Drivetrain help - Slow vehicle - 80 Series - 1HDT

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May 17, 2017
Hello team,

This is my first time posting here on the forum, although I have been reading them for over 3 years now.

I have some issues which I am trying to figure out for sometime now and I don't know the exact culprit, partly because I am quite illiterate when it comes to vehicles.

BTW I am writing this from Pakistan and we don't have good workshops here. The guys here at workshop mostly do experimentation.

The problem goes like this, I have HZJ81 which is 1992 model. The last owner swapped the engine to 1HDT so technically its HDJ81 now. When I bought this truck it was in terrible condition mechanically but looked really nice from outside. Anyways I bought that cos I was new to cars so couldn't check thoroughly.

Shortly after that I left my country for work assignment and I gave the truck to my father to drive. One day it stopped in the middle of road creating huge clouds of white smoke. The folks here at my home took the truck to a workshop and they suggested engine rebuilt. So the guys did whole rebuilt of the engine and drive train and changed the bushings underneath the body.

This all happened 2.5 years ago and the truck is being driven locally after that.

Now that I am back I have started using that as my DD and take it to long drives also.

Following are the issues I am facing,

- There is very less torque. I could climb steep roads in first gear only and very slow and seems like the engine/car is struggling heavily.
- On the other hand I get good fuel average 9 km/lit locally and 11 km/lit on highways.
- Last weekend I decided to go step by step and went for the compression test. All the pistons came around 650 psi on the compression test. (the pistons are +0.5 mm). Isnt 650 psi a bit on higher side?
- The biggest problem after the torque I am facing is the speed on highways. I checked with GPS that I am at 95 kmph at 3100 rpm in 5th gear. Now this rpm number is too high considering I am on a diesel engine. I assume I am running H151F transmission behind the engine. Its a manual btw. Even at 1st,2nd,3rd and 4th gear I am not even fast enough and RPM reaches 3000.
- The car doesn't cross 3000 RPMs easily, I can go max to 3100 rpm and its already too noisy and the car struggles after that.
- I am running 4.1 diffs, I checked them manually by putting car on jacks and rotating tyres and observing shaft.
- My turbo is at 7 psi at 3100 rpm. I never saw a figure above 7 psi.
- Do you guys think its problem with Clutch kit (RPM vs speed thing)
- Do you think that the gears in my gear box are messed up?
- Do you think its the issue with the transfer case (related to speed vs rpm)?
- Do you think its problem with Pump, Nozzles and Tappet settings?
- Can you please suggest what should I do next? Regarding both speed and torque issues.
- It seems my engine is in good health (referring to compression test) but something else is creating issue.

I am waiting for suggestions, meanwhile I will add here any description that I will remember more.

Cheers, Bilal
Addition: I am running on 31 inch HT tyres.

and apologies, Should have edited the orginal post.
Stock boost should be about 10psi, 7psi is low IMO. Air filter is clean?

31" tires are stock sized, larger rubber will bring the revs down on the highway, 33" rubber seems to be a good compromise on these trucks, still drives nice and fits with stock suspension.
@Bilal, greetings. Your engine is revving kind of high for the speed you're traveling; but Toyota diesels rev higher than a standard diesel like the Cummins. Have you checked to make sure you are not in 4hi? As far as your boost pressure goes; it seems a little low but keep in mind you're in Pakistan and the air is thinner at altitude so your truck will struggle a little more and make less boost. I'm sure if you were closer to sea level you would be making proper boost levels. The only way to really get boost up is to get a better turbo or burn more fuel. I'm not sure if the 1hd was fit with a altitude compensating device or not but I would suspect if ignition is that it may not be working properly. You may want to check your injection pump timing to make sure it isn't correct also. Then you should make sure your engine timing is correct. As far as cylinder pressures are concerned, the PSI is high, but again it will read differently at higher altitude than at sea level. Also, there is no telling how well calibrated the gauge was that was used for testing. I wouldn't worry too much, diesels run on compression, it is better to have higher compression than lower compression. I would start with checking to see get f you have an altitude compensating device; then check injection pump timing and then check engine timing. If all are good then check your turbo. You need to remove the intake hose and grab the nut on the compressor wheel and try to move it around, you're checking for too much play. You may need to rebuild or upgrade and replace your turbo. If the injection pump, engine timing and turbo are good you should have your injectors pop tested to make sure they are working correctly. If all of those things are good you may once again consider a turbo upgrade to a newer style ball bearing turbo. The other option is sending your injection pump to a competent shop to be rebuilt to pump more fuel. One last thought is that I'm not sure if diesel 80's came with electric fuel lift pumps or if it's mechanical; but if you don't have an inline fuel pump you might look into installing one. At altitude mechanical fuel pumps struggle to keep up with fuel needs because they rely on barometric pressure in the tank to help. An external electric lift pump helps resolve the issue. Good luck and keep us posted.
RPM sounds a little high, but not a lot.
Boost is,way too low. Question is, why?
Compression sounds good.
Definitely not in 4Lo, you'd be doing a lot more than 3100rpm to do 95km/hr in 4Lo

Sounds like it might just need a good tune up and more fuel

BUT . . .

Given the engine swap, and your illiteracy on cars, there's a few big questions here.

Are you certain the engine is a 1HD-T?
Does it have a standard 1HD-T turbo on it?
Does it have the correct wastegate actuator?
Is the fuel and air filter good?
Do you have an EGT gauge?

It's most likely got a H150 trans (standard to HZJ80). These have lower 5th which partly explains the RPM.
My HDJ81 on 35s and h151 and 4.11 gears did around 2750-2800 rpm at 110km/hr, tyres and h151 would equate to about a 13-15% difference to 31s and h150.
I wonder if your rig is getting enough fuel... especially when you say that the engine has trouble reaching high RPMs. Your boost is definitely low too. It almost seems like the engine is tuned for low fuel (which would give you good mileage) and the boost is pulled back to match.
Thankyou very much for the replies,

- Yes Air Filter is clean, I change them at every oil change i.e., 5000 kms
- I will install 33 inch tyres may be this weekend. I have a complete set of muddies at home, wheels + tyres.
- When I bought the car it was RWD and then you have to lock the hubs to make it 4wd. After I got the rebuild of engine and tranny its full time 4wd, locking hubs gone. Its either 4hi or 4lo now. Do you guys think this could be the reasons of higher than usual RPMS at highways?
- I am located in Islamabad which is only 500m above sea level, IMO it should not make a difference in boost pressure.. 1 psi max.. just my calculations. I think its my turbo which is weak. It was not touched in the rebuild.
- I will check my injection pump timing and engine timing. (btw I don't have any black smokes at idle or white smokes). During crusing no black or white smoke. I only see some smoke during the gear shift.
- Should I go ahead and try to increase the fuel setting myself? (Experimentation). I don't have EGT installed. Is there a need for pump rebuilt to increase the fuel.

- Are you certain the engine is a 1HD-T? ---- YES
- Does it have a standard 1HD-T turbo on it? ---- NOT SURE
- Does it have the correct wastegate actuator? ---- NOT SURE
- Is the fuel and air filter good? ---- Yes fuel fiter and air filter good
- Do you have an EGT gauge? ---- NO

- I am not sure if I have H150 or H151 but the 4th and 5th gear ratios are not much different.. so could be 150

I will see what I can do with the rig on this weekend.

Bonus question:- Currently I am running on 3" straight flow exhaust and the only thing attenuating sound is the turbo. I did that myself without involving any expert. I felt approx. 10% improvement in the performance, but its loud. Do you guys think it will reduce the noise if I install an exhaust tip at the end? The one with the mesh inside but no restriction (3" inlet - 4" outlet).

Cheers, Bilal
Fuel filter is another good thing to check, and I'd pull the tubing between the air filter and turbo inlet and check the turbo for play as the whole 7psi thing seems low, at altitude or not.

Are you planning on adding an EGT gauge? Pre-turbo is preferred, the collector just before the turbo flange is a good spot. It's required before I'd be making ANY fuel adjustments.

If everything checks out healthy, you may want to add a manual boost controller and bring the boost level up, a healthy stock turbo should be good for 14-15psi and would really wake that engine up.
This may be as simple as increasing the fuel settings.
Low fueling will limit power, and has the potential to limit boost. The turbo is driven by expanding, hot exhaust gas.
More fuel burnt equals more power, and more heat, equals more energy to drive the turbo. More drive energy, equals more air into the engine, and more potential to ve able to burn more fuel.

If there's an underlying issue, simply adding more fuel could be a recipe for disaster.

Yes, you could experiment with adding more fuel. If that's not the cause of your lack of power, you risk damage to the engine if your combustion temperatures are to high.
An EGT gauge helps monitor this.

Injection timing could be a worth checking too.

Post a photo of the front cover off the turbo.

For your exhaust, I would add the largest 3"full flow muffler you can fit at the rear.
If it's full flow, it won't harm performance.

Also, if you post a thread, or a link to this thread in the Diesel tech section here, you'll get more responses. Do some searching in the diesel tech forum. There's loads of good info that will help with your issues.

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