I would like to know how you would check the fuel injectors and coil with a ohmmeter.Please be specific, include which level to read on(high or low scale) and what the readings should be at.Thanks

 

I need to know the resistence on external coils(1988 TPI).

 

With high impedance injectors, they should ohm out at 12-16 ohms.

 

term [ A ] coil wire terminal
lllllllllllllllllllllllllllllllllll
[ B ]------[ C ]
[ D ]------[ E ]

A to C should read infinite (no reading)

B to ground should read infinite (no reading)

D to E should read zero or close to zero

If you don't get these readings replace the coil

Injectors should read 11 to 14 ohms, I don't use
them if they are under 12 ohms though.

 

Check the injectors while they are cold and jot down the readings.
Run the motor until it is warmed up and check them again, you will
get a lower reading when they are hot. Jot down the new readings
and compare them. They will all be a bit lower, this is normal. The
ones with the biggest variance are weaker than the others. If any
of them drop much below 12 ohms replace them.

 

The conductor in the injector should be copper which has a positive temperature coefficient. That means the resistance of the wire goes up as temperature increases.

 

Believe me. When an injector gets hot the resistance value drops.

 

Do you check them with the car on or off?

 

With the car off, pull the connectors and ohm check them and
write down the figures labeled from 1 through 8.

Plug the injectors back in and start the car and drive it around for
a while.

With the car off, pull the connectors and ohm check them and
write down the figures next to the origional numers you got
from the first check.

The "hot" figures should be within 1/2 ohm from the first set of
numbers. If any of them have droped below 12 ohms, they should
be replaced.

An injector or two with a resistance of less than 10 ohms will
eventually burn out the injector driver in the ECM.

I like to see injectors above 12.5 ohms. A new injector will have
readings between 15 and 16 ohms. The value drops with age as
the coil inside starts to break down and short out internaly.

As the resistance drops it not only increases the load on the
injector driver but also causes the injector to spray less fuel
causing loss of power because the orifice is not being opened
all the way because of loss of magnetic flux created by the
failing coil.

 

Oh, by the way a73camaro, any conductor will flow more current
when it is at a higher temp. Raising the temp of a conductor
speeds the frequency of the molecules which allows them to
transfer current at a higher rate, thus more current from a lower
working resistance at the higher temp.

Sorry to be so blunt but but it's late and I'm tired.
Put 2 trannys in the same piece of sh** Contour today.
The first one didn't shift right so had to put in a second one.

 

Actually it increases the energy in teh system, wich in turn allows the electrons around the Atoms of the element (Cu) in question to be less bound to the nucleus, wich Will let them escape and "flow" more easily...

But yeah thats basically it


Band-Gap theory.

This is how Semi Conductors work. At Room temperature their electrons are held too strongly by the nucleus, And not allowed to escape. Hence it dosent conduct well. As you heat the material, The electrons absorb the energy and eventually jump the "Gap" Into the "band" Of free flowing electrons, and all the sudden that Silicon is able to Conduct electricity.



look mom, I did learn something in College!

 

That's what I was trying to say but couldn't quite get it out.

It's nite nite time.

 

All i can say is, a lot of confused folks in this thread.
First i simply point to http://library.thinkquest.org/10784/phys7.html

And observe that a73 is correct. Copper has a positive temperature coefficient which does in fact mean that its resistance increases w/ temperature.

Why this happens is simple. Things actually work the exact opposite of how bort described them. When a metal is hotter, it does indeed have more energy. All the molecules come further apart as they all thrash about in their higher energy state. This makes the gaps paths that the electrons follows that much harder.
I also know that semiconductors work the opposite. For example, i know from experience that the write cycles on our radiation hardened SRAMs are longer at our best case characterization corner just because the resistance of the polysilicon resistors we were using increased to the point that it made it that much harder to flip the state of the RAM cell. Of course those of you not familiar with radiation hardened ASICs are thinking why the hell is their a resistor in a RAM cell.
I just did a quick simulation of an off-chip driver circuit to verify the conductivity characteristics of FETs. As i rememebered, more current flows at a lower temperature (only change was temperature input to the FET models, wiring and C stayed the same)

So you guys can argue all you want, but i can assure you that metals resistance increases with temperature. I even provided one reference source, and a quick search on google will give you plenty more. If an injectors resistance decreases when hot i would assume that it was starting to go bad as the only explanation that could be tendered would be that as the coils expanded they started shorting internally more.

 

I can not debate electrical conductivity of conductors with relation
to tempurature as I am not an electronics whiz. BUT, what I can
debate is the fact that an injectors resistance value WILL drop
when it's temp rises. How do I know this? Buy doing the above
test on countless cars through the years.

I presume the reason is because the coil starts to break down
and the coating on the wire deteriorates to a point that wire
windings start to touch each other thus reducing the resistance
value while also reducing magnetic flux which reduces injector
output.

A nasty side effect of this is, it starts to draw too much current
through the injector driver causing it to overheat and eventually
fail. Requiring a new ECM.

 

I wasn't debating your experience, i know what you're saying about injectors is true. I think the coil expansion / shorting factor explains this one pretty well. Especially since you typically see a worse change in R on injectors that are going south.
As nice as physics is, if you aren't accuratley modeling your problem you won't hit the right answer. I actually went and looked it up, and like i said, even ran a quick simulation here at work just because i wanted to make sure i was right about the general case. Even if the temperature coefficient was ( - )it still wouldn't explain that much change in R, you'd typically see more like 1.5% change per 40'C

 

I was just describing it from a Chemists Perspective, Weather it works that way in the real world is Beyond my experiance

If you Don't agree, Don't argue with me, argue with Dr. Singmaster. ( and the book Ive got right here )

Superconductors Decrease resistance as the temperature drops. Semiconductors won't conduct untill a certain temperature is reached.

That Much I KNOW is right.

But then again... this is Ed's Job

 

I'm out, this is beyond me.

 

Zimmer, have you checked the injectors yet?

What symptom does your car have if any?

 

Thats what i said. When temp goes up, resistance egenrally goes up as well. Except certain things.

 

Like ed's mom For example. The Hotter She gets, the less resistance she puts up to getting naked....


But thats a Fairly specific example.

 

Quoting my eight year old daughter.

"That's below the line"

 

Now ya'll made me whip out my college Physics book.

Serway Physics - 1990

Temperature Coefficient of Copper (a) is +3.9 x 10^-3

Resistance of a conductor based on temperature differental is

R = Ro (1 + a(T - To))


Say Ro = 12.0 ohms at 70°F

We measure the temperature of the injector after running for 20 minutes and find that it is at 100°F.

Plug and chug

R = 12.0 (1 + 0.0039(100 - 70))

R = 12.0 (1 + 0.117)

R = 13.4 ohms


As a typical metal conductor warms up, the molecules become more excited and bounce around more. This increases the number of collisions that occur between the conductor atoms and electrons. These collisions impede the flow of electrons. Hence the resistance of the conductor increases.

You can cool almost any metal to close to absolute zero and it will become a superconductor.


As for the injector's resistance decreasing as temperature goes up due to internal shorting, I'll buy into that. Another test would be to measure the inductance of the injector. Inductance is based on the number of turns within a coil. If coils are shorting out against each other, then the number of turns that current flow through will be less, lowering inductance.



BTW, what the hell is "frequency of the molecules"

 

BTW, what the hell is "frequency of the molecules"

Hell if I know.

Actually that was 20 something years ago, when I was doing that
crap, I guess the old memory aint what it used to be.

 

Close, except for the coefficient is in ohms/' celcisus. And 0.0039*30 wouild be 0.0117, not 0.117

 

Thanks Ed. That 1.2 ohm increase seamed like a lot. I didn't double check my math.

And I jacked up the units as well.

I'm fired!!!