Tachometer Dead
#11
07-23-2011, 06:38 PM
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I would suspect that there is nothing else electrically between the tach and the alternator, so you could run a new wire, or even just a long temporary one on the floor to test the tach. But if the harness has a short or ground, you might still want to disconnect tha wire from the tach, which might be a small challenge. Good thing the ETL has photos and connector layouts. I would rather chase a cable than pull all that stuff out of the dash. On the other hand, you might enjoy a new tach, oil pressure, and voltmeter set of guages.
#12
07-23-2011, 07:59 PM
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#13
07-24-2011, 03:58 PM
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I did some searches on Sun Tach's. They have quite a selection. If I can get the appropriate pickup device I may just go with Sun Tach, OiL Pressure, Oil Temp, and Engine Coolant temp guages to totally improve the instumentation.
I did some limited troubleshooting this morning and got no readings on the alternator output post. I think I will visit the local Auto Electrical shop nearby and have them take a look at both my original alternator and the used one I bought and see what they can tell me.
This has gotten me really frustrated with the Beast at present.
I did verify that the wire is not shorted to the frame. My only meter is a cheap GreenLee Digital Multimeter.
I am so frustrated with the factory wiring on this damn thing.
I had to just walk away from it today, too damn hot and humid outside to deal with the thing.
At times like this I really wish I had a totally different vehicle. I used to enjoy the Discovery,now that pleasure is fleeting.
Anyone want to take it away?
I need to win the Lottery or something on that magnitude to get me out of this deep funk I am in with the Beast.
I did some limited troubleshooting this morning and got no readings on the alternator output post. I think I will visit the local Auto Electrical shop nearby and have them take a look at both my original alternator and the used one I bought and see what they can tell me.
This has gotten me really frustrated with the Beast at present.
I did verify that the wire is not shorted to the frame. My only meter is a cheap GreenLee Digital Multimeter.
I am so frustrated with the factory wiring on this damn thing.
I had to just walk away from it today, too damn hot and humid outside to deal with the thing.
At times like this I really wish I had a totally different vehicle. I used to enjoy the Discovery,now that pleasure is fleeting.
Anyone want to take it away?
I need to win the Lottery or something on that magnitude to get me out of this deep funk I am in with the Beast.
#14
07-24-2011, 04:11 PM
Super Moderator
Well, with zero volts out on that tab it would tend to point to the alternator. You can verify your meter is working by reading the battery (DC) and an outlet inside the home (AC). And there is nothing cheap about Greenlee, they keep the IBEW going..
I don't like the Rover design that pushes radiator air through the alternator, but that's just me. Have also though about conversion to some other alternator as some others have done.
I have a multi-lingual shade tree shop library, Kia, Mercedes, Rover, F250 - each has unique quirks that waste a lot of time. And in the salvage yards you see a good representation of most brands. Lots of Jeeps. Should I ever hit that lottery, I'll build a multi-vehicle garage, and it will be air conditioned!
Some tachs take different drive points, be sure you have a spot for it to connect to. I even looked at a diesel tach that had a sensor that clamped on an injector line to pick up the signal.
I don't like the Rover design that pushes radiator air through the alternator, but that's just me. Have also though about conversion to some other alternator as some others have done.
I have a multi-lingual shade tree shop library, Kia, Mercedes, Rover, F250 - each has unique quirks that waste a lot of time. And in the salvage yards you see a good representation of most brands. Lots of Jeeps. Should I ever hit that lottery, I'll build a multi-vehicle garage, and it will be air conditioned!
Some tachs take different drive points, be sure you have a spot for it to connect to. I even looked at a diesel tach that had a sensor that clamped on an injector line to pick up the signal.
#15
07-24-2011, 04:30 PM
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When I said cheap, I meant the purchase price (30 bucks). I like the GreenLee, it's very rugged and lots of functions and ranges for that low of a purchase price.
I do somewhat suspect there could be a problem with the alternators but not a strong suspect, unless they somehow both got damaged, which is a possibility. That's why I want to take them to the local old fashioned electrical shop nearby. They have been there for ages and word is they are well stocked and well equpped to rebuild virtually any alternator around.
I read quite a bit on the Sun Website and sent them an email. They also offer a toll free phone line where they will help you select from their products. They have a clamp on device that is made to use as an alternative pickup to drive their tach depending on your specific vehicle. I do plan on calling them as well as getting a code reader that does pickup live data. Turns out that Sun makesthe Actron brand of code readers as well. They advertise they will help you select the best products for your specific vehicle, so I plan to call them and see what they suggest. They do offer direct web sales as well.
My temp guage quit about the same time. O may be pulling that damn instrument cluster apart to check a few things out. The Sun Guages may be the best route so I can have more accurate temp and oil pressure guages also.
I just had to let it rest for today. Will hopefully get back to it early in the coming week. It has become a Love/Hate Affair lately.
Damn Tempermental Discovery.
Wish I had another Mercedes to enjoy for a while.
I do somewhat suspect there could be a problem with the alternators but not a strong suspect, unless they somehow both got damaged, which is a possibility. That's why I want to take them to the local old fashioned electrical shop nearby. They have been there for ages and word is they are well stocked and well equpped to rebuild virtually any alternator around.
I read quite a bit on the Sun Website and sent them an email. They also offer a toll free phone line where they will help you select from their products. They have a clamp on device that is made to use as an alternative pickup to drive their tach depending on your specific vehicle. I do plan on calling them as well as getting a code reader that does pickup live data. Turns out that Sun makesthe Actron brand of code readers as well. They advertise they will help you select the best products for your specific vehicle, so I plan to call them and see what they suggest. They do offer direct web sales as well.
My temp guage quit about the same time. O may be pulling that damn instrument cluster apart to check a few things out. The Sun Guages may be the best route so I can have more accurate temp and oil pressure guages also.
I just had to let it rest for today. Will hopefully get back to it early in the coming week. It has become a Love/Hate Affair lately.
Damn Tempermental Discovery.
Wish I had another Mercedes to enjoy for a while.
#16
07-24-2011, 09:11 PM
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Hold on a minute. It may be just a wire. I don't agree with priceg because of the following test.
I just took my "flying lead" off the alternator, and my tach stopped, but my scanner still tracked rpm. That means the source of the ECU rpm is somewhere else, not the tach wire from the alternator. Probbaly because the ECU would like the rpm sensor to be real accurate, not subject to change by substitution of a different pulley.
If the tach is not plugged in, if the connector has the female lug pushed back too far, or just loose from heat stress, if the wire is skinned and grounded - all these could stop the tach.
The circuitry inside the alternator sends pulses from the diodes to the tach, so it can count them. When the diodes go out in the alternator the tach dies and you are not charging the battery,
I took these readings just now after a 30 minute drive:
AC on, idle at 695-715, outdoor temp 95 F, coolant 201 F per scanner
Alternator housing 195 F per IR thermometer.
Battery volts 13.82
Brown/yellow wire from alternator - 13.5 volts
Main stud on alternator 13.94 volts
Drop across 100 amp fuse in fuse box 0.0204 volts
Tach "flying lead" prong 6.93 Volts DC, 7.68 volts AC, 230 Hertz
Meter = Fluke 189 ($450 - $575 depending on vendor). Many smaller digital meter do have a separate AC and DC setting, but usually not Hertz.
Suggest you read AC volts on alternator to tach prong, with and without wire connected.
The Simpson 260 does have an AC input, which is basically a capacitor in series, to block the DC. But no freq meter function. IMHO if no AC voltage present then nothing for tach to count. You areorrect on the freq change, I saw it shift when I tugged on the throttle cable.
I just took my "flying lead" off the alternator, and my tach stopped, but my scanner still tracked rpm. That means the source of the ECU rpm is somewhere else, not the tach wire from the alternator. Probbaly because the ECU would like the rpm sensor to be real accurate, not subject to change by substitution of a different pulley.
If the tach is not plugged in, if the connector has the female lug pushed back too far, or just loose from heat stress, if the wire is skinned and grounded - all these could stop the tach.
The circuitry inside the alternator sends pulses from the diodes to the tach, so it can count them. When the diodes go out in the alternator the tach dies and you are not charging the battery,
I took these readings just now after a 30 minute drive:
AC on, idle at 695-715, outdoor temp 95 F, coolant 201 F per scanner
Alternator housing 195 F per IR thermometer.
Battery volts 13.82
Brown/yellow wire from alternator - 13.5 volts
Main stud on alternator 13.94 volts
Drop across 100 amp fuse in fuse box 0.0204 volts
Tach "flying lead" prong 6.93 Volts DC, 7.68 volts AC, 230 Hertz
Meter = Fluke 189 ($450 - $575 depending on vendor). Many smaller digital meter do have a separate AC and DC setting, but usually not Hertz.
Suggest you read AC volts on alternator to tach prong, with and without wire connected.
The Simpson 260 does have an AC input, which is basically a capacitor in series, to block the DC. But no freq meter function. IMHO if no AC voltage present then nothing for tach to count. You areorrect on the freq change, I saw it shift when I tugged on the throttle cable.
#17
07-24-2011, 09:31 PM
Super Moderator
priceg and I agree that if there is normal output from the alternator AND the harness is OK then the tach has died, even if the scanner shows rpm. But scanner reading OK and tach died would not always mean tach.
I had gone through a couple of Auto Zone rebuilts, and like Mike always says - they tend to fail. After trying to plug mine back in with the engine running, I can say that the alternator is getting a lot of very hot air directed into it by the fan shroud. A rebuilder may cut costs and select electronic parts that are not rated for these sort of temperatures (MIL-SPEC?). Next time mine tanks, I'm taking it to the local shop, or going with one of those conversions to something else. Seems like in my other vehicles the alternator is outside the radiator fan air flow.
I had gone through a couple of Auto Zone rebuilts, and like Mike always says - they tend to fail. After trying to plug mine back in with the engine running, I can say that the alternator is getting a lot of very hot air directed into it by the fan shroud. A rebuilder may cut costs and select electronic parts that are not rated for these sort of temperatures (MIL-SPEC?). Next time mine tanks, I'm taking it to the local shop, or going with one of those conversions to something else. Seems like in my other vehicles the alternator is outside the radiator fan air flow.
#18
07-24-2011, 11:41 PM
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If it is the tach in the instument panel, I will ignore it and go with a Sun Tach or similar product. I don't really care for the Binnacle anyway. I have already taken out the switches for the factory radio which is also out. The dimmer mounts broke, I rednecked engineered that mounting, I just pulled those cheap plastic woodgrain pieces off and the dimmer and mirror adjustment fit where the trim piece was. I may make up my own instrument panel. Sun also makes speedometers as well. I might fashion a nice metal replacement panel with all new accurate guages.
My key mechanism is acting funky, so I was considering redoing that clusterfukk with all new switches and doing away with the key using a push button starter switch and just do new switch panel for positions 1 and 2 and start (3).
Yank out all the junk and do it up right. That would be a good project. Just keep the key for locking and unlocking the doors as I have abandoned the fob completely.
My key mechanism is acting funky, so I was considering redoing that clusterfukk with all new switches and doing away with the key using a push button starter switch and just do new switch panel for positions 1 and 2 and start (3).
Yank out all the junk and do it up right. That would be a good project. Just keep the key for locking and unlocking the doors as I have abandoned the fob completely.
#19
07-25-2011, 04:48 AM
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#20
07-27-2011, 04:58 PM
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Saga Continues
Today, I called the Customer Service Line for Sun Tach. They also make the Actron Code Readers.
I spent 15 minutes with their online tech support. It turns out all of their tachs require a 5 volt square wave input signal to function. He could find no possible product they make that would work in our Discovery's.
Also, the used tach I purchased starting giving me a problem. Battery was not charging. I read up on the alternator testing in RAVE. Hooked up my meter to the battery, reved the engine and the out put was all over the place. So I put the original alternator on. It was the Italian made MM LR original. Retested, good output.
The used one turned out to be a rebuild and you could see strings coming loose inside! Called the recycler, he agreed to refund my money with the receipt since he did not have another in stock at present. That was fine with me.
Next step I guess is to run a temporary wire and see if tach responds.
Long term plan is to buy a live data code reader and just leave it plugged in if the wire doesn't fix it. I may go ahead and buy the cluster from Shadow Merchant.
I spent 15 minutes with their online tech support. It turns out all of their tachs require a 5 volt square wave input signal to function. He could find no possible product they make that would work in our Discovery's.
Also, the used tach I purchased starting giving me a problem. Battery was not charging. I read up on the alternator testing in RAVE. Hooked up my meter to the battery, reved the engine and the out put was all over the place. So I put the original alternator on. It was the Italian made MM LR original. Retested, good output.
The used one turned out to be a rebuild and you could see strings coming loose inside! Called the recycler, he agreed to refund my money with the receipt since he did not have another in stock at present. That was fine with me.
Next step I guess is to run a temporary wire and see if tach responds.
Long term plan is to buy a live data code reader and just leave it plugged in if the wire doesn't fix it. I may go ahead and buy the cluster from Shadow Merchant.