Engine sound difference

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
I would like some help figuring out what could possibly cause a sound difference/power difference on my 84 6.9 t19.
This morning bringing the truck to work (first/second real trip since I got the truck) truck drives excellent, but I noticed going down the highway the motor is some what quite than all of a sudden the motor sounded like a idi diesel and gained a bit of power (enough to go 70 no problem over 60). I'm thinking it's just all the old fuel in the system is finally getting through it, And possibly my return lines leak isn't helping (kit on the way). If I can get a video I'll post it up, hard to do while driving her.
 

franklin2

Full Access Member
Joined
Feb 24, 2009
Posts
4,618
Reaction score
936
Location
Va
That can happen when you lose fuel pressure. I have had that happen when it was sucking some air into the fuel system from a leak. The most common place for a leak are the metal elbows on the sending unit on top of the fuel tanks. And look for any other spots on the suction line to the pump. Your theory about old dirty fuel may be plausible also.

From what I understand from the other guys, the injection pump uses fuel pressure from the lift pump to activate the timing mechanism. If the fuel pressure drops and then comes back, it messes with the injection timing in the pump for a short time period.
 

IDIBRONCO

IDIBRONCO
Joined
Feb 5, 2010
Posts
9,525
Reaction score
7,709
Location
edmond, ks
I have to agree with the air intrusion. That's what it sounds like to me. One other thing that sticks out to me is that fact that it sounds like you usually have trouble driving over 60MPH. Yes the air intrusion will mess with the timing and I believe that it causes the timing to advance. When the timing's advanced due to the air intrusion, you have the amount of power that you should have. I also think that your timing is too retarded. You should have your timing checked and set if it's not right.
 

Cubey

Full timer RVer
Joined
Oct 18, 2017
Posts
3,309
Reaction score
1,155
Location
USA
I have to agree with the air intrusion. That's what it sounds like to me. One other thing that sticks out to me is that fact that it sounds like you usually have trouble driving over 60MPH. Yes the air intrusion will mess with the timing and I believe that it causes the timing to advance. When the timing's advanced due to the air intrusion, you have the amount of power that you should have. I also think that your timing is too retarded. You should have your timing checked and set if it's not right.

My RV could barely get up to 60mph after i put the Holley Red pump, until i added a regulator and dropped the pressure by 1-2psi. 5psi at wide open throttle was too much and was throwing off the timing really badly. Even 40-45mph was acting just wrong. Just throwing that out there too. It didn't have that problem before with the old weeping mechanical pump and hasn't been a problem since with the regulated Holly Red.
 

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
Update for y'all. I added a a bunch of stanadyne additive to both tanks. I don't have the issue at speed, but right off the line I can kinda feel it doing it for a split second. Fuel return kit came so I'll be installing part of that today to remove the leaky stuff. Thanks for the help guys. I'm going to keep an eye on it and see if anything else comes up with the issue.
 

DrCharles

Full Access Member
Joined
Dec 18, 2017
Posts
932
Reaction score
512
Location
West Plains, MO
Also, think about the showerheads (fuel pickups) in both tanks. Those are well known to crumble with age, and contribute to air intrusion especially when getting down near 1/4 tank.
 

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
Another update. Decided to swap out the fuel pump as I noticed the pressure from the fuel filter schrader wasn't shooting fuel across the engine bay, was only coming out a little. Swapped that out and truck runs a whole lot better but she does continue to advance timing. I unplugged the timing advance on the engine and she no longer advances, but while going down hill above 65ish, I take my foot of the pedal and after a moment she starts to surge a bit. Possibly looking into a refurb IP soon I'm guessing?
 

Attachments

  • received_306614568070679.jpeg
    received_306614568070679.jpeg
    31.7 KB · Views: 4

Cubey

Full timer RVer
Joined
Oct 18, 2017
Posts
3,309
Reaction score
1,155
Location
USA
It shouldn't "shoot" across the engine bay from the valve, at least in my experience. It should spray out a little as a steady stream but nothing extreme, as you'd expect for 3-6psi. I have an electric pump and even that doesn't shoot out very far without the engine running.
 

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
It shouldn't "shoot" across the engine bay from the valve, at least in my experience. It should spray out a little as a steady stream but nothing extreme, as you'd expect for 3-6psi. I have an electric pump and even that doesn't shoot out very far without the engine running.
Im exaggerating a bit. But there is a significant notice in pressure.
 

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
A new update. Coming home yesterday the truck was loosing power and finally died. Fires right back up but started to kind miss than dies. Drove it about 2 miles 100 feet at a time to get into cell service. Talk to warden and he mentioned to clean out the ball check valve in the return line of the IP. So I pulled it and looked into it and there's no plastic pieces but looked clear chunks. So cleaned that out put it all back together and truck runs great again.
So I'll drive it again to see if it comes back or not. Gatta swap the 7.3 head I got from another gentleman from the Facebook page so I can run a water sep.
Last but not least (if your on the Facebook group page) I posted a video of my buddies Honda pulling me up hill back to the house lol. I'll update again tomorrow. I'm off work so I'm going to drive it up and down the big hill by the house and see what's up.
(Long post sorry)
 

DrCharles

Full Access Member
Joined
Dec 18, 2017
Posts
932
Reaction score
512
Location
West Plains, MO
I can't remember what part it is, but recall reading that those plastic bits are something important in the IP coming apart? Anyone's memory working better than mine? ;)
 

Broken_Season

Registered User
Joined
May 16, 2014
Posts
66
Reaction score
43
Location
San Jose
Latest update is truck is down. The check valve immediately gets clogged after cleaning. Gatta wait for a new/used pump, which I do have a lead on but I'm not in any rush to get it going as weather here in Colorado has been hit or miss so Ive been just taking the gas guzzler crawler. Hopefully have her back up and running in the coming weeks.
 
Top