1996 Suburban Hard to Start when not Plugged in.

[akskycowboy]

Hi all,

I have a 1996 Suburban K2500 and in the recent weeks it has become hard to start if I don't keep the block heater plugged in. This happens in temperatures ranging anywhere from 10 degrees F to 40 degrees F at 9100 ft elevation. I suspect it's something within the glow plug system as when it's plugged in it only sputters black smoke for a few seconds and I can coax it to normal idle with the accelerator pedal. Prior to the most recent weeks it started normally and only required being plugged in for a few hours in the middle of the night (had it on a timer to come on three hours before I had to leave for work). In Oct I changed the Glow Plugs and controller. The wait to start light comes on as if the system is working, and it has not thrown any codes. Any input would be greatly appreciated.
Thanks in advance

[john8662]

Test your plugs individually first. Some plugs depending on which brand and type might have already failed. Simple test, unplug each one, test with a test light (test light lead plugged onto + side of battery) the poker side to the glow plug terminal. If it lights, probably good plug.

[More Power]

from 10 degrees F to 40 degrees F at 9100 ft elevation.

The altitude is a big factor here.

Aside from verifying all eight plugs are working correctly like John suggested, you could try a fuel treatment that increases the fuel's cetane. It makes the fuel easier to ignite.

Also, I'd consider having the injection timing checked. I'd set the TDC Offset to a value in the -1.5xx range. More negative means more timing advance. Some suggest -1.9xx for best performance, but it's not known what more negative than -1.5xx might have on head gaskets. The GM service manual calls for ~-0.5xx.

Jim

[akskycowboy]

I should mention that the vehicle has 89K on the odometer, the new plugs are from NAPA and are Bosch brand. The fuel filter was recently changed as well and I run fuel additive in every tank, even though they have a good winter fuel mix here (Frisco, CO). I may have to search high and low for a mechanic that's familiar with these engines, could possibly have to go to Denver? Again all input is welcomed and needed. Would the altitude not also be problematic when it's plugged in too?

[More Power]

I should mention that the vehicle has 89K on the odometer, the new plugs are from NAPA and are Bosch brand. The fuel filter was recently changed as well and I run fuel additive in every tank, even though they have a good winter fuel mix here (Frisco, CO). I may have to search high and low for a mechanic that's familiar with these engines, could possibly have to go to Denver? Again all input is welcomed and needed. Would the altitude not also be problematic when it's plugged in too?

Diesel combustion occurs because of heat (due to compression and glow) and the fuel's ignite-ability. There's less O2 at higher altitudes. The block heater helps to overcome that.

Advancing the injection timing can help a hard cold starter because the fuel is in the combustion area a little earlier and little longer, allowing whatever heat there is more time to act on it.

Look at the bottle your fuel treatment came in. Look for the words "cetane" or "cetane booster".

Extending the glow cycle could help too. It's a little more complicated to get a longer glow cycle in the electronically controlled vehicles, but in the past we've discussed how to do it a couple of different ways. Search the forum for ideas.

Jim

[akskycowboy]

Thanks Jim,

What you are saying is valuable info. But, I still am wondering why it would start at -19F not too many weeks ago (plugged in) with virtually no "dieseling"on start up and I could even let it sit in a parking lot for 6 or 7 hours after running in the morning, and it had no difficulties (temps @ or near 0 F). If the glow plug harness fails does it throw a code?

[DennisG01]

I'm not sure if a failed controller will throw a code - I'll let someone else answer that.

But, I think the first thing to do here is verify that you have 12V leaving the controller (when the WTS light is on). If that's good, check to see that you are getting 12V to all plugs (when the WTS light is on) and then verify that all plugs are good. Just 'cause they're new don't mean they's good!

EDIT: Are you familiar with "how" to use a multimeter to check voltage and resistance? And, do you have one? Just asking.

[More Power]

Thanks Jim,

What you are saying is valuable info. But, I still am wondering why it would start at -19F not too many weeks ago (plugged in) with virtually no "dieseling"on start up and I could even let it sit in a parking lot for 6 or 7 hours after running in the morning, and it had no difficulties (temps @ or near 0 F). If the glow plug harness fails does it throw a code?

A correctly operating block heater will raise the engine temperature to somewhere in the 70-80F range, if given enough on-time, and the vehicle isn't parked in the wind. Block heaters are essential.

Sitting overnight has more of an effect on very cold starts than sitting 6-7 hours during the day. I drove a 6.2/6.5 to work for 15 years here in Montana. During the coldest of days I'd drive the truck for 15 minutes during lunchtime just to make sure it'd start at 5pm. I always used the block heater (on a timer) during the 2-3 coldest winter months, and my truck sat overnight in a garage.

Sounds like something changed. Things to consider... fuel filter, lift pump, fuel quality or thick motor oil. Also stuff happens... maybe the glow controller/plugs is/are slacking off. Maybe the injection pump and injectors have finally reached a point in their useful life that they impact cold-very cold starts.

Do what you can, eliminating the easiest and least expensive possibilities first.

A faster cranking speed helps a diesel start easier. Fuel is more easily atomized with a faster/higher pressure injection event. More heat is generated in the combustion area of each cylinder with a faster cranking speed. Synthetic motor oil is useful to preserve cranking speed during cold weather.

Your vehicle PCM will generate a glow system fault code if the glow relay doesn't energize when the PCM calls for it. It reads the "wait to start" lamp circuit. If the WTS lamp is cycling normally, your PCM will see that as being OK.

It's about 3000' feet elevation here in western Montana. I used to hunt in an area that was at 7500'. It was also cold there during hunting season. My diesels always started harder (sometimes barely started) there at say +10 to 20F than it did here at the same overnight temp.

Jim

[trbankii]

But, I think the first thing to do here is verify that you have 12V leaving the controller (when the WTS light is on). If that's good, check to see that you are getting 12V to all plugs (when the WTS light is on) and then verify that all plugs are good.


A faster cranking speed helps a diesel start easier. Fuel is more easily atomized with a faster/higher pressure injection event. More heat is generated in the combustion area of each cylinder with a faster cranking speed. Synthetic motor oil is useful to preserve cranking speed during cold weather.

What is the condition of your batteries? I know I've had to put my truck on the trickle charger a few times this winter to "top if off" so that it would start readily on those under 20℉ mornings. As Jim says, if it is spinning a bit slower it is harder to start - which takes longer - which puts more strain on the batteries - which slows it down more - which...

[akskycowboy]

I have new batteries, and I'm running synthetic 5W-40 for the winter. Logic tells me it's in the glow plug system somewhere. I'll have time next week to look at it, until then I'll keep it plugged in and if I can't, start it every couple of hours. Thanks for all of the input.

[trbankii]

How new are your battery cables? Searches will show you that even if the ends look decent, there can be corrosion inside the cables. And since the alternator feeds the driver's side battery and the starter/glow system pulls from the passenger side battery, if the cables aren't in excellent shape the passenger battery can easily get worn down and not fully recharged - particularly in cold weather when the demands on the batteries are high.

[akskycowboy]

The batteries are fairly new, but I will check them both to determine that they are at the proper voltage. Thanks for the info!

[trbankii]

I have new batteries,


How new are your battery cables?


The batteries are fairly new

Again. You can have brand new batteries and if the CABLES are shot it won't make much difference.