Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 284 (ENGINE CONTROLS - TROUBLE SHOOTING - NO CODES)SYMPTOMSHARD STARTSENSOR/SYSTEM
1999 GMC Forward Control 5.7 R, Automatic
Hard Start: Sensor/System
1999 GMC Forward Control 5.7 R, AutomaticSECTION Sensor/System
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
- Verify that the Engine Coolant Temperature (ECT) sensor is not shifted in value. Connect a scan tool. Compare the engine coolant temperature to the Intake Air Temperature on a cold engine. The ECT and IAT sensor values should be within 5°F of each other. If the ECT sensor is out of range with the IAT sensor, measure the resistance of the ECT sensor. See TEMPERATURE VS RESISTANCE .
- Inspect the Mass Air Flow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start.
- Inspect the Camshaft Position (CMP) sensor for proper mounting and/or a bad connection. An extended crank occurs if the PCM does not receive a CMP signal.
NOTE:
The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine. Install the MAF in the proper direction.
TEMPERATURE VS RESISTANCE
| Temperature °F (°C) | Ohms |
| 302 (150) | 47 |
| 284 (140) | 60 |
| 266 (130) | 77 |
| 248 (120) | 100 |
| 230 (110) | 132 |
| 212 (100) | 177 |
| 194 (90) | 241 |
| 176 (80) | 332 |
| 158 (70) | 467 |
| 140 (60) | 667 |
| 122 (50) | 973 |
| 113 (45) | 1188 |
| 104 (40) | 1459 |
| 95 (35) | 1802 |
| 86 (30) | 2238 |
| 77 (25) | 2796 |
| 68 (20) | 3520 |
| 59 (15) | 4450 |
| 50 (10) | 5670 |
| 41 (5) | 7280 |
| 32 (0) | 9420 |
| 23 (-5) | 12300 |
| 14 (-10) | 16180 |
| 5 (-15) | 21450 |
| -4 (-20) | 28680 |
| -22 (-30) | 52700 |
| -40 (-40) | 100700 |
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.