Ed Brock

fuel guageOHM's readings

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    Early '71 240. I am trying to find out the ohms reading for the fuel sending unit to fuel gauge. We have installed a AutoMeter Ultra Lite gauge that reads 0-73 ohms. Part of the problem is the person at Auto Meter states that 0 is empty and 73 is full. Then, I spoke with some one else at Auto Meter (for a different matter) and they say they own a 240, and the sending unit is 0-90 ohms but the gauge we installed is a 90-0 ohms.

    What is the ohm's on the 240 fuel sending unit? Which is the empty reading (should be 0 I believe).

    Thanks Ed

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    10-90 ohm (F - E) is the spec I’ve always worked with. I can test a few senders....

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    Thanks, I reread my post and discovered a typo. When I was saying empty was 0, I missed the 9. (should have written 90 not 0).  Opps.

    Thanks for the refresher.  Nice drawing however. Where did you find that picture?

    Ed

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    I'm not sure if the 240 is the same as the 280, but if it is...

    annotated.JPG&key=2e695e53239044a446648a57f92cadcf545c03033bacde9f5c6ca79e6c14f1de

    Bunch of other related discussion in this thread:

    https://www.classiczcars.com/forums/topic/55746-fuel-gauge-accuracy-1975-280z/?

     

     

     

    Utter genius captain!!!! I have saved it for future ref.

     

     

    It also shows me that I have some additional impedence as mine never quite gets to F even with the breather hoses in tact and the fuel all the way up the filler neck. Then again, the PO wasn’t into cleaning contacts when he did things. One to look at for me on my next Z play date.

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    I have never had consistent, repeatable, long term stability fuel gauges in any Datsun regardless of how clean the wiring, how new the sender or how stable the voltage. You just learn how much you use for how far you travel and how much is left when you fill up. The gauge just means “yep you just filled up” or “got some still”, but that’s about it.

    Pretty much gave up and went to modern senders and aftermarket gauges that you program. 

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    6 hours ago, Ed Brock said:

    Nice drawing however. Where did you find that picture?

    I made that picture. I hooked the gauge up on the bench and tested it and that's what I got.

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    5 hours ago, AK260 said:

    It also shows me that I have some additional impedence as mine never quite gets to F even with the breather hoses in tact and the fuel all the way up the filler neck.

    I have the same situation. Never gets to F, and I still have about three gallons in the tank* when the needle is on "E". I need to clean some contacts as well, but it's just further down the priority list.

    *estimated knowing the claimed FEM tank volume versus how much I can put in at fill-up.

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    Oh, and remember... That's just one gauge that I had laying around. I have no idea how much variability there would be if I were to test a bunch of them and average the results. I suspect the gauges themselves are relatively consistent, but without testing, that's speculation.

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    @AK260, I had a few spare minutes yesterday, so I took a quick preliminary look at my fuel gauge system.

    Not sure if all the years have this, but my 77 has a convenient access port in the rear deck to get to the tank sender unit:P1160841.JPG

    Take the screws out and pop the cover:
    P1160843.JPG

    I pulled the wiring up a little and found the connector between the body harness and the sender unit. Looks a little crusty, but it's not green. Disconnected it and then took turns grounding the gauge connection and the "FUEL" warning lamp connection:
    P1160846.JPG

    Here's what my fuel gauge does when the sender wire is grounded. Clearly my gauge itself and all the connections leading back to the sender are fine:
    P1160847.JPG

    And just since I was working back there, I verified that my fuel lamp works when I ground the other wire:
    P1160851.JPG

    So I cleaned up that connector and put it back together. I don't know if doing just that will have much effect on the needle position on my gauge. I'm assuming that most of my issue is within the sender unit inside the tank and I'm not going to pull that to mess with it until I'm really ready.

    I won't know if simply cleaning that one connector up did anything until I fill up next time. I'll keep you posted.

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    Not all the fuel senders are as easy to get to as yours. This car an early 71 series has the sending unit assess at the front of the tank (towards the front of the car). It is easy to get at, just not as easy as yours. 

    Thanks Ed

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    [mention=32052]AK260[/mention], I had a few spare minutes yesterday, so I took a quick preliminary look at my fuel gauge system.
    Not sure if all the years have this, but my 77 has a convenient access port in the rear deck to get to the tank sender unit:P1160841.JPG.07a3f00aa0133525a589035d984d4596.JPG
    Take the screws out and pop the cover:
    P1160843.JPG.39b5fb14460b346d0b3d84fa101562ac.JPG
    I pulled the wiring up a little and found the connector between the body harness and the sender unit. Looks a little crusty, but it's not green. Disconnected it and then took turns grounding the gauge connection and the "FUEL" warning lamp connection:
    P1160846.JPG.72858c0379267d5b46ddd383bfb5b779.JPG
    Here's what my fuel gauge does when the sender wire is grounded. Clearly my gauge itself and all the connections leading back to the sender are fine:
    P1160847.JPG.745d6629d2e8b30f780aebfeb6e34d71.JPG
    And just since I was working back there, I verified that my fuel lamp works when I ground the other wire:
    P1160851.JPG.72242dbcfbf8087e6c2497596d1afc81.JPG
    So I cleaned up that connector and put it back together. I don't know if doing just that will have much effect on the needle position on my gauge. I'm assuming that most of my issue is within the sender unit inside the tank and I'm not going to pull that to mess with it until I'm really ready.
    I won't know if simply cleaning that one connector up did anything until I fill up next time. I'll keep you posted.


    Thanks for sharing CO!! I envy that hatch - my ‘77 260z doesn’t have that!

    I’ll take a photo of mine tomorrow and share - the connectors are different to yours and awfully crusty!!! The are positioned perfectly for being splashed with road crud. Also we didn’t get fuel warning lights in Europe so my connector is just like spade connectors.

    I will have to pull the tank or some tubing as the small fill up today resulted in a lot of smell inside. Also going hard on the anchors did the same so I suspect something has come lose or given up the ghost.

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    5 hours ago, AK260 said:

     The are positioned perfectly for being splashed with road crud.

     

     

    Haha! Probably took a lot of testing and revising to get that just right!

    So you don't have that 77 style hatch? I knew the UK stopped engine sizes and carb evolution with the 260, but I thought the rest of the car was the same as the US. So your entire car, body stampings, electrical, all that? All that stagnated*  in 1974 and held through until 79?

     

    * Not intended to be derogatory. Used for description only.

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    Quiet the contrary old bean! The “superior” :p late (‘77/‘78) 260z had many improvements over the early ‘74 260z. In between we got the 2 by 2 version.

     

    It has the stiffer unibody, the fatter chassis rails / floor supports that go all the way back, suspension improvements, the hubs are bigger, 3.54 R200 diff, better torque spread and 161bhp on a more tractable engine, a more plush interior, different wiring loom and so on. On that note, my old L26 would pull strongly from 1100rpm in 5th all the way to 5.6k. It’s a shame we didn’t get the 280 engine - without the smog stuff it would have been a very decent bit of kit.

     

    But the UK had protectionist taxes in place so they were expensive compared with British Layland cars and we got, relatively speaking, very few S30s. So very sadly we have to go to US / Japan for parts and still pay stupid import duties of about 30% on the parts and the postage + the obligatory £8 handling fees!!!!!

     

    It is lighter than the 280z but I guess the 280 got aircon, a plushur interior and those “robust” bumpers etc.

     

    I’m sure there are many many other things I have failed to mention, but at the risk of being a heretic, it’s mechanically closer to the 280z than the 240 from what I have seen. But no secret hatch in the boot!!

     

     

     

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    So I'm confused then... If you got the "improved" 77-78 cars, it sounds like (other than the engine), it's the same thing I have.

    So why don't you have that convenient access port-hole in the rear deck for the fuel sender unit? is yours an early 77 or something?

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    1 hour ago, Captain Obvious said:

    So I'm confused then... If you got the "improved" 77-78 cars, it sounds like (other than the engine), it's the same thing I have.

    So why don't you have that convenient access port-hole in the rear deck for the fuel sender unit? is yours an early 77 or something?

    Access port hole *should* be on all post Aug 76 models. Key #34. Did not search for 2+2 applications.

    Unsure if the microfiche sold by the club covers *only* export to US models...

    image.png

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    You made me think again and looking through my photos it appears I may have such a thing but buried under sound proofing!!

    7ca64dcf42a219a0af554b7caa6520b8.jpg

    Will have a proper look at the next play day!

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    Thanks Wayne!

    So AK, I'm not sure if you've got the access hole or not. Your sheet metal deck looks different than mine. Starting in 77 they put the stiffener frame rails on the interior side (top side) instead of underneath (gas tank side). My guess is that since they had to use the raised floor for the spare tire anyway, they figured they had the room and moved the stiffener braces. It doesn't look like you've got those braces.

    Another way to tell... Do you have a full sized spare, or the collapsible inflatable one? I'm thinking you've got the full sized spare and rear decking that we would call "76" over here.

    There's no guarantee that what we call "77" over here has to be the same as what you got in the UK.

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    To be frank I don’t know what spare wheel I’m supposed to have as my car had a few owners before me. It did have a diamond cross wheel with a full size tyre on it and VERY old rubber. So I would say it’s safe to assume it was designed for a full sized wheel.

    When I finish home schooling* later today, I will go to the garage and remove the sound proofing in that area as I am very intrigued!

    * I feel my work here is done!!

    e61f89694f52120dc7a2317741b8c4a1.jpg


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    So that was "Physics" class?  Potentially followed by "Pre-Med"?  Haha!!   LOL

    What's your build month/year on your door jamb plate? If you've got a full sized spare,  I'm thinking that here in the US, we could call your car a 76, not a 77.

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    So that was "Physics" class?  Potentially followed by "Pre-Med"?  Haha!!   default_laugh.png

    What's your build month/year on your door jamb plate? If you've got a full sized spare,  I'm thinking that here in the US, we could call your car a 76, not a 77.

     

    Exactly right, except I was “that dad” who fell and had grazes!! I was merely, as a good parent, sacrificing by demonstrating what not to do and the merits of wearing their knee and elbow pads! ;)

     

    aac4b2ec36a69e6195aa8bdfd393d13a.jpg&key=856cf159f139858f50f6c04bc9a9011432d93b3f571ec200028023bcbe520854

     

    I couldn’t take the sound proofing off, however I’m pretty sure I have the bump but not the hole / inspection lid below it.

     

    Having said that, my fuel sensor is on the back of the tank in the same place as a 240zeee further back from it so I’m not sure it would have served a purpose for me anyway.

     

    Finally, I’ve been investigating fuel smells and drained the tank with the full intent to drop it. But as it happens my courage and time ran out so upon further investigation I found some deteriorating breather hoses inside the car. Replaced and no more smells - for now.

     

    Why am I telling you this? Because:

     

    Here’s the gauge with ignition off ....

     

    4abd6a9c2e4088159b3264c222cd30a8.jpg&key=8869423624a11a926d143e451b7e6b8043caa103a32e927d73dadc43753ffaf3

     

    And ignition on but totally drained ...

     

    65db7860806e642f124ecf1dd61a767c.jpg&key=2c1e31d6b305e02dde9f87cc0fb94799d3328fbe777d2e395a47812f7716e64d

     

    And with 9 litres or just under two imperial gallons poured back in ....

     

    30d7aeb7d25019ce95bf5271d94eab3e.jpg&key=b4934005ad7cc1cefd07b8ad20306ef96e03ad729867552bc943b86a277e463b

     

    Unfortunately I didn’t measure the impedance as I was in a hurry to beat sunset (which is currently about 20:50 here) and de-grump my wife.

     

     

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    Yeah, your fuel gauge looks like it reacts the same as mine. Always too low. I haven't done anything else with mine (since I cleaned up the connector right at the sender unit), but I fully expect my issue is inside the tank. Murphy's law pretty much demands it. That Z hasn't come back around on my work sheet yet. I've got all sort of other car work to catch up on. Today I changed the plugs on a V6 Kluger. Including the three invisible ones in the back... That's no fun.

    As for the bike "teaching moment"... Very nice!   LOL   Thankfully, tis but a scratch!

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    I filled up my gas tank yesterday for the first time since cleaning the connector pair at the sender unit, and guess what!!!!?? 

    My gas gauge now reads significantly higher than it used to before cleaning that connector. Here's a full tank now. It used to read at about 7/8 full (even when full), but now it looks a whole lot better:
    P1160944.JPG

    So for me, cleaning this connector made a big improvement:
    P1160846.JPG

    I may still pull the sender unit out of the tank for inspection, but the priority just dropped down on the list a bunch!

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    That is such a nice treat for you after such a simple effort! Well done chap. Funny how these little things can make us go to bed feeling all is well with the world now! ;)

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    Yeah, that one was a real bonus! I was cleaning that connector with the 100% expectation that it wouldn't have any effect, but (roll eyes) I had to perform due diligence and clean it before I moved on to more difficult solutions. It was just the right thing to do.

    Bonus!!!  Sometimes you win one!   :beer:  

    I guess I'll keep that new sender lock ring and sealing O-ring in a box on the shelf!  Haha!!  And buy a lottery ticket?

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