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Fuel System Presentation: Basic Fuel Supply & Coolant Fan Control

Join us for a club meeting on March 21, 2009, where Nick DiMonte will discuss basic fuel supply operation, tips for recalibrating fuel sending units, and a new switch mod for coolant fan control.

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Fuel System Presentation: Basic Fuel Supply & Coolant Fan Control

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  1. March 21st, 2009 club meeting Presentation topics: Basic fuel supply operation with tips on how to recalibrating fuel sending unit and New switch mod to control coolant fan. By: Nick DiMonte

  2. Agenda…. • Fuel system supply • Fuel Sending Unit • Coolant Fan Control

  3. Topic #1: Fuel system supply • Basic operation (up to the fuel regulator) • Fuel tank size, what changed • Fuel Evaporator function • Fuel pump components & controls • Testing fuel pump • Common fuel pump problems

  4. Basic fuel supply components • Tank • pump & strainer • pulsator (V6 only) • fuel pressure regulator • sending unit • supply and return lines • filter • vapor pressure regulator • vapor/air line • vapor storage tank (’87 & ’88 only) • vapor storage canister • filler gas cap All of these components are used to supply and manage fuel and to control emissions.

  5. Fuel tank ’88 tank with V6 sending unit • ’84 to ’86 • Size 10.2 gal • ’87 & ’88 • Size 11.9 gal Seam near bottom The gain of 1.7 gallon was due to two things, 1) enlarging the tank and 2) moving the vapor dome from the gas tank to a separate storage tank. Visual differences between the two tank size can be seen by the location of the tank seam. The 10.2 seam is in the middle of the tank while the 11.9 is near the bottom of the tank.

  6. Fuel pump • Specs: • V6 (50-65psi) Oper. ≈40psi • L4 (14-26psi) Oper. ≈10psi Probably the most troubling component, if not the sending unit, is the fuel pump. The pumps use bushings instead of bearings, which is the main cause for pump failure, but…… Multiple Pump replacements? In short period of time? Then check gray wire, from pump to connector. If the connector pin (gray wire) is darken, then it may have been damaged from a bad pump, causing voltage & current to be reduced going to the new pump. This will make the new pump work harder, causing it to prematurely fail. Some warranties on new pumps either require a new strainer or wiring harness. From Napa $12.59 From Advanced Auto $3.89

  7. Pulsator (V6 only) It reduces the fuel pressure variations that occur as the fuel injectors open and close, and to reduce operating noise. Has built-in grommets to seal the unit to the tubing ends. Failure would result in increased noise or loss of fuel pressure or volume. The pulsator isn't a routine maintenance item, although replacing the unit is recommended with a fuel pump replacement.

  8. Pressure Regulator To maintain a constant pressure differential across the injectors at all times, by controlling the flow in the return lines, basically, a calibrated leak. Quick vacuum control test: V6 Ignition “ON”, not running: 40.5-47psi V6 idling: should be less , but > 34psi. L4 Ignition “ON”, not running: 13-18psi L4 idling: 9-13psi Note: Applying 12v to terminal “G” on the ALDL connector can be used to test pressure.

  9. Sending Unit Vapor pressure/air inlet valve ( ≈4psi) (V6) C502 (‘84?) Fiero Store (V6 only) $197.95

  10. Evaporator system ’84 to ‘86 ’87 and ‘88 Vapor dome Note: V6 shown, L4 very similar.

  11. Evaporator system Summer heat creates vapors in the tank, which are funneled to the charcoal canister. • Standard charcoal canister storage • (acts as a trap) • In-tank or external vapor • expansion storage. • Gas cap (maintains tank pressure) • Sending unit pressure relief valve (4psi) • Air filter? Why? • Fresh air is used to purge the carbon • element, which is then consumed • in the normal combustion process. • Fuel tank source for air, when fuel • level drops in the tank. Poor idle, stalling or poor drivability if system is not working correctly.

  12. Fuel pump circuit/testing • Fuel pump controls: • Oil pressure switch • ECM controlled relay • Parallel control for pump • Why? • As a backup? • Checking / testing pump at ALDL • With DVM set to volts, measure • across terminal ‘A’ and ‘G’ • Turn ignition “ON”, should see 12 volts • for two seconds. Is pump on for 2s? • Checks fuse, relay & wiring (120). • Turn ignition “OFF”, apply 12 volts to terminal ‘G’. • Forces pump to run. Good time to measure pressure. (L4 similar)

  13. Topic #2: Fuel sending unit • Testing gauge & sending unit • Common problems • Recalibrating sending units • Repairing sending units • Source for parts & service

  14. Testing gauge & sending unit • Resistance values for the fuel gauge. • Full = 90 ohms • ½ = 45 ohms • ¼ = 22.5 ohms • 1/8 = 11.25 ohms • 1/16 = 5.625 ohms • Empty = 0 ohms • Note: One bad ground connection could be 4-6 ohms easy. Times this • by two or three other bad connection and your gauge could falsely • be reading an 1/8 to ¼ tank.

  15. Testing gauge & sending unit • First, verify that the gauge is working. • Previous owner may have attempted to fix gauge error? • May have remove needle and repositioned it?! • Band-aid solution! • You still have a problem, and, overtime, may only get worse.

  16. Testing gauge & sending unit • Check for “Empty” on gauge first • Disconnect C502 connector • Short Pink and Black wires together on C502 (on firewall) • Ignition ON • Should get “Empty” on gauge • If not, short pink to ground • Empty = yes: repair black wire • Empty = no: repair pink wire or gauge Note: The Black wire should be zero ohms to ground, if not, this resistance will add to the Empty error condition.

  17. Testing gauge & sending unit • Cont. • Check for “Full” reading on gauge • Need 90 ohm resistor (Radio Shack: 68Ω and 22Ω ohm resistor in series) • Connect 90Ω across Pink & Black wire. • Wait about one minute….. • Should read “Full” • If not, check Pink wire and/or gauge • Most likely a gauge problem at this point.

  18. Testing gauge & sending unit If gauge is functional, check sending unit • Only make sense to remove from tank to test. Two types of rheostats used on Fiero. • V6 plastic case • L4 metal shell • Both are 0-90 ohms.

  19. Testing gauge & sending unit L4 V6

  20. Testing gauge & sending unit • Using an analog multi meter will be more desirable than a digital multi meter. • A DVM can be to bouncy. • Test “empty” reading by moving float to bottom position. Measure resistance • across Pink and Black at C502 connector. Should get a reading of zero ohms. If not, measure the resistance from C502 to the rheostat. This should be zero. If not, check for corrosion.

  21. Testing gauge & sending unit Now check the full range of the rheostat, starting from empty position. (This is were an analog meter comes handy) You should notice a linear increase from 0 ohms to 90 ohms. If not, look for dead spot on the rheostat and on the wiper arms.

  22. Sending unit (repair) • A complete replacement unit can be found a the Fiero Store for $197. Web site • states it can be fitted for the L4 by changing the connector. Not sure about the • angle of the fuel lines that an L4 may need. The ’87 & ’88 will need extra rubber • hose for the vent tube. • Tri-Star Radiator will sell rheostats or repair your sending units or even sell • you new (or rebuilt) sending units. For both L4 and V6. • replacement rheostat $59 • repair or rebuild $75 to $150 • Web site: www.tristarrradiator.com • Phone #: (800) 216-4940 • The Fiero Factory will sell a used recalibrated unit for about $175. They use • solder and/or rewind the rheostat.

  23. Adjusting sending unit Note: Due the limitations of the metal rheostat, only the plastic rheostat assembly will be discussed here. The main problem with the plastic rheostat assembly is when the cooper film under the windings corrode, causing about 5-6 ohms of resistance.

  24. Adjusting sending unit Remains of cooper film. Zero adjustment plate (mod). (Better solution than trying to use solder.) Provided by Tri-Star Rad. (used)

  25. Topic #3: Coolant Fan Control • Why ? • You can use a simple solution….. boring….. • A cool (no pun intended) solution. • Use your rear defogger circuit! • You don’t use it for defogging anyway.

  26. Coolant Fan Control What’s involved: • Modify defogger relay (disable timer) • Need extra relay. Any relay that has at least one N.O. (normal open) contact. • I used one from a Nissan quest. • Some wire. Recommend 16ga in black, green and purple (or blue). • Connectors.

  27. Coolant Fan Control L4 similar Connection point for manual control. Green Black

  28. Coolant Fan Control To C100-F9 Dk-Grn/Wht Modified Relay Green Purple (or blue) Cut here. Or disconnect? Black SPST N.O. Relay

  29. Coolant Fan Control Defogger relay circuit

  30. Coolant Fan Control Jumper wire to disable timer circuit. Defogger relay

  31. Questions?

  32. Thank you for your time.

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