SERVICE BULLET. LOW SPEED FUEL IJlMlTER

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NO:: 520 SERVICE BULLET SUBJECT: LOW SPEED FUEL IJlMlTER As legislation continues to mandate decreases in diesel engine emissions, engine manufacturers find it necessary to more closely control fuel

1 NO:: 520 SERVICE BULLET SUBJECT: LOW SPEED FUEL IJlMlTER As legislation continues to mandate decreases in diesel engine emissions, engine manufacturers find it necessary to more closely control fuel delivery and injection timing functions. Stanadyne plays a significant roll in this effort by developing special injection pump features such as the Low Speed. This new feature is designed to reduce wide-open throttle (WOT) fuel delivery below engine peak torque speed in order to control low speed black smoke and exhaust emissions. It is at speeds below peak torque speed (generally below 1600 ERPM) where there is insufficient air to burn the fuel normally injected. This is particularly true with turbocharged engines. The Low Speed (LSFL) feature is located in the hydraulic head assembly and uses an adjustable orifice screw and a fuel limiter piston to restrict the flow of fuel to the metering valve at wide open throttle. Figures la and lb show the locations of the adjustable orifice screw and fuel limiter piston. Adjustable Orifice Screw Figure la Figure lb Operation of the Low Speed The adjustable orifice screw and the fuel limiter piston are located in passageways that feed fuel under transfer pump pressure to the pump s Diesel Systems Division, Stanadyne Automotive Corp. 9 2 Deerfield Road, Windsor, CT 06095, USA Tel: (860) ; Telex: 99218: Telecopy: (860)

2 -2- S.B. 520 metering valve. At low engine speeds when transfer pump pressure is relatively low, the fuel limiter piston is seated blocking one of the two passageways leading to the metering valve. As such, the only fuel that reaches the metering valve is that which flows past the restriction created by the adjustable orifice screw. Figure 2 shows the position operation. of the fuel limiter components during low speed Piston Seated Preventing Flow Adjustable Orifice Screw Metering Valve L Fuel Flow Below Peak Torque Speed Figure 2 J As engine speed increases, transfer pump pressure also increases. The fuel limiter piston adjusting screw is set during pump calibration so the fuel limiter piston will be fully open by peak torque speed. When the fuel limiter piston is fullv onen, fuel flows unrestricted to the metering valve as shown in PimIre.? Piston Lifted Permitting Unrestricted Fuel Flow Fuel Flow Above Peak Torque Speed Figure 3

3 // -3- S.B. 520 t-- Maximum (wide-open throttle) fuel delivery from peak torque speed to rated speed is then controlled by the roller to roller dimension (leaf springs) as is the case with non-fuel limiter pumps., Figure 4 WOT Fuel Delivery Curves Low Speed vs. Baseline 100 ~~ ~. ~~.~..~~ 5 85 z 80 ;g O-._~~~..- ;E_ 70 --O-Non- 65 a- 60! I I I I I I I I I I Engine RPM Figure 4 compares the wide open throttle (WOT) fuel curves of a non-fuel limiter pump to a pump with the low speed fuel limiter feature. The orifice screw setting determines how much WOT fuel is.trimmed back while the fuel limiter Ipiston adjusting screw setting determines when the fuel delivery curve returns to the normal fuel curve. Servicing the Low Speed Feature The serviceable components and torque specifications for the low speed fuel limiter are shown below in Figure 5. Adjusting Screw Locknut Ibf-inches (9.0-l 0.1 Nom) Ibf.-inches Figure 5

4 -4- S.B. 520 Adjustments Whenever disassembly or calibration of a pump with the LSFL feature is required, the Welch plugs will have to be removed in order to disassemble and inspect the LSFL components and to adjust the fuel limiter settings during pump calibration. I. Welch Plug Figure 6 To remove the Welch plugs, position a l/s punch (or equivalent) in the center of the Welch plug and carefully strike the punch with a hammer until the punch pierces the Welch plug. NOTE: Use care to avoid damaging the adjustable orifice screw and fuel limiter piston adjusting screw. Once the Welch plug is pierced, use a prying motion to remove the plugs from the locknuts as shown in Figure 6. A fuel limiter adjusting wrench, P/N 33195, is required to make fuel limiter adjustments during pump calibration. To adjust the fuel limiter, insert the tool into the locknuts and loosen the locknuts with a 3/8 wrench. While holding the locknuts in place with the 3/8 wrench, use a l/8 hex key to set the adjustable orifice screw. Use a 5/32 hex key to set the fuel limiter piston adjusting screw as shown in figure 7. Refer to the individual specification for preliminary settings and the correct calibration sequence. Adjustment Figure 7

5 -5- S.B. 520 After each fuel limiter adjustment, tighten the locknuts to specification using a 3/8 crowfoot socket and the appropriate torque wrench. While holding the L,r*, adjusting screw firmly in place, to prevent calibration changes, tighten the locknuts using the tool to specification (refer to Figure 5). Following pump calibration, the fuel limiter Welch plugs must be installed into the adjusting screw locknuts to prevent tampering with these adjustments. Install the Welch plugs into the locknuts so that the bulge in the plug is facing outwards. As shown in Figure 8, position a 3/8 dowel pin (or equivalent) in the center of the Welch plug and lightly strike the dowel pin several times with a small hammer. The Welch plugs are properly seated when they are flat in shape. 3/W (9.5mm) Figure 8 Technical Support Group Product Support Departme:nt

DATE: April 5, 2005 SUPERSEDES: S.B. 373AR1 dated 2/26/99

NO: 373AR2 SERVICE BULLETIN DATE: April 5, 2005 SUPERSEDES: S.B. 373AR1 dated 2/26/99 SUBJECT: COLD START ADVANCE MECHANISMS Diesel engines have a tendency of producing white exhaust smoke during startup