1HDT Low and Weird Idle Issue (1 Viewer)

[Magic Spool Bus]

Moving this from 80Tech to Diesel Tech where it belongs

I did find a few old threads about this issue. It seemed some people were having success with fixing the low idle commonly experienced by people with the 1HDT by replacing a dampener spring and idle control spring in the IP. So that was my first course of action to try and resolve the problem. The problem being that almost 100% of the time while facing uphill the idle will drop to around 400rpm from the desired 700ish rpm. It is to the point now that mine will do this almost all the time not matter the angle of the truck. As of today I got my truck back from a shop that replaced the springs and the issue is not resolved and has developed some more strange symptoms.

The old characteristics before the new springs were:

-Cold or hot cranking would idle at 700 or 400rpms.
-Blipping or lightly applying the throttle may or may not get it to idle correctly at 700rpm
-Randomly if I would let it idle at 400rpm something would take control and bring the idle up without me touching anything

The new characteristic's after the new springs are as follows:

-Starting the truck cold or hot it may idle at 700rpm or idle at 400rpm.
-If I every so slightly put pressure on the throttle it will jump by itself to 800rpms. (as if something else take control).
-If I blip the throttle hard it will either fall straight to 400rpm or stop at 700rpm then fall 400 or it may stay at 700rpm.

I am taking it back to the shop tomorrow as the mechanic is very eager to figure out the issue. I did see that people brought up that the dashpot could be out of adjustment causing some of these symptoms. The ACSD is still attached to the pump and does not make any noises but it also does not work with a cold crank. I always just use the hand throttle when warming the truck up. If anyone has any advice on this matter it would be greatly appreciated.

-Cheers.

 

[mudgudgeon]

So to add to comments in your other thread

It's a fairly common issue.
Mine did it. Removing ACSD had no impact on mine.

What replacement spring was used? The same part number, or a different spring?

Dash pot may be a contributor?
1HD-T idle problem - need help!

From what I've read, a pusher pump won't fix it

 

[Loober]

@Socal81, I am in San diego as well, curious which mechanic you use, been looking for one that is knowledgeable in these engines, thanks

 

[Magic Spool Bus]

So I just dropped it off at the shop again. I’m not sure what it’s part number is but it’s from a Denso dealer. I’m assuming it’s oem replacement. I did find out though that he only changed the dampener spring and not the idle control spring. He says the idle control spring is responsible for on throttle not while its idling. I can’t pretend to know if he is right or wrong but he is fairly certain it wouldn’t produce the low idle. He is however going to play with the dash pot today and see if that is the issue. The ACSD linkage is also doing something strange. The mechanism itself doesn’t work but the linkage has some unusual behavior it sometimes it’s pressing harder on the throttle linkage more so than the idle control screw. I’ll check back in after.

 

[Magic Spool Bus]

@Socal81, I am in San diego as well, curious which mechanic you use, been looking for one that is knowledgeable in these engines, thanks

Wayne at PCE diesel. He has worked in injection for quite some time and he’s a great dude. He is very eager to learn and get it fixed. Every other place I took it too wanted to immediately rebuild the pump and injectors and to me that wasn’t the right direction right off the get go. The truck runs very well and only has 100k/km so I don’t believe just yet it’s the pump or injectors.

 

[mudgudgeon]

So I just dropped it off at the shop again. I’m not sure what it’s part number is but it’s from a Denso dealer. I’m assuming it’s oem replacement. I did find out though that he only changed the dampener spring and not the idle control spring. He says the idle control spring is responsible for on throttle not while its idling. I can’t pretend to know if he is right or wrong but he is fairly certain it wouldn’t produce the low idle. He is however going to play with the dash pot today and see if that is the issue. The ACSD linkage is also doing something strange. The mechanism itself doesn’t work but the linkage has some unusual behavior it sometimes it’s pressing harder on the throttle linkage more so than the idle control screw. I’ll check back in after.

A bit of discussion relevant to this in here
1hd-t vs 1hd-ft injector pump

@Antony had some interesting input

 

[Magic Spool Bus]

So it appears that the issues were resolved with the dash pot adjustment. Mine was too far in and effecting the idle in a weird manner. Now I’m holding about 650rpm all the time. I still need some more time with it but as of right now the idle is much much better. I’m sure the new spring also played a roll in this and for only 10 bucks why not try it.

 

[mudgudgeon]

Interesting.
Hope the fix sticks for you!

 

[Magic Spool Bus]

It appears that I still have the low idle issue. It does happen a lot less often I’m guessing it could have been from a result from the new dampener spring or dashpot adjustment. Back to the drawing board

 

[joejoe21]

Did you ever resolve this? I’m having the same issue

 

[Magic Spool Bus]

Did you ever resolve this? I’m having the same issue

Wow it’s been so long since all of this. I can’t quite remember what happened after my crankshaft snapped. A brief recollection that probably won’t help is that:

ACSD failed, pump and injectors got rebuilt. Problem was still around. Crankshaft snapped not even 10000km after pump rebuild. Got a new engine and reused freshly rebuilt pump and injectors. Problem still there obviously. I vaguely remember getting a new dampner spring but can’t remember if I installed it or the injection shop did but the problem never went away until….

I started tuning the pump and ended up raising my idle at the throttle linkage to about 750-800rpm which I think is high for the manual transmission engine per spec from FSM. I haven’t had this idle drop in years. I also moved to a flat part of Texas and remember this idle drop being more of an issue on inclines facing uphill.

It’s really tough to say. I know this won’t help much.