Retarded timing on cold start......

[packmaster2r]

....that is the best way I can describe it. I am having a problem with my 1998 K2500HD 6.5/4L80E (48,000 miles) that only happens within a very narrow set of circumstances. Perhaps someone can help point me in the right direction. I'll avoid any opinions of my own, and just state the facts.

On cold starts (roughly 40 or below) the engine cranks and "starts" within 1-3 seconds consistently, but initially it vibrates violently, emits heavy, fuel-laden smoke, and lacks the usual clatter (sounds just like retarded IP timing on my old 6.2). Within 1-10 seconds, these symptoms go away, the usual clatter returns and the engine goes through the normal warm-up cycle without incident. However, a pronounced hesitation occurs under accelleration until the engine nears operating temperature.

The above problem is progressive, being more pronounced (and longer in duration) the colder the temperature is. If the block heater is used, there is no problem, and no hesitation.

Most Recent service: Dec 2004-Replaced fuel filter and installed new Stanadyne FSD+resistor on aftermarket cooler in hope of curing problem (to no avail).

Past major service:
Sept 2003: lift pump replaced (myself, warranty expired)
Jan 2003: IP replaced 37,120 m.(dealer, under 5/100 warranty)
Jan 1999: PMD replaced 6710 m. (dealer, under 3/36 warranty)

Took delivery new in April 1998. Above warranty repairs were to correct same symptoms, except for the hesitation which a new twist. Since the new IP was installed in 2003, a noticeable increase in cranking time was noted: used to fire instantly, after new IP it fired in 1-3 seconds.

I love this truck, the first and only new truck I've ever owned, and 4L80E shifts better than may car transmissions. Too much $$ invested in it to cast away lightly. Any help would be appreciated.

Thanks in advance,
Eric/packmaster2r

[joed]

I've been experiencing the exact same thing lately. My truck is also a 98. I also had my Inj. Pump replaced recently - this past year-about 7 months and 12,000 miles ago. Ever since then I've noticed the cold hestitating while accelerating and poorer cold starting.

As far as cold advance goes, as I understand it is determined by the coolant temp. sensor near the thermostat. The test would be to unplug the sensor (unplugging it tells the PCM it's -40 below) and start it. The advance should certainly be called for under those cicurmstances and glow time should be increased as well. I've checked this a couple times and haven't noticed any difference with it plugged or unplugged. I suspected the sensor before so I replaced it with really no change. I'm been beginning to wonder if the PCM is at fault as it processes the sensor input.

I've mentioned this to my dealer and they said to check the glow system, which seems okay.

I'm stumped as well.

Joe.

[joed]

To follow-up, what should the timing setting be (not TDC), when advanced versus normal operating temp?

One-thing that seems kind of strange on my truck is that my timing setting seems to be around 14 (according to my Car-Code software). I thought I read somewhere it should be more around 8 degrees? My TDC is -1.4, which is right where it was set by the technician a few years ago.

Any thoughts? Thanks. Joe.

[TAG]

There was a thread on this subject awhile back with many posts but nobody seems to know a solution. My 95 has started hard hot or cold since picking it up at dealer after warranty inj pump replacement over 3 years & 70,000 miles ago. I believe the problem is inside certain pumps, possibly a leaking check valve of some sort. The symptoms sure seem like air in the lines or pump head. Ihave replaced several pumps for customers out of warranty & they all start instantly like mine used to. I am almost aggravated enough to spend a thousand dollars on a new pump for mine as i believe these pumps last a long time & it grinds my a-- i have to put up with this. It always starts & runs great after it starts. This truck has been reliable as a rock & pulls hard with the mods i have done, slow starting my only complaint.

[nigeljones]

Hello there, Yes, I too have the exact same issue as packmaster2r with my 96 Sub. My IP was replaced under warrenty at 120,000 miles. I posted a similar question about a week ago, I believe titled "marine injectors". I now have replaced the glow plug timer, and replaced the fuel injectors with new not rebuilt ones, with no improvement.

I suspect one of two things. 1)As the engine wears cylinder pressure drops and on the compression stroke does not develop enough heat to ignite the fuel on cold days. 2)I replaced my original glow plugs after the IP was replaced for preventative maintenance. I suspect the newer plugs 60g needs a longer glow time to develop the same heat as the 11G (original plug). So now I am considering the "quick/instant heat plugs or the glow plug over ride kit.

There is a third point which I don't want to contemplate. That the head is cracked and weeps a small amount of antifreeze into the cylinder when cold, when enough heat is generated the crack seals up. I read that this is a known issue with Hummer and they have a recall on it. But I don't see any loss of fluid that I can not attribute to other issues. You can check for this. When cold check to see if the radiator tank is under pressure-it shouldn't be. Then start the engine and run for 60 sec's then recheck. If there is pressure it's coming from the leaking cylinder pushing back into the water jacket

Regards

Nigel

[BUZZ]

I believe that these new pumps are different somehow internally. Before mine was replaced it started great even in very cold conditions. 20 deg. no problem. Now it starts very lazy in warm weather and when below 40 plenty of smoke. There is another thread going with Shad having this issue and his is at the shop right now. After a new pump the shop indicates it still starts poorly.
Hopefully his experience will help determine the cause.
Buzz

[packmaster2r]

Yes, I read Shads post ("new pump"), and his problem does sound similar.

I may be able to get some help here locally, will keep posted.

-Eric