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Category: Chevy
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Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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I have a 91 chevy lumina 3.1 It starts to misfire when hot.

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I have a 91 chevy lumina 3.1 It starts to misfire when hot. Replaced the map sensor and coil pack. Started to do this after replacing the head gaskets.
Customer: replied 10 years ago.
Relist: No answer yet.
Greetings! When was the last time the engine was tuned up? No, not just plugs, but a full tune up! The whole nine yards! Any part of the secondary ignition will do this including the ignition coil or coils! Where new tune up parts put in after the heads were replaced? This sounds like a classic ignition misfire! They usually go bad under a load like under acceleration, but can be noticeable at any time. It is very important to have your engine equipped with good tune up parts or you may be causing damage to other components of you car like the catalytic converter which can be expensive!
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Customer: replied 10 years ago.
I believe that there was a full tune up done on the car, but before the heads were replaced. What does a full tune up include? Also the car is not getting spark to # XXXXX and 5 with new plugs and wires, and new coil pack.
A module could very well do this. You are just going to have to check the inputs to the module and computer. Camshaft and crankshaft position sensors.
Customer: replied 10 years ago.
Thanks very much for your help, I will give this a try. If it doesnt work I hope I can talk with you again.

Thanks for the accept!

If you have any more questions, just repost back to the same question and I will get it.

Customer: replied 10 years ago.
Relist: I still need help.
Customer: replied 10 years ago.
Now when I put in a new coil pack had spark to all six but after about 10 minutes lost it in #3 and 6. It was in # XXXXX and 5. Why would that change and what would be causing it? Still not running right.
What about if you swap coils? Does that make any difference?
Customer: replied 10 years ago.
Tried that. Didnt make a difference

You are going to have to check the inputs to the module. If they all check out ok, I would rec to replace the module.


Here is some info to get you started. Let me know if you need more.


The DIS module monitors the crank sensor signals and based on these signals sends a reference signal to the ECM so that correct spark and fuel injector control can be maintained during all driving conditions. During cranking, the DIS module monitors the "sync pulse" to begin the ignition firing sequence, and below 400 rpm the module controls spark advance by triggering each of the three coils at a pre-determined interval based on engine speed only. Above 400 rpm, the ECM controls the spark timing through the module (EST), and compensates for all driving conditions. The DIS module must receive a "sync pulse" and then a crank signal in that order to enable the engine to start. The DIS module is not repairable. When a module is replaced, the remaining DIS module components must be transferred to the new module.

The coil output test is used to locate DIS problems.

- Check the power and ground terminals to the

DIS system.

- If only one coil has weak output, switch the position

of the coils.

- If the weak output moves to the new coil position,

replace the coil.

- If the weak output stays in the same position

with a different coil installed, check the connection

to the coil and replace the module if the connections

are good.

Electronic Spark Timing Signal To DIS Module:

Wire color is white. Pin #C-9.

3X Crank Reference Signal

Frequency At Idle Frequency At 55 MPH

38-48 Hz. 85-95 Hz.

Wire color is Purple-white. Pin #D-13.

Crank pick up resistance is(NNN) NNN-NNNNΩ.

Key Facts:

- The DIS module creates a 3X crank reference signal from the 7X magnetic pickup signal.

- A no start will result if magnetic pickup signal is missing.

- Magnetic pick up signal must be at least 0.2 V AC cranking, resistance is(NNN) NNN-NNNN/strong>Ω.

- The DIS module selects the coil pack to fire by using the 7X crank reference signal.


1.The magnetic pickup sends 7 pulses to the DIS module each engine revolution.

2.The DIS module sends the 3X signal to the PCM for fuel control.

3.The PCM sends an electronic spark timing (EST) signal to the DIS module when engine is in run

mode (over 400 RPM)

Magnetic Pick up Testing

A magnetic pick up responds to magnetic materials

rotating close to the pick up. Magnetic

materials with air gaps change the magnetic

field around the pick up coil which generates a

small voltage. The size of the voltage signal is

determined by several factors:

- Speed of rotation

- Distance of the air gap.

- Strength of the magnet in the pick up

- Number of turns in the pick up coil

A complete test should check for all four factors.

Our specifications give the resistance and the AC

voltage expected. Resistance testing checks the coil

for shorts or opens but not the other three factors. A

good example is a pick up that is cracked, the

resistance may be normal. The crack reduces the

strength of the magnetic field which will reduce the

size of the pick up signal. Another example is an

improperly installed pick up that does not seat well

in the holder because of grease and dirt packed into

the holder. This will cause a wider air gap and

reduce the size of the signal. All these cases are

infrequent, but that can make them harder to

identify when they do happen. The lab scope

pattern is the best test for a magnetic pick up. The

specifications give the resistance and the cranking

AC voltage that is normal for a magnetic pick up.

Starting is the most critical time because the engine

speed is low which results in a low output signal

from the pick up. The sync signal is also important

because it identifies the coil pack to fire. Noise can

appear as false sync signals.

Based on the crank pulses, the DIS module sends reference signals to the ECM which are used to indicate crankshaft position and engine speed.

This sensor protrudes into the block, within approximately 0.050" of the engine crankshaft reluctor. The reluctor is a special wheel cast into the crankshaft with seven slots cast into it, six of which are evenly spaced 60°apart. A seventh slot is spaced 10°from one of the other slots and serves to generate a "sync pulse." As the reluctor rotates as part of the crankshaft, the slots change the magnetic field of the sensor, creating an induced voltage pulse.

The ignition module will continue to send these reference pulses to the ECM at a rate of one for each 180°or crankshaft rotation. The ECM will activate the fuel injector based on the recognition of every other reference pulse beginning at a crankshaft position of 120°after top dead center.


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