1HD-FT stalls when slowing down after long periods of highway driving (1 Viewer)

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Sep 18, 2021
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Location
Durham
Hello all,

Full Disclosure: I'm a bit of a newbie here when it comes to Toyota as well as anything diesel. I am a bit of a wrench turner and have pretty heavy experience with LS engines (swaps, troubleshooting, etc.) so i'm not a complete lost cause.

I recently purchased a 1995 HDJ81 w/ the 1HD-FT that has an issue that i'm having difficulty diagnosing due to my lack of knowledge of the engine. I should note that it drives perfectly around town and can do so for hours, this issue seems to only crop up if i'm doing long(ish) sections of highway driving (+30 minutes @ +65MPH).

When slowing down or coming to a stop after driving for a while on the highway, the engine will go to about 300-400 rpm, sputter, then die, instead of nicely settling on 800RPM as it usually does upon coming to a stop. During a road trip to test if it was vacuum booster related I instead shifted into neutral and the removal of the transmission load also caused it to dip down and die. After stalling if I'm still moving or at a stop I can restart the engine just fine but the issue will continue until the engine "cools down" after which the issue disappears. Blipping the throttle keeps it alive until I'm underway again.

Any ideas where to look and how to diagnose where the problem lives? I've started with the obvious, checking vacuum lines and associated diaphragms.
 
My guess is its the governor spring is weak and the fluctuating temperatures is having an effect on it. Some times when the vehicle is facing uphill, it can make it worse
There is also a gadget that ensures it goes back to an idle and doesn't stall if you ease off the throttle quickly, its name escapes me.
You really need a FSM to start playing around with diesel injection pumps

Does the injection pump still have the lead/wire seals connected to the controls on the pump? If not, its an indication someone has played with it. A qualified shop usually replaces the seals if they have worked on it.
 
@roscoFJ73 it's a funny name like a honeypot or something...
 
it's a funny name like a honeypot or something
DASHPOT!!!


A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring. Wikipedia
 
DASHPOT!!!


A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring. Wikipedia
Awesome, just got my hands on a service manual and will take a look.

On another note, are these vehicles supposed to have a good amount of negative pressure on the fuel tank? Seems like maybe I also have some sort of blockage issue somewhere. When filling it up I get a good amount of suction when loosening the cap.
 
All the Toyotas I have owned have positive pressure, cars , trucks and landcruisers. Its more noticeable on warm days.
 
Don’t know anything about the 1HD-T, so was wondering if yours has a manual idle adjuster knob? All the “old school” diesels have these. Sometimes when I fiddle with the idle before a road trip and come off the hwy it idles lower than when I set it before the road trip, and possibly dies.
As to your tank pressure, my dual tank 75 Ute the front tank had pressure and the rear tank didn’t. I changed out the vent breather filter and that solved the pressurization issue.
 
FIXED

This problem ended up getting worse and worse over time. Eventually what started happening is I would let off the throttle at any time (hot or cold, although it was worse cold) and this would cause it to shoot past the idle rpm and either stall or get to about 200rpm (if it didnt stall it would eventually recover to normal idle). Just for sanity sake I replaced the fuel filter (seemed unlikely but I didn't want to take it to the mechanic and have it be something stupid, my ego cant take that). As I primed the fuel, I saw a small leak at the fuel inlet to the injection pump. After retorquing it feels like a brand new truck, with no issues.... Although the alternator died during my shakedown test, but that's an easy fix.

Video showing the leak when priming

Location of the leak
1642988152463.png
 
You could be sucking air under vaccum via fuel system, check your system and ensure hoses and connections are tight.
Try loosening the fuel cap and drive around.
A great visual is clear fuel line between the filter and the IP feed, air bubbles=vaccum leak.
Also open the hood and test the primer, if it is soft but stiffens while priming then again she is sucking air from somewhere. Primer should be stiff in a couple of pumps.
 

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