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Goodwrench9124, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 3432
Experience:  Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer,Hrybrid certified
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Ive got a 96 cadillac deville with a code PO300. Have been

Customer Question

I've got a 96 cadillac deville with a code PO300. Have been on here and paid 2 different techs, both with the wrong answer. Car will idle but rough, and theres NO power on acceleration. Sometimes it'll barely move. It also pops on acceleration. Has new plugs, wires, ignition module, new fuel pump (theanks to a wrong diagnosis from a tech on here). There is good spark at each plug, fuel pressure is 3 pounds under spec with key on engine off. I unplug regulator and it goes up about 7 pounds like it should. drove car like that no difference. Checked compression, all are between 165-175 psi, except number one is 120psi (spec is none should be under 140) and number 3 cylinder is 140psi. Low but not that low that car barely moves. Driving me nuts. If solved its well worth 20 bucks.
Submitted: 8 years ago.
Category: Cadillac
Expert:  Goodwrench9124 replied 8 years ago.
Hello, and welcome to JA!!! the fact the engine pops on acell and the fact that you have one cylinder below spec on compression and a another cylinder that is marginal. you might want to pursue this a little deeper. are you familer with a test called cylinder leakage test?
Customer: replied 8 years ago.
Yes, went to tech school 15 years ago but been out of it awhile. Please refresh the old brain though. Also forgot to add replaced one crank sensor.
Expert:  Goodwrench9124 replied 8 years ago.

Ok, I have seen you had some bad luck on isolating this problem. Let me say, you have trusted us with your concern with no luck. Lets try to resove your issue, before you accept my answer's. We rather you be happy with our help. Ok, I am thinking maybe a valve is not seating properly, causing this problem. here is the instructions, let me know what readings you come up with.



Cylinder Leakage Test

Tools Required

J 35667-A Cylinder Head Leakdown Tester or equivalent

A leakage test may be performed in order to measure cylinder/combustion chamber leakage. High cylinder leakage may indicate 1 or more of the following conditions:

Worn or burnt valves
Broken valve springs
Stuck valve lifters
Incorrect valve lash
Damaged piston
Worn piston rings
Worn or scored cylinder bore
Damaged cylinder head gasket
Cracked or damaged cylinder head
Cracked or damaged engine block



Disconnect the battery ground negative cable.

Remove the spark plugs.

Rotate the crankshaft to place the piston in the cylinder being tested at top dead center (TDC) of the compression stroke.

Install the J 35667-A or equivalent.

It may be necessary to hold the crankshaft balancer bolt to prevent the crankshaft from rotating.

Apply shop air pressure to the J 35667-A and adjust according to the manufacturers instructions.

Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent is considered excessive and may require component service. In excessive leakage situations, inspect for the following conditions:

Air leakage noise at the throttle body or air inlet hose that may indicate a worn or burnt intake valve or a broken valve spring.

Air leakage noise at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or a broken valve spring.

Air leakage noise from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block, or a damaged cylinder head.

Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.

Perform the leakage test on the remaining cylinders and record the values.




Customer: replied 8 years ago.
I will have to run and get a leakdown tester. will you still be on in about 2 hours? All i have is a standard compresion tester.
Expert:  Goodwrench9124 replied 8 years ago.
I will be on here off and on all day!!! I will make sure I check back with you in a couple of hours!!!!
Customer: replied 8 years ago.
ok thanks. Tester i'm going to get goes up to 100psi, is that enough?
Expert:  Goodwrench9124 replied 8 years ago.
yes, most tester reads 100 psi. just follow the tools manufacturers instructions. simple test, and more accurate than a compression test.
Customer: replied 8 years ago.
ok, will let you know when done testing.
Expert:  Goodwrench9124 replied 8 years ago.

Great, I will Look for your results!!!



Customer: replied 8 years ago.
running late, just got back. going to do test now.
Customer: replied 8 years ago.

got a question. Gauge isn't going down at all on even the cylinder that had low compression. But i can hear air constantly going into the gauge also.


Expert:  Goodwrench9124 replied 8 years ago.
ok, I take it is a single gauge tool?
Customer: replied 8 years ago.

ok, got the readings. wasn't using the tool right. I hooked up the air hose, then adjusted the gauge to read 0. Then hook it to the cylinder hose. readings were as follows.









Expert:  Goodwrench9124 replied 8 years ago.
Ok, looks all the cylinders are border line, not uncommon for a northstar. rings like to stick in the pistons. but i dont see one the cylinders that really stand out. did you hear any air out the exhaust or throttle body?
Customer: replied 8 years ago.
i'll check, did # XXXXX again. This time was 30%. I do hear air from the dip stick tube and oil cap.
Expert:  Goodwrench9124 replied 8 years ago.
that means some compression is going by the rings. but like I said before this not uncommon for a northstar. rings stick in the pistons causing blow by. although this may be a issue, I dont believe this is your problem. there is a kit you can buy from GM that will helps this concern of excessive leakage. you said you only replaced one crank sensor and not both?
Customer: replied 8 years ago.
I checked #8 again, this time it was 32%. Nothing from the exhaust. But can hear air at the throttle body with it open. Should i replace both crank sensors? could this be the problem?
Expert:  Goodwrench9124 replied 8 years ago.

I would replace both crank sensors. they had allot of issues with the crank sensors on these engines. if you hear air out the throttle body, that indicates a intake valve leaking, which will cause a popping on acceleration and a no power. I would try a couple of things first. one is replace both crank sensors. the other is do a engine decarbon, this may help the intake valve to seat and bring the rest cylinders back up to a passable number.



Cleaning Procedure

  1. Place the vehicle gear range selector in Park.
  2. Start the engine. Raise the engine speed to 2000 RPM.
  3. Warm the engine coolant temperature to a minimum of 93° C (200° F).
  4. Shut the engine off.
  5. Remove the ignition coils and module for access when using the evacuation tool.
  6. Remove the spark plugs and ensure that none of the pistons are at TDC.
  7. Install the induction hose manifold, J 45076-24, (4 hoses) into the front bank of spark plug holes. Press each hose into the spark plug opening to retain the hose.

    Remove the original hose from the canister and install the hose provided in the J 45076 kit.

  8. Connect the CPFI canister, J 35800, to the induction manifold.
  9. Pour the first can of Piston and Ring Cleaner, P/N 12378549 (in Canada, P/N 88901334), included in kit P/N 12378545 (in Canada, P/N 88901333) into the canister, J 35800-A.
  10. Pressurize the canister to 103 kPa (15 psi).

    If the hose pops out while inducing cleaner into the cylinder, simply reinsert the hose back into the hole.

  11. Open the valve on the canister hose to induce the first can of Piston and Ring Cleaner into the front bank of cylinders.
  12. Depressurize the canister (use the pressure regulator to release pressure, then close the canister valve) and remove it from the 4 hose manifold.
  13. Move the 4 hose manifold to the rear bank of cylinders.
  14. Pour the second can of Piston and Ring Cleaner into the canister and reconnect the canister to the manifold.
  15. Pressurize the canister to 103 kPa (15 psi).
  16. Open the valve on the canister hose to induce second can of Piston and Ring Cleaner into the back bank of cylinders.
  17. When the canister is empty, depressurize it (use the pressure regulator to release the pressure, then close the canister valve) and disconnect the canister, J 5800-A, from the manifold. Remove the induction hose manifold assembly from the engine.

    The piston and ring cleaner solution must remain in the cylinder for a minimum of two hours. If the solution is removed in less than two hours, the cleaning process will not be 100% effective and may not correct the condition. Additionally, do not allow the cleaning solution to remain in the engine more than three hours. If the dissolved solution is left in the cylinders more than three hours, it will soak back into the rings and cause the rings to stick again.

  18. Allow the chemical to remain in the engine cylinders a minimum of two hours.

    While evacuating the cleaning solution from each cylinder, manipulate the hose around the circumference of the cylinder to ensure all fluid is removed.

  19. After the two hour soak period, connect the evacuation pump assembly, J 45076-2, to shop air and evacuate the piston and ring cleaner solution from each cylinder through the spark plug hole.
  20. Properly dispose of used cleaning solution by putting it into waste oil.

    If a second application of piston and ring cleaner is necessary (see Correction above), repeat Steps 7 through 20.

  21. Change the engine oil. The filter will be changed after the road test.
  22. Add 6.6 L (7 qts) of oil and inspect for visible oil leaks.
  23. Place shop rags over all plug holes and intermittently bump over engine to ensure no hydraulic lock is present.
  24. Crank the engine continuously for 20 seconds.
  25. Remove the rags and reinstall the spark plugs.
  26. Reinstall the ignition coil module.
  27. Remove the mass air flow (MAF) sensor and the air cleaner for access to the throttle body.
  28. Use the aerosol Throttle Body Cleaner, P/N 12378550 (in Canada, P/N 88901335), included in kit P/N 12378545 (in Canada, P/N 88901333) and manually clean the throttle body and the idle air control (IAC).
  29. Remove the exhaust gas recirculation (EGR) valve.
  30. Install EGR Cleaner adapter J 45076-45 and throttle body cleaner adapter. For 1996-1999 models use the J 45076-46 throttle body adapter. For 2000-2003 models use the J 45076-55 throttle body adapter. The J 45076-55 is held in place by the air intake duct.
  31. Remove the position crankcase ventilation (PCV) valve. Inspect for proper operation and clean or replace as necessary.
  32. Connect vehicle exhaust pipes to shop ventilation system.
  33. Pour induction cleaner, P/N 12378552 (in Canada, P/N 88901336), included in kit P/N 12378545 (in Canada, P/N 88901333 ) into the CPFI canister, J 35800-A, and connect the canister to the EGR Cleaner Adapter and Throttle Body Cleaner Adapter, J 46076-46.
  34. Pressurize the canister to 138 kPa (20 psi).
  35. Start the engine. Connect the Tech 2® and raise the engine RPM to 1100 RPM with Tech 2® at F3- RPM Output.
  36. Open the valve on the canister to induce the induction cleaner through the MAF and the EGR Adapter. Regulate the air pressure to obtain a good fan pattern of the solution into the throttle body, but not so much that the fluid overflows out of the throttle body.
  37. When the canister has been emptied (use the pressure regulator to release pressure then close the canister valve), exit the Tech 2® F-3 function to reduce the engine RPM to normal idle speed.
  38. Turn the ignition to Off.
  39. Remove the EGR Cleaner Adapter and the Throttle Body Cleaner Adapter, J 45076-45 and J 45076-46.
  40. Reinstall the EGR valve, MAF Sensor and air cleaner.
  41. Use the Tech 2® to clear any DTCs set during the cleaning procedure. Disconnect Tech 2®.

    Start the vehicle and gradually increase the RPM to 2000 RPM in park. Engine damage could result from any fluid left on top of the piston if RPM is increased too quickly.

  42. Maintain the RPM at 2000 for 1-3 minutes. Then promptly road test the vehicle for a minimum of 20 minutes in the third gear range. Include several short, wide open throttle bursts.
  43. After the road test, allow the engine to idle for one minute with the A/C off and the gear selector in the PARK position.
  44. Connect the Tech 2® and inspect and clear any codes from the road test. An EGR pintle code may set from debris binding the valve. Clean the EGR valve, if necessary.

Turn the ignition to Off. Disconnect the Tech 2®.

Change the engine oil and filter.

Verify the oil level.

Reset the Engine Oil Life monitor.

It is not necessary to deglaze the cylinder walls when installing the new rings. The new rings can be installed in the cylinder bore as they are. The bores should be inspected for any cracks or damage before reassembly.

If the post oil consumption test results for a 2000 to 2003 vehicle indicate the oil economy is still less than 0.946L (1 qt) in 3200 km (2000 mi) on vehicles still in the warranty period, then the piston rings should be replaced. The new part number for the piston rings is 89017413. Be sure to install the second compression ring notch side down. Rings with the increased tension and other improvements are now available for the 1996 to 1999 vehicles. That ring package is P/N 89017431.

There is a new head bolt torque angle specification that should be used when installing the head bolts. The new spec is 175 degrees total torque angle (the previous specification was 190 total degrees). The 15 degree reduction should be subtracted from the final pass. The final pass would be 45 degrees instead of 60 degrees. This new specification will reduce the possibility of head bolt thread damage and localized stresses, but still provide the necessary clamp load.

Part Number







Kit, Engine Cleaner


12378549 (U.S.)

88901334 (Canada)

Piston and Ring Cleaner (for second application)

1 (if req'd)


Gasket, EGR Mounting



Valve, PCV

1 as req'd


Piston Ring Kit 2000 to 2003 Model Years

8 as req'd


Piston Ring Kit 1996 to 1999 Model Years

8 as req'd

Customer: replied 8 years ago.
have a question about the crank sensor. On ALLDATA it states in the flow chart to test DC voltage on the plug from the crank sensor. When i do that i get none, even on the new one. But i have continuity from the flug at sensor to the plug at ignition module. I thought if i remember right from tech school, when you test a magnetic pick-up such as the crank sensor you use AC voltage. When i do that i have voltage.
Expert:  Goodwrench9124 replied 8 years ago.


the crank sensors dont produce a voltage. it is a on and off pulse signal to the pcm. here is some info on how they work.

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.





The crankshaft position (CKP) sensor is a sensor based on the magneto resistive principle. A magneto resistive sensor uses 2 magnetic pickups between a permanent magnet. As an element such as a reluctor wheel passes the magnets the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. This system uses 2 sensors within the same housing for the V6 engine, and 2 separate sensors for the V8 engine. The powertrain control module (PCM) supplies each sensor a 12-volt reference, low reference, and a signal circuit. The signal circuit returns a digital ON/OFF pulse 24 times per crankshaft revolution.





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.





Customer: replied 8 years ago.

wondering if your online?