Top 20 1999 GMC Sierra 3500 Questions & Answers

The video may help? https://www.google.com/search?q=1999+GMC+Sierra+Classic+3500+4x4+shift+down+while+driving+down+the+road ..

check fuel pressure should be 42 lbs. check filter if low some engines have 2 filters

You can have someone stand by the truck and they should hear the pump kick on when you turn the key in the on position. Can you spray fuel into the throttle body and will it start that will tell you if the ignition is ok or not and also tell you if you have fire to the cylinders. If it start right up and shuts off you either have a bad fuel filter, fuel pump or a plugged catalytic converter in the exhaust system.

Stalling when the engine is running could be faulty spark.look for faulty cables also.
Change the plugs and cables if you have nt done that during last maintenance

The ignition module is under the distributor cap. Mark the spark plug wires location then remove the cap. Remove the 2 screws and connectors.

Replace with new bulb you must not touch the glass part of the bulb.oils from fingers will cause it to burn out, also make sure that there is no condensation inside of the bulb housing as this will cause the bulb to short out and possibly cause a fire

There are two ECM fuses - marked ecm 1 and ecm B.ECM B powers the fuel pump and the Veh control module which handles most of the sensors.ECM 1 powers the ignition module, coil, injectors and the rest of the engine sensors.You may need a repair book with diagrams to check all of the circuits for shorts.

you have a wire grounding out somewhere. The only way I know how to find it quickly is not very safe and requires extra work later.

spark plug wires or coil pack

Yes, the system is called Passlock, and malfunctions regularly. Go to this link for an explanation of how it works, plus some tricks and tips on how to reset it, or bypass it.http://vatspasslockpasskeysecurityhelp.yolasite.com/

For the ECM 1 fuse to open you obviously have a short to ground , start with the injector disconnected and see if ECM 1 fuse still blows.If it does disconnect crank sensor, also inspect wires for the injectors or any rub through wires here is a diagram

The fuel filter may need to be replaced, but wont fix the problem you have. Its just a maintenance item that should be done every 15k miles anyhow. Check it over, check the large hose between the air filter and the engine make sure its secure. see if all hoses are ok, if you see/hear a vacuum leak. If all looks ok, time to have it checked by a shop.

there could be a bad wire somewhere between the solenoid and battery. that is the only thing i can think of if you have done everything else. I will lean towards starter relay, it should be in fuse box. if not that I would check for a bad ignition switch. not letting power to go to starter. good- day !!

Here's the best answer I can find-
http://www.fixya.com/cars/t5684489-eng_1
I've got one on a 2005 GMC Envoy so it must be pretty common.

I would check your throttle control valve. good luck.

Check your transmission fluid, if it is low, the transmission cannot shift into the correct gear from lack of hydraulic pressure. Be sure to check it while the truck is running.

If it is full, you may need to change the fluid and filter; over time the fluid will break down and trash the filter leading to low pressure problems which is why your truck fails to shift any more than 2nd.

Another problem may be that the torque converter is failing to lock yet again from lack of hydraulic pressure or its just worn out.

Yes if the lock switch is bad then you will loose control of the other windows. The switch is easy to replace and is available at NAPA parts online or your local NAPA parts house. This is a common problem with drivers door controls on gm vehicles.

i would think that the ign switch is really your problem if you wiggle it does it make any diff

check voltage at the connector with a 12 volt test light--grey and black wires.
Before doing this, check the ECM B fuse in the engine compartment relay box. You can also check the relay or interrogate the relay socket.

Please see my tip at http://www.fixya.com/cars/r6022358-relay_check for how to check a relay. Your wiring is pasted below. Please let me know if you have questions.

belt in tire might be broke?