GM Repair Questions? Ask a Mechanic for Answers ASAP
Thank you Mark, I understand but on my motor the timing indicator on my engine is different than any I have seen. It is just a small hump with a v grove cut in it. Is this the zero time mark.
You cannot adjust the ignition timing. You may need to adjust the distributor in order to prevent crossfire. To insure proper alignment of the distributor, perform the following:
Important: The Cam Retard Offset reading will not be accurate below 1,000 RPM.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Tighten Tighten the bolt to 3 N·m (25 lb ft).
Goodmorning Mark, I did as you explained to bring the #1 cyl to TDC. I had my son bump the ignition until I felt pressure on my finger at the #1 cyl and then looked at the harmonic balancer for the timing mark and finished rotating it to the timing hump on the block. When I first started this after speaking with you I realized I had installed the distributor incorrectly it was somewhere close to the #8 firing position and of course the engine would not start. I corrected that and the engine started. I have traced all the plug wires to be certain that the firing order is correct and it is.
To recap this is a 1999 GMC Suburban 5.7L. To clearify, when you said the rotor should be pointing at the #1 spark plug wire, do you mean the actual wire where it connects to the distributor cap or to the contact post in the distributor?
Also, I am not sure if I explained but the engine at idle seems to miss or skip every so often, could this be due to a faulty spark plug wire? I may have not explained earlier that all these skipping problems started when I put a small amount of gas in the tank, but all that gas has been replaced with fresh gas (super unleaded). Not sure if that was important.
The mass air flow (MAF) sensor measures the amount of air entering the engine. The VCM uses this information to determine the operating condition of the engine in order to control the fuel delivery. A large quantity of air indicates an acceleration. A small quantity of air indicates a deceleration or an idle.
The scan tool reads the MAF value and displays the MAF value in grams per second (gm/sec). At idle, the MAF value should read between 5 gm/sec - 7 gm/sec on a fully warmed up engine. The values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. When the VCM detects a malfunction in the MAF sensor circuit, the following DTCs will set:
The scan tool scan tool will display camshaft position sensor data as a 0 and 1 as the sensor pulses, the scan data will switch from 0 to 1. All camshaft position sensor data should be checked at idle. An error in the camshaft position sensor circuit should set a DTC P0340. The camshaft position sensor sends a signal to the VCM which uses it as a sync pulse to trigger the injectors in proper sequence.
The VCM uses this signal to determine the position of the #1 piston during its power stroke. This signal is used by the VCM to calculate fuel injection mode of operation. A loss of this signal will set DTC P0340.
If the cam signal is lost while the engine is running, the fuel injection system will shift to a calculated fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. The engine can be restarted and will run in the calculated mode as long as the fault is present .
The distributor is actually an assembly that contains the camshaft position (CMP) sensor, the cap, the rotor, and the shaft. The distributor is splined by a helical gear to the camshaft and rotates providing a spark to each spark plug wire. When servicing the distributor, it is critical to ensure proper cap sealing to the distributor body and correct installation to the camshaft. If the distributor is installed a tooth off in relation to the camshaft, a DTC sets. The distributor is repairable.
The camshaft position (CMP) sensor is located within the distributor. The CMP operation is very similar to the crankshaft position (CKP) sensor, however the CMP provides one pulse per camshaft revolution (1X signal). This signal is not detrimental to the driveability of the vehicle. The VCM utilizes this signal in conjunction with the crankshaft position to determine which cylinders are misfiring.
Thanks Mark, we are in the same page here I was making sure we were. I went and bought a timing light after I posted my last question and used it and found that the timing mark on the harmonic balancer was to the left of the timing hump on the block, toward the passanger side of the truck. Does this mean the distributor needs to be rotated clock wise on the installation??
Also, I was just asking about the other codes to see if they were signifcant to this part of my problem.