Weird power loss at high speed...(troubleshooting)

[wagonjunkie]

G'Day,
I have a strange problem with my '93 Liberty & I'm hoping someone might have some ideas about the cause...?
(I'll admit I haven't searched the forums much because the problem is so strange and specific I doubt there will a post with the same scenario / problem...)

The car is an AWD '93 Lib. wagon with the EJ22E & and a 4EAT auto.
It has about 185,000 on the clock and is our daily driver / family bus.

The engine is strong and the AWD system works well.
The car drives fine and accelerates smoothly under almost all circumstances and any speed....except the following....

There is a hill near our place heading out of town. It's quite steep and it's looong. Like over a kilometre long. The speed limit is 110 km/h and it's a real car killer. You start from the red light at the bottom and just as you're getting to about 100km/h with your foot down, the gradient really starts to kick-in. Half way up and the tranny is now back in third (and sometimes screaming in second) and the engine is pulling around 4000 rpm to maintain about 100 km/h. This is normal. Your right foot is pretty deep into the pedal. It's the same for any car, it's a long hill that sorts out the slugs from the rockets. For the drive-train it is a combination of high fuel demand, high load and high speed.

At around 2/3rd 's to 3/4 of the way up my engine starts to lose power quite quickly. At first it seems to slow a little so you push the pedal even further, but within about 100 meters the revs are falling quickly and the speed is dropping rapidly. The engine seems a little rough but there's no weird noises or vibrations.
All I can do is pull over (it will literally slow to a stall if you don't, I've pushed it to complete failure once) and restart the car. It then drives away normally.
The worst part is, it doesn't do it every time we go up that hill.
The problem cannot be replicated anywhere else or under any other circumstances....and we live on a steep hill that the car goes up & down every day without issue.

It doesn't throw an ECU or TCU fault code when it happens either.

I have replaced the fuel pump with a new unit but has not solved the problem (although it seemed to go up the hill a little better at first....)

My thoughts are:
1. Fuel pressure regulator is leaking vacuum and not pulling open enough at high fuel demand...??

2. Air Flow Meter signal breaking down...? (but why no fault code generated?)

3. Spark integrity breaking down at constant high load...? (I replaced the plugs, leads and coil about 10 - 15,000 kms ago...)

Sorry for the long post, but it's a very specific problem and I wanted to give as much info as I could.

Many thanks.

[RoughDiamond]

While you mentioned you changed the fuel pump, did you change the filter in the engine bay? 185K km is nothing to shake a stick at in terms of filtration (especially in the Oz). For a cheap peace-of-mind, I would. Next, I'd borrow a fuel pressure tester, run it in-line from the filter to the fuel rail, run the gauge inside (from an open driver's window or such) and take that hill and watch the fuel pressure.

Other than that, I'd try pulling the gear lever from OD (4th) to D (3rd). This will tell the TCU that you could be in for some high-load demands and will be "easier" on the trans.

[TurnNburn]

Also a suggestion from someone on this board that turned out to be spot on for me. Try unplugging your oxygen sensor and running with disconnected.

I had a simalar problem although not as bad as you, hooked up my air fuel gauge before i did it and when it was acting up it was off the charts rich, like pegged at 10:1. Once i unplugged it, it started acting normal (still rich) at 13ish:1. And mine wasnt setting any codes either.

Worth a shot, wont cost you any money and you wont need any tools

[wagonjunkie]

Thanks muchly for your replies guys....

I failed to mention in my OP that I changed the fuel filter last w'end when I fitted the new fuel pump.
The filter actually wasn't particularly old....I just wanted to eliminate it from the process.
I would like to get a read on the fuel pressure as rough diamond suggested though....

TurnNburn - I was doing some more reading last night and I found plenty of people in "internet land" that had O2 sensor and cat converter problems that produced similar behaviour. I think the Cat con. has plenty of miles on it....so maybe it's getting red-hot half way up the hill and generating too much back pressure?....the only thing that doesn't fit with this is that I don't remember any bad smells when it happens....?
I spoke to a couple of exhaust workshops this morning. They had ideas about fitting new cat con's and getting rid of the three-way style converter that seems to be unique to gene Legacy's......but neither of them had any way to definitively test or trouble-shoot a cat con. and say with little doubt that it is toast.....

[wagonjunkie]

....and the other thing I thought might be giving trouble is the knock sensor...?
Although I don't know much about the how / why / when with the knock sensor? What is it's relationship with the ECU? Is it only called upon at certain times?....or is it "listening" constantly and if so, what is it about that hill that activates it...?

(so many damn "what-ifs" !)

[TurnNburn]

could be a cat, i visual inspection would help if you can put eyes on it. To bad it only intermittently craps out, you could take off the exhaust (manifold back) and see if it does it. I do that all the time at work to tell if a cat is clogged up. But if a cat went out from over fueling and clogging, then that is just the symptom of a different problem. probably an 02 sensor or possibly a injector.

Did you try unplugging the 02 sensor?

[wagonjunkie]

I haven't gone up the hill for a few days....but I will try it with the 02 sensor out as soon as I do.

Does anyone know what the typical life span of the fuel injectors would be...? I always thought they were pretty trouble-free for the life of the car....?

[TurnNburn]

leave the 02 sensor in the exhaust, just unplug it from the harness.

Usually pretty reliable, but anything can happen

[Legacy777]

I think a catalytic converter issue sounds plausible. I suppose something with the MAF sensor could be causing some problems, possibly over fueling and heating the cat up more.

Try disconnecting the O2 sensor as suggested and see if that changes anything. You could also try using MAF cleaner on the MAF sensor. Only use MAF cleaner.

Other than that, if you could find a spare exhaust manifold setup, cut the cats out, put a muffler on (or not ) and do a test run up the hill.

The other thing I just thought of is the muffler or possibly some other type of restriction in the exhaust system.

[wagonjunkie]

Thanks for your thoughts so far guys...

I drove the car up the hill three times yesterday. My plan was to disconnect the O2 sensor after the first run.
.....but it drove up PERFECTLY three times. So if I had disconnected the O2 sensor it would have proved nothing (at least yesterday anyway...)

Currently searching FleaBay for a straight jacket.