Problem may be in Passlock security system

Hey there, time traveller!
This article was published 26/08/2005 (7346 days ago), so information in it may no longer be current.

Q I have a 1998 Chevy Silverado with 5.7l engine. About two months ago I had the fuel pump and fuel filter changed, because the truck wouldn’t start. The truck had been running fine until recently. Now, from time to time, the truck will not start. It will crank over and fire for about a second and die. This has happened several times lately. The last few times I have put a small amount of fuel in the tank and it starts. When this happens it doesn’t matter how much fuel is left in the tank. It could be 1/4,1/2,or 3/4 full. Could this be related to the Passlock system on this truck, because around the same time as this trouble started the security light has been coming on and staying on from time to time.

I have been told it could be in the fuel pressure regulator bleeding down. With the truck running, it runs at 52 lbs of pressure. The other thing I have been told is that the fuel pump check valve could be leaking at times. I should mention that when this happens, I can hear the fuel pump go on when I turn the key on so I don’t think it’s a wiring problem. It only seems to fail after the truck has been running for a while and then shut off. Any information you could give would be appreciated.

A. Your starting problem sounds typical of a weak fuel pump. The fuel pressure is fine when running but check the pressure when you first turn the key on but before cranking the engine. The pressure should go up to above 62 PSI. If it doesn’t, then the fuel pump may be faulty or a bad electrical connection to the pump is lowering the voltage to it.

Having said that, the Passlock security system would cause a similar fault. If the system doesn’t see the correct signal, the engine will start but then stall. The security light would come on to indicate a problem. Because the security light has come on sometimes, I would check this system out first.

The Passlock system uses two hall effect sensors in a module placed around the ignition lock. When the key is turned, a magnet on the tumbler assembly passes the first sensor. The second sensor is a tamper input and the magnet should not move past it to turn it on. Wires from the sensors run to a theft deterrent module near the base of the steering column. If this module sees the correct sensor input, it will send a signal to the engine computer to enable fuel injection.

I would first look for broken or loose wires at the hall effect sensors and theft deterrent module. If nothing is obvious, a computerized scan tool is needed to complete the diagnosis, so it will need to be looked at by a dealership. Because the problem is intermittent, look carefully for partially broken wires first, though.

Q. I am a relatively proud owner of a 2001 Dodge Ram 2500 4×4. Gradually, a noise has developed in the clutch system. The noise sounds like marbles, which goes away when pushing the pedal to the floor, so the Dodge folks changed the transmission, and low and behold it was still there.

Could you find out if they use a constant contact release bearing on my truck or is there really supposed to be some free play? Maybe you have some connections that I obviously I will never have.

A. The release bearing on your Dodge Ram is a constant contact bearing. This means that the release bearing is constantly touching the clutch pressure plate and turns all the time. There is a small spring inside the clutch hydraulic slave cylinder that keeps the bearing in contact.

This type of bearing is very common now. In the past, the release bearing was only supposed to touch the pressure plate when the clutch pedal was pressed. Those systems use a return spring on the release bearing mechanism and have some freeplay in the clutch pedal linkage that required occasional adjustment. With constant contact bearings, there is no freeplay adjustment. A new release bearing is needed if it is making noise. Too bad they didn’t change it when the transmission was out, because it will need to be removed again to replace the bearing.

Jim Kerr is an experienced mechanic, instructor of automotive technology and freelance journalist. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net