Slight rough idle and it 'burbles'

[hayhauler69]

Hi,
My 1995 GMC 2500 6.5TD has been running great.
Now all of a sudden it is giving me a intermitent 'burble' or missfire mostly at off throttle or idle.
I've changed the fuel filter.
The idle seems a little rougher than normal.
I've got a new Amzoil cone filter on it, with a 40HP chip and new ECM.
But when all that was installed it ran great.
Haven't been driving truck much, just to the lumber yard and such on the weekends.
Has a 116000 miles on it.
So, it's pretty random when it happens, it's not all the time.
Has plenty of power and my mileage is OK. around 17 to 19 MPG.
Thinking a sensor, but any help will be greatly be appreciated.
Buzz

[hayhauler69]

So, no one wants to take a shot at this?
I've browsed through past post and have come up with a few ideas.
I'll check my grounds, but their good, I'm always checking them I'll check the fuel pressure, but it seemed fine when I cleared the air out after changing filter.
I looked at the T/S guide but doesn't really pertain to what my truck is doing.
Maybe I'll buy a new gas cap, would be nice if it was something as simple as that.
It's just that the truck runs good, no smoke and fires right up, all the time.
No codes or anything.
Just this miss every so often mostly at idle in gear. When I put it in neutral it goes away.
So any of you experts, I'd love to hear from.
Oh BTW, I went to a shop that an experienced 6.5 guy owns and of course he wasn't there. I hate going to repair shops, I've always done all my own work.
Thanks for letting me ramble, Buzz

[JoeX87000031]

Did you try changing the gas cap? When you say "burble" what do you mean. Like one hard misfire at low RPM. Mine does that to, but its real random, also, when you take you gas cap off what is it supposed to do? Suck air in like it has a vacuum, blow air out like the system built up pressure, or nothing like the pressure has been equalized. My 94 sucks air for a second or two when I open it up, I wonder if that is bad. I am gonna change the cap just for good measure anyways and then post in this thread again to let you know how a new one works unless you have already changed yours. If you have, please let me know how this thing is supposed to act. Take care,

[N9Phil]

Have you tried throwing some injector cleaner in the fuel? When I was running my Iveco diesel I would have the same problem when ideling. After a can of injector cleaner it would clear up. This happened 3 or 4 times mainley in the winter when I would leave the truck idle through out the day.

Phil

[JoeX87000031]

I cannot Speak for HayHauler of course, But I have been running the CRC Diesel Injector Cleaner and Lubricity Additive they sell at NAPA at double dose. It's Helping. I did buy a bottle of the more popular stuff pictured on the website with the "Slick Diesel" in it. Do you recommend a particular brand, any to stay away from. I personally dont like STP, I figure with all that money spent on advertising I bet there product suffers, just like penzoil.

[JFerg65]

I run power services (winter White can?) and 1/2 oz per gallon of 2 cycle marine oil in my 96 suburban 2500.

This has seemed to keep things running smooth and quite.. as quite gets in the 6.5 T

[Robyn]

Yank the injectors out and get the little beasts tested.
You may have one that has issues.

Any codes popping up?? Sensors will set a code as will most other electronic issues and these would generally present more than the little "Burble" at idle.

A miss with a diesel is either fuel or compression related.
A fuel problem related to the electronics will normally set a code

An injector can do all sorts of things when they get a lot of time on them.

I would start here first before chassing the wind around.

Best

Robyn

[hayhauler69]

Thanks to all for the ideas.
I'm using Amzoil diesel additive if anyone is interested.
I think Roybn is spot on though.
I'm pretty sure it's carbon and probably from the EGR valve.
Burble=missfire:) Sorry that's what the Wife called it and it sounded good:rolleyes:
So now what injectors to buy, marine or stock. Would marine really boost HP even though I've got a 40hp chip installed?

[Robyn]

Get a set of stock injectors that are set up on the high side of the POP spec.
Many shops can do this. Stay away from the online stores unless you know them.

The vendors that advertise here are great folks and will serve you well.

The Marine injectors are not really going to do you much good for a stock application.

Good luck

Robyn

[hayhauler69]

Thanks for the advice Robyn but I bought some marine injectors from SSD.
I've dealt with Walt before, I know he's competition for this site but his price is right. I've bought quite a few things from him. I also got new glow plugs and a
controller.
I'll post my results after I get them installed. Just have to fine time to do it.
Again, thanks to all who gave advice.
Buzz

[damork]

hayhauler69,
I'd agree the injectors are something that will help, but with the miles you have you might consider looking at how steady your timing is to understand if the timing chain is getting loose. My 95 began acting up like you describe just after the 100k mark and I did several things until it became apparent that the timing chain might have stretched. Because I was installing a dual thermostat / HO waterpump, I went ahead with the gear drive update and the chain it replaced was pretty loose. The gear drive ended the "burbling" sound for good.