in the logs is consistently over 12V. I didn't see any evidence of low voltage or fluctuation like gauges going haywire, or low voltage on the voltmeter in the dash.
- I just looked at the car, and didn't see any obvious signs of wiring damage, loose grounds, etc.

It seems like a telltale sign that multiple sensors are giving issues at the same time. I assume these sensors need a voltage source (5 volts?), and perhaps that is flaky? Or a bad ground?

Thanks in advance for sharing any thoughts.


Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Mon Jun 21, 2021 8:34 am
by SprinterTRD
Sounds like a 0V issue check MoTeC drawing Z05 for a start.

How old is the wiring 25 year old ECU, is the loom 25 years old as well, possibly time for a new one.

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Mon Jun 21, 2021 8:55 pm
by stownsen914
On looking again, it seems the bundle of sparkplug wires (4 running in parallel) had settled onto the ECU loom that contains leads for all the sensors, injectors, etc. It was perpendicular, but touching the sheath that covers the loom. Bit of a rookie mistake, I realize. Could this explain the multiple sensor errors I've been seeing?

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Tue Jun 22, 2021 8:36 am
by SprinterTRD
There is always a possibility. What kind of sparkplug wires are you using, on that note are you using resistive spark plugs?

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Tue Jun 22, 2021 11:38 am
by stownsen914
Thanks Sprinter for sharing your thoughts. Wires are Magnecor (which I believe are suppressed), plugs are Champion non-resistor racing plugs.

Thinking about it, I re-routed the wires in the engine bay a couple races ago, just before the sensor errors started occurring. Previously I'm pretty sure the plug wires were routed just under the harness. At that time I was seeing injector errors in the logs. Injector leads are in that same portion of the Motec harness.

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Tue Jun 22, 2021 12:03 pm
by SprinterTRD
Non resistor plugs can also cause missfire problems as they also radiate noise. Show me a OEM that does not use them!

Never had a problem using resistive plugs on a race engine. I also use NGK rather than Champion.

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Sun Oct 17, 2021 4:45 am
by stownsen914
So the saga continues ...

Had another outing with the car a couple weeks ago. I was hoping I'd addressed the sensor errors by putting some distance between the sparkplug wires and the Motec loom, and putting some EMI suppression covering over the loom. Well, the interference was worse than ever and the engine was misfiring pretty badly. When I downloaded the Motec logs, I saw more sensor errors than ever, including a ton of sync and ref errors - occupying like half of the log. I've spent a few hours looking over the logs. I'm seeing lots of the following errors:
1. No ref
2. Sync error - I don't see any "No Sync" errors, so I assume "Sync Error" are due to the No Ref?
3. E7 - I have no idea what this is. Anyone know? It seems to often be coincident with sync and ref errors.
4. SynP in the logs seems to drift between 50 to low 60s, and sometimes gives transient values in the 5-90 range, usually coincident with sync and ref errors. I'm guessing that this variation means that ignition and injection events are also way off. Could be the cause of the misfiring?
5. Injector errors from all 4 injectors - I don't see any evidence of shortage of fuel or high lambdas in the logs. Not sure what to make of these. I see injector errors in older logs when the engine appeared to be running great.
6. Air temp - this sensor appears to have been going bad and now dead. A static check shows open circuit, so I'm replacing it. Air temp gives +-2% comp across the entire range and defaults to 25 deg C when faultly, so I'm thinking this may not be the source of my problems.
7. Aux temp - this isn't connected to anything, need to turn it off.

Engine starts and seems to run fine at low load, gets unhappy as load and RPMs increase. It ran well with this configuration previously, and older logs show no errors at all.

Looking for some suggestions of things to check/troubleshoot. A few possible sources of the problem?
- Bad Ref sensor causing loss of sync
- EMI from bad plugs, wires, or a coil is screwing up sensor signals
- I think it was suggested in an earlier post that a bad 5V signal to sensors/injectors. Or maybe a bad ground. Is there a convenient way to check the 5V source?

A few things I've checked already:
- Did the Motec sensor diagnostic check, including cranking to look for sync errors. All good (#6 and 7 above show errors as expected).
- Examined plug wires (Magnecor) for damage or signs of age, look good.
- Plugs looked a little fouled but perhaps this is expected with all the sensor errors. I'll replace them.
- Did static checks on the coils (Saturn/GM) and they appear within spec.
- Fuel pressure is stable at ~45 psi including during the misfiring episodes based on the gauge in the dash.
- Did a leakdown test to rule out internal engine source of misfire. 2-3% leakdown on all cyl.
- Motec voltage in logs seems stable in the 12-13V range during pretty much all conditions outside of cranking.

Any input on this would be most appreciated! I'm including the most recent log file in case someone can give an opinion. Also including the Motec config file for reference in case it's helpful.

Thanks very much in advance!

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Mon Oct 18, 2021 12:17 pm
by SprinterTRD
Did you try to get drawing Z05 in my first post and try what it covered? You didnt indicated that you covered that suggestion.

If not Try and get it from a MoTeC dealer as I did a quick search on the website and could not locate it.

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Mon Oct 18, 2021 1:12 pm
by stownsen914
Thank you sprinter. I did download that drawing when you suggested it earlier. Attached below for reference. Is this the one you mean? It appears to be instructions on how to crimp the connectors for the 36 pin plug into the Motec box. Is the suggestion to inspect that the wiring to the 36 pin connector has been done correctly, or see if it's been damaged?

In looking at some of the other Motec wiring diagrams, I see that pin 27 is the 0V for the M4. Per your earlier comment about a possible 0V issue, would pin 27 and the wire connecting to it be a place to investigate?

Re: Multiple sensor errors - ref, sync, air temp

PostPosted: Tue Oct 19, 2021 2:07 pm
by SprinterTRD
Yes, that's the drawing.
Over time the small flaps inside the loom pins flatten out and can cause bad or no contact with the male pin on the ECU connector.

Internally, Pin 25 ECU power ground is connected to Pin 27 0V so that's a starting point however you might as well do all the other pins while your at it ;)

Another check would be to make sure Pin25 is connected to Pin27 on the ECU side. Possibly a 12V short to 0V has blown the internal track on the circuit board.