1HD-T idle problem - need help!

[samuel payet]

Thanks David, good to hear its not a compression issue. Since posting I've had my injectors rebuilt, valve clearances done and removed ACSD but with no luck.

I'm also starting to suspect its the pump, keen to hear how it goes

 

[David60series]

It would be worth taking a fuel sample from your filter in a narrow glass and try shining an LED torch through or using a strong magnet to check for rust particles.

I did this a few months back and saw nothing, but apparently it can be small enough to pass the filter.

We still don't know what's going on, other than its fuel delivery. Having happening twice now it could be contamination - just don't know yet.

Are you experiencing low power off idle?

Hopefully after dozens of lost weekends and many many thousands of dollars I will be able to assist you.

 

[mudgudgeon]

I hope you get a good result after all that

 

[samuel payet]

I've been chasing this for a couple of months so I can only imagine your frustration!

I've tried all the usual suspects, power is fine, fuel tank and pickup is clean as a whistle, I ran clear hose and there were no bubbles in the line, fuel filler cap breather is clear, cracking injectors doesn't isolate it to any particular cylinder.

I forgot to mention I replaced the fuel filter with a genuine Toyota one as well. The old one seemed ok but had some orange coloured flakes in it, although they looked more like sediment than rust.

I'm going run an alternate fuel source this weekend and try to rule out the fuel line. Will also park it on some steep hills nearby to see if it gets any worse which I believe will hint to a tired governor spring, I'm assuming you have tried this too?

 

[David60series]

Yes I've tried a fuel supply from can and it does not change.

Governor spring is new.

 

[David60series]

I've been chasing this for a couple of months so I can only imagine your frustration!

I've tried all the usual suspects, power is fine, fuel tank and pickup is clean as a whistle, I ran clear hose and there were no bubbles in the line, fuel filler cap breather is clear, cracking injectors doesn't isolate it to any particular cylinder.

I forgot to mention I replaced the fuel filter with a genuine Toyota one as well. The old one seemed ok but had some orange coloured flakes in it, although they looked more like sediment than rust.

I'm going run an alternate fuel source this weekend and try to rule out the fuel line. Will also park it on some steep hills nearby to see if it gets any worse which I believe will hint to a tired governor spring, I'm assuming you have tried this too?

Update:

Do not spend a cent or waste anymore time than you already have looking for the problem.

This afternoon I fixed it. Get your trucking to operating temp. Make sure idle us within spec for your transmission type. Screw in dashpot very steadily, blipping throttle to settle the miss as you go. Stop as soon as the miss goes away. Tighten lock nut. That's it.

 

[IanB]

Great to hear you got it sorted! Where/what is the "dashpot" you reference as the fix?

 

[samuel payet]

Haha! you're joking... I ended up getting the pump rebuilt in the end, no improvement, fortunately only a couple of the internal parts were worn so it wasn't too expensive. Since then I've noticed it only idles rough within a very specific range 800-900rpm and clears up above and below that.

Glad to hear you fixed yours, but what made you think it was the dashpot? Do you think the pump builder didn't set it correctly in the first place?

Will give it a go when I get home in a couple of weeks.

 

[David60series]

Long story short: after being asked to test everything under the earth the outcome was that fueling was the only possible problem I.e. Pump. A short spray of ether actually resolved the miss.

After a year of back and forth and parking it up for six months inbetween, there was talk of governor chatter from the shop which causes unequal delivery at very low fuel delivery.

He set the governor up slightly differently with more load on it which is not what Denso say, and this made the cold start better but did almost nothing for the miss. He then said that when you mod the early pump to the recommended Denso rebuild spec the dashpot is disabled as it's considered redundant. It is a small dampener on the side of the pump that works on hydraulic action like a lifter.

He thought this may give it further cushioning and stop the chatter.

It did.

Sorry I could not give you this advice prior to you spending money. It's the first opportunity I had with being home from work to look at it.

If you google dashpot, there's a PDF called scheme VE which details all the optional devices fitted to the pumps. It has a lock it and screw and is located close to the main fuel set screw. Sometimes it has a cover on it.

If your pump hadn't been modded, or the dashpot is in the disabled position you could try bringing it in as described.

If it's not functioning properly you could get a new dashpot. It screws in from the side.

 

[roscoFJ73]

We were discussing dashpots 4 years ago. I think you replaced one, how come it didn't remedy the situation then?

 

[David60series]

It did not actually have the miss during that period. It had some other idles issues, but that was following a number of pump rebuilds undertaken by an incompetent fuel shop. The new dashpot didn't change anything then.

I did find during that period that the dashpot was disabled also. Yotahead suggested bringing it back in until revs rise by ~100rpm but this did not have any effect on the issue at the time.

The dashpot adjustment is really fine; too much and it hunts up and down a bit I guess due to the hydraulic nature of it.

This time the pump was built to the correct Denso overhaul spec which includes mods that are in a service bulletin and under this procedure the dashpot is said to be redundant.

I tried warming the vehicle to operating temp, but not to the point where it shook and missed so I could get a better listen to idle quality. I wanted to bring the dashpot in until revs just increased then road test.

It took a while, and during this time I also went back to disable the DP and tried starting again with more idle speed. During this time it started to miss badly and I wasn't sure I would be able to make a five adjustment with such a poor idle.

Once I set the idle speed at just over 700, I brought the dashpot in 4 & 3/4 turns from its disabled position. The last ~1mm of turn the miss just stopped... Completely cleared.

I marked the dashpot grub screw with paint pen so I wouldn't lose track of adjustment.

 

[mudgudgeon]

Wow! Good that you finally sorted it.

Frustrating that it was such a simple fix, but good that it was such a simple fix to.

 

[David60series]

A belated thanks to all that assisted with suggestions. It has been a long, frustrating and expensive process. I hope anyone else unlucky enough to get this symptom can now resolve it.

It is a good reminder to always start any trouble shooting with the least expensive option.

It would also appear that this has dampened a lot of roll over noise I was hearing via the HD clutch especially on cold start.

I will post a before and after video when I get a chance.

I'm now able to put some spare time into 'normal' maintenance and TLC without feeling like I am completely wasting my time and money.

 

[Magic Spool Bus]

A belated thanks to all that assisted with suggestions. It has been a long, frustrating and expensive process. I hope anyone else unlucky enough to get this symptom can now resolve it.

It is a good reminder to always start any trouble shooting with the least expensive option.

It would also appear that this has dampened a lot of roll over noise I was hearing via the HD clutch especially on cold start.

I will post a before and after video when I get a chance.

I'm now able to put some spare time into 'normal' maintenance and TLC without feeling like I am completely wasting my time and money.

Finally found the thread you referenced mine is at the shop now getting the dashpot adjusted I’ll report back if it fixed my idle issues.

 

[Magic Spool Bus]

So after taking my truck to the shop to get the original intermittent low idle while facing uphill issue resolved (by replacing the dampener spring that others had success with fixing this issue). when i get the truck back it had developed other strange characteristics such as searching around a bit at idle and as well as a situation were if you put your foot every so slightly onto the pedal some type of other mechanism would idle the truck up about 150rpm. After taking the truck back and suggesting to play with the dashpot it resolved everything except the still uphill facing low idle. the low idle is a lot less likely to happen now with the new spring but on a few occasions it does happen. The only difference now is that if i blip the throttle it will settle back at around 650-700rpm where it is set at and before the new spring it would not do this. still chasing the rabbit.