Engine Controls - On-Vehicle Adjustments: Other GMC Yukon Denali

ENGINE MECHANICAL

Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.

VALVE CLEARANCE

Note. All models are equipped with hydraulic lifters. Adjustments are not required.

IGNITION TIMING (GASOLINE)

Note. On all models, ignition timing is controlled by control module and is not adjustable.

CAMSHAFT RETARD OFFSET

Note. Distributor can be adjusted to prevent crossfire.

INJECTION PUMP TIMING

Original factory injection pump timing is usually marked with a static timing mark (a line scribed across both the pump mounting flange and front cover). This static timing mark should be used as a reference. If timing mark is not present on mounting flange, scribe a line to assist in how far injection pump needs to be rotated. To check and adjust injection timing, perform the following procedure.

1. Start engine and allow it to reach normal operating temperature. Connect scan tool to Data Link Connector (DLC). Set scan tool to OUTPUT TEST/INJ PUMP mode. Activate TDC TIME SET. The DES INJ TIME value will read zero. NOTE: If engine stalls when TDC TIME SET is activated, turn engine off. Loosen injection pump nuts. Slightly rotate injection pump toward driver's side of vehicle. Tighten injection pump nuts. Repeat step 1 .
2. With engine running at idle, ensure ACT INJ TIME displays 3.5 degrees. If timing needs adjustment, turn engine off. Adjust injection pump. A .039" (1.0 mm) pump movement equals about a 2 degree timing change.

TDC OFFSET LEARN PROCEDURE

This procedure is only used when one of the following conditions exist

1. DTC P1214 is set.
2. Engine has been replaced.
3. Front engine cover has been replaced.
4. PCM and injection pump have been replaced.
5. CKP sensor has been replaced.

1. Start engine and allow it to reach normal operating temperature. Connect scan tool to Data Link Connector (DLC). Clear all DTCs. Turn ignition on, with engine off. Using scan tool, select OUTPUT TEST/INJ PUMP mode. Activate TDC OFFSET LEARN.
2. If learned TDC OFFSET reading is between -.25 and -.75 degree, procedure is complete. If reading is not as specified, hold accelerator pedal in wide open throttle position for at least 45 seconds. Turn ignition off for 30 seconds. Start engine. TDC OFFSET reading should be zero. If reading is not zero, repeat step 1 .
3. With engine running, PCM will learn new TDC OFFSET when normal operating temperature is obtained and engine speed is less than 1500 RPM. New TDC OFFSET will overwrite previous reading. If new learned TDC OFFSET reading is not between -.25 and -.75 degree, turn ignition off.
4. Slightly rotate injection pump and repeat step 1 . A .039" (1.0 mm) pump movement equals about a 2 degree timing change. To achieve a negative reading, rotate pump toward driver's side. To achieve a positive reading, rotate pump toward passenger's side.

GASOLINE ENGINES

Note. DO NOT attempt to adjust idle mixture and idle speed. Both are controlled by Powertrain Control Module (PCM). Incorrect idle speeds are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.

Note. Controlled idle speed and IAC count can be checked using scan tool. See CONTROLLED IDLE SPEED & IAC COUNT table.

Controlled Idle Speed Check

1. Ensure no DTCs are present, IAC system is okay, and ignition timing is correct. Block drive wheels. Apply parking brake. Connect scan tool to Data Link Connector (DLC). Put scan tool into OPEN mode.
2. Start engine and allow it to reach normal operating temperature. Check for correct state of transmission range switch on scan tool. Check if idle speed and IAC valve pintle position (counts) are as specified. See «CONTROLLED IDLE SPEED & IAC COUNT»(ref-3756-S08172276832000051200000) table.
3. If idle speed is not within specification, see appropriate TROUBLE SHOOTING - NO CODES article.

CONTROLLED IDLE SPEED & IAC COUNT

DIESEL ENGINES

Note. Diesel engines are equipped with electronic fuel injection in which PCM controls all fuel delivery modes based on inputs from APP, ECT and BARO sensors. Idle speed is not adjustable.

Throttle Position (TP) sensor output voltage should be as specified. See TP SENSOR VOLTAGE table. TP sensor is not adjustable. If TP sensor output voltage is not within specification, throttle body may need cleaning. Check for binding throttle linkage or faulty TP sensor.

TP SENSOR VOLTAGE (1)

Throttle control is electronic with no mechanical link from engine to accelerator pedal. PCM monitors position of accelerator pedal based on signals from a nonadjustable Accelerator Pedal Position (APP) module. APP module is mounted above accelerator pedal.