valsetz

96 Silverado K1500 4x4
5.7L 350 Vortec
175K Miles

I was having a problem getting it started in the winter when it was mid twenties and below. It would turn over more than the usual before it would catch and start. Sometimes it would start and sometimes it stop the starter from turning over but you could here it still trying and then it would just get it past that point and do it again. It also missed bad around 1600 rpms and up. I took it to a mechanic and he thought that it was the injectors and they needed to be replaced. So I bought the injector kit that changes them over to MPI and now I have a different problem. It starts up just fine but when you go to take off it almost dies. If you give it a bunch of gas from startup it almost backfires through the throttle body. The problem is at a much lower rpm than before and when the rpms get above 800 or so you can't tell that there is any problem. Also when I come to a stop and I still have it in gear it will rev up maybe 100 or 150 rpms twice and then go back to the normal idle speed. I am wondering if I have a vacuum leak somewhere. I double checked all vacuum lines they seem fine. Checked the PCV valve and it seems good. I did not replace the gasket on the plenum because it is rubber and was told that I could reuse it. It looked in good condition. Also checked the distributor cap to make sure the wires are in the correct order and they were.
When I took the plenum off I did see some oil in the intake. It was coming from the vacuum line that goes to the PCV valve. There was not a ton but enough to make the backside of the intake a little wet with oil. I was wondering how I can check for vacuum leaks? How can I check when I have to leave everything on for the engine to run? Any help would be great.

Valsetz

Blasterhappy71

A trick I use to look for vacuum leak around the throttle body is a spray bottle of water. While the truck is running/idling spray/mist around the throttle body and listen for the idle to change. The water will temporarily seal up the leak long enough for you to find it or put you in the ballpark. Hope this helps. Good Luck!

Also take a look at your EGR Valve and the EGR Solenoid if this doesn't work for you. Are you getting any codes?

valsetz

I checked for vacuum leaks by spraying with water around the intake but nothing. So decided to take it to a mechanic friend of mine. He found one hose that was broken and I installed one of the sensors that mounts on the left side of the plenum towards the front wrong and so it was not seated correctly and had a gap on the underside of it. Once he fixed these two problems then that made a big difference. But he said that it still had a rough idle that was real slight. Come to find that the mass air flow sensor would every now and then not work and when that happened then it would idle real rough. So we replaced that and that has solved all of the issues that I had. After the injectors were replaced and everything back to normal, I sure can tell the difference with the amount of power that it has and how smooth it runs now. Sure is nice to have everything back to normal. I think that next time I will take pictures of everything before I tare it down so that I remember the exact way that it goes back together. I had a question on that sensor the way to mount it when I was putting it back together but I thought that I had figured it out. Lesson learned.
Valsetz