1HD-T idle problem - need help!

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David60series

Joined
Jun 30, 2013
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Team,

Having some frustrating idle issues.

Engine is 1HDT. Issues started around 6 months ago with a bad idle shake. No noticeable drop in rpm. Shaking so bad that transfer lever moving side to side.

I undertook the following:
  • New engine mounts - no change
  • Transfer case rebuild and mount - no change (had to do this to address a transfer issue that arose at the same time.
  • Injector pump and injectors rebuild - probably the best shop in australia Nd had all the Denso mods done, new delivery valves etc. no expense spared.
  • Valve clearances adjusted - thus was done while pimp was off. The problem was solved. We assumed it was pump as the previous rebuild was very poor they had used a 1HZ plunger spring and it had broken and passed through the pump

3000km later and the same symptom has just come back! Problem:
  • Starts and runs ok
  • Once hot and at idle for 10 seconds or so (sometimes longer) it will start shaking like crazy. It does not do it all the time, but it seems to get more consistent. A bit like an engine about to run out of fuel. If you give it the smallest amount of throttle for just a moment it will recover to smooth and the goes back to its shaking again.
  • Idle is ~700rpm
  • AC idle up ~750 rpm
  • Even if you set hand throttle at 800rpm it will do the exact same thing.

I just changed the filter head assembly and thought I had cured it but all if a sudden after 20min of driving it started again.

I'm basically ruling out an actual pump and injector problem. Last time you could crack an injector line and it would recover slightly and then shekels again.

I reckon it might be air... But a weird air problem.

Next steps if no luck will be to check pump timing again, but at this stage the biggest clue lies in what was changed for it to go away for a while... That is:

  • Inlet manifold came off and new gaskets
  • Injection pipes off
  • Valve clearances adjusted
  • New fuel filter and hoses either side of primer pump
I'm yet to run clear hose as I work away and haven't got back home. Only other symptoms are a little bit sluggish of standing start (but it's factory spec tune at 3.2t on 33s) and I feel the idle is a bit lumpy especially on cold start.

Wondering about tank change over solenoid or an old timer told me the nylon warning sensor in fuel filter can cause similar trouble without a leak being detected.
 
Have you tried to crack the injector lines loose at each injector while running to see if it is isolated to one cylinder misfiring?
The weakest cylinder will change the idle/misfire the least.
You may need a helper to put the vehicle in gear and hold the brake to help identify the concern.
Once you identify a weak cylinder you can then swap injectors with another cylinder to see if the misfire follows.
 
I haven't tried cracking injectors this time, but before the pump rebuild we did this and it could not be traced to any one cylinder.

I should add compression test showed 470-480 on all six pots.

I can't see it being a timing gear - did it before and after timing belt replacement.
 
It doesn't sound like air in the fuel to me.

When I've had problems with air in the fuel system, it's either caused the engine to shut off instantly (loose filter), or it's caused misfire/stumble at midrange rpm under acceleration (leaking primer pump).
I think if an air leak was a problem at idle, it would definitely be a problem at higher RPM when there's more of a demand for fuel.

Having said that, it's easy to test with a bit of clear hose.
 
David60series said:
A bit like an engine about to run out of fuel. If you give it the smallest amount of throttle for just a moment it will recover to smooth and the goes back to its shaking again
Click to expand...

I would be looking in the fuel tank for a blockage on the fuel pick up. You could also rig up a temporary fuel supply in the engine bay to isolate the problem between tank and engine.
 
I have thought about this too. I ordered two new pick up filters.

I have draws and heavy tool boxes bolted in back of 80 (no rear seats). Is it possible to get to these pick ups from below via tank removal or do I need to disconnect from top before hand?

I've thought about a temporary fuel supply but I really need to run it for a while to start getting the problem consistently.

I do believe the new filter assembly made it run nicer (pulled nicely from low rpm) but the shudder did come back. I do think it's a fuel supply problem but not necessarily the injection.

Mud - I do agree with all your points based on logic and common sense but this really is a strange one.
 
I have also run with no fuel filler cap and checked I can suck through cap ok.
 
Certainly sounds fuel related. Based on what you've already done, check all the fuel lines back to the tank. A small crack or leak can seal up at higher negative pressure. Then to the fuel tank pickup. I'd definitely try a temporary fuel source and new hose to the filter housing to see if it clears up. Start with the easiest tests first. Sorry if I missed it, but have you done a compression and leak down test?
 
David60series said:
but this really is a strange one.
Click to expand...

Ive seen or heard of 4-5 doing this and its usually a week governor spring. But you said it had a good rebuild and they would normally have covered it.
 
roscoFJ73 said:
Ive seen or heard of 4-5 doing this and its usually a week governor spring. But you said it had a good rebuild and they would normally have covered it.
Click to expand...

Cooma Diesel replaced all the springs as a precaution. It did it before and after rebuild so I think safe to rule out spring at this stage.

SteveJackson said:
Certainly sounds fuel related. Based on what you've already done, check all the fuel lines back to the tank. A small crack or leak can seal up at higher negative pressure. Then to the fuel tank pickup. I'd definitely try a temporary fuel source and new hose to the filter housing to see if it clears up. Start with the easiest tests first. Sorry if I missed it, but have you done a compression and leak down test?
Click to expand...

Yep the compression test came up ok 470-480 on all pots at 390k.
 
roscoFJ73 said:
Ive seen or heard of 4-5 doing this and its usually a week governor spring. But you said it had a good rebuild and they would normally have covered it.
Click to expand...

fluctuating idle is a somewhat common problem. mine hdj81 did this, it would occasionally, repeatedly fluctuate from 650 rpm (normal) up to 850ish, and drop back to 650 no AC on.
Denso were aware of this and issued a bulletin on how to fix it.

The rough idle above sounds like it might be a different issue. I found mine idled sweet at 650rpm and 950rpm, anything in between, it idled rough (or less smoothly).
I found idle at 650 worked fine. It idled nice, never stalled out. AC idle up still worked OK. It crawled in 1st gear with no throttle on a flat road.

Maybe tweak the idle down or up a little and see if there is a sweet spot
 
I drove this to work today for another test run. About 20km.

On the return trip it became quite bad at the end. Shaking intermittently at idle, then after left idling for sone time became quite consistent. I cracked each injector line with the same result in all of them:

The burble/shake recovered, running a bit lower in rpm whilst the line was partly open, then as a tightened it it would recover completely and then return to the awful shake and miss a few seconds after tightening back up.

If I turn it off it starts and idles ok for 30 seconds or so before getting the shakes up again.

I haven't run the clear hose yet.

I tried setting the idle via hand throttle up around 800rpm (manual) and this masks the problem slightly but it still gets the shakes.
 
I took some video but it's too large to upload. It's quite severe. No noticeable drop in RPM - just rough exhaust note and shaking very badly.
 
If you pump the fuel filter primer while it's idling and shaking does it change anything?

gb
 
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