70% of my power has slowly slipped away!!

[Zantus Design]

I have a '96 South African spec hilux fitted with a 1UZ-FE.

A year ago it developed a slight missfire and since the problem it slowly grew to the point where it's now running very rough and the power at the wheels is only 30% of what it was before the problem started.

The engine management is done by a South African system, which was my first suspect. Recently I fitted my system to another hilux with the same set-up and it developed the power mine had before, so that elimanted the engine management system.

From what I read on this, I suspected the coils, so I replaced the plugs and the coils, but it made absolutely no difference.

I also had the engine checked for any major mechanical failures or blown gaskets, but no problems could be found. The plugs were checked one by one and they all fire. On removal, the plugs all looked the same, which should indicate that all the cylinders are getting fuel and combusting.

What else could cause the 70% loss of power???

Thanks

 

[cribbj]

Here's some random ideas:

Timing belt jumped a tooth or two? This will definitely cause rough running.

Plugged cats, or other major restriction in the exhaust?

Air filter OK?

Fuel filter plugged and/or fuel pump not up to snuff?

Dirty injectors?

I'd run a compression and a leakdown test to see if either one showed anything.

I'd also hook up a vacuum gauge to see if you're still pulling healthy vacuum at idle, and it's steady.

 

[Zuffen]

A misfire that slowly ate away at your power?

I would be looking at plug leads.

First one died then another etc.

 

[Zantus Design]

Timing belt jumped a tooth or two? This will definitely cause rough running.
Possibly, how do I check this?

Plugged cats, or other major restriction in the exhaust?
No cats on my rig, and I've alray had the exhaust system checked.

Air filter OK?
Yip, it's got a cone filter, which was replaced recently.

Fuel filter plugged and/or fuel pump not up to snuff?
Filter was replaced to check if the old might be blocked, but it made no diffrence. Fuel pressure is one of my suspects, how do I check if I have the correct pressure?

Dirty injectors?
Possibly, can these be checked/cleaned or is it a case of just replacing them?

I'd run a compression and a leakdown test to see if either one showed anything.
Did a compression and all seemed fine.

I'd also hook up a vacuum gauge to see if you're still pulling healthy vacuum at idle, and it's steady.
Vacuum was checked by someone else and I was told it's good, but I'll check it again, what is a good vacuum?

 

[Zantus Design]

A misfire that slowly ate away at your power?

I would be looking at plug leads.

First one died then another etc.

Will it cause the plugs to die completely? All the plugs were still firing when I checked it a week ago, so there aren't any completely dead plugs.
Or will it cause weak spark, and will that weak spark cause the massive loss of power?

 

[cribbj]

Timing belt jumped a tooth or two? This will definitely cause rough running.
Possibly, how do I check this?

Put the motor at #1 TDC compression so that the mark on the dampner lines up perfectly with the "0" on the timing cover, then check that the timing marks on the cam sprockets line up with the fixed marks on the covers. A one tooth misalignment isn't much, so don't let your eyes play tricks with you. The cam sprocket marks should be bang on with the fixed marks.

Fuel filter plugged and/or fuel pump not up to snuff?
Filter was replaced to check if the old might be blocked, but it made no diffrence. Fuel pressure is one of my suspects, how do I check if I have the correct pressure?

You'll have to rig something on the fuel system possibly where the line crosses over between the rails. I don't know the exact factory specification for the idling pressure, but if it's like most Toyota's it'll be around 3 bar with the key on, but the engine stopped, and then drop down somewhat - perhaps around 2.0 to 2.5 bar with the engine running at idle.

Dirty injectors?
Possibly, can these be checked/cleaned or is it a case of just replacing them?

Easily cleaned, either in situ with a special flushing rig that dealers or independent shops have access to, or you can pull them all out and send them off to an injector shop to be cleaned and flow tested.

I'd also hook up a vacuum gauge to see if you're still pulling healthy vacuum at idle, and it's steady.
Vacuum was checked by someone else and I was told it's good, but I'll check it again, what is a good vacuum?

500 to 550mmHg or better at idle is a good figure

 

[Zantus Design]

Any more ideas?

I'm taking the vehicle to my mechanic on 3rd Jan, and then he'll go through everything I've already checked and everything mentioned here.

 

[Zantus Design]

A friend of mine tested the fuel pressure over the weekend and it was 2.5bar at idle speed and went up to 3bar when I blurped the throttle. Is this ok?
It is definately running way too rich on the current mapping, last tank only gave me 1.5km/l. Will be switching back to the previous map that gave me 6km/l and had the engine running much smoother than it's running now. On that map it produced 65kW ATW instead of the 145kW ATW it used to be! Once that is done we'll continue checking the basics.

 

[mshawari1]

A 3 bar = 44.1 PSI for the fuel pressure is acceptable… ​

 

[Zantus Design]

My mechanic showed me today that my cambelt slipped 2 teeth on the right-hand cam and 1 tooth on the left cam.
Hopefully this will resolve my power loss problems and also help with the overheating issues.

Now the question is, why did it happen??? And how do I prevent it from happening again???

 

[cribbj]

Replace the timing belt & the timing belt tensioner.

Recommend you use only OEM parts for this - many of the "will fit" Chinese parts that are being sold now don't tension the belt enough and brand new belts will slip (ask me how I know this).

If the new belt & new tensioner still do not result in a belt with enough tension, you may have to put a shim cap of some sort on top of the tensioner piston. We've seen this problem too, and frankly don't know why.