: No Fire from 1 coil pack! ?'s about ignition!

01-21-10, 05:57 PM
'95 Eldorado, car was fine when I parked it, but the next I started it there was an obvious misfire of at least one cylinder.

When I checked it the coil pack for cylinders 6 and 7 was not firing, so I swapped it one of the others. I had the same problem, no fire from the swapped coil pack, but the original worked fine.

Next I swapped the ignition control module with a known good one and still have the exact same problem.

There were no codes, although I now have P119, Open or Shorted Fuel Injector, because I have disconnected the 6 and 7 injectors to keep from from throwing raw fuel into non firing cylinders!

Anyone seen this before? How do I track down the problem?

I am familiar with wasted spark ignition, but I have questions about what I have now! Still I am much more familiar with engines that use a distributor. I have used aftermarket computers, such as SDS and MegaSquirt to run engines from lawnmowers, motorcycles, daily drivers to super and turbocharged engines, but these all used a single crank sensor! These were all Hall Effect, 2 points for a 4 cylinder, 3 for an even fire 6 and 4 for an 8 cylinder.

This one sensor let you set initial timing, rpm based advance, timing retard based on boost and retard based on knock!

Things that I don't understand!

Why 2 crank sensors?
What does the cam sensor do?
What tells the ignition control to fire a particular coil?

I have searched the forum and can't find a situation such as mine and any help is much appreciated! I am confused and at a dead end!

01-21-10, 07:29 PM
The CMP (CaMshaft Position sensor) is the compression TDC reference for each cylinder. The diagram is misleading: the CMP actually receives a trigger from a stud in the face of the rear exhaust cam: 1 pulse per cam rotation - 1/2 engine speed.

The 2 CKP (CranKshaft Position sensors), as you surmised, are Hall effect units which trigger the ignition pulse from the PCM to the coil pack (ICM) based on comparison of two angular signals - timing advance/retard. The reluctor wheel is cut to supply accurate timing pulses (< 1 degree error) at all speeds to redline. One CKP goes out, the timing defaults to a fixed value (10 BTDC, I think) with no advance curve.

The coils sit on the ICM and have contacts - any one contact on the ICM and that coil won't fire, as well as a bad ground........

Make sure everything is squeaky clean, both dust and electrically, and connected as shown.....click to enlarge

01-21-10, 09:41 PM
submariner409, thank you for your reply! The diagrams are nice to see, but I am not seeing anything that I don't already understand! I just don't understand the ICM on any of the wasted spark ignitions, because I am used a distributor! I mean that thing either fires or it doesn't and you can usually track it down to a ground. This ICM I don't understand!

What tells it what coil pack to fire? The ICM is nothing but a Black Box to me! Even though I can read schematics and have a technical diploma in electronics, including digital stuff, I think I would be clueless! I am still used to an ignition module that fires one cylinder at at a time with a distributor.

I still don't understand why there are 2 crank sensors or the cam sensor, when 1 could do the job of all! None the less why would one particular coil pack not fire?

01-21-10, 11:07 PM
submariner409, Thank you for the info and the diagrams! I have pulled and looked at all the connectors that I can think of, (the 3 on the ICM, the 2 for the crank sensors and the 1 for the cam)!

Please be blunt, treat me as I am stupid! I mean seriously, what would keep one coil pack from not firing? I just don't understand how the ICM works! I understand how an ignition module works that only has to deal with one cylinder at time, but I don't understand how one can drive multiple coils!

01-22-10, 10:11 AM
The 2 CKP's and CMP "tell" the PCM which cylinder is approaching TDC on the firing stroke. (The PCM modifies timing advance constantly, based on many sensor inputs). See the irregular sequence of teeth cut into the reluctor wheel ? The positioning of the CKP's and which "teeth" they sense determines what cylinder number signal to send the PCM which triggers the injectors and ignition (ICM). Google "waste spark ignition". The plug wire tower connections are critical because 2 plugs fire at the same time - 1 at the proper timing for the power cylinder, the other at the same timing in the corresponding exhaust cylinder. If the individual coil connectors of the plug wires is reversed you get a nagging miss on 2 cylinders.

Somehow you'll need to track down the PCM trigger signals to both the coil and the corresponding injectors. It's entirely possible that the ICM is faulty: yours would not be the first. I haven't looked, but you could try www.rockauto.com or call Luke in Parts at Lindsay Cadillac over there >>>, or, for used, www.car-part.com

01-22-10, 11:55 AM
When I checked it the coil pack for cylinders 6 and 7 was not firing, so I swapped it one of the others. I had the same problem, no fire from the swapped coil pack, but the original worked fine.

Next I swapped the ignition control module with a known good one and still have the exact same problem.
So as I understand it, the misfire does not follow the coil and stays on #6 & #7. Likewise after swapping the ICM. That leads me to think of wires or plugs. How old are they? It doesn't take much on old wires. I had developed a misfire on my '97 after the fuel rail recall just because the wires where moved to pull the rail. Could this be a case of not seeing the forest through the trees? I tend to do that a lot. Overlook the obvious searching for the difficult.

01-22-10, 11:28 PM
Thanks for the reply; unfortunately it is not that simple! Any coil that is placed in that position just does not fire! Just to be sure I did swap plugs and wires around, but as expected, no change!

01-23-10, 01:01 PM
How have you determined that it is not firing? Timing light? Spark tester? Plug grounded on the engine and watch the spark at the electrode? What I am getting at is, are you positive that it is ignition and not 2 injectors that are not pulsing?

01-23-10, 06:44 PM
Originally I just used a test light to isolate the non firing cylinders, then I swapped the coil pack, next I swapped wires and plugs and finally I swapped the ignition control module with a known good one. Yes the injectors are pulsing, but I have since disconnected them. Thanks for the reply, any ideas are welcome!

01-23-10, 07:29 PM
You have ruled out, Plugs, Wires, Changed Coils around and swapped a Known good ICM, Still no spark on that one coil . I think this problem is internal to the ICM as Sub Mentioned and should be changed out to a new one, problem is that is very pricey, around 4 bills.
I have enclosed some info on this system. I hope you find the problem, I know it can get frustrating.

This Powertrains Ignition Control System controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture in each cylinder at the correct time. This ignition control system has several advantages over a mechanical distributor ignition system.

No moving parts to wear out.
No mechanical load on the engine.
Elimination of mechanical timing adjustments.
Located for easier service and improved reliability.
Improved high engine speed performance.
The Ignition Control System consists of the following components:

Two crankshaft position sensors (A and B).
Crankshaft reluctor ring.
Camshaft position sensor.
Ignition control module.
4 separate ignition coils.
Eight spark plug wires and conduit.
Eight spark plugs.
Knock sensor.
Powertrain Control Module (PCM).
System Operation
The Ignition Control System does not use a conventional distributor or a single ignition coil. In this ignition system, both ends of each of the four ignition coils are connected to a spark plug. Each coil is connected with spark plugs on companion cylinders, i.e., on top dead center at the same time (1-4, 2-5, 6-7, and 3-8). One cylinder is on its compression stroke when the other one is on its exhaust stroke.

When the coil discharges, both plugs fire at the same time by using the engine block to complete the electrical circuit. The cylinder on the compression stroke is called the event cylinder and the one on the exhaust stroke is the waste cylinder. The two cylinders share the energy available from the ignition coil to fire both spark plugs. This method of ignition is called waste spark ignition.

Since the polarity of the ignition coil primary and secondary windings does not change, one spark plug always fires with a forward current (center electrode to ground electrode) and its companion plug fires with a reverse current (ground electrode to center electrode). This is different from a conventional distributor ignition system that fires all the plugs with the same forward current flow.

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion spark plug. The disconnected plug wire acts as one plate of a capacitor and the engine block acts as the other plate. These two capacitor plates are charged as a spark first jumps across the gap of the connected spark plug. The plates are then discharged as the energy is dissipated as the spark continues. Voltage requirements are very high with an open spark plug or wire. The ignition coil may have enough reserve energy to fire the connected plug at idle, but possibly not under some engine load conditions. A more noticeable misfire may be evident under load; both spark plugs may then not fire.

Crankshaft Position Sensors and Reluctor Ring
The two crankshaft sensors are located on the front bank (BANK 2) of the engine block between cylinders 4 and 6. Crankshaft position A sensor is located in the upper crankcase and crankshaft position B sensor is located in the lower crankcase. Both sensors extend into the crankcase and are sealed to the engine block with O-rings. The crankshaft position sensors are not adjustable.

The magnetic crankshaft position sensors operate similar to the pickup coil in a distributor. When a piece of steel (called a reluctor) is repeatedly moved over the sensor, a voltage will be created by the sensor that appears to go On-Off-On-Off-On-Off. This On-Off signal is also similar to the signal that a set of breaker points in a distributor would generate as the distributor shaft turned and the points opened and closed.

The reluctor ring is cast onto the crankshaft between the #3 and #4 main bearing journals. The reluctor ring has 24 evenly spaced notches or air gaps and an additional 8 unevenly spaced notches for a total of 32.

As the crankshaft makes one complete revolution, both the A and B sensors will produce 32 On-Off pulses per revolution. In addition, the A sensor is positioned 27 degrees of crankshaft revolution before the B sensor. This creates a unique pattern of On-Off pulses sent to the ignition control module so that it can recognize crankshaft position.

Camshaft Sensor
The camshaft position sensor is located on the rear cylinder bank (BANK 1) in front of the exhaust camshaft. The camshaft position sensor extends into the rear cylinder head and is sealed with an O-ring. The camshaft position sensor is not adjustable.

As the rear cylinder bank exhaust camshaft turns, a steel pin on its drive sprocket passes over the magnetic camshaft position sensor. This creates an On-Off-On-Off signal sent to the ignition control module similar to the crankshaft position sensors. The camshaft position sensor produces one On-Off pulse for every one revolution of the camshaft or every two revolutions of the crankshaft. This allows the ignition control module to recognize camshaft position.

Ignition Control Module
The Ignition Control (IC) module is located on top of the rear camshaft cover. The IC module performs several functions:

It monitors the On-Off pulses produced by the two crankshaft and one camshaft position sensors.
It creates a 4X and 24X reference signal (4X REF HI and 24X Crank) sent to the PCM for ignition control.
It creates a camshaft reference signal (CAM HI) sent to the PCM for fuel injection control.
It provides a ground reference (REF LO, CAM LO) to the PCM.
It provides a means for the PCM to control spark advance (BYPASS and IGNITION CONTROL) called IGNITION CONTROL MODE.
It provides a limited means of controlling spark advance without PCM input called MODULE MODE.
The IC module is not repairable. When a module is replaced the remaining components must be transferred to the new module.
Ignition Coils
Four separate coils are mounted to the module assembly. Each coil provides the spark for two spark plugs simultaneously (wasted spark ignition). Each coil can be replaced separately.

Spark Plug Wires
The spark plug wires connect the ignition control module to the spark plugs. It incorporates several plastic channels and conduits to keep it properly positioned and to protect it. The spark plug wires are 7 mm in diameter and the outer jacket is made of silicone to withstand high temperatures. The silicone jacket is also an excellent insulator for the high voltages used in the ignition system. The silicone spark plug boots provide a tight seal on the spark plug. Care should be exercised when connecting a timing light or other equipment. Do not force anything between the boot and wiring or through the silicone jacket. Connections should be made using an appropriate adapter.

Spark Plugs
Eight spark plugs are centrally located in each cylinder combustion chamber and can be accessed through holes at the top of both cylinder bank camshaft covers. The spark plugs have platinum pads welded to the electrodes. These pads extend the spark plug life to 160,000 kilometers (100,000 miles).

Worn, cracked or dirty plugs may give satisfactory operation at idling speed, but under operating conditions they frequently fail. Faulty plugs are indicated in a number of ways: poor fuel economy, power loss, loss of speed, hesitation, shudder, medium throttle intake manifold backfire, hard starting and general poor engine performance.

Fouled plugs may be indicated by black carbon deposits. The black deposits are usually the result of slow-speed driving and short runs where sufficient engine operating temperature is seldom reached. Worn pistons, rings, faulty ignition, over-rich fuel mixture or low heat range spark plugs may result in carbon deposits.

Excessive gap wear on plugs of low mileage, usually indicates the engine is operating at high speeds or loads that are consistently greater than normal or that a plug which is too hot of a heat range is being used. Electrode wear may also be the result of plug overheating, caused by combustion gases leaking past the threads, due to insufficient torque of the spark plug. Excessively lean fuel mixture will also result in excessive electrode wear.

Broken insulators are usually the result of improper installation or carelessness when gapping the plug. Broken upper insulators usually result from a poor fitting wrench or an outside blow. The cracked insulator may not show up right away, but will as soon as oil or moisture penetrates the crack. The crack is usually just below the crimped part of shell and may not be visible.

Broken lower insulators usually result from carelessness when gapping and generally are visible. This type of break may result from the plug operating too Hot, which may happen in periods of high-speed operation or under heavy loads. When gapping a spark plug, always make the gap adjustment by bending the ground (side) electrode. Spark plugs with broken insulators should always be replaced.

Each spark plug boot covers the spark plug terminal and a portion of the plug insulator. These boots prevent flash-over which causes engine misfiring. Do not mistake corona discharge for flash-over or a shorted insulator. Corona is a steady blue light appearing around the insulator, just above the shell crimp. It is the visible evidence of high-tension field and has no effect on ignition performance. Usually it can be dust particles leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between shell and insulator.

Base Ignition Timing
The base ignition timing is determined by the relationship of the crankshaft position sensors to the reluctor ring. This relationship is not adjustable and results in a base ignition timing of 10 BTDC.

IC Module Mode
There are two modes of ignition system operation: PCM mode and Ignition Control Module (IC Module) mode. In IC Module mode, the ignition system operates independently from the PCM. The ignition control module maintains a base ignition timing of 10 BTDC and is able to change this ignition timing slightly with increased engine speed. IC Module mode is in effect whenever an ignition control fault is detected while the engine is running and it will have a noticeable effect on driveability. In PCM mode, the PCM controls the ignition timing. The PCM calculates the desired ignition timing based on information it receives from the input sensors.

PCM Timing Mode
The Powertrain Control Module (PCM) controls spark advance and fuel injection for all driving conditions. The PCM monitors input signals from the following components as part of its ignition control function to determine the required ignition timing:

Ignition Control Module (IC Module).
Engine Coolant Temperature (ECT) sensor.
Manifold Absolute Pressure (MAP) sensor.
Transaxle Range (TR) switch.
Throttle Position (TP) sensor.
Vehicle Speed Sensor (VSS).
Knock Sensor (KS).

The crankshaft reluctor ring has 24 evenly spaced notches plus 8 additional notches (shaded) used for synchronization.
As the crankshaft rotates, the notches pass the position sensors and create a voltage pulse signal in the sensor that is an input for the ignition control module (ICM).
Because of the physical location of the 2 crankshaft position sensors, the signal of B lags the signal of A by 27 degrees of crankshaft revolution.
To synchronize the ignition, the ICM first counts the number of B pulses between every 2 A pulses. There can be 0, 1, or 2 B pulses between A pulses.
When the ICM sees 0 B pulses between A pulses , it starts counting B pulses between A pulses. When the ICM counts exactly 4, it synchronizes the ignition on the very next A pulse. If the ICM counts over 4 (jumps from 3 to 5), it waits for another B pulse between A pulse to start counting again.
This process allows the ignition to synchronize and fire the first spark plug within 180 degrees (1/2 engine revolution).
The camshaft position (CMP) sensor provides the ICM with cylinder #1 firing order information, which the PCM uses for sequential fuel injection.
Using 3 sensors allows the ICM to maintain ignition synchronization even if one of the 3 sensors fails.

01-23-10, 09:41 PM
:sneaky: I never had the patience to type it all out: your post needs to be isolated and posted as a sticky or down in Tech Tips.

Thanks, Caddyshack

(I believe CKP B is the top and A is the bottom.)

01-23-10, 11:24 PM
After some though I decided it was not really a "Tech Tip" so I stuck it here in the Northstar section. Thanks Caddyshack.

01-24-10, 12:51 AM
Cut and paste is a wondrous thing and I hope that is what Caddyshack100 did! As with you, it was a wealth of info, but I am still clueless!

I hate to tell you this, but I drive it everyday on 6 cylinders! We get along fine, but mpg has dropped by 3! What gets me, is that I don't even get a check engine light or any codes other that P119 because I those injectors disconnected!

Today I worked on a '96 Lincoln Continental with the 4.6 32 valve engine and I thought my engine bay was full! This car was a PIA to work on! I love that engine, but had only scene it i RWD cars until now! That thing is stuffed in there, the starter is even mounted on the transmission facing backwards from normal!

01-24-10, 01:30 PM
Assuming that the "known good" ICM was in fact good the only thing left is the PCM, but I'm not sure if that would affect only 2 cylinders. I still suspect the ICM.

01-24-10, 05:32 PM
Shucks Fellas, I only pasted in from the Manual, Credit GM engineers... As for a Stickie, I really think Sub should have his own in regards to Checking the Transmission Fluid on a 4T80E, he has only described it over a 100times LOL.

01-24-10, 07:33 PM
We're not allowed to post a Sticky with the title "Before you ask some dumb question, read the Cadillac Technical Archive and the Forums Rules and do some homework !"

01-26-10, 01:52 PM
Thanks guys, this has been a learning experience for me and I appreciate all your help!

Ranger, just as you, I felt that the ICM had to be to blame, so I did try another. Just as before, it came right of a running car and the problem was still the same.

Today I had the opportunity to probe the ICM connectors from both vehicles and got identical readings! So, I figured that nothing was wrong with any of the sensors or PCM and I was positive that my ICM was good because it was fine on the other vehicle! Next I closed the gaps on each connector to the ICM and Voila!

Thanks again!!!

01-26-10, 04:50 PM
Now that you say that, I'm kicking myself for not mentioning it. When I put the DTS floor console in my DHS I could not get the T/C button to work. After numerous tries, I finally narrowed it down to the connector. I finally pulled the pins and opened them a little and like you, VOILA!