1998/08/01 Caterpillar

Air cleaner contamination on these trucks may cause a number of concerns related to engine operation. "Engine running rough," "engine miss," and "excessive blow-by" can all potentially be caused by this condition. However, the same vehicle symptoms can also be attributed to other causes. It is important to diagnose each symptom, without bias, to determine the root cause. If one of these trucks exhibits any of these symptoms, or if one of these trucks is in your Service Department for general maintenance, it is important the truck receive an inspection specifically designed to identify the causes and corrections for this condition. If left untreated, this condition can result in possible engine damage.

In addition, Service Consultants should take time to explain this condition to the customer and to identify the preventative measures implemented. This includes explaining that if customer has reason to raise the cab, it is EXTREMELY IMPORTANT to pay close attention to the alignment at the tube. Misalignment can allow water to run down the side of the tube and enter the air cleaner canister and element. This connection must be secure, tight, and aligned properly.

All of these trucks should be inspected for air cleaner contamination, especially if the engine is exhibiting conditions such as "Engine running rough," "engine miss," and "excessive blow-by".

Inspection Procedure

* Remove the engine air cleaner element and inspect for excessive dirt, debris and/or water in the filter element and at the bottom of the air cleaner canister.

* Inspect the canister's condition on the clean air side of the filter element.

* Inspect the filter element for evidence of water intrusion.

* Remove the tube at the turbocharger compressor housing and at the clean air side of the filter canister. Disassemble and inspect all joints. Inspect the connection joint at the back of the air cleaner canister for dirt or water intrusion.

* Inspect the turbocharger blades for pitting and/or damage.

If your inspection shows evidence of dirt or water intrusion into the air cleaner canister or intake system, perform the following "Corrective Actions".

Corrective Actions

* Inspect the flexible canister drain valve at the bottom of the canister to ensure it is in place and operating properly. The valve drains water and debris from the canister and should be open when the engine is off.

* Vehicles with a metal canister may have the valve distorted by the air cleaner brace forcing the valve to pucker open with the engine running (engine vacuum normally closes the valve). If this is the case, loosen the mounting straps and move the canister outboard to eliminate the interference.

* Fabricate a valve shield to slip over the valve and protect it from road splash, etc. Use a six inch piece of sheet metal or tubing. Flange and shape one end of the tubing to fit the contour of the canister. Either weld or pop rivet the shield to the canister. Note, if welding the shield in place, first remove the canister from the vehicle and remove the valve from the canister.

* Spot paint any affected areas and then use some RTV to seal the joint between the extension and canister.

* For metal or plastic canisters, fabricate a 15 inch reinforced rubber extension and add it to the bottom of the existing splash guard.

* Also add a 6 inch extension to the inside edge of the splash guard.

To further help prevent contamination, there are several measures that should be kept in mind whenever working on or with these trucks.

* Whenever the cab is lowered into normal position, pay extremely close attention to alignment at the tube. Misalignment can allow water to run down the side of the tube and enter the air cleaner canister and element. The mating parts should come together securely at the rubber seal and the tube seal should be proper alignment.

* When power washing one of these trucks, do NOT aim the spray at the underside of the back of the cab air intake snorkel inlet.

* When installing the air cleaner element, make sure the element seats squarely on the bottom of the canister. Also, be sure to support the rear of the element when tightening the inner wing nut. This ensures a secure fit between the element and the seal at the canister's clean air side.

* Make sure the inner and outer wing nuts are tight to prevent gaps between the filter and the canister and/or between the air cleaner lid and metal canister.

Remember, it is easy to get the filter installed crooked or cocked, and this can cause gaps that allow dirt and water into the canister. So, take care to ensure everything fits properly, seals well, and is tight.

Information for this article was taken from SPV 98-7 Pontiac-GMC Service Professional video and summary card.