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Michael, Auto Service Technician
Category: Car
Satisfied Customers: 919
Experience:  21yrs.Foreign and domestic driveability diagnosis and repair/ ASE Cert./Fuel Injection Specialist.
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1993 pontiac bonneville: wont start..the crank and cam sensor

Customer Question

hi, i have a 1993 pontiac bonneville and it wont start we already replaced the crank and cam sensor the ignition module and the computer what should i try next?
Submitted: 11 years ago.
Category: Car
Expert:  Michael replied 11 years ago.

Here are the procedures to check for a no start on a fuel injected engine.It will require a couple diagnostic tools that you do nt most likely posess,but may be able to obtain through a tool loan or rental program at many parts stores.

In order for an engine to run it needs the following:

1. Fuel (Fuel pressure gauge)
2. Spark (In line Spark tester)
3. Injector pulse (Noid Lights)
4. Air/Compression

You must determine which one or more is missing to proceed.

You can reduce the troubleshooting by spraying carb clean or a little ether into the intake throttle body to see if it attempts to start.If it does, then there is a problem with fuel delivery and not ignition.This will tell you whether or not there is fuel being delivered and isolate the issue to fuel pressure/delivery or injector control circuits.




You can check for spark at a spark plug wire while cranking with a flat tip driver or in line spark tester inserted into the plug wire boot and placed close to any metal part on the engine besides the fuel system lines and fittings or just plugged back onto the spark plug if using an inline tester.

To check injector pulse you will need a noid light set which can be purchased at your local parts store or through tool rental or loan programs as mentioned above.(Picture below)

To check for air just make sure the air filter is not totally restricted.

To check compression install compression gauge in each cylinder,crank engine,record reading for each cylinder.Look for a big variance between cyls.

If all of this is OK you may have contaminated fuel.

Please post back with your results so that we may help you through you car trouble.

Noid light should flash while cranking.

If you are not inclined to do this I recommend that you take it to most any repair facility and let them diagnose it for you.It should not take more than one hour of diag. to isolate the problem.You can then make the decision to repair the problem yourself or have it repaired for you.

Customer: replied 11 years ago.
Reply to Michael's Post: we already checked that stuff its not getting any spark, do you think it could have to do with the factory anti theft system if so how can we bypass it. even when the key is not in the ignition and all lights are off the chimes still go on when you have a door open
Expert:  Michael replied 11 years ago.
Not anti-theft.Anti-theft on your car disables the starter.Are you sure there is injector pulse?Is or has the check engine light been lit?
Customer: replied 11 years ago.
Reply to Michael's Post: yes i can hear the injectors pulse but that wouldnt be why there is no spark.right?
Expert:  Michael replied 11 years ago.

Yes it could be related.If you are missing only spark we will proceed differently than if you have no spark AND no injector pulse.If we chase down just a no spark condition while there is no injector pulse,it's a waste of time and effort.If you are convinced that spark is all you are missing here then proceed below.

Testing the coil pack:


  1. Remove the ignition coil(s).

  2. Using an ohmmeter, check the resistance between the primary terminals on the underside of the coil. The resistance should be 0.50-0.90 ohms.

  3. Check the resistance between the secondary terminals. It should be 5,000-8,000 ohms.

  4. If the coil failed either test, replace the coil.

You say you have replaced the ICM already so no need to test that.

The cam sensor you replaced controls injector pulse.

The crank sensor controls spark.

You may have a problem with the circuit and not the sensor.That's why I asked about the check engine light,but you did not answer me about that for some reason?Here is how to test that circuit.

  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.

  2. With the ignition in the ON position, check the sensor voltage using an oscilloscope. When the starter is briefly operated a square wave pattern, varying between 0-12 volts and providing 3 pulses per crankshaft revolution should be seen at terminal V. The same signal providing 18 pulses per crankshaft revolution should be seen at terminal A. If voltage is within specification, the sensor is functional.

  1. If the voltage falls out of range, use a DVOM to check terminal C for battery positive (B+). If battery positive (B+) voltage is not present, check the circuit continuity and repair as necessary.

  2. If battery positive (B+) voltage is found at terminal C, check the terminal D for proper ground. If ground is not present, check the circuit for continuity and repair as necessary.

  3. If the sensor and circuits are functional, the PCM may be faulty.

Good Luck and happy troubleshooting.

Customer: replied 11 years ago.
Reply to Michael's Post: mike,im waiting fot ohms meter now but as far as the check engine light goes when the key is in the on position all dash lights shut off except the check engine light
Expert:  Michael replied 11 years ago.

OK.That's normal.I was hoping that you may have noticed the check engine light earlier,before this problem occured.If we had a trouble code it would isolate the issue to a specific circuit instead of having to check everything.

Here is how to get codes if you would like to give it a whirl.Who knows....It may save us a whole lot of time if we have a code to guide us here.You can print this for future use too.It will come in handy if you do your own work on the car.

The Assembly Line Diagnostic Link (ALDL) or Data Link Connector (DLC) may be located under the dashboard, and is sometimes covered with a plastic cover labeled DIAGNOSTIC CONNECTOR.

  1. The diagnostic trouble codes can be read by grounding test terminal B. The terminal is most easily grounded by connecting it to terminal A (internal ECM ground). This is the terminal to the right of terminal B on the top row of the ALDL connector.

  2. Once the terminals have been connected, the ignition switch must be moved to the ON position with the engine not running.

  3. The Service Engine Soon or Check Engine light should be flashing. If it isn't, turn the ignition switch OFF and remove the jumper wire. Turn the ignition ON and confirm that the light is now on. If it is not, replace the bulb and try again. If the bulb still will not light, or if it does not flash with the test terminal grounded, the system should be diagnosed by an experienced driveability technician. If the light is OK, proceed as follows.

  4. The code(s) stored in memory may be read through counting the flashes of the dashboard warning lamp. The dash warning lamp should begin to flash Code 12. The code will display as one flash, a pause and two flashes. Code 12 is not a fault code. It is used as a system acknowledgment or handshake code; its presence indicates that the ECM can communicate as requested. Code 12 is used to begin every diagnostic sequence. Some vehicles also use Code 12 after all diagnostic codes have been sent.

  5. After Code 12 has been transmitted 3 times, the fault codes, if any, will each be transmitted 3 times. The codes are stored and transmitted in numeric order from lowest to highest.

The order of codes in the memory does not indicate the order of occurrence.

  1. If there are no codes stored, but a driveability or emissions problem is evident, the system should be diagnosed by an experienced driveability technician.

  2. If one or more codes are stored, record them. Refer to the applicable Diagnostic Code chart in this section.

  3. Switch the ignition OFF when finished with code retrieval or scan tool readings.

After making repairs, clear the trouble codes and operate the vehicle to see if it will reset, indicating further problems.

Please click my Accept button if this will be helpful.Thanx Art.

Customer: replied 11 years ago.
Reply to Michael's Post: mike,will the codes still work even though the car hasnt run sience i put a new computer in?
Expert:  Michael replied 11 years ago.
If you have been cranking it since the new computer has been put in and there is a malfunction in the cranking circuit,i.e. crank sensor circuit,then there may be a code present.Won't hurt to check.It can only help.This may sound like a silly question,but did you swap out the PROM chip and make sure it was seated very tightly in the new ECM?Sometimes it's easy to bend one of those little pins on that thing.
Customer: replied 11 years ago.
Reply to Michael's Post: there is a cover that runs the length of the computer by two inches down on the computer?
Expert:  Michael replied 11 years ago.

?? I don't understand.Are you asking if there is a cover for access to the PROM chip you changed?You did put the PROM chip in right?Here is what you posted:

there is a cover that runs the length of the computer by two inches down on the computer? Did you mean to type the word IS in the beginning?If so,yes.That cover must be removed to access the place where the PROM chip goes.The new ECM comes without one.You must remove it from the old ECM and install it in the new ECM.They supply a little tool to do it with the new ECM.

Expert:  Michael replied 11 years ago.
Hello,how did you make out?Did you get the chip changed?