WARNING About Dieseling
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Mazda CertifiedTechnician
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From: Dallas/Ft. Worth
WARNING About Dieseling
I just wanted to post up something about a car that I just finished up today. The owner had installed many different aftermarket electrical assesories, such as underbody neons, amp, sub, etc. I got the ticket saying that the customer was complaining about their car dieseling (run on) after the ignition had been turned off. The only other time that I had heard about something of this nature was if people ran low grade gasoline. I waited for the little gas that was in it to be completely used, then put premium gas into it (93RON method). This didnt help. I spend quite a period of time diagnosing it, and finally, through the help of "tech line" figured out that the assesories were causing malfunctions in the high speed CAN communication system in the car, more specifically the instrument cluster harness, which is where alot of the other harnesses run through. Long story short, be careful when installing all of this stuff, even their's was installed professionally, and they are looking at a lot of $$$ that is not warrantied, spent on fixing it, if that is what they want to do. 
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From: Brisbane, Australia
So you're saying that the aftermarket wiring was causing interference in the CAN bus due to its proximity to the CAN bus wiring?
If there is a CAN bus problem shouldn't you get one or more of the Uxxxx codes?
If there is a CAN bus problem shouldn't you get one or more of the Uxxxx codes?
Consiglieri
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From: yourI'mgirl
I can totally see why this would happen. Having spent my entire career in the area of instrumentation of and data collection during missile tests, I have seen numerous problems created by poor electrical design. Ground loops and harmonic feedback can wreak havoc with sensitive electronic equipment. I am sure the neons alone could do this. If the grounding, EMI shielding and feedback are not well-designed (and I am sure they weren't even considered in this case) then you are asking for trouble.
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Mazda CertifiedTechnician
Joined: Nov 2005
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From: Dallas/Ft. Worth
exactly what he said about feedback. Apparently, this guy had a Mazda 3 that he wired into the power of the DLC for some wacko assesory. LMAO. Anyways, VOID warranty on this new RX-8. sucks to be him. 
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Mazda CertifiedTechnician
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From: Dallas/Ft. Worth
sorry, didnt address the question about the U-codes... The U codes come up during module to module communication. Since the car was dieseling after you turned off the ignition, the PCM detected a running engine, but missing a lot of other feedback from different modules such as the instrument cluster, ABS, DSC, TCM, etc. The instrument cluster acts as a busy intersection for all of these other systems. The U0155 code is "PCM lost communications with Instrument Cluster Control Module", which is the main module that routes about 5 wiring harnesses through the cluster. So no, that one U-code was all that was needed in this case. Had there been other communication problems, then yes, there would have been other u-codes.
Consiglieri
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From: yourI'mgirl
There are lots of electrical accessories other than audio that could cause the same thing - EGT sensors, WB02s, oil temp sensors, boost controllers, turbo timers, data loggers... I think most of these are more well designed and emit less EMI than the auido/neon would be so its less likely to happen with them. But I've seen stranger - like the time the grounds in two 110V outlets in the same room were more than 10V different. Having a common ground plane is essential for electronics.
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From: Brisbane, Australia
Thanks for the comments mazdaspeedtech. I was just curious. I can trigger a U series code pretty easily by deliberately misbehaving when sending data on the bus (when the key is on).
I'm a little surprised that the PCM doesn't detect this sort of problem and report some sort of code... obviously makes troubleshooting a bit harder.
As vehicle bus speeds increase and dependence on them increases I can see that protecting the bus from this sort of thing is going to need more focus from manufacturers.
I'm a little surprised that the PCM doesn't detect this sort of problem and report some sort of code... obviously makes troubleshooting a bit harder.
As vehicle bus speeds increase and dependence on them increases I can see that protecting the bus from this sort of thing is going to need more focus from manufacturers.
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From: NJ
aahaha...that sucks...motorsports told me that if you install electrical wires incorrectly that it can mess with your car...this goes especially for the high density wires that neon lights and subs use xP
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Originally Posted by mazdaspeedtech
exactly what he said about feedback. Apparently, this guy had a Mazda 3 that he wired into the power of the DLC for some wacko assesory. LMAO. Anyways, VOID warranty on this new RX-8. sucks to be him.
In your first post it sounded like some aftermarket wiring which was run next to the instrument cluster harness was causing interference/noise which corrupted the traffic on the CAN bus. I would believe it, but I'd be surprised that such a cable wasn't shielded.
In this quote you talk about tapping power locally at a module (in the dash I presume?) rather than tapping power at a fuse block. I don't understand how the Mazda 3 relates. Did he first do the same mod successfully on a Mazda 3 he owns, then do the mod on his RX-8 and find a problem?
I don't expect to add 50 neon tubes to my RX-8, but I do plan to add remote-start and maybe some other toys. Even a professional installation shop can have a nitwit on staff for a couple of weeks who does crummy work in a bunch of cars before he is canned. What can we learn from your experience to watch for in our own aftermarket installations?
I'm an electrical engineer so I can fully appreciate electrical noise, EMI, interference and exceeding current/power specs for fuses and supplies. I hate trusting the 17-year-olds with the saggy pants at the local stereo shops to rewire my automobile's electrical system.
My doctor prescribed RX-8
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From: Is it safe to say Ohio yet?
of all people who should have problems....it should be be....but I've never had an issue such as this....I am having an airbag issue, but that's a resistance (likely plug) issue...and that a warranty issue cause its unrelated, and common to many cars. Anywho...I just suspect the shop did something stupid...just my opinion.
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Mazda CertifiedTechnician
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From: Dallas/Ft. Worth
cool blue dad-
The DLC is the Data Link Connector, its the port that most cars after 1996 use to communicate with "scan tools" and such. It is a connector with many wires leading up to it that provide critical information to some of the most important systems on the vehicle.
But anyways, about the Mazda 3, that was the same person, and they had that car, before the RX8, and on the 3, had used some aftermarket assesories also, but had gotten their power for them from the DLC, a big NONO. The reason that I brought this up is to show the lack of reasoning with this guy
I believe he had several drivability problems with the MZ 3....
The DLC is the Data Link Connector, its the port that most cars after 1996 use to communicate with "scan tools" and such. It is a connector with many wires leading up to it that provide critical information to some of the most important systems on the vehicle.
But anyways, about the Mazda 3, that was the same person, and they had that car, before the RX8, and on the 3, had used some aftermarket assesories also, but had gotten their power for them from the DLC, a big NONO. The reason that I brought this up is to show the lack of reasoning with this guy
I believe he had several drivability problems with the MZ 3....
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From: Orlando, FL
I haven't read the 8's owners manual lately, but I can tell you that the owner's manual for one of my other cars, a lowly Ford, has a bunch of warnings about aftermarket electronics and tells you not to run any wires on the right hand side of the car.
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I believe this connects into the reverse ground problem 
very simple...these new electrical systems rely on a Negative Ground relay systems to allow for opening the windows after the ignition is off and other delayed system shutdown functions.
when you reverse the polarity on any of these systems or have a crossing of wires they system will not shut down when you do the normal off initiation (ie turn turn key and remove)
I discovered this a year ago when I had a shitty portable dvd player where the car power adaptor was wired for a Positive ground system, I couldn't figure out why I could turn off the car pull out the key, lock the door and leave ALL WHILE ALL THE INTERIOR ELECTRONICS KEPT RUNNING!!!
very simple...these new electrical systems rely on a Negative Ground relay systems to allow for opening the windows after the ignition is off and other delayed system shutdown functions.
when you reverse the polarity on any of these systems or have a crossing of wires they system will not shut down when you do the normal off initiation (ie turn turn key and remove)
I discovered this a year ago when I had a shitty portable dvd player where the car power adaptor was wired for a Positive ground system, I couldn't figure out why I could turn off the car pull out the key, lock the door and leave ALL WHILE ALL THE INTERIOR ELECTRONICS KEPT RUNNING!!!
Last edited by truemagellen; Nov 18, 2005 at 04:01 PM.
Hmmm just installed LED bulbs yesterday all the way around, and two wierd things happend since..... got the ABS/TCS lights on all the time and that night, my CarPC would not shut down as normal.... I am currently resetting the ECU via the battery unplug method. I brought up 3 codes on my sCANalyzer, one of them was the Cat, since it was removed a month ago... Today, the CarPC is shutting down normally, but the ABS lights will still not go out... I will do the steering wheel sweep here pretty soon, and since my car is on jacks, I will check the sensors too... but this is all really wierd to have happen right after installing VLEDS on the turn signals, break, reverse, front running lighs and the front driving lights. My turn signal circuit is blinking fast, even with one set of resistors on the rear signals... it looks like I will need them for the front too. ALso wonder if that has anything to do with it... Craziness..
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What if there is still an issue?
My 2004 8 is struggling with this issue but the only AM wiring is a charger cable running up inside from the lighter socket up to a nexus install in the old satnav housing . Tried 97 unleaded but when this is gone will try some 99 but if this still fails to fix the issue I am not sure what to try next
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