SOLVED: HDJ81 Will Continuously Increase RPM if Throttled in Park (1 Viewer)

[Bogan]

This is a weird one. After replacing my injectors with new Toyota injectors and putting in a rebuilt IP the Cruiser has been driving really well. Great power, great fuel economy (20mpg if I keep it around 2400 rpm). It drives better than it ever has.

Then the other day, I put it in park and revved the engine after tuning the pump to see if it produced any smoke. When I did that, the RPMs rose up and would have continued if I hadn't shut the truck off. This was in park. Next morning, I did the same thing once I started it up and it didn't do it. Only when the truck is warmed up.

I did a visual inspection and it doesn't look like the throttle cable is sticking or binding. The hand throttle knob isn't pulling either.

The turbo was rebuilt two years ago with all OEM parts and re-installed by Mudrak, so I doubt it’s the turbo seals. No leaks anywhere. 180,000 miles on the clock. New fuel filter and I just changed the oil. Compression numbers are 430 across all 6 glow plugs. A442F hydro transmission with new fluid that shifts clean. Kickdown cable is adjusted perfectly.

It's never done this to me while driving but I'm worried it could happen. We're supposed to take the truck on the road on Monday and would feel better if I knew what could be causing it.

 

[1HaytchZed]

I would say faulty TPS, throttle position sensor but I don't think 1hdt have a TPS on the IP.

 

[Bogan]

I would say faulty TPS, throttle position sensor but I don't think 1hdt have a TPS on the IP.

they do not, correct.

 

[KiwiDingo]

I had a slightly similar thing happen to mine when the rebuilt injector pump was installed. It would sometimes not hold revs at all and others it would sit at redline till I switched it off. Ended up being a loose nut on the throttle linkage.

 

[Bogan]

Good looks I’ll check that! I should also note that it will do it in neutral too but as soon as I put it in gear it goes back to normal.

 

[Bogan]

Went through the engine compartment and everything is tightened as it should be. It’s stumping me...

 

[Bogan]

I had a slightly similar thing happen to mine when the rebuilt injector pump was installed. It would sometimes not hold revs at all and others it would sit at redline till I switched it off. Ended up being a loose nut on the throttle linkage.

View attachment 2195826

ok mine was tightened fine but I loosened it while the truck is in park and idling and the bolt’s tightness does affect idle speed. Wrench tightened = higher RPM, hand tightened, lower RPM. My guess is it’s sticking and causing the RPM to rise...

Anyone have insight?

 

[KiwiDingo]

Then the other day, I put it in park and revved the engine after tuning the pump to see if it produced any smoke.

When you say tuning the pump, what exactly did you do? and this issue only started happening after you made this adjustment?

 

[KiwiDingo]

ok mine was tightened fine but I loosened it while the truck is in park and idling and the bolt’s tightness does affect idle speed. Wrench tightened = higher RPM, hand tightened, lower RPM. My guess is it’s sticking and causing the RPM to rise...

Anyone have insight?

That should not happen. It's only when the nut gets so loose that it allows the linkage plate to lift up high enough to disengage from the splines.

 

[Bogan]

When you say tuning the pump, what exactly did you do? and this issue only started happening after you made this adjustment?

Sorry, tuning the boost compensator. I just turned the off-boost "smoke screw" down. I removed the cover to make sure it was in the right spot. That's it. I honestly hadn't revved the engine in P or N since picking it up in early December so it could have been an issue all along. The pump was rebuilt and installed by a reputable LC shop, so I doubt they made any mistakes but who knows.

Only other thing I can think of is maybe it has something to do with the governor shaft maybe binding? 1 hdt leaking injector pump.

 

[arnott1t]

Try turning full power screw down. On similar Bosch pumps too much max fuel screw can lead to climbing rpms and run away.
Weird it cropped up

 

[Bogan]

Try turning full power screw down. On similar Bosch pumps too much max fuel screw can lead to climbing rpms and run away.
Weird it cropped up

Hrmmmm. Good looks! This is the first time touching the fuel screw on this particular pump. Looks like there's no lock limiter on the fuel screw. My old pump would only let you turn it so much. If I turn it down, it moves forward again when I lock the locknut back. I'll mess with it more tomorrow. I hate doing this at night with all the neighbors winding down. Thanks for the tip though!

 

[Bogan]

Try turning full power screw down. On similar Bosch pumps too much max fuel screw can lead to climbing rpms and run away.
Weird it cropped up

that was it! All it took was a 1/4 turn and it fixed the problem. Thank you! Phewww.

 

[KiwiDingo]

Glad you found it, weird the pump builder didn't set it right if it's only just been rebuilt and you didn't touch the fuel screw?

 

[Bogan]

Glad you found it, weird the pump builder didn't set it right if it's only just been rebuilt and you didn't touch the fuel screw?

Long story (all diesels are in the US) but the pump belonged to a diesel Cruiser collector that was friends with the shop in Texas where my truck broke down last year. He had a newly-refurbished pump attached to a rebuilt engine, IIRC tuned to a GTurbo with 25psi. The customer, out of the kindness of his heart and sympathetic to our situation of being stranded 1500 miles from home, sold me that pump for $1000. The shop then installed it as per the timing on my old pump and tuned it to about the same settings as my old pump, save for the smoke screw.

I was able to keep my old pump and just looked at where my main fuel screw was and compared it. My old pump had a limited/safety block on it and the new one didn't. The screws were almost exactly the same but the new one was barely 1/8 of a turn further in. The truck was driving great but that 1/8 of a turn was just too much. I backed it off and the RPMs stayed the same and now there's no revving when in park or neutral.

So TLDR, the new pump was turned 1/8 past where the limit lock was, causing the issue.

 

[arnott1t]

Glad it was that. A simple fix.