Fuel Relay Pin Voltage Readings

[IMSARS69]

Fuel Relay Pin Voltage Readings -

Pin 30 should read 12 v whenever the battery is connected, right?

Should Pin 87 read anything with ignition OFF? I'm getting ~9 v. OFF.

Was intending to jumper 30 to 87 to energize pump but this jes don't seem right to me.

Entire engine / engine bay wiring harness is disconnected from engine as it is presently removed. So, no connection at ALT or starter solenoid and of course other connections as well.

What am I missing here Folks?

TIA...

[george graves]

Can't say without diving into the ETM. Get yourself a PDF copy of it, if you don't already have it.

There are some wires on any car that will have a small voltage on it when probed with a multimeter, but it's really "powered" on, or able to drive anything.

One handy tool to check for that is a good old fashioned test light.



Another thing to remember is that not all circuits "switch" the power to the device. Sometimes a device will have constant power to them, and the ground is switched on and off.

Hope that kinda helps.

[IMSARS69]

All that said, the real question is...

Is it ok to jumper between 30 and 87 to energize the pump given a fair portion of the main harness isn't connected to anything, albeit most, if not all are logically unrelated to the fuel pump.

TIA...

[IMSARS69]

There are some wires on any car that will have a small voltage on it when probed with a multimeter, but it's really "powered" on, or able to drive anything.

Another thing to remember is that not all circuits "switch" the power to the device. Sometimes a device will have constant power to them, and the ground is switched on and off.

Tho only problem with this theory is that the relay circuit acts like purt near every fuel pump relay I've ever encountered and shows it's circuitry on the device. Clearly shows Pin 30 will be connected to Pin 87 when the relay is energized [ FWIW there are two Pin 87s, both which showed the low voltage readings ] and is what directs 12 v to the pump. Pin 30 we know from other sources and probing has a direct 12 v connection at all times from the battery.

Presumably any device looking to be grounded in order to work would be connected to a grounded circuit which Pin 30 obviously isn't. And Pins 87 are not connected to any other leads into the relay other than Pin 30 and only when the relay is energized.

I jes can't see connecting a full 12 v lead to a lead with 'some' voltage in order to run an electric motor or similar device. So, I'm still missing something here. Notwithstanding what any wiring diagram might add I'm having trouble with this entire concept. Can you help me out with this as a general idea?

As for yer std ol test probe light I have a couple, but since HF likes to give them multimeters away and I have a half dozen or so laying around everywhere it's just as easy and knowing what the voltage and polarity is jes that much more info to have at ones disposal in lieu of say, it's got 'juice'.... ';)

TIA...

[lcoleman]

HF meters are junk, keep that in mind. Always take their numbers with a grain of salt.

A test light requires current to run, whereas a voltmeter doesn't (or at least much, much less). This may eliminate the "ghost voltage" readings you're getting. Just a thought.

A (fused :p) jumper between 30 and 87/87a should be fine.

Presumably any device looking to be grounded in order to work would be connected to a grounded circuit which Pin 30 obviously isn't. And Pins 87 are not connected to any other leads into the relay other than Pin 30 and only when the relay is energized.

I jes can't see connecting a full 12 v lead to a lead with 'some' voltage in order to run an electric motor or similar device.

The chassis is the common ground. The fuel pump grounds there, the engine grounds there, and the negative post of the battery is tied in....without the grounds in place, the circuit is not complete.

Just out of curiosity, if you disconnect the fuel pump wiring from the pump itself, is there any continuity (or resistance) between the 87 pins and ground?

[IMSARS69]

HF meters are junk, keep that in mind. Always take their numbers with a grain of salt.

Perhaps yours are, but I've had them for several years, and of the half dozen or so they ALL read within 0.01 v on the 20 v scale, and have never shown to be faulty or erratic. A couple which I've had for 8-10 years and drug all over the country from track to track, throwed around, beat to death and they're still on the money. Thaz plenty good nuff fer me.


While some HF and other cheapo crap is just that, some ain't.

Might surprise you to find that their torque wrenches for instance, typically on sale for a little as $10 will compete with the much higher priced models. I recently had one that after SEVERAL years of hard use finally gave up and with their Life Time Warranty was replaced with a new unit. I also purchased one of the 3/8 inch drive units to use for 'finer' readings... did a fairly comprehensive [ IMO ] test of both new units and got consistently within 1-2 lb-ft or less of the setting. For the 1/2 inch drive in the 45 lb-ft range and in the 35 lb-ft range for the 3/8 drive. Again, thaz good nuff fer me.


Sears [ nee Craftsman ] OTOH are a bunch of lying crooks who refuse to replace my LIFE TIME WARRANTIED HIGH DOLLAR [ back in the day ] CRAFTSMAN torque wrench whose ratcheting, not the torque mechanism had given up and was seldom used, because, well they jes decided not to cover them any more, even though this one was clearly manufactured WELL before any such policy change.


But don't take my work for it, check out:

Torque Wrench Testing - Shop Tools

Jes saying... ';)

A test light requires current to run, whereas a voltmeter doesn't (or at least much, much less). This may eliminate the "ghost voltage" readings you're getting. Just a thought.

I'll have to ponder on that one, but certainly will give it some thought and take it into account in the future...

Ok, drug out my high dollar fancy arse test light and of course the bulb was burned out on it... as confirmed by my cheap arse HF multimeter... ';) managed to find my ol cheapo [ not HF, some other crap shop ] and it works...

So with the battery connected, ignition OFF, checked Pins 30, 87 and 87a with the HF POS and got the expected 12+ v at 30, and 9.9 v at 87 and 87a... then put the test light to um and it only lit for 30 which I reckon may, or may not prove some point you're making, what I ain't getting... ';) For instance I whadda thought that 9.9 v whadda at least made 12 v bulb put out a little glow at least, but I guess not, or it means something else... and if so, that would be?

A (fused :razz:) jumper between 30 and 87/87a should be fine.

The chassis is the common ground. The fuel pump grounds there, the engine grounds there, and the negative post of the battery is tied in....without the grounds in place, the circuit is not complete.

Frankly, given a life experience of sheeet what never happened to anyone else, ever, I'm a tad gun shy about trying SOME things... ';) Got stories that'd make yer toe nails curl up... ';) Les say I do decide to try that fused jumper deal... 7.5, 10 or 15 amps would be your choice?


Not sure what the obvious, that is everything that runs off the 12 v system of the battery has to have a ground common with the source in order to work has to do with this, but again I reckon I'm missing out on sump'n here. Which ain't the first, nor will it be the last time fer this OF... ';)

Just out of curiosity, if you disconnect the fuel pump wiring from the pump itself, is there any continuity (or resistance) between the 87 pins and ground?

If I can get to the connector without too much trouble I'll be glad to try that... would removing the fuse create the same effect you'd like to see; may be a dang sight easier...

And if there is continuity with ground at Pin 87 does that imply one ought to be seeing some voltage readings across it when the pump is connected... I would think not, but then whadda I know... ';)

Anything more you can add to this I do appreciate... please note the ref to disconnecting the pump power supply to check for continuity at 87 and let me know if pulling the fuse is adequate for your test...

Thanks for your input...

[IMSARS69]

Just out of curiosity, if you disconnect the fuel pump wiring from the pump itself, is there any continuity (or resistance) between the 87 pins and ground?

Ok, I tried with the battery disconnected and the fuse pulled, which I figure is the same as disconnecting the feed to the pump [ but maybe not, you tell me ] and got purt near 0 at Pin 30 as would be expected, but at 87 and 87a I got 32.5 on one and 35.5 on the other on the 200K scale, whatever that equates to [ ain't got time ta look it up and figure it'll tell ya what yer after ]...

That be of any help...

If not, what about with the battery connected but fuse pulled and if that ain't ok I'll see if I can get the time to dig up above all the crap in the way to disconnect it, and I presume we're talking BOTH pumps, or not?

Lemme know... and as always TIA...

[lcoleman]

The fact that the test light only lights for 30 to me pretty much means that your wiring is as it should be. Like I said, even if there is voltage on 87 as being read by the (inaccurate :p) meter, there is no current available on the circuit to light the test light. Honestly, you can overthink and triple-check all you want, but I'd bet a dollar that if you put a 10A fused jumper (or a momentary switch if you want to be fancy) in there, the fuel pump will run.

Resistance between pin 87 and ground (not power) should be 1, ie. infinite, no connection. If there is some connection/measurable resistance, you may want to investigate the wiring to the fuel pump for a short. If I recall correctly, the fuel pump will have some resistance in the comm/brushes, hence my recommendation to unhook it. Pulling the fuse only tests the wiring forward of the fusebox, and not the wiring going back to the pump.

A chafed wire could blow the fuel pump fuse immediately, after a month, or it could be fine for the life of the car. Then again, your wiring might be fine. At some point, ya gotta just try it.

[IMSARS69]

The fact that the test light only lights for 30 to me pretty much means that your wiring is as it should be. Like I said, even if there is voltage on 87 as being read by the (inaccurate :p) meter, there is no current available on the circuit to light the test light. Honestly, you can overthink and triple-check all you want, but I'd bet a dollar that if you put a 10A fused jumper (or a momentary switch if you want to be fancy) in there, the fuel pump will run.

I think you're probably right, least 'bout some of it... pretty sure my (inaccurate meter) ain't never shown any voltage what weren't there EVER, but I reckon it's possible... if that were the case would ALL of my (inaccurate meters) show up this phantom voltage the same [ I don't think so... but then that's jes me... ] having several mfr over several years they are made by different manufacturers...

FWIW I'm not nearly as concerned as to whether or not the pump will run as I am what might get screwed up and hit me in the ol wallet what's on the pretty thin side being on a FIXED piddling income...

Resistance between pin 87 and ground (not power) should be 1, ie. infinite, no connection. If there is some connection/measurable resistance, you may want to investigate the wiring to the fuel pump for a short. If I recall correctly, the fuel pump will have some resistance in the comm/brushes, hence my recommendation to unhook it. Pulling the fuse only tests the wiring forward of the fusebox, and not the wiring going back to the pump.

That might concern me, but it was working jes fine and there's no reason to think a short has cropped up while jes sitting there with nothing to cause it, NORMALLY [ see comment earlier re personal life experience... ';) ]

I think the resistance would be a function of the motor guts as suggested.

As for pulling the fuse, note that my previous test was with the battery disconnected so no juice anywhere, pump or otherwise. My suggestion to try with battery hooked up and fuse pulled was if having the power off to the pump via no battery affected the out come of the test you had in mind, and I'm guessing from everything said it don't. So does one need to have the battery hooked up and the pump disconnected to get the proper test you're seeking?

A chafed wire could blow the fuel pump fuse immediately, after a month, or it could be fine for the life of the car. Then again, your wiring might be fine. At some point, ya gotta just try it.

I reckon I may give the ol fused jumper a try as I presume it's unlikely to allow any actual damage if we're wrong about some oddball thing actually going on here [ see life experience comment above... ';) ]

Will try to get back with any results if worthwhile and my impending loss of regular Internet access ain't too bad; i.e. have to use iPhone and iPad only...

Thanks again and any follow up on whatever other stuff raised in this latest post is appreciated...

[IMSARS69]

On the subject of inaccurate meters, why would I consistently get pretty obviously correct readings on batteries, which is what I use them for a lot, and never ever got anything out of the ordinary while testing automotive circuits of other devices in the past... only time I'm getting oddball readings is when checking AC to DC charging adapters which from experience vary all over the map for various reasons, such as whether having an actual charging load from something or not...

Riddle me that please, Sir!

[george graves]

Grrrr. This thread is getting slightly annoying, cause people are trying to help you....but you like to argue/question! That's ok. It's r3v, we've seen worse. We;ll still try to help. To a point.

Rewind, and remember this. There is a huge difference between "voltage" and "ability to do work". In electronics, there are two thing. Voltage and amps. The ~9 volt you are seeing on a pin may be "stray" voltage that is passing through another part on the car that is on the same fuse/ground circuit. (That's why I recommended you get a test light.)

EDIT: SIDE NOTE: Your super accurate HF meter (LOL - they cost $3.) You really think it's a accurate meter? My fluke 87-5 cost me about $400. I have another 5 1/2 digit meter that sold for about $12k back in the day. Please.....

Anyways....yes, it will read 9 volts (or 11 volts, or 5 volts or 2 volts....blah, blah, blah) but the circut it's on is not really "powered". But it's only a "phantom" voltage. That's why I suggested you use a test light.

See, there is more to electricity then voltage, there is also current. Think of a water hose. Voltage is the pressure, and current is the flow rate. So you could have a hose that has a ton of pressure in it (say 9 volts) but it was turned off at the tap a bit ago. There is pressure in the hose - but it has no flow....it will piss out a 1/2 cup of water before it quits.

Anyways. I forgot what I was going to say....Oh yea....voltage is not a measure of "doing work" what you are seeing is a something else.

Get yourself the electrical manual. It's a free PDF. That's what we all do to figure out these things.

[IMSARS69]

Grrrr. This thread is getting slightly annoying, cause people are trying to help you....but you like to argue/question! That's ok. It's r3v, we've seen worse. We;ll still try to help. To a point.

Truly sorry to have annoyed ya George... surely wasn't my intent...

And I do sincerely appreciate all the help, consideration and patience shown by you and the others who've taken their time to deal with this OF's 'annoying' questions, an yes sometimes an 'argument', as in 'here's what my personal knowledge and belief is' which may vary from what has been presented... which clearly shows that my engineering education and background weren't primarily EE... ';) I'm not completely ignorant of the basics and am very familiar with the analogy between electricity and hydraulics mentioned below, which was heavily covered in my field of expertise...

It's when one gets into some of the, shall we say, 'weirder' less encountered aspects of electrical phenomenon that po ol OFs like me find things a tad hard to quite understand... given that it's infrequently that folks such as myself find a need for such expertise is a good example of the value of the Internet, with its plethora of folks such as yourself who do understand and hopefully are willing and able to explain in 'simple' terms enough info for us to make it past one of these infrequent oddball scenarios what's been encountered an jes don't make no sense...

Really not looking to become an expert in the field as I've got way too much left undone and way too little time or resources to do any where near nuff of it... hence folks like myself seek 'the easy way out' so to speak... a matter of survival and maintaining some sanity in this increasingly waayyyy over complicated, interconnected world that on the one hand is jes great, but on the other can drive one nuts... ';)

So, as I asked, please except my apologies if my sarcasm and 'back in the day' kinda stubbornness has got yer panties all wadded up... I have had plenty of my share of attempts to help folks out who 'jes don't get it' at times, but I try cuz I know what it's like on both sides ah that deal... unless you're the fellow who wrote 'The BOOK', I'm pretty sure you've found yourself lacking a bit of expertise in some matter or other and found it expedient to seek help as I have... then again maybe not... ';)

Rewind, and remember this. There is a huge difference between "voltage" and "ability to do work". In electronics, there are two thing. Voltage and amps. The ~9 volt you are seeing on a pin may be "stray" voltage that is passing through another part on the car that is on the same fuse/ground circuit. (That's why I recommended you get a test light.)

Which I did as suggested and it made the point that there is in fact some strange goings on with that circuit... lesson earned as I say...

FWIW one might also rewind and note that I was dealing with a circuit that was part of a harness that was completely disconnected from all it's 'normal' connections, least wise those associated with the engine / engine bay, but not the rest of the componentry.

EDIT: SIDE NOTE: Your super accurate HF meter (LOL - they cost $3.) You really think it's a accurate meter? My fluke 87-5 cost me about $400. I have another 5 1/2 digit meter that sold for about $12k back in the day. Please.....

As I noted previously for the purposes I normally need a meter, which is mainly checking 'normal' voltage sources and continuity they work jes fine... other than the VERY oddball instances such as this latest scenario they have never ever let me down and always provided accurate and consistent readings that have served me well... when one is on a FIXED income south of the poverty line one doesn't spend hundreds of bucks for something they seldom if ever need when they can get a half dozen or so for, not $3, but FREE, one takes advantage of it, especially when it proves to serve their needs... your needs are obviously waayyyy more'n what the average OF such as mesef could ever imagine... ';)

Anyways....yes, it will read 9 volts (or 11 volts, or 5 volts or 2 volts....blah, blah, blah) but the circut it's on is not really "powered". But it's only a "phantom" voltage. That's why I suggested you use a test light.

See above... I asked the question because as I noted 'It jes didn't make no sense' least wise to this OF and thought someone, such as yourself had actually run into the specific issue and knew right off what the deal was... turns out so far as I can tell no one else has actually had reason to have checked out the specific circuits in question and what's been related to me are a lot of possibilities, which admittedly took some soaking in so to speak to relate them to this particular situation...

See, there is more to electricity then voltage, there is also current. Think of a water hose. Voltage is the pressure, and current is the flow rate. So you could have a hose that has a ton of pressure in it (say 9 volts) but it was turned off at the tap a bit ago. There is pressure in the hose - but it has no flow....it will piss out a 1/2 cup of water before it quits.

See above re personal knowledge and belief regards this quite appropriate analogy...

Anyways. I forgot what I was going to say....

An unfortunately that sheeet'll be happen'n more an more as time passes... ';) I kin definitely vouch for it...

Oh yea....voltage is not a measure of "doing work" what you are seeing is a something else.

And at the risk of further annoying you... ';) That would be?

Get yourself the electrical manual. It's a free PDF. That's what we all do to figure out these things.

See above re why this ain't all that easy... or more to the point, possible nor necessary at this stage in the 'game'...


So to the real question at hand, based on all the expertise presented, there's not likely to be no harm, no foul ta jes jumper the thing like most folks woulda jes done right off and never bothered ta worry 'bout what kinda v or amp reading one might get from the subject relay's Pins... and hence not come 'round bothering folks with inane questions 'bout weird stuff they didn't understand... ';) Right?

And thanks again to all for the input, consideration and patience... it is sincerely appreciated...