No power at high RPM

[CappyKD]

I think I may have just diagnosed an exhaust restriction. I tested intake manifold vacuum at idle, it read 19.5 in Hg. I then brought engine RPM up to around 3000, the intake vacuum dropped to around 15 in Hg. I then removed the O2 sensor plugs from the end of the exhaust manifolds (simulating removing the restriction) and tested the intake manifold vacuum. At idle around 19.5 in Hg, at around 3000 rpm, it read 19.5 in Hg also. I will take it into an exhaust place tomorrow and see if they can test the exhaust back pressure.

Hmm, plugged cats?

 

[LX470 AUS]

Yea I checked the tip. its ok. And I don't have cats. I think its the muffler.

 

[2001LC]

Have you been in deep water/muck or could something have nested in the exhaust recently?

 

[2001LC]

My LX470 seems to run quite well, it has quite a bit of power between idle and 3000 RPM, but over 3000 RPM it doesn't seem to accelerate any more.
*******.
Vehicle details:
1998 LX470, Australian, ****pacemaker extractors, twin 2.5 into 3 in exhaust, no cats.
Also I just replaced spark plugs, cleaned MAF sensor and throttle body.

Thanks for any input.

Stew

I'm curious: When was exhaust modified & was muffler changed, did you use OEM recommend spark plugs and did you clean all three wires on MAF and with what?

Was your LX equipped with a catalytic converts from the factory?

 

[LX470 AUS]

The previous owner modified the exhaust. I think it would have had cats from the factory, but no O2 sensors. the whole exhaust is aftermarket, it has a really loud note to it, I think the centre muffler is a performance one, its too loud for my liking.
I cleaned the MAF with MAF cleaner from the local auto parts store. Sprayed it really well, and then did it again a week later just to make sure.
I havnt been in the mud or water since I bought it, but the PO might have been. There are no signs of it having been mud bogged or drowned.

 

[hoser]

Did you try and drive around without the O2 sensor plugs?

 

[2001LC]

I'm guessing you've recently bought LX, I'm I right?

It's hard to imagine the exhaust clogged unless something got in to it. Cat's yes i could see clogged up, but you don't have any.

Old carburetor engine form like the 1970, I did a lot of modification on. Found all kind of ways to get more HP out of them. That said, I'm pure stock (OEM) these days, it is near impossible to get me to modify my UZJ100 or any modern vehicle. I won't even remove the coolant pack from the skid plate. These are integrated systems, remove or modify one component and sensor can't read as designed. No O2 just doesn't sound like that's from the factory.

I'd resort to factory spec, putting back the parts someone has removed, starting with the o2's. Some good info on after mkt exhaust system that are o2 ready in mud. Possible the PO will be able to shed some light on what has been modified, he my even have chip it.

 

[LX470 AUS]

In Australia the UZJ100 didn't have O2 sensors from factory until 2002, mine is 1998.
No I didnt drive around without O2 sensor plugs, it was pretty loud. I might try that today.

 

[LX470 AUS]

Yes, I recently bought the car, about a month ago.

 

[LX470 AUS]

Its strange, when you put your hand next to the tail pipe to feel the exhaust flow, at idle it seems normal, then when the RPMs are increased, the flow gets greater, but then it reaches a point (around 3000 rpm) and the flow backs right off, there is around the same output at 3500rpm as there is at idle.
I took the o2 sensor plugs out and drove it for a bit, no difference. So that pretty much rules out muffler restriction.

 

[2001LC]

In Australia the UZJ100 didn't have O2 sensors from factory until 2002, mine is 1998.
No I didnt drive around without O2 sensor plugs, it was pretty loud. I might try that today.

Its strange, when you put your hand next to the tail pipe to feel the exhaust flow, at idle it seems normal, then when the RPMs are increased, the flow gets greater, but then it reaches a point (around 3000 rpm) and the flow backs right off, there is around the same output at 3500rpm as there is at idle.
I took the o2 sensor plugs out and drove it for a bit, no difference. So that pretty much rules out muffler restriction.

Sound like throttle valve is closing at higher RPM cutting off intake air, can you check that?

What am I missing, how can you take out o2 sensor plugs if the 1998 didn't come with o2 sensors?

Did you use factory recommended spark plugs?

 

[OregonLC]

If the throttle was closing the RPMs would drop. It's not like there's an autonomous rpm generator separate from the throttle body.

I'm starting to wonder if you don't have a stuck/sticking valve? Works ok up until a certain point then either floats or sticks.

 

[LX470 AUS]

The spark plugs are NGK laser iridium. Recommended from local auto parts store.
It has aftermarket extractors on it, pacemaker, and they have holes at the end for where the O2 sensors would screw in (on an AUS post 2002 model). They are plugged up with a threaded cap.
I dont like the sound of a sticking valve, would I need to remove the cam covers to inspect, or is it more complex than that?
I might connect to tech stream again and take a screen shot of live data at 3500 rpm, see what the MAF and ignition advance are doing at higher revs.
What are the symptoms of failing crank position sensor? This data would be used to set ignition advance wouldn't it?

 

[LX470 AUS]

So here are two screen shots of live engine and ECT data. The first is in park holding revs around 3200 RPM, the second is in 1st accelerating (foot flat) at around 3500 RPM.

 

[LX470 AUS]

The MAF is showing 119 gm/sec when under load, and only 27 gm/sec when in park (no load) at almost the same engine RPM.
Ignition advance is only 8 degrees when under load.

Im not too sure if these readings are telling us if there is something wrong, or if all is normal. Does anyone out there have techstream experience enough to know?
I might have to start making friends with random other UZJ100 owners and try to borrow a MAF for a test.

 

[2001LC]

OregonLC is right; rpm would drop if throttle valve closing, no mention of that (my bad).

I have no tech-stream experience, so I'll bump you and hopefully someone here this A.M. will interpret your results.

 

[Actualeyes]

The MAF is showing 119 gm/sec when under load, and only 27 gm/sec when in park (no load) at almost the same engine RPM. Ignition advance is only 8 degrees when under load. Im not too sure if these readings are telling us if there is something wrong, or if all is normal. Does anyone out there have techstream experience enough to know? I might have to start making friends with random other UZJ100 owners and try to borrow a MAF for a test.

I think Wilsil is in Perth.

 

[bcmotor]

the first picture you said it in park ? the scanner said is 2nd gear ?

 

[bcmotor]

I have the same problem , mi problem is muffler restriction i put new muffler but not all the muffler , i need to complete the rest, same size from the beginning 2 1/4

 

[PADDO]

The MAF is showing 119 gm/sec when under load, and only 27 gm/sec when in park (no load) at almost the same engine RPM.
Ignition advance is only 8 degrees when under load.

Im not too sure if these readings are telling us if there is something wrong, or if all is normal. Does anyone out there have techstream experience enough to know?
I might have to start making friends with random other UZJ100 owners and try to borrow a MAF for a test.

I'll do my best to hook up TechStream and get some screen shots at 3200rpm for comparison. Might well be exhaust obstruction at higher flow rates, what you've described to date just seems odd. Refresh us, has the problem existed since you purchased and you've just become aware of it, or was it initially fine and then developed? How easy/hard would it be to disconnect your main muffler? Clamps or a saw job?

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