2003 GMC van with a 5.3L vacuum

[missibarlow2889]

My 2003 GMC Envoy 4.2L Will quit while driving. Sometimes it will start right back and sometimes you have to let it sit a while then It will start. Have changed the fuel pump. Someone said it could be the Crank sensor?

[carriedi]

A lost crank signal will cause your engine to shut down. It will not restart until the signal resumes. The problem here is that a shop will have to diagnose this and they can only verify it if it happens while they are checking it. Do you have your check engine or service engine soon light on? If it is on, your computer may have stored vital information that the technician will need to help verify the problem. If there is no useful information stored in the engine control module the technician will only see that everything is working normally until the problem occurs. Everything is working if the vehicle is running. They will need to either shut down while they are graphing the crank sensor in correlation to other sensors or have it not start for them to see what is missing.

[damon]

I want to replace my 4 banger with a v6 can it be done. What do I need to do this will my wiring hook up or do I need other harnessse

[carriedi]

it would be better for you to go and buy a v6 truck than to spend the money and work (with the headaches) to change the truck over.

[doublejippo]

the speedometer stops working and makes the transmission downshift, we replaced the vehicle speed sensor with no luck

[carriedi]

check out your instrument cluster. speed sensor sends info to the cluster and then it goes out to other computers. If the cluster turns off the pcm sees no speed reading

[nzhoppy1]

97 GMC 5.7 auto. 4wd. Can't shift from 4wd back to 2wd ?

[carriedi]

you should check your 4wd module. have it scanned and see what it going on. Have you checked to see if the transfer case is staying in 4wd or is the front axle staying locked? The front differential actuator might be stuck in the engaged position while the transfer case is in 2wd. Or the transfer case could be stuck in the on position. You will have to find out which part is not turning off.

[nzhoppy1]

Where is the 4wd module located ?

[carriedi]

the transfer case control module (TCCM) is located under the dash mounted to the steering column support bracket. it's just a control module. It doesn't have any serviceable parts in it. why do you ask? Have you scanned it? What are the codes? You scan it through the ALDL, same place you scan the engine, ABS, airbag, etc.

have you found out if the transfer case is stuck in gear or if the differential is stuck locked in? You know, you could have a bad encoder motor...

need more info, feedback to say what to check for...

[byopautotire]

I changed the upper intake gaskets properly and changed valley cover gasket however it still sounds as if there is a vacuum leak! I checked the vacuum lines which aren't many, all of them look good. I do know that when I accelerate it sounds as if the leak goes away! but it has a hard time shifting gears in the transmission! Please help if you got an ideal, I am ready to breakdown...

[carriedi]

To find a vacuum leak, I use a stethoscope with the sounding drum off so it's just a tube that I can listen through and try to find where the sound is coming from. I also use a propane tool that has a tube and a small pipe that can let propane gas out and move that around to see when the engine sucks in the propane the engine speed will react.

you could also use a scanner to see if you have a vacuum leak by looking at your fuel trims at idle.

It's possible that you may not have an external vacuum leak. PCV valve whistle?

Other than the sound, how is the engine running?