i bought a 97-1/2 about three months ago, and have encountered a very frustrating starting problem. it seems to not want to start on the first start of the day. i live in so. calif so the weather is moderate, and never gets below 50 or so. i can hear the pump pumping-up (which takes about 30 seconds continually) but it doesn't seem to have the starting power to actually fire up quickly. every once in a while, the batteries will "kick-in" and it will spin the starter about twice as fast, and starts immediately. i've taken it in to the local dealer which cost me over $3,500 and it is still acting the same. they replaced the injection pump, filter, timing sensor, and some other stuff, but it still runs really bad on different occasions. it also will not run well if i do not let it completely warm up (run for 5 minutes or so) every morning. i just joined your format, and am looking forward to someone knowing more than the 20 year old "technician" at the hummer dealership. any advice?

 

Hey Krablin,
First of all welcome to Hummer Forum. It sounds like you could have a glow plug problem. I know that you live in So. Calif., I live in Florida where the temp is about the same. These diesels need to have the glow plugs working because they have lower compression ratios than the big rig diesels. When you turn the ignition switch to the run position you should hear the solenoid click, this will turn on the glow plugs and the light on the dash (there is also a temperature sensor or switch that alows the glow plugs to work until the engine reaches 86 degrees). A way to check the glow plugs themselves is to locate each glow plug and take the green wire off of all 8 glow plugs. Next take a test light and hook it to the positive terminal of the battery. Probe with the test light to the terminal on each glow plug, if the test light lights the glow plug is good. If the test light does not light the glow plug is open and should be replaced. If you have even one bad glow plug it will cause a hard start. Next check if you are getting power to the glow plugs. Hook the test light to ground, probe the green wire that hooks to the glow plug and turn the ignition switch to run. Be kind of quick and look to see if the test light is on, the glow plugs are on a timer. If the test light is on your glow plug controller (solenoid) is working. These glow plugs draw 100 amps total so all connections need to be tight. I have seen the wire from the starter to the glow plug controller loose causing a hard start. Check the connections at the starter also. The glow plug controller is located at the rear of the engine on top, driver's side bolted to the intake manifold. It has a wiring harness with 5 wires and 2 studs one has 2 wires attached and the other stud has 1 wire these stud connections need to be tight. The temp sensor is located at the rear of the engine screwed into the head opposite the glow plug controller and the glow plugs are located below each injector. Since the glow plugs draw so much current it can cause the engine to spin slow, then fast when they turn off. The glow plug system is the easiest to check. You must wait until the glow plug light on the dash goes out before trying to start. There just isn't enough heat created in a cold engine by the compression to start it without the help of the glow plugs.

Now the fuel system. If there is any air in the fuel system it will start very hard and may not start at all untill all air is bled from the entire system. If there is a leaking injector it will bleed down (into the engine) over night or after sitting awhile, this will cause a hard start. An air leek in the fuel systen can be as simple as a loose hose clamp, cracked fuel hose or line or bad transfer pump (lower right front of the engine). I have had to replace all rubber fuel hoses with clear hose just to locate air bubbles in the fuel system. When you mentioned that it doesn't run well until it's warmed up, this could be caused by a bad injector bleeding down. There is a timing advance and a fast idle solenoid in the injector pump that was replaced by your dealer, make sure the wire is conneced. There are 2 wires on the injector pump, one is a heavy pink wire wich is hooked to the fuel shutoff solenoid and the other is also a green wire I believe that hooks to the idle and timing advance solenoids. The green wire is the one that you want to check, it jumps from one terminal to the other. One other thing on an average Injector Pumps should last about 60,000 miles.

I hope that I have been able to help you, good luck and if you have any other questions post them here.

 

thank you so much for the information. i was hoping to find a group of people in the know about the h1, and it looks as though i have. i have printed your reply, and will have it looked at in the next couple of days. i really enjoy the truck, and hate to have some little items ruin the overall feeling. thanks again