Hello,

This is my first post and I hope I am posting it in the right sub-forum. My 1999 Mazda B2500 (2.5 liter engine) stalled suddenly while driving. After stalling, it will crank and not start. I got it towed to my mechanic and he has not been able to diagnose the fault. There is no spark. Here is what he has tested:

1. Fuel pressure is not a problem
2. He swapped coils with new ones just to check and did not help. He then returned the coils.
3. He also tried changing the PCM/computer with a new one, still no spark. He put the old computer back in the truck.

He has given up and now I am taking up the challenge. I learnt a lot from this forum, and have tried so far.

1. First, I noticed that the battery was very weak, so I got it replaced under warranty.
2. I swapped the PCM relay with the blower. Actually I was not sure about the blower relay (The fan makes noise but I don't feel any air, I am not sure why), so I replaced both PCM and blower relays in the engine fuse box. The diode next to it also seems to be working and I hear click when I remove and put it back.

3. I checked primary and secondary coil resistances. The exhaust side coil seemed to have a lot of rust on the connecter and the connector was cracked, so I replaced it. Although this might be 63 dollars wasted.

4. The mechanic said he was getting fuel pressure, but I checked the inertia switch anyways. It is in down position and I reset it just to make sure.

5. When I turn the key to ignition (without starting), I do get check engine light. Does this simply mean that the light is working or it also means that PCM is getting power?

I don't know how to proceed to check the cause for not getting spark. Next I will check if I am getting voltage on the primary coil (Should I expect it to have voltage with ignition switch on, or only when someone starts?). I will continue diagnosing but I thought I would post here to get more ideas.

Thanks a lot for reading my post!

 

One more thing, when I connect the scanner to the OBDII port and test live data, I do see rpm (few hundreds, as expected from the starter cranking the engine). So I suppose the crankshaft position sensor is working.

 

I did the following tests:

1. Check if the primary coils are getting voltage with ignition on. When I connect the red wire to the middle wire of the connector and black to battery's negative, I do get 12+ voltage, so the primary coils are getting power with ignition on.

2. I found elsewhere (Explorer Forums?) that I can check if the PCM is getting power by seeing if the throttle position sensor is getting 4 volts reference voltage when ignition is on. It is getting ~ 4.5 volts, so I guess PCM is getting power.

Still lost on how to solve this no spark issue!!

 

I did the following tests:

1. Check if the primary coils are getting voltage with ignition on. When I connect the red wire to the middle wire of the connector and black to battery's negative, I do get 12+ voltage, so the primary coils are getting power with ignition on.

2. I found elsewhere (Explorer Forums?) that I can check if the PCM is getting power by seeing if the throttle position sensor is getting 4 volts reference voltage when ignition is on. It is getting ~ 4.5 volts, so I guess PCM is getting power.

Still lost on how to solve this no spark issue!!

 

Just a heads up on the 2.3l and 2.5l Lima engines with dual spark plugs

Only the exhaust side coil is active when starter motor is, so for start up intake side coil will have no spark, this is to give a Hotter Spark, all the voltage goes to one coil pack not two
Intake side will start working at about 400rpm, engine started

Assuming a 1999 2.5l
The ICM(ignition control module) is in the PCM so not much you can check as far as spark control

Exhaust side coil needs 12volts with key on
PCM then Grounds the other 2 wires on the coil to power up and then Cuts the Ground to spark one of the two coils in that pack.

So with a No start(spark) focus on Exhaust side coil only

If the CEL(check engine light) comes on when key is turned on then PCM is powering up

Also test battery, 12.3volts key off is minimum battery voltage, below that there may be no spark.
Starter motor uses alot of AMPs so battery voltage will drop by 2.5 volts when starter motor is active, if voltage drops to 9.5volts PCM and coil can't provide spark, no lower than 10volts while cranking is spec

Mentioning this because of your TPS reported voltage, should actually be 5volts not 4.5v, so test battery

 

Thanks RonD,

Yes, I have been checking the exhaust side (going to spark plugs on the passenger side) coil only, as I had read that only the exhaust side gives spark with the starter on in Haynes manual.

The battery is brand new (got today). The battery voltage with everything off is 12.6 V. I will recheck the TPS voltage. 4.5 was what I remembered approximately, it might be closer to 5. I will recheck tomorrow.

Good to know that the PCM is powering up, based on the CEL.

Any other tests I can try? I am now clueless. I have checked all the PCM related fuses. The mechanic had already tried new PCMs, so I don't know what else I can try.

 

With the factory service manual or equivalent and the proper tools it should not be too hard to get your truck running or at least find out what is wrong.

From what I have read you do not have a full understanding yet of what the truck is or is not providing to make the truck to run.

You have no spark great that is good to know but you need to know more before grabbing for part replacements.

From your post I can see the fuel pressure is claimed to be good, ( what is the pressure )

Are the injectors getting a signal from the computer to open and close ( did you or the mechanic check this with a noid light ? )

Does the engine have compression? has a compression check been done?

If the teeth are stripped off the timing belt you will not have compression, spark or injector reference pulse.

It sounds like the incredibly simple basic checks have been overlooked by your mechanic or not reported to this thread properly by you.

let us know about these basic test.

If your mechanic skipped these test or worse did not know these test should be done, ( find a new technician not a mechanic to work on your truck in the future ) .

 

Thanks EaOutlaw,

Sorry if I missed some details, I am mainly trying to diagnose the no-spark condition, so did not include all the details.

1. The fuel pressure on the fuel injector rail is 40 psi. I know this is lower than spec, but should not affect the spark issue.

2. Yes, he did check for injector pulse and he was getting injector pulse.

3. Mechanic or I did not check compression. I have the tool and can check it, but could you explain why should I? I am not getting spark when measured using a spark tester on the exhaust side (which is supposed to spark when the starter turns the engine) and I thought any other issues should be dealt after the spark issue is resolved.

4. The timing belt appears to be in good condition. Actually it was recently changed (few thousand miles)

5. I guess discussion on the semantics of technician vs mechanic deserves a separate thread :)


I forgot to mention one more thing. Both mechanic's and my scanner do not give any error codes! I have a generic scanner. I am mostly familiar with European cars like BMW, VW and Audi and for those cars the generic scanners often do not give complete information and I had to purchase BMW/VW specific scanner or software. Is this true for Ford? Is there any Ford/Mazda specific software or tool that is needed. Any recommendations?

 

Both Coil packs are powered by Fuse 19(25amp) located in the Cab fuse panel

You should hear the in tank fuel pump "HUMMMM" for 2 seconds when key is turned on, and each time key is turned on, so repeat as you see fit to confirm you hear that, that indicates PCM is Booting up and running its startup routine.

Use a test light or volt meter on the Exhaust side coil pack 3 wire connector
Center wire will have Battery voltage(12.6v) with key on, connect tester to this wire

Connect test light/meter's other wire to EITHER of the other wires, tan/white or tan/orange in my diagrams
This is the Ground wire from the PCM
When you crank the engine the PCM should Ground and Unground this wire to spark the coil, so flashing test light or jumping meter voltage

An ignition coil has worked the same way since the first gasoline engine.
The Primary coil inside has a few windings, it gets 12volts, that voltage creates a magnetic field
The Secondary coil has many more windings than Primary, and is "charged up" by the magnetic field of the Primary.
When power is CUT to the Primary coil the magnetic field collapses, with nothing to hold the "charge" it is sent out to a Spark plug(ground)
Then Primary coil is powered up again and process is repeated
The Ground of the Primary coil was used to CUT power because it is simpler to use, i.e. the "Points" in an older distributor, isolating 12volts is harder than isolating a ground
The Points were the Ground for the Primary coil, as distributor rotated the points were pushed open, cutting power and sending a spark out, then allowed to close to power up Primary again.
With Electronic systems a transistor takes the place of the Points, cutting the Ground for spark then Grounding again.

But the ignition coil itself has not changed in 100+ years, certainly better and more reliable, but internally they are the same as they have always been.

So you are testing to see if the Transistors inside the PCM are Grounding and unGrounding the Primary coil in the coil pack, thats what "makes the spark"
Similar to testing for fuel injector pulses.

Pins 26(tan/white) and 52(tan/orange) on the PCM are connected to the transistors inside the PCM, so you may want to test that end of the wire to the coil pack wire of the same color with an OHM meter, 0 OHMs is a good connection, could be wires in the harness are damaged.


If possible pull out 1 spark plug, check its tip, wipe it off
Re-install, now crank the engine over a few times
Pull out same spark plug, it should be WET with gasoline
If it is then PCM is getting timing pulses so should also be sending out Spark Grounding/unGrounding to the Coil Pack
If spark plug is DRY then PCM doesn't even "know" you want to start the engine, no timing pulse from Crank or Cam sensors, so no spark along with no fuel

 

Thanks RonD, These are some great troubleshooting instructions and they will be useful for many ranger-owners! The good news is that I got the spark, but perhaps it is too weak or there is something else going on. I have one question regarding voltage between the middle wire and the wires on the outside in the primary coil connector, but I thought I will reply to all your suggestions for the benefit of future readers of this thread.

Checked, Fuse no 19 is good.

Yes, I do hear the fuel pump humming (by putting my ear near the gap between the cabin and the bed, while my wife started the ignition).

I used a voltmeter, and with ignition on I do get 12.6 volt (red on middle wire, black on negative of battery)

This is where I was not too sure. I measured the voltage by poking the multimeter's terminal into the insulation of the middle and outer terminals (didn't have a piercing probe handy). When the engine was cranked, the voltage fluctuates, but only in the range of 0.4 to 1.1 or something close to that. I was expecting it to go from zero to 12 V. What should I expect?

I thought it will be nice to check the spark one more time. I did and I got a spark! I don't know how bright it should be, to me it appeared weak. It was getting dark, so I was able to see it. I was cleaning the connections with electronic parts cleaner and emery paper while diagnosing, so I am not sure if better connections was reponsible or I just missed the weak spark while checking earlier due to brighter daylight.



I did this since I was unsure about the grounding and ungrounding voltage test and continuity between PCM terminals 26/52 and primary connector is good.


Done, The spark plugs are getting a little wet. I only checked no 3 spark plug on the exhaust side (which is easiest to access, 4 is not bad either though). But the spark plug appears to be in a really bad shape and it appears that the electrode is worn out. I will go buy a new set of plugs tomorrow, and hopefully if I get an answer on the amplitude of the fluctuating voltage on the primary coil upon cranking, I will be able to troubleshoot this further and hopefully start the truck!

Thanks everyone for your help.

 

This is where trying to help people online becomes frustrating, If the person needing help leaves out key information, how is someone supposed to help them effectively?

Your saying in one hand that you do not have spark and are questioning why I would do basic tests, yet to only find out your engine is getting spark.

Problems like yours is the exact situation where you need to know exactly what is wrong and what is right with the truck.

Critical need to know basics for any fuel injected engine with a no start condition is, fuel, injector reference pulse ( part of the fuel test ) spark,and compression.

The number one reason for performing a compression test on each cylinder when you have a no start condition is to confirm the health of the engine.

A compression check is one of the basic checks any competent mechanic will do while diagnosing a no start condition.

Doing a compression check also gives the technician a opportunity to read the spark plugs which can further help with diagnosis and determining the health of the engine.

Performing these basic test recording the results is less time consuming than
getting overly technical braking out a DVOM and checking all sorts of readings for no reason at all or worse parts swapping in hopes of skipping a few basic test.

Once you know for sure what is missing from your truck fuel spark and compression then and only then can you perform the correct pin point test
that will give you a accurate diagnosis and timely repair.

Right now from what I have read low fuel pressure and possibly flow that your blowing off as a secondary problem may very well be your primary and only problem.

Please lets try and keep this simple and focus on the basics, then progress quickly to the correct pinpoint test you need to focus on.

I will mention while doing these basic test it is important to use quality known good and known calibrated tools for diagnosis.

A junk diagnostic tool will cost you more time and money than buying quality tools from the start.

 

You can remove the coils 3 wire connector for testing, and yes coil voltage will not change much when cranking, each coil sparks every 1 RPM, (waste spark system), so if cranking at 200RPM thats 200 sparks per MINUTE, lol, so not alot of down time for meter to go to 0volts, fluctuation means PCM is pulsing the ground

Glad you have spark
Blue/white is the color of good spark
Yellow is weak spark

Ford is using a Waste Spark system on your model, most models in the Ranger line
So TWO spark plugs on each side spark at the same time, exhaust side 1 and 4, and then 2 and 3 spark at the same time.
So they are splitting the spark power.
Not a weak spark but enough to start cold engine.
But this can lead some mechanics to confuse no spark issues since spark travels differently thru the system

Spark travels from 1 spark plug wire at the coil pack to the spark plug, and jumps the gap to ground(engine) then travels THRU THE ENGINE to the other spark plug on that coil and jumps the gap traveling back thru the spark plug wire to the coil pack

So Series wiring

One spark plug sparks from center to tip(normal spark), the other one sparks from tip to center(reverse spark)

testing for spark you need to ground spark plug to the Engine, not the battery to see spark level

 

Thanks everyone. Since I was getting erratic results with the voltage fluctuation at primary (and getting very little voltage), I replaced the PCM and now I am getting little less than 12 volts between the middle and side wires of the primary coil connector. I can see it fluctuating but fluctuation is very little, which is probably due to it doing it more than 3 times per second as RonD explained.

I am getting spark, but as I said I doubt it is too weak (I a using a spark tester, not touching the plug to the block).

I have one question. I get voltage between the middle wire and outside wire of the primary connector when it is NOT connected to the coil, but get 0 reading when it is connected (by measuring on the punctured wires outside the connector). The coil itself is new and I had checked the resistance both on primary and secondary side before installing.

Is this normal or abnormal behavior? I am confused because I am getting weak spark in spite of this.

If I should see voltage fluctuating even when the connector is connected, My guess would be that the connector is not making a good connection with the primary coil. I was able to get voltage by poking probes into the connector, but it is still possible that it is not making a good connection.

Please advice and I will change the connector if necessary. I am surprised that this little connector is 38 dollars at auto zone!

Duralast Ignition Coil Connector 1091 - Read Reviews on Duralast #1091

Thanks

 

The Primary coil is about 1 OHM, volt meter has higher OHMs so it doesn't cause a short circuit when testing voltage.
So you wouldn't see voltage or fluctuation when Coil is connected, electricity travels on the path of least resistance, which would be the 1 OHM coil primary.

Center wire should show FULL battery voltage with key ON, no loss it is a direct connection.
PCM is the Ground, and it has several Ground points that are NOT shared inside the PCM.
This thread: 104 pin PCM Pin layout | Ford Explorer and Ford Ranger Forums - Serious Explorations

Lists the PCM Ground pins and wire colors, I would disconnect battery, then test each Ground wire at the PCM, 0 OHMs to engine

 

Thanks RonD,

I noticed that my battery has lost some charge from sitting for a week and all that cranking and I am going to repeat the tests after I charge the battery, but I am sharing what I just found:

1. Battery has 12.3 V (without anything on)
2. When the ignition is on, the battery voltage drops to like 12.05 V
3. The voltage between the middle and side wire on the primary coil connector with the ignition on is 11.67 V

So it is surely not FULL battery voltage. Any suggestions? I will check the ground points in PCM later tonight and get back to you.

Thanks!

 

Yes, that is quite a voltage drop, cranking voltage would be 9volts at coil, maybe under that

Charge battery and then see what it is

 

Thanks. Ok so now I fully charged the battery overnight and did the readings again.

1. Just after charging, the battery (not connected) voltage is 13.1 and also charger was showing full charge.
2. After connecting and cranking for say 10 seconds, the voltage on the battery (without key in the ignition) is 12.95
3. When I put the key in and turn on ignition, the battery voltage is 12.67, so very similar drop to last time (around .3 V)
4. With ignition on, the voltage on the primary coil connector is 12.24, I checked on both sides and it was the same.
5. Upon cranking, the voltage fluctuates from about 9.7 to 9.4

I have to say that the fluctuation measurement is not accurate. First, simply due to the fact that it is changing fast and also I am just trying to keep the connection using multimeter prongs on wires through the insulation while the whole thing is shaking, but it does show that it is changing and seems to be close to what suggested.

If you think all this is normal, now I can go diagnose on the mechanical issues (compression, etc).

Also, I noticed that the connector to the primary coil has broken tabs so it doesn't click. As I mentioned before this can result in loose connection. I will change it or at least zip tie or something, but after I cranked it was still sitting there snugly.

THanks!

 

Based on RonD's suggestion, I went ahead and checked all the ground connections from the PCM. I followed the circuit diagram given in Haynes repair manual. All the terminals that are supposed to be ground show good ground with the engine (except for 33, which is actually absent in the wiring harness).

So I am still struggling with this truck and I think the problem is still a very weak spark. (I can see the faint spark only if I put my hand around the tester. I hear I should easily see the spark).

I also checked fuel pressure and it s 55 psi on cranking. Also compression is 150 (I haven't checked all the cylinders since I didn't have an assistant).

It still looks like a spark/electrical issue. Any more tips? This has been really a difficult problem.

 

Batteries need to sit a few hours after charging to get a valid storage reading

This is why it was dropping so fast when you connected it and used it

9.5v cranking should be OK

To see what kind of spark the coil can generate hook up your spark tester
Unplug the coil pack wires
Have a 12v and Ground wire that will reach to coil pack
Center pin on coil pack is the 12v
outside pin is the ground for the two spark plug wires on that side

Apply the 12volt to center pin
Then touch Ground wire to outside pin and pull it off, should see nice bright spark, each time you remove the ground wire
The two spark plugs are wire in series so the "other" spark plug MUST BE hooked up to complete the circuit thru the engine block

 

Thanks. I understand that this procedure will tell if the problem is after the ignition coil or before. Correct? Pardon my ignorance, could you please confirm if I am understanding this correctly?[QUOTE=RonD;2123800]

So this means one end on the spark plug and the other end on the spark plug wire that is coming from the secondary coil. Right?
You are referring to the primary coil connector, right?

Thanks for reminding. Yes I have been testing one spark plug while all others are connected.

 

Yes, to all

The Primary Coil gets 12volts and a ground, this causes it to generate a magnetic field and charge up the secondary coil
When Primary's ground(or 12v) is removed the magnetic field collapses and the Secondary's charge is released, to the spark plugs

Now when the Ground is removed from the Primary there is a Voltage spike so you should see a spark/arc between ground wire and pin, and the spike can ramp up Primary to 250volts, which also spikes Secondary when released.

The winding ratio between Primary and Secondary is what sets Spark plug voltage out
100:1 is common in most ignition coils
If Primary has 100 loops/windings, then secondary would have 10,000 loops/windings
So 250volt spike would result in 25,000volt spark at the plugs.

Low voltage spark could be from Transistor that UnGrounds the Primary, it isn't cutting it completely so no spike to 250volts in primary, might be 100v or less so weak spark
Each coil in the pack has its own transistor in the computer that cuts Ground

The spark/arc from unGrounding the coil is what caused the Points to wear out in the old distributors, just eats away at the metal pads, much like how spark plugs still wear out from the arcing.
Transistors are better but no electric circuit is immune to this type of arcing if a connection is loose, or corroded.

All this grounding and ungrounding happens in milliseconds when engine is running
At 800 RPM(revolutions per minute), with Waste Spark system(1 spark per TDC), each coil in the pack is sparking 13.3 times EACH SECOND, at 3,000RPM it's 50 times EACH SECOND

 

Thanks RonD, That was useful and quite educating.

I performed the test and also have repeated some tests I did earlier, now with a test light:

1. Sparking the 12 V (red, middle) wire and the ground wire on the primary coil did give a nice spark on the spark tester. So now it is clear that there is no problem from the coils to the engine. Additionally, now I know how a good spark looks like in the tester and can confirm that the spark that I get by connecting the tester and cranking is extremely weak and actually almost impossible to see in bright day light.

2. Additionally, I repeated some tests on the wires coming going to the primary coil. My earlier tests were giving ~ 9.5 V on cranking, but I was never able to confidently tell if it was actually fluctuating, because the change on the voltmeter was very low and of course because it is changing more than 3 times per second (plus all that shaking when the engine is cranked). So I bought a test light and repeated some tests. I still don't understand everything, so please let me know if this is normal or not.

I did learn that in some cases a light can be much more useful than a digital multimeter. Also, I cut the wires going to the connector since I was anyways going to change the old connector and I wanted to make sure I make a good contact.

A) When using voltmeter, with the ignition on, there is a 12.2 V voltage between the red wire and the 'ground' wires (the tan wires going to primary), but when I test using the light tester, I do not get any light. This kept be baffled for a long time (the light is a simple 6v/12V test light and it should light up even if there is no full charge) and I then did some additional tests:

B) connecting the test light leads to the red (middle,12V) wire and the ground (or negative terminal) gives a fat light on the tester, but when I connect it between the 'ground' wire and the positive battery terminal, I do not get any light. Then I connected a voltmeter between the 'ground' wire and the positive battery terminal and I do get 12.4 V, but as soon as I connect the light tester in parallel, the voltage drops to zero (and also I do not get the light). So this means that as soon as the circuit is completed, there is no potential difference. (Repeating the parallel circuit test using 12V red wire and the ground gives a light and a potential drop in the order of 1-2 V, which is expected)

I also checked that the voltage between the 'ground' wire and the engine ground is 12.2 volt. My understanding is that this is all normal if the "ground" wire remains at ~ 12 v normally and if it becomes zero only when it is grounded ( by the PCM).

I repeated the cranking test with the light tester, and still there is no light fluctuating. So the problem still seems to be coming from the PCM, but since it is a new one, I am really confused.

I asked my wife to check if the PCM relay clicks when I put the ignition on, and it does click.

What else can I check?


Thanks,

A very confused ranger owner

 

PCM gets timing pulse for spark and fuel injectors from the Crank sensor.

I think you checked before if spark plug was wet after cranking, that would mean Crank sensor was working, dry spark plug would mean no timing pulse is making it to the PCM

About all that left is the wiring to the PCM from the coil pack, need to pull off PCM connector and see if the 2 Ground wires are 0 OHMs, a good, no loss connection

 

Yes, I had done the wet plug test earlier, but will repeat. Also, when I connect my OBD 2 scanner and look at live data, I always get RPM. I guess this means that the crank sensor is working right?

 

Hi

I repeated the tests. Spark plug is getting wet on cranking and the tan/white and tan/orange (26 and 52 on pcm) is indeed grounded.

Can you confirm if the tests I reported in my earlier post shows normal behavior?

Thanks