Andy A

94 3vze. Recently the truck started throwing a code 14. In checking the primary coil resistance I am a little confused. The Hayes manual states the primary resistance should measure between .36 and .55 ohms. This is to be measured across the + and - terminals. When I attempt this my multimeter starts with some resistance but drops to 0 and stays there. When I check the secondary resistance from the coil tower to either the + or - terminal I get 11.73 k ohms which is in the spec range of 9 to 15.4 k ohms. Am I doing something wrong in checking the primary resistance or is the coil bad.

thanks in advance
Andy

MudHippy

The ohms shouldn't decrease during measurement. So you might be doing something wrong in checking the primary resistance, or the coil might be bad. Or both, I don't know.

What I do know is, you're definitely doing something wrong by checking the ignition coil resistance. Since code 14 could only be caused by the igniter, not the coil. It's happening because there's no IGF voltage signal being recieved by the ECU.

To troubleshoot the issue you need to do as the fsm says on page EG2-195.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf

Andy A

Mudhippy reason I bring up the coil is from doing various different searches on the subject. I ran into about 4 different issues that were causing a code 14. 1 as you mentioned the igniter, 2 the coil, 3 the O2 sensor wire shorting and 4 being the distributor. So I figured I would try and check them all which is why I brought up the coil and it being very easy to check.
Checking the primary resistance should be just as easy a checking the secondary resistance just different contact points. What I do know and you somewhat confirmed it, is that for the primary resistance there should be a constant resistance between the + and - terminals and it should not drop to 0. As per the manual it should range between .36 and .55 ohms which I am not getting after multiple attempts with multimeter. What I can assume is that the coil is possibly bad/going bad due to the 0 resistance reading and needs to be replaced but that it may have nothing to do with the code 14,
Will move on to checking the igniter and thanks for the link.

yoder519

If meter jumps around like that, it maybe be a bad coneection inside the coil, especially if it reads a certian amount of ohms then goes to zero

MudHippy

Are you measuring the resistance without first unplugging both the igniter connector(at the wiring harness) and the HT wire from the ignition coil to distributor cap?

Like the FSM says on page IG-22 here.

If not, that could potentially affect the measurement.

Andy A

yoder519
it initialy reads a resistance then continues to drop to 0 and stays there until I remove one of the probes. Wash rinse repeat. Although secondary checks out fine.

Mudhippy
yes, as per FSM. Something just not adding up, no primary but spec secondary.

At least the coils are not to bad in price, Advance has one for about 47 and there are some coupons floating around. Not sure about quality but if it works it works.

RJR

I expect you're just seeing the inductance of the coil. At such low resistances, the inductance of a large coil like that is significant, and impedes (resists) the current flow from the meter until it sits on it a while and reaches steady state.

Most meters can't measure resistances in the .5 ohm range accurately anyway. The eventual zero answer you get to may be your meter's best try at that low a reading, once the current stabilizes.

RJR

RJR

Bottom line, there's probably nothing wrong with that coil.

RJR

scope103

Unless you have a (relatively) fancy micro-ohmmeter with a 4-wire (Kelvin) connection, you can't measure 0.36 ohms. The resistance of the leads on my good (non 4-wire) multimeter is around 0.7 ohms. Add to that the resistance of the connection to the coil. Why they put that measurement in an early-90s manual is a mystery to me.

RJR is probably right; your meter is trying to give you what it believes to be the most accurate measurement it can do: 0 ohms.

MudHippy

It doesn't really matter what the primary resistance of the ignition coil is, unless maybe it were extremely high. And since the engine runs, it's safe to say it's probably not an issue. Atleast not a major one.

Anyway, it's almost certainly not THE issue(cause of code 14). Which is most likely caused by the igniter(internal circuitry), and/or the IGT or IGF circuit(s) between the igniter and ECM, and/or the ECM itself. As for the IGT circuit, the ignition switch itself can be ruled out entirely, since it runs(and/or code 14 is present). And, based on the same theory, it can also be reasonably assumed that the ignition coil and distributor are functioning correctly, and/or that the IGT circuit(as a whole) has no faults. As such, it's more than likely caused by a fault in the IGF circuit(within the igniter, and/or between the igniter and ECM, or IF NEITHER OF THOSE then within the ECM).

Here's a pic showing those circuits.

Andy A

Mudhippy, Scope103, RJR, and yoder thanks much for your time and suggestions.

Scope103 and RJR you are probably right, the meter I have probably will not read that low of a resistance and the coil is fine and I need to look elsewhere as Mudhippy suggests and more than likely at the igniter.

Pretty much everything on the truck is close to 20 years old with 230000 miles now and things are starting to wear(original ower). The motor was replaced by toyota at approx the 10 yr/100000 mile mark under the head gasket program and I had to do a head gasket replacement approx 2 yrs ago. So the majority of items on the truck are still original.

Mudhippy I will work on checking/replacing the igniter. Will probably just replace it and go from there. They seem to run in the 150 to 200 dollar range, and one manufacture is probably no worse than the other.

again all thanks for your help
Andy