GM 6.5 TD engine poof problelm

[Bezzer]

The strangest thing about my problem and main reason I joined this site was about the 6.5 TD and I can't imagine that nobody (so far) has had a backfire when starting their 6.5TD engine.

Being you are a "Well-Known Member" of this sight...Your last remark was crude and un-called for in this discussion!

I hope that there are others that will understand what I meant and continue to offer better 6.5 TD solutions to my problem.

 

[dbrannon79]

The backfire you are experiencing is a cold cylinder not fully burning the fuel injected into it. if the glow plugs aren't working properly on all 8 cylinders, you will experience this. as soon as the cylinders have a little heat in them, the backfire will be gone.

find your glow plug relay. this will look like a starter solenoid having two large terminals on the top. use your meter and test to see if you have a full 12 volts to the hot side of this relay. then connect to the other side of the relay, place the meter where you can watch the display while cycling the key on and off. with the key on (engine cold) you should see at least 11 or so volts (slightly less due to the amp draw from the glow plugs) for about 5-8 seconds then it will switch off.

report back with what your voltages are on both sides of the relay. (it should be located on the drivers side rear of the intake close to the valve cover and looks like this photo.

 

[Bezzer]

Thanks for your quick reply!
To answer your questions:
I have 12.65 volts on the glow plug relay.
The other side of the relay read 00.6. Then after the 8 seconds it jumped to 12.24 volts and on and off to 12.20 volts.
Thanks!

 

[ak diesel driver]

somethings not right there, even with all the glow plugs working it should be around 9-10v

 

[Paveltolz]

Thanks for your quick reply!
To answer your questions:
I have 12.65 volts on the glow plug relay.
The other side of the relay read 00.6. Then after the 8 seconds it jumped to 12.24 volts and on and off to 12.20 volts.
Thanks!

The Glow Plug Relay runs steady until Glow Plugs are sufficiently warmed. Then, it will stop sending power to the plugs BUT, it will cycle off and on several times.
Are you still only seeing 6v at the Glow Plugs then?

FWIW, I had a couple of backfires once but, it was on initial start of my rebuilt engine. We'd squirted 40w oil in the intake runners for each cylinder and got a few very loud Pops & POW a few times. Scared the "Tesla" outa me. So, while self induced, it can happen.

 

[Will L.]

I am not a fan of just installing parts. But glow plugs are like an oil filter- a consumable component.
Our friend from AK is correct there are some 6v glow plugs and there are also some 24v glow plugs along with the more common 12v ones.
Hmmwvs and the military square body trucks all run the 24v as an example.
I tell everyone the same thing about glow plugs:
ONLY USE AC Delco 60G. Rip out and throw away all the others.
If a person has a 6v or 24v system- alter it. In this case the rv has a 12volt system.

Glow plugs are good usually for 75,000 miles. Extremely cold or hot gets less more but on average 75k. Roughly $10 each so pony up and do some maintenance. ONLY buy them from a brick and mortar authorized AC Delco distributor. Napa, Oriellys, etc. there are tons of fakes out there and they will destroy your engine.

Unscrew them, slide them out. If it doesn’t slide out, screw it back in by hand and leave it for the moment. Then order the removal tool from LeroyDiesel.com.
Personally I bring that piston to TDC before using the extraction tool. Then use a rubber tipped blower from compressor and blow out the hole afterwards.

A great idea while all 8 plugs are out is to do a health check on the engine via compression tester. Dry test only. Write down the results of each cylinder and post here.

Then before installing new GP, a dab of anti-seize on the threads.

As to electrical testing glow plugs- I have learned it is often a waste of time and can lead to chasing down the rabbit hole when not needed and can mislead the chase when it is needed. How?:
A glow plug has set ohm. But when it crystallizes that increases resistance.
When it is burning away that lowers resistance.
I have removed plugs that tested good and did not heat well at all. I have had plugs that failed testing and worked well.
I recognize some folks don’t understand how to do proper testing but outside of all the ase certifications I held- I am also a licensed journeyman electrician, so know what I am doing there.
If you ever have to test glow plugs- just remove them, apply power and see that they glow red across the entire tip and shut off cycling properly.

 

[dbrannon79]

@Bezzer when your measuring the two posts on the glow plug relay, one side will have 12V full time. the other will only have voltage when the relay is energized. this only happens with the key in the run position and will only stay energized for a couple of seconds. so it might be helpful to have someone in the cab ready to turn the key at your command. if you can. take a pic of what you are probing and when (showing what the meter is reading) we can help you further once we are certain the relay is working properly.

 

[WarWagon]

The strangest thing about my problem and main reason I joined this site was about the 6.5 TD and I can't imagine that nobody (so far) has had a backfire when starting their 6.5TD engine.

Again a picture is worth 1,000 words. A video with sound eliminates strange words used to describe sounds. Best attempt ever made to put sounds to words was MAD Magazine.

Otherwise we are down to "a funny noise" Could be nothing to worry about or can get real expensive. Even with video I find that NO ONE on forums can identify a repair sleeve moving in a cylinder from the funny knock noise it made during a combustion stroke as the rings floated over a low spot in the sleeved cylinder. The noise quit when the companion cylinder did not experience combustion during the power stroke. Always questioned the scanner IF it was shutting off the proper HPCR cylinder...

So unless you do and post a video linked on here we are really Deaf and Blind to help you guess as to what may be wrong.

@Will L. The OEM Glow plugs on most 12V battery 6.2 and 6.5TD engines are indeed labeled 6Volt to reduce the heat up time. Said another way: so the trick fancy time/temp controller can F-Up and swell/burn glow plugs out while trying to heat them up in less than 60 seconds a 12V plug would take.

 

[Big T]

The backfire you are experiencing is a cold cylinder not fully burning the fuel injected into it. if the glow plugs aren't working properly on all 8 cylinders, you will experience this. as soon as the cylinders have a little heat in them, the backfire will be gone.

find your glow plug relay. this will look like a starter solenoid having two large terminals on the top. use your meter and test to see if you have a full 12 volts to the hot side of this relay. then connect to the other side of the relay, place the meter where you can watch the display while cycling the key on and off. with the key on (engine cold) you should see at least 11 or so volts (slightly less due to the amp draw from the glow plugs) for about 5-8 seconds then it will switch off.

report back with what your voltages are on both sides of the relay. (it should be located on the drivers side rear of the intake close to the valve cover and looks like this photo.

View attachment 86002

We don’t know this to be a cold cylinder because he has not done any tests. Just reports back that the “poof” is now a backfire and we don’t know that as there is no video.

Backfires are highly unlikely with 4 stroke diesels, especially a cold cylinder not firing. You would need a hot exhaust manifold to ignite the unburnt fuel and his description “only on cold start” basically eliminates that.

Test the glow plugs to eliminate them as an issue. Pull them out and see if they glow properly. If they check out, then it’s air in the fuel and you’re off on another chase as to the cause. It could be as simple as leaking seals at the fuel sender connections. At this age of the vehicle, you need to go through the entire fuel delivery system. Age is a wicked thing on this stuff.

 

[Will L.]

@Will L. The OEM Glow plugs on most 12V battery 6.2 and 6.5TD engines are indeed labeled 6Volt to reduce the heat up time. Said another way: so the trick fancy time/temp controller can F-Up and swell/burn glow plugs out while trying to heat them up in less than 60 seconds a 12V plug would take.

I edited above quote to relevant section.

Yes, I am aware.
If you look up many electrical components the rated voltage doesn’t match applied use. Many automotive switches are actually rated 600v ac. Many of the motors and actuators for door locks are rated for 6v dc.

The rating determination is done by electrical engineers with what gets through UL or other determining agencies for the components production. How it is used has biggest impact on function and reliability.
Many of the glow plugs that have been made were ok. SS diesels insta heat plugs are a prime example. They do heat up incredibly quick and get much hotter than the 60G. But it’s like plugging in a 120volt light bulb into a 240volt source. If it has the right properties it will light up much brighter and have longer after glow than the other way. And if you unplug it fast enough so it never overheats- great.
Could be I just shared how their plugs instantly heat up so fast since they don’t have a manufacturing facility where they make their own plugs. Hmm.

The reason I push everyone to the 60G is it’s the only one I have never seen evidence of it causing major engine damage. You might take 45 seconds longer on ridiculously cold days to get going- but you don’t spend weeks of work to pay for a new engine because of it. The replacement of near $100 in parts every 75,000 miles and 3 hours replacing the plugs is far less cost and time extracting one swelled plug when damage has occurred.

If a person wants to get creative and wants faster results, add air heaters like a cummins. When they fail they don’t kill engines. But keep the 60G in place.
For so many years my recommendation of glow plugs was 15,000 mile intervals as the only responsible way to heat and protect a 6.2/6.5. Then the 60G was created.

 

[ak diesel driver]

IIRC some of the 6.2 plugs were 6v and some were 9v

 

[Will L.]

IIRC some of the 6.2 plugs were 6v and some were 9v

Yes. And all of them should be thrown in the trashcan.
AC Delco quit making one so long ago that the old part number if ordered will get you parts to a duramax.

Why did they stop making them. Why did GM get away from them? It wasn’t because they decided the old ones lasted so long they were missing out on millions of dollars in parts sales. It’s because so many engines were getting damaged still under warranty.

 

[Bezzer]

dbrannon79: I reported back to you about two hours later than your post...something got messed up...but here is what I wrote that you wanted to know-"I have 12.65 volts on the glow plug relay.
The other side of the relay read 00.6. Then after the 8 seconds it jumped to 12.24 volts and on and off to 12.20 volts." When I took these readings and turned the key on myself.... I was right by the glow plug reading with my multi-meter at the same time and these are the finding. Didn't need any help reading the figures.

 

[Will L.]

Well, that tells you the relay is most likely working.
Tells nothing of the wires or the plugs.

 

[ak diesel driver]

.6v is working?

 

[Bezzer]

This info is for everyone in hopes it helps me. This is a new update.....especially about the glow plugs.

About the glow plugs: I looked up on our Trek motorhome site that I belong to...and there is a man that has the exact motorhome that we have. And he found the ones that came with his Trek are the "AC Delco G11's."
Forget that picture little picture because it was in my Chevrolet Motor Home Chassis Service Guide that GM sent me in 1997 and it states "automatic glow plug system 1985 and forward"... The manual has multiple info for other set ups. I will attach a copy of the whole page which will make things more clear including my 1996 is set up this way...Their mistake or confusion.(see attached 1c pdf file)

The motorhome has a front engine with a 4L80E transmission. Rear wheel drive. My code reader is showing "No Codes".

My new motorhome came with Stanadynd electronic diesel injection pump with an electronic throttle. A new Stanadynd electronic diesel injection pump was installed at 55,620 miles under warranty at my Chevrolet dealer.

The turbo is bolted to the passenger side exhaust manifold.
I've included the original pictures that I posted earlier as a reminder.

Hope this additional information helps you guys!

 

[jrsavoie]

Just get a set of AC Delco 60G glow plugs and install them already

 

[dbrannon79]

Ok, so you have 12v going into the GP relay and 12v going out. that deems the relay seems to be working. now do the same test but probe the pos lead of the meter on one or more of the glow plug wires. disconnect one of the wires at the glow plugs and probe there. post your results.

if you are able, do this for each of the 8 connections at the glow plugs one at a time. what I have suspecting is you have some failed glow plugs.

Here is a link that might help explain the differences in the 11G and 60G's mainly don't use the 9G's they will overheat and expand. not sure about the 11G, but 60g's are self regulating meaning that you can leave power to them and they only reach a given temp and won't overheat and pop. they do take a little more time to heat up though.

once you check and verify you have 12v at each GP connector, then proceed to remove a glow plug. but use extreme caution. unscrew and pull straight out. no bending or wiggling as the tip can break off and leave you with having to pull the engine apart to get the broken piece out of the cylinder else can cause severe damage to the engine if left in there.

if any one of the glow plugs wont pull out with ease after unscrewing the threads. FULL STOP. you will need a special puller and some prayers....

others here can assist you on removing a swollen glow plug that have more experience. Leroy Diesel rents the puller (fellow member and vendor here)

 

[Will L.]

.6v is working?

He also said :
Then after the 8 seconds it jumped to 12.24 volts and on and off to 12.20 volts.

So yes.
The relay is getting the coolant temperature sensor information (depending on year either directly or via control module) and cycling the power on and off.
Before the 60G plugs were made glowplugs all just got hot and stayed how under power- this burned them out, swelled them up, sometimes made them burn in half.
So the relay system was altered over the years in different attempts to control the plugs more accurately as needed, powering on and off. on style the voltage output even changed in 0.5 intervals from 0-14.5, and in the cucv from 0-29volts.
That set up was quickly disposed of because it was blowing plugs apart in a hurry when the ground went bad.

But every since the self limiting plugs- it really doesn’t matter if power is supplied too long. They break the connection internally. And even when the coolant is cold but the fuel is not within diesel spec- like military running jp8 with much higher btu- the plug itself gets hotter quick from the flame and this heats the different metals inside causing the plug to not fail. Unfortunately the military doesn’t use the 60g as the standard but individual bases will convert to 12v and run them so they stop blowing engines over it. The guys on the hummer forum always get an ear full and know they should swap out the bod and plugs. Many of the guys running hmmwvs are not running diesel fuel but black diesel, kerosene, or jp8 that gets cycled out.

 

[ak diesel driver]

What it says to me is when the load is applied it craps out and when the load is removed, ie cycling, the voltage comes back until the load is applied again