98 Dodge Ram Magnum - Engine Rebuild

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  WELCOME TO SOFTWARE FOR CARS - engine rebuild incident: why you need an OBD scan tool 

Henry Crichton, Software For Cars Repair Journal, June 10, 2001
98 Dodge Pickup - Engine Rebuild 318 cu. in. V8

by Henry Crichton
Chief Mechanic
Software For Cars
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Why is it a good idea to have one of our personal scan tools, even for a new vehicle? Read this story from our repair journals about a vehicle just out of warranty, and you'll find out why ...Number 6 rod bearings are worn thin

As in many cases, this 98 Dodge Ram pickup arrived under tow to our shop with an urgent request for us to find out what happened. The customer had described the sudden occurrence of a loud knocking sound, at which point he had shut the engine down and called for a tow truck. I pulled the pan off and discovered that the rod bearings had failed, with most of the trouble originating from number 6 cylinder.

As you can see in the picture on the right, the bearing shells had worn through to the point where they were disintegrating, causing unrecoverable damage to the crank. All the other rod bearings were worn down and would have failed soon.

Those bearing shells are from the number 6 rod connection. There are two pairs of bearings arrange side by side on the crank journal. One half had deteriorated before the other, leaving a 50 thou ridge gouged out of the crank journal, probably the cause of the loud knocking sound. The ridge can be clearly seen in the picture below, in the area around my thumbnail. This was the worst case, but I could see that all the bearings were substantially worn.

As I pulled it apart further, Ridge gouged out of crank jornal by rod bearingit became apparent that this engine would require a new crank and more or less a complete rebuild to bring it back to normal functionality. Since it had just passed out of warranty (75,000 miles), I prepared a repair estimate and discussed it with my client; he then gave us the 'go ahead' to start the rebuild process. 

Despite receiving a new set of faulty hydraulic lifters (internal pistons jamming, which would have blown the engine again immediately had I not spotted the problem), I managed to get the engine removed, rebuilt and reinstalled in less time than the factory spec of 40 hours. I then drove the vehicle for several days to ensure that proper break-in procedure was exercised and just to make sure everything felt like it was running correctly. This driving period also allows the OBD computer system to 're-learn' the operational parameters so that the client gets it back in optimized running condition.

This was also no thanks to the 'cab forward' recessed engine design which puts the back half of the motor well into the firewall pocket. So where do they put the distributor? In the front? On the side of the block? No, they put it right at the back of the engine, deep in the darkest recesses of the firewall pocket, with very little clearance for adjusting anything! I'm not a contortionist, but I had to become one for a half a day ... 

Technician's Note: When attaching the CPS (Crank Position Sensor) at the rear of the engine, be sure to get the stamped spacer from your Chrysler parts dealer to set the proximity spacing relative to the internal pulse generator. This is not mentioned in the service manual and it won't run beyond a rough idle without it.

So why did all this happen? I can only speculate about this, as we may never know the true cause. I looked for obvious causes, such as blocked oil passages, oil pump failure, customer abuse, etc. but none of these things were evident. Loose electrode in rotorIn talking with the client, I learned that it had previously cracked a head between the valve ports on the port bridge on one cylinder due to arcing between the secondary coil wire and one of the plug high tension wires, caused by poor routing separation (Chrysler has issued a TSB - Technical Service Bulletin about this known problem).

Thus I knew it had been previously stressed and probably overheated, which may have contributed to the bearing failure. After talking further to my client about some of the history of this vehicle, I learnt that while my client was away traveling, he had experienced misfiring problems and gone into the nearest Chrysler dealer for servicing. They were apparently very busy and not able to look at his vehicle for five days, so he went to an independent shop where they replaced the cap and rotor with aftermarket parts.

When I examined  the ignition cap and rotor, I found definite evidence of timing problems. Looking at the rotor, I found that the rivet that holds the rotor electrode in place had become loose, allowing it to flop about with a considerable amount of motion inside the distributor as it was running. Aside from a lot of wear, the distributor cap had plenty of white powdery material near the contact points, a sure sign of arcing and ozone generation. Furthermore, the carbon rotor pickup 'button' in the center of the cap was also heavily worn.

All of this adds up to the possibility of a condition known as pre-ignition, Distributor cap showing evidence of arcingwhereby the spark plug fires prematurely as the piston is still coming up to TDC (Top Dead Center). This causes a great deal of stress on the connecting rod bearings and piston assembly as the plug is not supposed to fire until the piston has more or less reached to top of its travel, ready to go back down again. Essentially, it was attempting to reverse the direction of the piston in mid-travel, creating exceptional loads on the piston assembly (including bearings). Since this engine doesn't have a knock sensor, the client may not have been aware of this condition. 

Yes, hindsight is a great thing, but our scan tool could have prevented this failure, as it would have shown clearly that there were timing issues associated with this engine. This would have been especially important in this case, as the engine does not have a knock sensor and thus would not necessarily generate an OBD trouble code, causing the 'check engine light' to come on. Henry makes final inspection of Dodge 318 engine rebuildTo get an idea of the kind of detailed reporting available on your PC with our scan tool, please see the actual sample data screens from our Toyota Solara demo vehicle below. A relatively small investment today can potentially save you thousands of dollars in repair bills down the line, as was the case here. And please, don't forget we have our online clinic facility where we are standing by online to help you understand any problems you may be having ...

Thanks, Henry

Actual screen capture of Toyota V6 datastream Software scan tool real-time parameters - Toyota Solara V6

Digital metering of V6 parameters with min/max tracking turned on Toyota V^ realtime digital metering with min/max trapping


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