jfw432

I have a 99 5.3 LM7 out of a Silverado in my Jeep. I was recently working on a brake booster/master cylinder combo and the test drive felt fine but when I was pulling into my trailer for a wheeling trip I noticed a minor surge when cold. I suspect I noticed it at this time because I was making very small moves so it was more noticeable than just a normal drive. This surge did go away after the engine warmed up but I could hear a very slight hiss at idle. The hiss would change pitch when braking so I knew there was a vacuum leak in the booster but it never affected the engine once warm even under heavy braking. I drove all day like this and other than the hiss, everything was normal until the end of the day. I shut the vehicle off to look at a new obstacle like I had been doing all day but this time it refused to restart. It acted like the fuel pump died. It would fire for a second and then just crank like it had no fuel. If I turned the ignition on several times, it would fire for a second and then shut off. If I revved it a bit to try and keep it running a little longer it would still choke out and die but it would last a little longer. Every time I checked the fuel rail, there was fuel in it and I could hear the fuel pump priming. Obviously, I didn't have a fuel pressure gauge at the time though.

I tried for a while to start it but ultimately gave up for 15-20 minutes and tried again...still nothing. Tried disconnecting the battery and nothing. Eventually I pulled the MAF sensor connector and was able to get it running and it ran like normal for the rest of the day. The next day I went through the same thing. Pulled off the trailer and went about 100 yards and then it died. Went through the same process over about 30 minutes and never got it to run more than 1-2 seconds. I had 1/2 of a tank of gas but added 5 gallons to my 15 gallon tank just to rule out a bad gauge. Still nothing. Eventually I plugged the MAF back in and it seemed to run fine again. Long and short term fuel trims confirmed the booster is the source of my vacuum leak and I will fix that but I can't even find the leak with a smoke machine so it's very minor. Either way, everything cleans up when I plug the vacuum line.

Everything seems to be working perfectly now so troubleshooting is going to be a little tricky. Any ideas?