Hard starting issue has me baffled

[pacificdrumma]

Okay guru's this is one is for you. Here we go. 1996 K2500 OBD2. 175k miles, 75k on engine.
Symptom: Intermittent hard starting. Extended period of cranking for truck to fire. Starts to fire and slowly comes to life, runs, skips, puffs, coughs for first 2 mins. After that, runs fine. Drives fine, has normal power, does not skip or miss under heavy acceleration. Driving at night, I seem to see a little more haze than I am used to. Once it starts once, its good for the rest of the day. This is intermittent and happens without warning, and has happened at 50-65*. By the same token, the truck has also started fine in the same weather. It has thrown P0335 crank sensor circuit a malfunction 2x.

Work done: New AC Delco crank sensor, timing at -0.7 TDCO (within spec per local reputable garage that did it), glow plugs are 2 year old AC Delco 60g, lift pump is Napa/Carter for 93 truck, IP is 2 year old reman from Pensacola. Confirmed fuel pressure at filter, test light lit up when touched to glow plug terminal, have not check with multimeter, so not sure of actual voltage, but enough to light up the test light.

Again, once the truck does start, it is good for the rest of the day, which to me sounds like either losing its fuel prime or a glow plug problem. The lift pump is on a relay and runs whenever the key is on, and I did confirm pressure to the filter, so I think I am getting adequate fuel. I hope its not glow plugs, as I bought AC Delco so that I wouldn't have to replace them every other year.

I am stumped, ideas?

 

[ak diesel driver]

try disconnecting the temp sensor by the tstats before you start it

 

[JMJNet]

PMD on the way out? Make sure you have a spare?

 

[WarWagon]

"Starts to fire and slowly comes to life, runs, skips, puffs, coughs for first 2 mins." This has air in fuel written all over it. Clear return line on IP. When it starts to give you trouble, shut it off, pop the hood and look for air in the line. Then with the hood open look at the line while cranking and it's giving you trouble. GM manual is "check for air in fuel" Step #1.

Step #2: DID YOU CHECK FOR AIR IN FUEL!? Goto step #1.

Then and only then try everything else including electrical. Air can be intermittent from kinked hoses etc.

Does parking nose down in the driveway help?

 

[pacificdrumma]

Warwagon, thanks, I have not checked for air in the lines. To my knowledge, none of the lines are transparent. I will get some see-thru line at work.

 

[Will L.]

Needs to be the 1/4" return line coming out of the front of IP.

 

[pacificdrumma]

Looked the line this morning, its the 1/4" rubber line coming off the front of the IP and is about 8" long and goes down to a metal line?

 

[Will L.]

Yes.

 

[cornemuse]

My 6.2 Blazer ('84) had been hard starting for years. I replaced the batteries a month ago & it starts literally like brand new. I was truly amazed.

fwiw -corne-

 

[pacificdrumma]

I parked nose-down tonight to see what effect it has. On a theory level, can someone explain how air in a return line would get air into the IP and thus create a hard start?

 

[Will L.]

It's not that it is going from the return line into the ip. If you see air in the line at that location, you are getting air in the line inside the ip, and therefore need to repair a line somewhere that is sucking air in. Keep in mind the ip creates enough suction to pull fuel from the tank through a nonworking LP. The vacuum that is created will draft air into the fuel supply line and once it gets to the IP it will disrupt the proper pressure and flow of fuel going from the IP to the injectors.

 

[pacificdrumma]

Well 4 days of parking nose-down and no hard starting, which followed 4 days of nose-up parking and hard starting. Time to find the source of the air. Im thinking the FFM to IP line.