1990 HDJ81 Bad shake at idle while in gear

[carguy81]

Hello, I've been chasing a problem for almost a year now. The truck is a 1990 HDJ81 with 120Ks. It started off barely noticeable, and only happened when the truck had been driving for 20min+. When riding the brakes in gear, it would start to shake, but not badly during the first couple months. It wouldn't shake if I had the truck in 2nd when in stop-and-go traffic. Eventually, it started to do it in 2nd as well, and at some point I noticed smoke out the exhaust. Now it shakes so bad in any gear at low speed that it's undrivable and definitely has more smoke coming out of the exhaust than it used to. Cruising at any speed above like 5mph+, it's perfectly fine.

To try and resolve it, I've adjusted the valves, replaced engine and trans mounts, replaced the injectors, deleted the ACSD, adjusted the idle both to spec and higher than spec, replaced all the rubber fuel lines, replaced the air filter, replaced the fuel filter housing, and checked the tank and pickup. None of these had any effect, and the problem just slowly got worse.

The problem started maybe two months after I bought the truck. The person I bought the truck from didn't know if the pump had been rebuilt. We both guessed it was rebuilt to get the truck to the auction in Japan, given how clean the pump was compared to the rest of the engine bay. I'm thinking maybe the pump didn't get a full rebuild and something that wasn't replaced is the issue. I'm open to any suggestions before I take the pump off.

If the pump does need to be rebuilt, what are some recommendations for shops? I'm located in Michigan, but I assume I'll have to ship it somewhere.

 

[mudgudgeon]

Is the smoke white?

Color of the smoke will give some clues. Doors it only smoke when it's running rough?

Sounds like it could possibly be air getting into the fuel system. Maybe.

It sounds like you've done the right things to fix this, but it's easy to test.

Temporarily install a piece of clear pvc house between the filter housing and the fuel pump. Leave a short loop that you can poke out past the edge of the hood.
When you re-prime the fuel pump, you should see fuel passing through the clear hose with no bubbles.
Take it for a drive with the good closed to the first latch only. Watch the exposed loop of clear hose.
When it's running rough, do you see bubbles passing through the hose?

If you see bubbles in these scenarios, you have a leak in the fuel system.
The fuel system is under a vacuum, it's very common to have enough of a leak to allow air to be sucked in, but not show any visible fuel leak.

Usual suspects
- fuel filter/primer assembly
- bad O-ring on fuel filter
- loose fuel filter
- cracked fuel hose
- stretched fuel hose. If you've removed & reinstalled fuel hoses over a tube with a raised crox/swage/bead, the hose can stay stretched, and not reseal.
- pinched fuel hose. Worm clamps can pinch the rubber hoses and cause minor leaks. I personally you its hard to beat the OEM Toyota spring clamps. I remove any worm clamps off any new to me vehicles asap

 

[carguy81]

Replaced the feed lines on either side of the fuel filter housing with clear line, and a stream of air bubbles is coming up from the firewall to the filter housing. There's also an air bubble on the other side.

I'm going to order some OEM Toyota spring clamps. It currently has some Amazon worm clamps that aren't the highest quality.

 

[mudgudgeon]

Replaced the feed lines on either side of the fuel filter housing with clear line, and a stream of air bubbles is coming up from the firewall to the filter housing. There's also an air bubble on the other side.

I'm going to order some OEM Toyota spring clamps. It currently has some Amazon worm clamps that aren't the highest quality.

I would replace rubber hoses too. By the time you go to the effort of replacing clamps, may as well.
IMO if you've used worm clamps, and now know you have a leak, the hose is compromised