I know this many have been covered before in one fashion or another, but I’m lost. Last year my 96 Suburban started have cold start problems, so I figured that with 160k on the clock, I figured it was time to replace the glow plugs. With that done starting did improve just a little but I dealt with it. Now this year cold starts have gotten worse, if the truck sits for more than about 6hrs not plugged in, it takes several cranking cycles before it starts. Just last week I pulled it in the garage to change the oil and put a manual glow plug circuit in, which works well. After sitting in the garage for 4 days, I let the truck go through its normal cycle and then extended the glow time manually. After 5 tries and the truck not starting, I plugged the block heater in at about noon. This morning @ 4:30am I went out, let the truck cycle once and it started right up. I check and the glow plugs are getting 12vdc. I’m totally lost as to why it will not start unless it has been plugged in. I know the injectors and/or IP pump may be an issue now that the truck has 180k on it. I would have thought that using the manual glow pug control would have been just as good as plugging in the block heater.