[nobes]

Hey all,

My V6 GV has a slight hesitation or surging when taking off normally at light throttle.
seems to do it more in the higher gears and its at around 1800 to 2200 RPM. Fine if i rev it out and fine under 1800 rpm.
I would prefer to have some ideas on where to start rather than replacing things willy nilly.

So far i believe it to be either O2 sensors, Fuel pressure or coil packs; or maybe even engine or gearbox mounts?

Would either of these be the contributing factor to a not very smooth take of or surging at certain rpm?

spark plugs are new, Coil packs are cleaned and have di-electric grease, however half of them look like the originals.

Its a little annoying because i travel in 4 or 5th gear around 75km/h a lot and it makes the car even more jerky again.

Thanks all.

[GeckoXL7]

My Engine use to be slugush up to around 2500 then take off.

Changed the 02 sensors didnt make a difference. (doesnt mean it wont be the problem a GV does no if the 02 sensors are not running efficient and will display a error code)

Cleaned the Air intake and maf sensor made a big difference. And make sure its all tight any air leaks the engine hates even if very small.

Also other things to look at is changing the fuel filter, they last around 40,000k.

Mine still is a tinny bit hessatent which the only thing left on my car is the Pre cats, but i dont think the 98 GV has them.

If engine mounts are going under slight throttle eg pulsing it you can feel the shock in the drive train its not dampend very well.

[nobes]

Thanks for that.

The fuel filter was changed around 6000k's ago.
getting error code 12 or 13 can't remember which means everything is fine.
adjusted throttle position sensor but seemed fine anyway.
I took the MAP sensor out. Is it ok to clean it with some throttle and carb cleaner? I've heard they can be very sensitive?
I also pulled my ECU to check for moisture damage but looks fine.
Might hold off on replacing the O2's then as i'm not getting the fault code.
Intake looks like a bit of a pain to remove with gaskets etc but i'll have a go at doing that.
I have a fairly new cat installed only a few thousand ago also. Its not a high flow but the rest of the exhaust is from a later model and is slightly larger.

[GeckoXL7]

To Clean the MAF there is special MAF Sensor cleaner about $19 a can, They are sensative and dont like anything on the sensor spraying carb cleaner will leave a fine coating on it. You can clean the air intake by using intake cleaner with its tube in the intake pipe then tightend back up rev to around 2000rpm and give a couple of sprays and repeat. Engine will almost stall as you spray so only quick bursts of spray.

[fordem]

GeckoXL7 wrote:

Changed the 02 sensors didnt make a difference. (doesnt mean it wont be the problem a GV does no if the 02 sensors are not running efficient and will display a error code)

A 98 GV will be OBD1 (confirmed by the the OP mentioning code 12/12), the O2 sensor would have to be dead before it would figure it out, and that's if it has any (mine doesn't).

[nobes]

So the car could still display tell-tale signs of an O2 going bad before the light on the dash displays?
I guess being a service item and at $210 for NTK it's worth trying. I will give the intake a clean first.

[GeckoXL7]

02 sensors usually start outputting a weaker signal which the ECU should pick up or make the engine richer, slugish etc, can be flat spots too like what i had.
Its not a bad idea changing can improve on fuel economy and performance if are starting to deteriate.

They suposidly are meant to be reaplced at 100,000k dont think any are mine was done at 160,000 Got Denso's for around 98 each. NGK are good too.

Try the intake clean first thats where i saw the biggest improvment then if dont help look at the o2 sensors as it seems you have done everything else

[murcod]

A dieing O2 sensor will give sluggish voltage changes - hence the surging. I've experienced it on a different vehicle and the symptoms were exactly as described. It won't occur on full throttle as the O2 sensor isn't used for feedback under those conditions.

Given they have a limited life (I've seen 80000km mentioned) it would be a good place to start. If you can access the O2 sensor signal then monitor it with a multimeter while driving- the voltage should change straight away (with no delay) if you floor the throttle. Any delay and it's time to change it.

Also check (if it's a single wire sensor) that the exhaust system is properly earthed, otherwise it won't have a hope of working!

[atari4x4]

it will be a 4 wire o2 sensor, can pick them up at repco for around 150 & comes with the correct plug.

[murcod]

atari4x4 wrote:

it will be a 4 wire o2 sensor, can pick them up at repco for around 150 & comes with the correct plug.

Make sure you always buy one with the correct plug, you don't want to be trying to re-terminate or join the special high temp wires they use.

[nobes]

Logicar have 2 O2 sensors in stock and i'll make sure i check the plug and number of wires beforehand.
I know them in there so returns etc. will be fine.

Regarding the intake cleaner: do i just pull off a vacuum line and spray it through one of them after the MAF sensor?

I'll report back when i get around to having a look at it.

On a side note my new front crank seal is leaking again, so that will have to come off again.
Was speaking to a local mechanic i supply parts too and he mentioned about any worn surfaces on the harmonic balancer pulley and i think there may have been so will have to try some light wet and dry sanding next time.
EGR looked reasonable so hope its not blow by and hopefully the seals aren't that finically that you have to install them 100% flat. Quite certain i installed in nice and flat so hopefully its just the balancer surface.
Atleast its relatively easy to get too.

Thanks all for your valiable information.

[GeckoXL7]

I undo the first clamp on the aibox or the Silencer the plastic tank like thing on the side of the pipe, stick the tube in there tighten the clamp and spray.

Cleaning the MAF i take the top off and air intake and spray both ways in the MAF to make sure both sides are clean.

On the Crank seal did you put motor oil on the lip to lube it before pulley went back on? Could be the surface too like the mechanic said, its quite a tight fit any dirt or rust i recon could chew up the seal quite quickly.

[nobes]

There was grease already on the genuine seal but i'm pretty sure i ran a little extra grease also.
I don't remember the lip on the balancer to be that badly grooved at all.
I guess the new seal wouldn't have gone back in exactly the way it originally was so that wouldn't help.
The seal only lasted a couple of weeks before i saw oil dripping down the front of the sump again off that little metal water pipe bracket piece. Its very minimal but it could fling onto a belt.



So pull the whole top inlet piece off? can't just pull the MAF out, clean it, re-install?

[GeckoXL7]

Yeah just the airbox lid with maf

[nobes]

So i finally got around to replacing both O2 sensors today.
Got a pair of 'walker' american brand for around $220 for both.
Seems to run smoother and cleaner. Time will tell if its any better on fuel.
Still a very very minor hessitation still there but could still be a few things.
i'm also going to replace the spark plugs again tonight.
O2's weren't realy black, little bit white in spots.
Thanks again everyone for your input. now onto the next mod.

[fordem]

GeckoXL7 wrote:

Yeah just the airbox lid with maf

The GV MAF is on the throttle body not out by the airbox like your XL-7 is.

[nobes]

Maybe he meant the IAT sensor?
Either way..... Its still jerking very lightly.
Will swap all the coil packs out next then maybe go down the fuel pump/regulator/injector route...

[murcod]

Have the coil pack (spark plug) boots ever been replaced? They can cause problems.

[atari4x4]

^^ This, if the surge feels like spark jump. Have you washed the engine bay recently? Pull the coil packs, dry them, blow out the spark plug tubes & inspect the coil pack probes for marks from where the spark has been tracking on the outside, can be a brown burnt looking mark or a white substance.

[nobes]

Not long after i got the car 7 months ago i had to replace a coil pack.
It looks like it already had 2 replaced and 4 originals still in there.
I have cleaned them all up twice now and ran di-electric grease on the springs etc.
Have not had the engine bay washed recently.
Its basically near non existent now. Ever so slight and still around the same 2000rpm.
I'll live with it untill i can afford to replace the remainder of the coil packs.
I actually disconnected the IAT to see if this was causing the issue given i now have a snorkel and it seems to run a little smoother at that rpm.
Maybe the IAT needs to be plumbed higher up into the snorkel?

[atari4x4]

Checked the ECU for water damage, the a/c drain gets blocked & can drown the ECU. tonyevans had one recently that was surging like a mofo!!!

[nobes]

Yep, pulled the ECU out and took the lid off after I read his post a few weeks ago.
It's really not bad at all now so I'll leave it for the time being.

[atari4x4]

Ahhh cool, yeah it's popped it's head up a few times now over the years & it's one to keep an eye on.

With the coil packs you can eliminate each one if you can get it to consistently surge, just like pulling a plug lead off an old car you can disconnect a coil pack one at a time & take note if it drops a cylinder badly or if it was already a weak spark & then dropping off to 5 cylinders. I use a flat bladed screw driver to bring the revs up on the throttle body, you can slide it in between 2 bits near where the cable goes & the wedge of the screw driver gives you good control of what RPM to hold... it's pretty obvious when looking at it, I have the dumb at the moment & can't think of the parts I'm talking about.

Checked the cat?

[nobes]

The catalytic converter was replaced about 4 months ago.
I replaced the O2 sensors only in the last few weeks so hopefully the cat hasn't blocked up in 4 months.
The light on the dash (#26) only just came up recently also.

Ok it seems like it does it more cold and around the same revs that it surges, i can also feel a physical loss of power?
That might scaled down the possibilities of what it could be.
I can't really remember, but i don't think it did it as much before i ran the snorkel which makes me think its the Intake air Temp sensor. However the random loss of power around the 2000 - 2300RPM has always been there and mainly when cold. Coolant temp sensor maybe? So many options its rediculous.
Also i have let the car run out of fuel by accident before.

[murcod]

The IAT and CTS are easy to check with a multimeter (providing you can find the specs in a workshop manual.)

[tonyevans]

Did you look at the bottom side of the ECU as that is where the damage is done?

[nobes]

Hey tonyevans,
Yep checked the back side also.
I'm going to go ahead and figure out how to check these sensors as its more prominent when cold so i'd really like to try and figure out where the CTS is and check that.

[tonyevans]

Have you got a manual? if not PM me your Email and I will send you a PDF with all the testing/tuning stuff in it.

[nobes]

get the PM ok tonyevans?
should get time this weekend to do some fault finding.

[tonyevans]

nobes wrote:

get the PM ok tonyevans?
should get time this weekend to do some fault finding.

I sent the Manuals to the email you gave me and a second one asking if you got them as I never got a reply - They did not bounce so someone got them?