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Misfire

Last August I had a problem with my truck. (see Hard Drivin' 2). I will get back to this in a paragraph or two.

Yesterday when I got in the truck to head out for lunch, the Check Engine light came on. The engine was running rough and concensus from the peanut gallery said the engine was missing. What could this be? A bad plug, a bad plug wire, distributor cap, bad sensor, bad computer. Who knows?

I called my mechanic on the way home and left a message saying I would be dropping the truck off this morning. This morning I dropped the truck off at 7:15 am. A sign on the door said, "Don't drop off your vechicle without calling first." I had already called and the truck was running rough so I left it there anyway.

David M drove me back home and I took the Miata out for the day. Cool and cloudy, top up.

I never got a call back from the shop. I suspect they must be on vacation. I went back by this evening and picked it back up. It is barely driveable. It gets really rough if the speed gets up around 35 or 40 mph. The check engine light flashes if you go over 40.

I Googled today for Dodge RAM 1500 engine missing 40 mph shakes hoping to get some insight on what to do to resolve exactly what the problem was. I found something interesting I will share with you in a moment.

Tonight I drove the truck to the parts store. They hooked up the computer and reported "misfire on cyclinder #8". This is one of those moments when I actually begin to love computers again. The problem seems to be narrowed down to either a plug, wire, or cap. The cheap-skate in me says, I will try the plugs and see what happens from there. Home again. I replaced the plug in #8. It runs smooth now. Only 15 minutes of effort. The light is still on but I think perhaps this is something they will have to reset. I will replace the remaining plugs this weekend.

Now why is this plug bad? It could be because of excess oil in that cylinder. Remember last August? This is what I found today. It should be easy to test. I just need to borrow the neighbors vacuum gauge.

Technical Service Bulletin

Engine - Spark Knock/Oil Consumption
NUMBER: 09-05-00
GROUP: Engine
DATE: Feb.25, 2000
MODELS:
1994 - 1999 (AB) Ram Van
1994 - 1999 (AN) Dakota
1994 - 1999 (BRIBE) Ram Truck
1998 - 1999 (DN) Durango
1994 - 1998 (ZJ) Grand Cherokee
1996 - 1998 (ZG) Grand Cherokee
THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 09-06-99,
DATED SEP.10, 1999, WHICH SHOULD BE REMOVED FROM YOUR FILES. THIS
IS A COMPLETE REVISION AND NO ASTERISKS HAVE BEEN USED TO
HIGHLIGHT REVISIONS.
SUBJECT:
Spark Knock And Engine Oil Consumption Due To Intake Manifold Pan Gasket Oil
Leak
OVER VIEW:
This bulletin involves the replacement of the engine intake manifold plenum pan gasket.
NOTE: THIS BULLETIN APPLIES TO VEHICLE EQUIPPED WITH A 3.9L, 5.2L.
OR 5.9L GASOLINE ENGINE.
SYMPTOM/CONDITION:
An engine intake manifold plenum pan gasket oil leak may occur on some V-6 and V-8
style engines. The oil leak is internal to the engine so no external oil leakage will be
present. Two symptoms of this oil leak condition may be present. The vehicle operator
may experience an engine spark knock during acceleration and/or an increase in the
amount of engine oil consumed by the engine.
DIAGNOSIS:
Make sure Technical Service Bulletin (TSB) 18-48-98 has been performed.
NOTE: IT IS IMPORTANT THAT THE COIL AND SPARK PLUG WIRES ARE
ROUTED EXACTLY AS SPECIFIED IN TSB 18-48-98 TO ACHIEVE THE MOST
BENEFIT.
Inspect the Positive Crankcase Ventilation (PCV) valve. Shake the PCV valve to verify
that the pintle inside of the PCV valve is free. Replace the PVC if the pintle is not free.
If the intake manifold plenum pan gasket is leaking, an additional vacuum source will be
created inside of the engine at the location of the pan gasket leakage. Engine combustion
blow-by gases, oil vapor, and air from the crankcase filter/breather may be drawn past the
leaking pan gasket and into the intake manifold. In most cases when this condition
occurs, an engine at idle will create the highest vacuum and lowest amount of engine
blow-by.
1. Allow the engine to reach normal operating temperature.
2. Stop the engine.
3. Disconnect the breather hose from the air cleaner.
4. Attach a vacuum/pressure gauge to the end of the breather hose (Figure 1).
5. Disconnect the PCV valve hose from the intake manifold.
6. Seal off the intake manifold PCV valve hose port opening.
7. Seal off the open end of the PCV valve hose (Figure 2).
NOTE: DURING THIS DIAGNOSIS, IT WOULD BE NORMAL FOR THE ENGINE
TO DEVELOP PRESSURE WITHIN THE ENGINE CRANKCASE. THIS IS DUE TO
THE NORMAL PROCESS OF EXHAUST BLOW-BY GASES LEAKING PAST THE
ENGINE PISTON RINGS AND ACCUMULATING IN THE ENGINE CRANKCASE.
DO NOT ALLOW MORE THAN 3 PSI (20.7 kpa) OF PRESSURE TO BUILD
WITHIN THE ENGINE WHEN PERFORMING THE FOLLOWING DIAGNOSTIC
PROCEDURE.
8. Start the warmed engine and observe the vacuum gauge.
9. Allow the engine to idle for approximately 30 seconds. Do not allow more than 3 psi
(20.7 kPa) of pressure to develop in the engine crankcase.
10. If the attached vacuum / pressure gauge does not indicate that a vacuum is present in
the engine crankcase, then the intake manifold plenum pan gasket is good and no
further internal engine vacuum leak diagnosis is required.
11. If an internal vacuum leak is present then perform the Repair Procedure.
PARTS REQUIRED:
For the 5.2L / 5.9L:
1 04897383AC Package, Intake Manifold Flange Gasket and Bolts
1 05017208AA Gasket, Intake Manifold Plenum Pan
15 06034583 Bolt, Intake Manifold Plenum Pan
1 53030541 Gasket, Throttle Body
2(AR) 04318001 Conditioner, Combustion Chamber
For the 3.9L:
1 04897382AC Package, Intake Manifold Flange Gasket and Bolts
1 05017207AA Gasket, Intake Manifold Plenum Pan
14 06034583 Bolt, Intake Manifold Plenum Pan
1 53030541 Gasket, Throttle Body
2(AR)04318001 Conditioner, Combustion Chamber
REPAIR PROCEDURE:
1. Refer to the appropriate year Service Manual, Section 9: ENGINE for removal and
installation instructions.
NOTE: CLEAN ALL OIL RESIDUE FROM THE INTERIOR SURFACES OF THE
PLENUM PAN AND THE INTAKE MANIFOLD PLENUM CHAMBER.
NOTE: THE PROPER BOLT TORQUE AND TIGHTENING SEQUENCE IS
CRITICAL AND MUST BE FOLLOWED WHEN TIGHTENING BOTH THE
PLENUM PAN BOLTS AND THE INTAKE MANIFOLD FLANGE BOLTS.
3.9L Bolt Tightening Sequence and Torque Procedure:
3.9 Plenum Pan Bolt Torque Procedure
3.9 Intake Manifold Flange Bolt Torque Procedure
5.2L / 5.9L Plenum Bolt Tightening Sequence and Torque Procedure:
5.2L / 5.9L Plenum Pan Bolt Torque Procedure
5.2L / 5.9L Intake Manifold Flange Bolt Torque Procedure
2. With the engine reassembled, inspect the coil and spark plug wires for proper routing.
Refer to TSB 09-48-98 for additional assistance.
3. Start the engine and allow it to warm to normal engine operating temperature.
4. Decarbon the combustion chamber using Mopar Combustion Chamber Conditioner
(p/n 04318001) per the instructions.
NOTE: ALLOW THE COMBUSTION CHAMBER CLEANER TO SOAK INSIDE OF
THE ENGINE FOR 2 TO 2.5 HOURS.
NOTE: A SECOND APPLICATION OF THE COMBUSTION CHAMBER
CONDITIONER MAY BE REQUIRED IF THERE WAS A LARGE QUANTITY OF
OIL LEAKAGE PAST THE INTAKE PLENUM PAN GASKET.
5. Verify proper engine oil level.
POLICY: Reimbursable within the provisions of the warranty.
Time Allowance
FAILURE CODE: P8- New Part


I will check into this...later. In the meantime I will replace the remaining plugs, watch the oil level and assume I now know where the oil is going. And why it is going there!