I just joined the forum and hope some one can help me. I have a 1999 f 150 with a 4.2. I am not getting any fire. I tested the coil and got a reading of about 13.5 ohms for secondary resistance on all three tests. Is that about right ? I got a primary resistance reading of right at 1 ohm. OK ?


My big problem and question involves the 17 volt reading I am getting from all 3 pins when I tested the drivers from the computer at the connecter going to the coil. My understanding is ( the connector pins going into the coil) #4 is power in from the ignition switch and #!, #2, and, #3 are from the computer, complete the ground from the coil, and should read 0 voltage. Why am I reading 17 volts ? I tested with 2 meters and both read 17 volts.


HELP PLEASE !

 

Somebody ?

 

This ain't twitter, there should be no expectation of an answer in only an hour and forty minutes.....

Don't know about the coil resistance readings, never waste time taking them.

Measure the battery voltage and see if your meter(s) read the correct voltage. If so, there's something wrong with your testing procedure (most likely, insufficient details were provided).

 

I checked battery voltage and the battery is actually a little low (11.something volts) from attempting to unsuccesfu)y startt. If you want to use that as a test for the two meters I used then my meters are fine.

You seem to be saying that if my meters are good then something is wrong with my test procedure as I can only assume , you don't think I can be getting a true reading of 17 volts from the computer drivers to the coil. Is that your opinion ?
What more details do you think I need to provide ? Do you understand the way the ignition system works on the single coil 4.2 ? There should be no current present on 3 of the pins on the connecter to the coil as they are grounds going back to the computer.

I am thinking the computer is bad and or somewhere a transformer is causing 17 volts to get in to the circuit.

 

Yes. What is your testing procedure (meter connections, testing conditions, etc)? There may well be a plausible reason the meters are giving that reading, but the provided data is insufficient to form any reasonable hypothesis.

Yes, I do understand how it's supposed to work. I've been working on this style of ignition system since my 89 SHO. I've been doing electronics testing for four decades, I do have some background.

Insufficient data for the first assumption, the second is unlikely. The only transformer in the system is the ignition coil.

It would likely help to go back and provide the history of this project. The details provided are pretty sparse as to how you got to your current point.

 

Only thing I have to say is you cannot get 17 volts DC from (this) auto or engine control system unless the regulator on the alternator is faulty allowing the alternator to run full output with no control, >>>>when the engine is running.
A condition like this will cook the battery in time, run the head lights and lighting system over bright and apply excessive voltage to all systems.
Good luck.

 

I'm under the impression that the engine doesn't run, so I didn't bring up that as a possibility.

 

I was telling Tnalan that he can't measure this much with the engine off and it would be a fault if he did, with the engine running.
No problem.
He must be reading the meter wrong or the meter is out of calibration.
Good luck.

 

Seems to me you need to charge or replace the battery if you are only getting 11 volts. That may help solve your problems.

 

My original post stated that I was not getting any fire. That is how I got to this situation. The truck wouldn't start. I used a timing light on several ignition wires and the light would not come on. I tried the timing light on my Chevy Truck, which does run, and the timing light comes on. I then concluded that my timing light works and that I am not getting any fire from my coil on my Ford F150.

I tested my coil s primary and secondary resistance and it seemed with in reason as I notes in my original post.

I then wanted to test the signal coming in from the computer to the coil at the connecter going into the coil. With the ignition switch to the on position I probed the pin in the connecter which I believed was power in from the ignition switch. I had my negative lead on the negative post of the battery. I got a readireading of 17 volts. I wasn't sure if I was on the right end of the connector for the ignition switch ( I wasn't) so I probed the pin on the opposite end and got 11.57 volts. I then decided to check voltage on pins #2 andb#3 and also got 17 volts. I then got a second meter that I keep in my truck for work and got the same results. When I did all of this resting the truck had been sitting 24 hours since last ran ( last time it would run).

This morning I deciddecided to double check everything and got 15.5 volts on the ground pins going back to the computer with the ignition switch in the on position instead of the 17 volts yesterday. I read 11.57 on the pin from the ignition switch. I then turned the ignition to the off position and got a reading of 0 volts from the ignition switch pin and 2.5 volts on the other 3 pins going to the computer.

My battery voltage is reading 12.59..

I decided to try a test light and got unusual resulresults considering my meter readings. With the alligator clip attached to ground and probing the 3 pins going back to the computer the test light would not light with the ignition switch on or off. Testing the ignition pin with the test light causes it to light with the switch on and not light with the switch off.

I connected the alligator clip to the positive post of the battery and probed the pins going back to the computer and it did not li g ht with the switch off and did light and stay lit constantly and steadily with someone else holding the switch to the start position for a few seconds. This was the result on all 3 "ground pins". .

My thoughts now are that I have no idea why my meter readings are showing voltage from the coil connecter going backto the computer and that since my light is staying on while the switch is in the on position that the computer drivers are not opening the circuit and firing my coil.

Sound right ? Crankshafthe position censor possible cause ? Definitely compute ? Oh yeah II'm in a little pain. I broke my big toe today. Thanks for all comments !

 

Now start all over on this problem.
The PCM must get power through a relay in the distribution panel when the ignition switch is on.
Next, the system uses the crank sensor as a reference as cranking begins.
This sets up the fire order and fuel injection in the same order but offset in time..
Check the crank sensor plug seating.
Re set the PCM relay or swap with another relay to be sure.
It appears there is a basic loss of power to the PCM or the crank sensor is not supplying pulses to the PCM.
Good luck..

 

That appears to be an illogical result although, perhaps, it was the residual charge on a capacitor. Was that with the coil connector disconnected or were you back-probing the wires with the connector still on the coil?

Certainly possible. What is the state of the CEL when you turn the key to RUN (pause several seconds), then START, then continue cranking?

No, insufficient data to suspect it.

Ouch! Hope it wasn't from kicking the truck....

 

I can't add anything intelligent here to the diagnosis, but wanted to let the OP know that he has 2 of the BEST guys here helping him. Follow everything they tell you to do and provide them with any info they ask for............they will get you through this.