QuestionQUESTION: I noticed that the trip counter adds mileage when sitting at a stop light or when shifting into gear , regardless if reverse or forward the counter moves , plus when I tug on the main harness under the hood by the TCM and power distribution centre sometimes the counter either slows down or stops adding unused mileage.I've tried changing and isolating different wiring going to the PCM,TCM and crankshaft , camshaft sensors , plus changed the wiring going to the crankshaft,camshaft sensors , fed the comp systems a new sensor ground signal via new wires, rewired transmission input and output speed sensors ,changed the speed sensors too.Also I've fed the different comps fresh grounds , fresh 12 volt feeds ,tried 4 dif BCM's, dif gauge clusters,changed and tried a few dif clusters ,rewired comp bus wiring.I've also have noticed my car doesn't start up as quickly as it use to and that the engine idles a bit off but I've done a tune up etc on it and same thing, also the mileage seems to be off at times and other times I get 28 miles per gal via hwy.
Could this problem be related to a faulty cam or crankshaft or knock sensor?
I'd be very greatful for your help and I hope that you can please explain exactly what's going on bec it's mind boggling.Need help asap thank you in advance and I do hope that you are having a great summer etc so far.
ANSWER: Hi Bob,
That is interesting. I have a '94 and a '98 manual but not a '97. When you say trip counter, I assume you mean that it is part of the speedo/odo cluster unit, correct? And while the trip adds units, the odo does not, correct? That is very strange. It would seem to be something in the cluster itself, or at worst the output speed sensor. I don't comprehend how any other sensor would cause this. Have you tried for fault codes using the ignition key? Let me know and we'll go from there.
Roland
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QUESTION: Hi Roland , how are you?
Well yes the trip counter and the mileage indicator both add mileage by themselves lol I have tried pulling codes via the ignition several times for this problem and a lean fuel problem but I fixed the lean fuel problem as well as some other minor problems over the years.There hasn't been any error codes other then what I've mentioned.
I too thought it must be a speed sensor issue and changed them both but there was not a bit of difference at all,plus there has been 3 differen't transmissions installed due to unrelated problems and bec they were under warranty and used and every time the speedo issue was still there.So you can see how mind boggling this issue has been with me.By the way I do have a 97 factory service manual that I purchased last month, it has been helpful in fixing other wiring issues but has nothing regarding this speedo issue.
ANSWER: Hi Bob,
Given that it exists no matter which cluster/trans/bcm you have installed (all those have been changed out as I understand it) it would seem to be an issue with the wiring, such as 'noise' on the digital bus. Does your '97 manual wiring diagram show any details about the cluster internal connection (my '94 does not, but my '98 does)? The '94 just shows a CCD+ and a CCD- pair of wires is involved, but the '98 just uses a single wire (yellow/violent)on pin 5 of the green plug to be the digital data wire. It would seem to me that there is an issue with noise on that wire(s) being mistaken for a digitizing incremental pulse on the odometer so my thought would be some sort of a shielding issue of either the single wire between the bcm pin 13 of the gray plug if you have the '98 wiring, or something to do with the twisted pair not being twisted tightly if yours in the '94 type of wiring. Is there any sort of an aftermarket digital electronic unit on-board which might be putting out noise? You could try putting a wire-mesh sleeve over the digital wire(s) and grounding one end of it to sheild against noise.
Please let me me know which wiring your '97 seems to have ('94 or '98 type)?
Roland
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QUESTION: Thank you Roland.
Yes I've even tried other PCM'S as well as TCM's and BCM's. I too think it's a wiring issue and as you know I've tried almost every wire going to the TCM etc.
My system uses pins 7-8 on the white plug c-3 of the BCM for the bus signal and the manual does show some of the cluster internal info.There is no digital aftermarket device on my vehicle.
Where can I purchase a wire mesh like you're suggesting?If I wrapped bare wire around two 20 gage wires then ground the bare wire , do you think that work? By the way the wiring changed on the 96-97 models they use some different wires , for example the 95 has the sensor ground running into the car and the 96-97 only uses the sensor ground for all the sensors under the hood including the o2 sensors.
AnswerHi Bob,
I was thinking about the kind of shield that is used in audio/video/tv antenna cables such as RG-59U which has a mesh sheath surrounding the insulated center signal wire. You could take a length of that cable and carefully slit the outside rubber covering which reveals the mesh. Then by gently pushing it from both ends toward the middle it would 'fatten' and you could slide it off like shedding the skin. Then you could either slit the mesh lengthwise and slide it over the twisted pair of CCD wires and spot solder along the slit mesh to re-establish the surrounding shield, or cut those two twisted CCD wires at one end, slip the mesh over the cut ends and then splice the cut wires together again and insulate the splices. The last thing to do would be to attach (solder) a grounding wire to the mesh, grounding it to a chassis ground point. The mesh would probably provide a better electro-magnetic shield than a self fabricated looping of wire, but maybe something like a grounded steel spring length would do it as well as mesh. Now that I think about, the problem will likely be that the wires in question run all the way from the cluster over to the bcm on the right kick panel...that may be a challenge to try this techniques on. Have you looked at the existing twisted pair of bus wires? Do they appear to be unwound noticeably. My thought is that the twisting is for the purpose of shielding so that if someone in the past untwisted it a bit it would be more subject to noise.
Thanks for clarifying the transitions in the wiring. I was aware of some changes on the engine wiring in '97, but it appears that the bem/cluster was valid from '93-'97.
Let me know if you try it and whether it helps.
Roland
