1HDT Low and Weird Idle Issue

[Magic Spool Bus]

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.

 

[Tapage]

I will try to feed the pump close to it ... just to discard any problems on the fuel line from the tank will check on returns too .. maybe a electric fuel pump to discard a fuel feed issue ..

 

[IanB]

Air conditioning & console cooler are both off for this testing?

I’ve also read something about adjusting a “dashpot” on the pump that affected the idle speed.

I’d scrap the ACSD at your earliest opportunity, it can be a liability.

 

[Magic Spool Bus]

Air conditioning & console cooler are both off for this testing?

I’ve also read something about adjusting a “dashpot” on the pump that affected the idle speed.

I’d scrap the ACSD at your earliest opportunity, it can be a liability.

yes all this is off. I do plan to scrap it just haven't gotten around to it. although I don't believe its causing this issue.

 

[badQtip]

i have the exact same problem but my 1HDT will stall, at red lights, reversing, slow turns . If i drive home from work and park it then drive somewhere 20 minutes later its stalls and stalls and stalls. then it will fix it self and be perfectly fine. I feel like its a fuel issue or something to do with the ASCD. it does not have this problem in the winter, Im located in PA

 

[Magic Spool Bus]

I moved this to diesel tech where I assume it belongs but didn't realize I couldn't delete a post. sorry for double posting

 

[Topi79]

i have the exact same problem but my 1HDT will stall, at red lights, reversing, slow turns . If i drive home from work and park it then drive somewhere 20 minutes later its stalls and stalls and stalls. then it will fix it self and be perfectly fine. I feel like its a fuel issue or something to do with the ASCD. it does not have this problem in the winter, Im located in PA

Did you find the problem out?

 

[badQtip]

So I deleted the ASCD and that fixed it over the winter but once summer hit and I started using the AC. Now it only stalls at red lights and any idling around in drive or reverse with the ac on. So my guess is that the ASCD was the main issue and now I just have to mess with the high idle once the ac compressor kicks on.

 

[Topi79]

So I deleted the ASCD and that fixed it over the winter but once summer hit and I started using the AC. Now it only stalls at red lights and any idling around in drive or reverse with the ac on. So my guess is that the ASCD was the main issue and now I just have to mess with the high idle once the ac compressor kicks on.

Have you replaced governor speed control and damper springs? My hdj80 idle stalls when turning wheel, using high beam...done everything but sprins. I Wonder is it even possible replace them when pump is mounted?