TOOL AS-WRENCH 3673534 - Caterpillar

Engines:
3508 (S/N: 5XM; 3LS; 3PS; 3TS; 5PW)
3508B (S/N: 2BM; 3DM; 4GM; 7SM; 6PN; 5PS; 1TW; 2HW; 3DW; 5KW; 1FZ)
3512 (S/N: 6PM; 3MS; 3RS; 3WS)
3512B (S/N: 2RD; 2AF; 8DF; 7HM; 8EM; 8RM; 4TN; 6WN; 1PW; 2GW; 3ZW; 4AW; 5AW; 6GW; 2EZ)
3516 (S/N: 7KM; 3NS; 3SS; 3XS; 1LZ)
3516B (S/N: 2TD; 9WF; BCK; 6HN; 7RN; 8CN; 8KN; 9AN; 1NW; 2FW; 2JW; 3CW; 3EW; 4BW; 8NW; 1HZ; 6HZ)
Reference: Engine News, SEBD9260, May 1998, "New Procedures For Eliminating Engine Speed Purps During Throttle Synchronization"Sometimes, one of the above engines may experience rapid fluctuations of engine speed. These rapid fluctuations are called speed burps. Use ET to check the throttle duty cycle and the desired engine speed. The throttle duty cycle and the desired engine speed should be steady. If the throttle duty cycle and the desired engine speed are changing at the same time as the speed burps of the engine, the Engine Control Module (ECM) may be having trouble with reading the speed signal.First, perform the "Throttle Position Sensor Test" that is in the applicable Troubleshooting Guide. If the problem is not resolved, carefully inspect all of the ground connections for each engine and each source of the throttle signal. These ground connections must be clean. This is especially important for the applications that follow:
Marine applications with two engine control modules
Applications that have the feature of synchronization of the throttlesEnsure that the throttle position sensor uses the same power supply and ground reference as the ECM. In marine applications with multiple engines that have synchronization of the throttles, be sure that large ground cables are used to connect all of the negative posts of the batteries.If the problem still exists, see the Reference Article.