DB2 Pump doesn't respond to full throttle

[charredsteak]

First post here, haven't been able to find any threads for this specific issue and none of my buddies can seem to figure it out. Truck ran great up until a couple weeks ago when I pulled the pump out to put new shaft seals in. Doesn't seem like it has full throttle anymore. Took some time to get the timing dialed in, now runs fine at idle to around half throttle and then just stops adding fuel. Also loses all clatter at full throttle. Throttle response is very slow. Added a couple extra flats on the fuel screw, which it didn't respond to either. Ran it for a few seconds with the top cover off just to confirm the metering valve has full travel, which it does. Currently at a loss of ideas. Didn't have the head apart at all when the pump was off, no idea what I could've screwed up.

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[WrenchWhore]

Did you verify the timing gear is meshed the same way it was before? Could be a tooth off?

 

[charredsteak]

Did you verify the timing gear is meshed the same way it was before? Could be a tooth off?

Yeah ran through that already, was a tooth off. Got it timed at the factory mark with no problems

 

[Clb]

Not trying to discourage you, but...
You need a new pump, look at some stickies.
Factory timing mark is usless once a new pump is put in service.
125k is pretty much the ond of the line.
What literature did you use when you disassembled the pump?

 

[charredsteak]

Not trying to discourage you, but...
You need a new pump, look at some stickies.
Factory timing mark is usless once a new pump is put in service.
125k is pretty much the ond of the line.
What literature did you use when you disassembled the pump?

Used the factory service manual, currently at 67k but definitely rolled over.
Don't/didn't have any hot or cold start issues but I'll look into it. Already quoted around $400 for a rebuild if that'd cut it

 

[WrenchWhore]

Also, you timed it with a timing tool right? Not just lined up the marks?

 

[Clb]

Today...
Hit up russ

 

[Old Goat]

Do not buy a replacement pimp from the local Auto Parts store, Amazon or E-Bay, there is a list some where here ion the Forum.

Yeah there are 4 highly recommended rebuilders here on the Forum.

www.russrepair.com (Oregon)

https://classicdieseldesigns.com/ (Texas)

https://idiperformance.com/ (Wyoming)

https://moosediesel.com/ (South Carolina)

You can Nickle and Dime things together, or do it right.


Goat

 

[IDIBRONCO]

Do not buy a replacement pimp from the local Auto Parts store, Amazon or E-Bay

That's right. The girls might not like it very much!

 

[The_Josh_Bear]

Welcome to the forums!

First thing that comes to mind: have you checked the throttle cable for full travel? It's fairly common for us to have a plastic piece near the IP break off and jam sideways so we don't get full throttle. Pedal travel can also be impeded inside the cab, I'd check there, too.
I'd take off the throttle cable and actuate the throttle arm by hand. Then re-attach and see if it moves the same distance with your hand.

After that you mentioned the timing curve is off, did you change the position of the advance cam on the driver's side? It should generally be right at the foot of the "ramp" on the cam at idle, as soon as the throttle moves it should begin actuating that advance piston. That's generally speaking, the only way to know for sure it's position is on a flow bench, AFAIK. If you didn't change it, that's not the issue...

Beyond that, yes the IP timing factory mark is just for static timing to get it started. Needs dynamic timing, using a pulse meter or luminosity probe. Worth buying one if you plan on keeping the truck a while.

$400 is very low and I'd be suspect of anyone charging that price. There are many more bad rebuilders than good ones. @Old Goat has you covered on the good online rebuilders. I know of a couple more that do the work but don't really advertise, so it IS possible to find good one locally, just do some homework first. The last thing any of us want is to spend $400 on a bad rebuild to turn around and have to spend $800+ on a good rebuild when we could have gotten the good stuff right away without the double downtime. Ask me how I know!

I hope you get it sorted out, and happy wrenching!
-Joshua

 

[charredsteak]

Also, you timed it with a timing tool right? Not just lined up the marks?

Do not have the tool, just messed with the advance until it sounded happy. About half a dime off the mark

 

[charredsteak]

Welcome to the forums!

First thing that comes to mind: have you checked the throttle cable for full travel? It's fairly common for us to have a plastic piece near the IP break off and jam sideways so we don't get full throttle. Pedal travel can also be impeded inside the cab, I'd check there, too.
I'd take off the throttle cable and actuate the throttle arm by hand. Then re-attach and see if it moves the same distance with your hand.

After that you mentioned the timing curve is off, did you change the position of the advance cam on the driver's side? It should generally be right at the foot of the "ramp" on the cam at idle, as soon as the throttle moves it should begin actuating that advance piston. That's generally speaking, the only way to know for sure it's position is on a flow bench, AFAIK. If you didn't change it, that's not the issue...

Beyond that, yes the IP timing factory mark is just for static timing to get it started. Needs dynamic timing, using a pulse meter or luminosity probe. Worth buying one if you plan on keeping the truck a while.

$400 is very low and I'd be suspect of anyone charging that price. There are many more bad rebuilders than good ones. @Old Goat has you covered on the good online rebuilders. I know of a couple more that do the work but don't really advertise, so it IS possible to find good one locally, just do some homework first. The last thing any of us want is to spend $400 on a bad rebuild to turn around and have to spend $800+ on a good rebuild when we could have gotten the good stuff right away without the double downtime. Ask me how I know!

I hope you get it sorted out, and happy wrenching!
-Joshua

Looked into Russ, most likely gonna send it out there considering y'all's horror stories with local shops.
The face cam was set like you said where it starts to ramp immediately off idle. My understanding is these pumps will naturally add advance as the pump plungers take more of a bite of fuel. It almost seems like the face cam is over-retarding, which wouldn't make any sense.

Also did my best to confirm the throttle cable isn't screwed up. Will check it again. Even working the pump arm manually it seems messed up though.

 

[KansasIDI]

Looked into Russ, most likely gonna send it out there considering y'all's horror stories with local shops.
The face cam was set like you said where it starts to ramp immediately off idle. My understanding is these pumps will naturally add advance as the pump plungers take more of a bite of fuel. It almost seems like the face cam is over-retarding, which wouldn't make any sense.

Also did my best to confirm the throttle cable isn't screwed up. Will check it again. Even working the pump arm manually it seems messed up though.

I had a pump that did very similar things. I had it rebuilt by Moose Diesel. I am now a happy IDIer.

 

[Old Goat]

That's right. The girls might not like it very much!

You got me on that one.

I always proof read before sending one on.
Must have been late at night....
Stupid computer should have known better...


Goat

 

[The_Josh_Bear]

Of all the random censored words around here, and somehow pimp is ok. It's not like it has a second, common meaning

Do not buy a replacement pimp from the local Auto Parts store...