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Update here. Still waiting on some parts for the oil pressure sensor work, but got into the oil temp sensor. Pretty easy and straightforward, about 5 minutes of work and the new, year appropriate sensor was in. Connection all cleaned on both the sensor and wire connector. However, still no reading on the gauge. I assume because of this, I either have a wire or connector issue thats fizzing out somewhere. Will check all the connections behind the gauge once again. Other than connections or bad wires, would anything else cause 0 reading?
http://forums.pelicanparts.com/uploa...1677982764.JPG http://forums.pelicanparts.com/uploa...1677982764.JPG For the oil pressure sensor, after everyone's suggestions im definitely opting for the "removal all in 1 package" method to have the least amount of possible failure. With that being said, do I just undo the line nut holding the through bolt to the case, and disconnect the hard line on the right so I can move the oil line out of the way and remove the through bolt and housing all together? http://forums.pelicanparts.com/uploa...1677982906.JPG Also have a question about the tach. PO said once the new 3.0 went in, the tach never worked again. Sometimes when I'm driving it will just randomly jump to 2000 for less than a second and then just go back to its resting spot of 0. It doesnt jump often, its only once in a blue moon that it'll randomly jump. Been searching these forums about info, seen a ton on the black and purple wire in the engine compartment that might be an issue (i cant even see it back there) but..its not completely dead since it does randomly jump from time to time. I have the gauge thats in the car (I assume it is the stock 77 gauge?) and I also have this gauge (pictured below) thats stamped 5/77 but has different red line readings etc etc. I think its more so a wire connection issue that others have gone after but not sure. Thanks again for the help Jordan http://forums.pelicanparts.com/uploa...1677982764.JPG http://forums.pelicanparts.com/uploa...1677982764.JPG http://forums.pelicanparts.com/uploa...1677982764.JPG |
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If it doesn't, either the block isn't grounded, or there's an issue with the wiring, or the gauge. Try grounding the gauge input somewhere behind the dash to eliminate the wiring/connections from the engine bay. Work towards the fault until you find it :D Quote:
Earlier (like '75, IIRC) tachs can have special needs (pullup resistors or updated driver boards) when used with non-factory inputs, but I think '76 and later are more accepting/compatible. Not a problem I've had... Have you looked at the 14-pin connector in the engine bay? Worth cleaning that thoroughly. Although this actually sounds like the sort of symptoms you get from damaged instruments to me. I had a 944 that would quite often not show anything on the speedo until you hit 30MPH for the first time that day - and then it would be fine until the next day. Only did it in cooler weather... Note that the tach and speedo both have capacitors in them rated at 15V (I believe), and really are not fans of being fed 18V, as very often happens when you have a voltage regulator fail. Also, electrolytic capacitors are well-known to simply die eventually from old age and need to be replaced. Leaking dialectic from the can is a sure sign (and often indicates either polarity reversal or overvoltage) - but they can just stop working without external visible signs too. 46 years old if original? Seems over-engineered to me... If the capacitors have been damaged from over voltage, instrument can act flakey for several (like 4-5) years, before they finally die completely and stop reading anything. Ask me how I know... |
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Still trying to tackle the temp gauge not working - been going after grounds the last 2 weekends. Going to replace the body / trans ground seeing as this one is pretty grim and also, its mounted on the wrong location. I know the trans location is on the stud right about the transaxle mount, but would this current ground location cause any ground issues relating to the engine? its grounded from body to the cross member..
http://forums.pelicanparts.com/uploa...1679891947.jpg http://forums.pelicanparts.com/uploa...1679891947.jpg When it comes to grounding the gauge input to somewhere under the dash, I'm pretty electrically slow with all that. I'm pretty much a body and paint kinda guy so electrical is way above my pay grade. Is this the correct way to ground the gauge to eliminate any wires to the engine bay? Or do I need to remove the green/black connector that runs to the sensor on the engine and ground from that? http://forums.pelicanparts.com/uploa...1679891947.jpg Last grounds I tried to find/tackle are on the left side of the engine bay by the fuse panel. Theres a ton of stray wires that I have no idea where their home is. Anyone have any clue about these or where the grounds are/need to go? http://forums.pelicanparts.com/uploa...1679891947.jpg http://forums.pelicanparts.com/uploa...1679891947.jpg http://forums.pelicanparts.com/uploa...1679891947.jpg -Jordan |
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The usual location is on the transmission (I want to say on the bell housing, but its been a while), where there's no paint. Usually it's good advice to make the metal shiny (both ends) for a good electrical connection. (A fiberglass rust-removal pen is great for getting the body stud nice and shiny without removing any metal). The ground straps themselves don't last very long either; they're exposed and have a hard life. They're also cheap; I'd junk that one. You're obviously getting ground from somewhere - otherwise the car wouldn't start or charge. But looking at that strap and what it's bolted to, well... |
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The body of the instrument (the case) is grounded, but I believe that is only used to complete the circuit for the lighting (otherwise you wouldn't need the negative/ground for the temperature gauge). So I'd check for power (+ and - 12V) on the back of the gauge with the key in the 'On' position. If you don't have that, the gauge won't work - so would need to figure out why the gauge isn't powered. Connect the sensor input to ground (which duplicates shorting the sensor lead in the engine bay to the block, but eliminates all the intermediate wiring and the 14 pin connector). The gauge should (probably, LOL), peg to maximum - as there'll be no resistance. If it doesn't, duff gauge. If it does, gauge is working, so only thing left is the sensor or the connection to it. Trace it back. I'd probably check continuiting/resistances between the instrument input to the 14 pin connector, and then other side of the 14 pin connector to the sensor terminal. It's worth mentioning that it is possible that the SC motor harness uses a different pin in the 14 pin connector than the '77 body harness that it mates to - you should check for that, if the gauge has never worked. |
Jordan, sent you a PM.
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I have a '77 Euro 2.7 (with flares, an '82 US engine, and US tranny, now an SC).
1) When I did the conversion in the late '80s, the word was that you needed to change the speedometer to one for an SC, so I did. Later I heard that at least some people had no trouble with their 2.7 speedo. 2) My '77 had the 4 pin CDI box. Happily, the used engine came with the 6 pin box. The early CDI system had no special provision for a tach signal. Porsche just ran a wire from where the points joined the CDI up to the speedo, so the speedo was reading the points, so to speak. With the 6 pin CDI, there is a tach output circuit in the box, which sends a filtered tach signal to the tach. Of course, it may be that late '77s already had the 6 pin CDI - Porsche did that sort of thing during model changes if they had run out of the old version. However, you can find and purchase a tach adapter, which will clean up the signal. Should not be needed if you have the 6 pin CDI. 3) Your '77 came with an external voltage regulator. Starting in '82 the SCs changed to voltage regulator internal to the alternator. I don't recall the year of your transplant engine, but if '82 or later whoever did the swap left the external VR in place, plus the 3 pin plug tar filled aluminum box piece below it which are prominent in one of your pictures. Both should be able to be removed if the internal VR is in place. 4) I hope you have acquired a good wiring diagram for the '77, plus one for the year of your SC engine - at least if it is an '80 or later. 5) Matching oil pressure gauge with sender is easy, since the senders have their max pressure stamped on them. If you get tempted to deal with the perennial leaking from the idiot sender on the front (of the car) side of the engine, I suggest you remove the old sender, block the hole in its threaded piece (or otherwise just block off the oil's access to it), add a wire to the idiot system, and connect it to one of the VDO combo idiot/pressure sensors installed where access is convenient. Those idiot senders always eventually leak, even when you have slathered JBWeld all around the crimp joint on a new one when last you replaced it. The idiot sender is hard to access, but a partial drop (search for the term) makes it feasible, even if you don't pull the rubber boot joining the two halves of the intake system. 6. If you disconnect the sensor wire from the oil pressure sensor, with the key on the gauge will peg. Low resistance means low pressure reading on the gauge. High resistance means a higher reading. A disconnected wire = infinite resistance, so the gauge pegs. The sensor is a wrapped wire rheostat - as oil pressure rises, copper fingers are moved along the resistance coil, raising the resistance. So any additional resistance, whether from inside the sensor, or a cruddy connection somewhere, will cause the pressure to read high. If the coiled resistance wire wears through and breaks at any point, the gauge will read normally until that point, then immediately peg. For the 1978 model, Porsche changed the gauge and sensor from 10 bar (~150 psi) to 5 bar (~75 psi). Speculation has been that customers freaked out at the very low seeming idle pressures a well used 911 exhibited, with the needle way low on the dial. So they doubled where it would appear. But the basics of this have been well covered. The temperature sensor has no moving parts, so I don't know its failure mode. If Spuggy says its behavior is the same, I can't quibble. I've had a lot of experience with the pressure sensors (especiallly with the wire connector getting loose, and opening up the sensor cover to view the innards), but not with the temp sensor. The part number changed in 1977, but I don't know if its resistance values changed. The one in my 1982 motor is original and works fine. 7) There is a strange failure mode for the electronic speedometers. They are designed so they can be used with a positive ground system, as well as the normal negative ground. This means that the ground (for the usual configuration) of the actual speedometer insert in the big round can is not connected to the ground for the rest of the stuff (like dash lighting). There is a ground lug on the speedo part (which is otherwise isolated from the rest of the case). When I bought my gray market car the speedo (which had a US speedo as a replacement) didn't work. The car came with a new speedo as a spare. I installed it, and it promptly failed. What the heck? I opened the speedo, and found a blown diode. Some poking around led me to understand that feeding 12 volts into a speedo which didn't have a solid ground ran way too much current through a part which wasn't intended to handle it. I replaced the diode, hooked up the separate ground, and it has worked ever since. Not apt to be an issue here, as not a gray market car whose speedo was replaced by someone who didn't understand this detail. However, this may be similar to what Spuggy alludes to for the other gauges (though they are all resistance devices, so shouldn't care about positive vs. negative grounds globally). 8) Two or three of the pins in the 14 pin connector are different in the SC versus the 2.7 version. A search might find someone explaining this, but if you have access to the two wiriing diagrams it is easy to figure out, as the diagrams have the wire color codes (alas, for the 2.7s the diagram doesn't include the pin numbers, unlike the 3.0 wiring diagrams). You just switch the ones which are different around and all is good. The idiot, pressure, and temp wires pass through this connector.. |
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At least some who report problems seem to indicate that they can read higher resistance than spec as they age - so the Motronic provides too much enrichment thinking it's colder than it really is, leading to poor running: https://forums.pelicanparts.com/porsche-911-technical-forum/1052215-verify-my-cht-sensor-test-results.html It's possible they could go open circuit - eg infinite resistance - too. Would be the work of moments to check with a multimeter. But unlikely to be the problem, as a new one was just fitted. I'd be astonished if Bosch, having developed their own chemical composition for NTC sensors, were to then turn around and use different ones for the 2 types of temperature sensor (Magnetti Marelli temperature sensors, for example, are different composition - and have a different curve). Instead, I'd bet dollars to doughnuts that the two sensor types actually have identical temperature curves - but that one has an internal resistor in series, biasing the initial reading at the dash meter to get it into the desired range. From the NTC datasheet, the CHT sensor resistance is 89 Ohms @ 130C. Grounding the sensor lead will peg the temperature gauge at maximum. If it is connected, powered, working etc. Quote:
At least on my car, the purple/black tach signal wire exits the harness just a few inches back from the 14 pin-connector. The other end of that goes to the front of the car, to the terminal labelled "TD" on the back of the tachometer - and should carry the (nominally) 12V square wave signal to drive it. |
Spuggy - My '77 rolled out of the factory in August, 1976. So likely they still had plenty of the old 4 pin CDs. The wiring diagram for the '77 shows the 4 pins only. Black/purple tach wire tied to the points circuit. Wonder just what Porsche did for the models late in the run by way of a speedometer? By the time yours came out they had switched. My '77 also did not have power brakes, though luckily the steel vacuum tube running from the engine compartment to the front of the tunnel was in place. However, later production nominal "77"s had the booster.
I tend to forget what parts are NTC and what are PTC. So the test for the pressure sensor is the opposite of that for the temp sensor. I couldn't remember. Having the tach signal from the 6 pin box go back to the engine through the 14 pin connector seems a bit odd. Perhaps that is because the SCs don't use points. The 2.7 points wire doesn't go through the 14 pin plug. So my guess is that Porsche used the tach wire which was already in a separate loom from chassis to engine to connect to the black/violet tach wire now running to the engine? The tach signal is, indeed, a 12V pretty square wave - I've scoped it. |
After going over wiring diagrams, I've had another thought. The tach signal system works by grounding the black/violet wire. On the old system, that happened when the points closed. So the 6 pin CDI internally provides a ground for that wire, either when the CD discharges, or when it is charging. This much is clear from the diagrams.
This means that a very crude check of the tach, and a very good check of the integrity of the violet/black wire, would be to pull the 6 pin connector, find the pin to the tach wire, and use an alligator clip to a wire with another clip on the other end (standard jumper) to ground, manually, the tach wire with the key in run (tach has power). The tach needle should move. Maybe not far, but move. If you tap quickly enough it should move up quite clearly. This is how one checks the speedometer, and its connecting wires. You are manually reproducing what the signal source does when it is working and doing what it does. If the tach needle doesn't move, you then pull the tach from the dash, clip onto its input (really, its output?), and tap. If it works that time, there is an open or short in the wire back to the engine compartment. |
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The tach signal comes out of the body harness just behind the 14 pin connector - there's no need for it to go to the motor via the 14-pin connector, and it doesn't. My bad. Will correct my original post in case someone reads that and not the correction. |
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Not an expert - and can't actually remember the cutover month now - but sounds as though yours may have been a late production '76 MY with some accommodations made for the next MY (vacuum line etc)? Did it come with a mech speedo? (PET seems to indicate some 915 types had the mech drive quite late, but others cut over earlier. And there was me naively thinking it was both earlier and and all-or-nothing cutover, LOL). An 80-300F temperature gauge? (it's kind of both weird and fascinating to be doing analysis on factory practices 50 years later). Quote:
Not that I just spent several days researching tachs because my new one needed a pullup resistor to work with my Motec or anything.. |
Spuggy - not so bad on the tach signal routing. My car is put away so I can't double check, and being an SC clone now isn't the best SC specimen. But the wiring diagram for the 82 US SC shows the CDI pin TD connected wire going straight to connector T12/14. So this is a bit confusing but doesn't ultimately matter - follow the black/violet wire for checking continuity. That color for the tach input wire doesn't change.
A friend's 1974 came with the then much prized aluminum S calipers up front. He had the "what's in the parts bin" theory also, as the 1974 S model did not show the S caliper on its specs. Something to be aware of - there are idiosyncrasies out there, and not just from we owners futzing around and then selling the car. My car for sure is (or was) a 1977 model - I found the German language driver's manual under a floor mat. Now back to our regular programming. |
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So even worse as an example of either a '77 or an SC... Quote:
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The Carrera/Model 77 wiring diagram in the red-binder FSM doesn't show T14 pin assignments. It is annotated "I, 1977" on the bottom right hand corner. The grey-binder reprint (seems to be printed on blotting paper for the wiring diagrams as opposed to the glossy paper in the earlier manuals), is annotated "Printed In Germany, XXXV 1977" on the bottom right hand corner - and it does... Here's an exclamation mark-delimited pin assignment table transcribed from the later version; should be able to copy/paste & load straight into a spreadsheet. Quote:
On the '77 wiring diagram, TD terminal on G5 (tachometer, current flow 94), is shown connecting directly, (at current flow position 119), to pin 1 of a switch/diode arrangement next to what is obviously the distributor. And In Real Life, my tach wire exits the harness a couple of inches away from T14. |
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Routed and changed the ground strap under the car to its stock mating position, but I'm going to be tackling the wiring/gauge situation for the oil temperature hopefully within the week. Will be using yours and spugs guidelines to hopefully remedy the situation. Also, if my info is correct I believe my 3.0 is from a 79. I have no idea if the CDI in the car currently was the stock one or if it came with the 3.0 All I know is I have a separate rear electrical panel that came with the car in a box with the blue CDI that I showed above so I assume the panel and CDI in the car currently came with the 3.0 swap, not a stock panel. I also have a color wiring diagram for the 77 as well as a SC wiring diagram but trying to follow it - for me - is like reading brail. Been studying up on it every night though to try and make sense of it. Will report back my findings. thank you again to you and spuggy - lets hope I can get it right LOL -Jordan |
As you can tell from the sticker, the blue CDI box is a Permatune. It may work or it may not. I'd plug it in and see if it works, and if it works the tach, but otherwise keep it as a backup in case the Bosch CDI box fails.
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Just wanted to hop in here and get some closure for anyone going through the same thing. Turns out after running a bunch of tests on the gauge, it was the gauge itself that was broken. There was a hairline crack in the circuit board on the temp side of the gauge which was the culprit. Sent it over to John Bell here on the forums, fixed it and shipped it back in the same day. Cant say enough about it. fired it in, and worked like a charm.
Will update this thread again once I go after the oil pressure sensor in the engine compartment -Jordan |
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VDO 360-023 is a combo switch/10 bar sensor in M10x1.0 that O'Reilly list for less than $40. Mine said "Made In Germany" on the packet. I've not got around to fitting it yet (want it to log oil pressure, so will still drive the gauge from the factory sender) - so can't 100% confirm the thread size is correct.. It's a little awkward to get to in the "triangle of death" - but it's not as involved to swap out either. |
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