A very mysterious problem

Trimac20 · Post by **Trimac20** » Wed Jul 22, 2009 5:11 pm

Hey all, great forum, I'm in a pickle with this problem I'm having...

I have a '99 Liberty RX 2.5 which has done 210,000 km, bought it second hand in 2004. Anyway, I got it serviced in April and I noticed it was 'jerking' and 'surging' and stalling. For instance, it would see it almost stall to a stop, but the engine would rev up (the tacho needle would skyrocket). After a delay of perhaps two seconds it would surge forward as if all the energy being withheld was released. This happened infrequently enough that I foolishly did not consult my mechanic about it.

Anyway, in June I drove all the way from Perth across the Nullabor, and after arriving in Adelaide the problem got much more frequent, severe and noticeable. I THOUGHT at the time it was a tranny problem, that the gears were not shifting up smoothly and getting 'caught', that's kinda how it felt. It would happen on and off: sometimes the car might go a few days problem free, while at other times it was almost constant. It seemed a lot worse shortly after turning the engine on.

Anyway, brought it to a few mechanics, but didn't have tim eto stay in Adelaide so drove to Melbourne where I am now. I brought it to Fluidrive, which does transmissions, and the guy diagnosed it as a faulty speedo sensor, after i told him the speedo needle seemed to stall. So he orders in a geniune subaru sensor and i have to fork out $470 for that and a transmission service. The result? It seemed even worse! Sometimes so bad the car would basically move forward in a series of staccato like spurts, lunging forward between stalling. As you can imagine it makes the car undriveable at times. Today, however, it only happened a few times, but it's unpredictable and always seems to return. Oh yeah I should mention it only seems to happen below 60 km/h, esp in stop/start traffic, which is why i thought it was a first gear problem.

Anyway, I went straight back to the mechanic first thing in the morning (as you would). A young bloke was there and he said that when he tested it he felt the surging/stalling too and was pretty positive it was a fuel problem! None of this was mentioned to me prior to paying for it. What was more annoying was that the mechanic who did it is away in Adelaide til next Monday and I need to get to Sydney very soon...but that's another story.

Anyway, I intend to get some more opinions (something I should've done before). The mechanic did a service of the tranny, cleaned out the filter and replaced fluid, which was fine...Any idea what it could be, and if it had anything to do with the speedo sensor at all? Does the problem sound more engine related than electrics related? Any help greatly appreciated. Thanks!John

sss1600 · Post by **sss1600** » Fri Jul 24, 2009 10:49 am

i'd take it to a dyno tuner not just any old mechanic and get him to load test it until it fails.
He should be able to monitor fuel pressure, vacuum leaks and what not...

AlpineRaven · Post by **AlpineRaven** » Fri Jul 24, 2009 12:04 pm

check fuel pressure, might be fuel pump. Other thing i would also look for is air lines that is connected to air intake from start to the inlet manifold, check all connections (pipes etc) that is connected there bec if there is a leak it'll stall or rev like crazy. Other thing i can think of is maf sensor playing up. Isn't that fluid drive in flemington? Where about are you now?
Cheers
AP

AlpineRaven · Post by **AlpineRaven** » Fri Jul 24, 2009 12:08 pm

have you checked the error codes?

About the speedo, does it goes up and down smoothly or delayed or jerking to give you speedo reading?
Cheers
AP

Outback bloke · Post by **Outback bloke** » Fri Jul 24, 2009 1:13 pm

Personally I would book it in to Subaru and have them look at it. They can plug their computer in to it and it will tell you what the problem is with out doubt.

riksta · Post by **riksta** » Fri Jul 24, 2009 10:11 pm

I had much of the same problem with my Liberty, turned out to be a folty nok sensor playing up, have not had it happen since I replaced it .

Rik.

Trimac20 · Post by **Trimac20** » Sat Jul 25, 2009 6:20 pm

riksta wrote:I had much of the same problem with my Liberty, turned out to be a folty nok sensor playing up, have not had it happen since I replaced it .

Rik.

Thanks, what is a nok sensor?

Trimac20 · Post by **Trimac20** » Sat Jul 25, 2009 6:21 pm

AlpineRaven wrote:have you checked the error codes?

About the speedo, does it goes up and down smoothly or delayed or jerking to give you speedo reading?
Cheers
AP

No I haven't checked the error codes, the speedo just functions normally, but is jerky because the car is moving jerkily.

bobbyjimmy · Post by **bobbyjimmy** » Mon Jul 27, 2009 10:54 am

He meant to spell Knock Sensor.
If it turns out to be the fuel pump - I've got a spare one here, pay for postage and its yours.

AlpineRaven · Post by **AlpineRaven** » Mon Jul 27, 2009 8:51 pm

bobbyjimmy wrote:He meant to spell Knock Sensor.
If it turns out to be the fuel pump - I've got a spare one here, pay for postage and its yours.

Wouldn't bad (doesn't show up in check engine) knock sensor affect fuel economy?
Cheers
AP

tony · Post by **tony** » Mon Jul 27, 2009 10:46 pm

check the fuel filter or filters, this is symptomatic of fuel filters being blocked.

Trimac20 · Post by **Trimac20** » Wed Jul 29, 2009 2:27 pm

tony wrote:check the fuel filter or filters, this is symptomatic of fuel filters being blocked.

Thanks Tony, will get that looked at. The mechanic diagnosed a faultly O2 sensor using the computer as well, does that sound right to you?