Service slants

Motor, Nov 2003 by Savasta, Bob

GM Truck

Exhaust noise. GM says that a slew of its 2001-03 minivans (full list below) can give off an annoying rattle or buzz from underneath the vehicle, and that the most likely cause of the ruckus is contact between the inside and outside pipes of the dual-wall exhaust system. Installing a heavy-duty exhaust clamp to cinch the two pipes together should help alleviate the problem.

To home in on the diagnosis, start the engine and let it reach operating temperature to allow the exhaust system to expand. Now shift into Reverse and vary the engine speed between idle and 2000 rpm. If you don't hear the rattling or buzzing sound, look elsewhere for the problem. If the noise does become obvious, get hold of a 2 ½-inch exhaust clamp (Part No. 15712422 or equivalent), put a buddy in the vehicle, then put the van up in the air on a lift. Next, locate the front weld of the catalytic converter, then measure 3 inches in toward the front pipe (see illustration). This is where you should position the exhaust clamp. Install the clamp, then tighten its two retaining nuts to an initial torque of 30 ft-lb. Now have your buddy put the gearshift lever in Reverse while varying the throttle between idle and 2000 rpm. If the noise is gone, you're done with the fix. If it's still there, continue tightening the clamp nuts in increments until you've got adequate pipe crush to eliminate the noise.

Vehicles that can benefit from the above repair include 2001-03 Chevy Ventures, Oldsmobile Silhouettes and Pontiac Azteks and Montanas, as well as 2002-03 Buick Rendezvous.

Chrysler

Delayed transmission engagement. The owner of a 2003 minivan (Town & Country, Caravan, Voyager) equipped with the 3.3 or 3.8L V6 and 41TE automatic gearbox may come into your shop one day complaining of delayed or temporary loss of transmission engagement after startup. According to Chrysler, the condition usually follows an extended soak (four hours or more), and may be accompanied by a harsh 4-3 downshift and DTC P0944 and/or P1791 set in computer memory. Loss of prime in the front tranny pump is the most likely cause of the problem.

To narrow the diagnosis, hook up your scanner and pull and record any DTCs that might be present in computer memory. If codes other than those mentioned above are logged, take care of them first. If all you're left with is the P0944 and/or P1791, replace the front transmission pump with a revised unit (Part No. 05127197AA), which is less susceptible to leakage. Once you're done with the pump R&R, make sure the TCM is operating at the most up-to-date software level. If it isn't, reprogram the controller using the latest revision. Check with a dealer for those details.

Ford Truck

Steering fluid leakage. Some 2001-02 Escapes (build date prior to 2/12/02) may leak power steering fluid at the return and/or cooler hose connection to the intermediate tube assembly. According to Ford, the hose blowout occurs most frequently in very cold temperatures (-5° to -20°F) and is due to the increase in viscosity of the fluid at these low temperatures, coupled with weakness in the design of the original intermediate tube.

A new-design steel intermediate tube (Part No. 2L8Z-3A713-AA) is now available to address the problem. When installing the hoses onto the beefier tube, Ford recommends chucking the original spring clamps in favor of worm-type clamps, to increase hose retention.

Audi

Crank, no-start. Some 1998-99 A4 models with the 1.8L turbocharged Four may crank over but have difficulty starting. According to Audi, one likely cause is carbon buildup in the combustion chambers or on the intake and/or exhaust valves. Decarbonizing the top end of the engine should help alleviate the problem.

First, though, allow the engine to cool overnight, then do a complete scan of the engine management system and check for DTCs. If none materialize, turn on the key and make sure the ECT sensor reads the approximate ambient temperature of the air in the shop. Toss the sensor if it doesn't. Next, turn your attention to the altitude sensor, which should read zero at sea level and -5 for each 1500-foot increase in altitude. Replace the sensor as necessary. Also check that the throttle plate moves smoothly throughout its travel and that the throttle angle during cranking is greater than 6°. Clean or replace the throttle body, then reprogram the unit as required.

Now turn your attention to the fuel system and make sure pressure and volume are up to specs. No problems yet? Remove the spark plugs and check for fouling. Still nothing out of the ordinary? Perform compression and cylinder leakage tests on all cylinders. Low compression typically indicates carbon buildup on the intake and/or exhaust valves or in the combustion chambers, all of which result in the valves not seating properly.

Audi recommends decarbonizing the engine with Wynn's X-Tend V.I.C. Combustion Chamber Cleaner (Part No. 61510) hooked up to Special Service Kit No. 9025. Refore releasing the car to the customer, road-test it under load for approximately 10 miles with the engine between 4000 and 6000 rpm to blow out all the remaining junk and debris.