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Jeremy Abram
Newbie
Cambridgeshire
Soarer V8

Posts: 1
Reg: 08-2007

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Monday, August 20, 2007 - 09:29 pm, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Hi guys, first post here!

Ok my V8 runs fine when stone cold and starts first time everytime. But once it's warmed up, the engine hesitates and feels like it's missing under load. But it idles smoothly and on full throttle over 3500rpm it's fine. It's under normal acceleration that it's most noticable.

If I disconnet the air flow meter the engine runs much better with great acceleration and really highlights how bad it is with the AFM connected. The fact it runs much better with the AFM disconnected should rule out the ignition system and suggests the mixture, correct?

I've tried another AFM and it was just the same, although this AFM was unknown if it was working properly. Whats the chances of two AFM's being faulty?

I've tested the voltage from the O2 sensors with a multimeter and got the following:

Starting with the engine stone cold, as the engine warms up the voltage goes from 0.00v and to about 0.50v when the engine was roughly half warm. It then sits at 0.05v and jumps to about 0.50v every seven seconds. This was at idle and I'm not sure it should do that at idle. But if the engine is held at a fast idle, the voltage jumps from around 0.20v upto around 0.90v roughly every second, which my understanding says is what they are ment to do. I'm gussing that at idle the ECU will run a very lean mixture to save fuel, hence the 0.05v with a jump to around 0.50v every seven seconds.

Also if I disconnect the air flow meter (which makes the engine run much better, with no hesitation) the voltage rises upto 0.9v and pretty much sits there, suggesting a rich mixture as would be expected.

So it appears my O2 sensors are working as they should.

Any other suggestions please, as I'm getting to the end of my tether with this now!
Jeff Harper
Trader
NSW
UZZ32 Active V8

Posts: 1369
Reg: 07-2005

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Monday, August 20, 2007 - 09:53 pm, by:  Jeff Harper (Jeffh) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Borrow a coil pack and an exciter of a known working V8. Do the swapsies dance and see if its that.

Do you have a factory filter or a pod? If a Pod swap it with a factory filter for a week, you may have oil on the AFM ... DO NOT CLEAN THE AFM!!!

Something simple, did you wash the engine? If so you may have a gut full of water in the spark plug holes.
Jeremy Abram
Newbie
Cambridgeshire
Soarer V8

Posts: 2
Reg: 08-2007

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Monday, August 20, 2007 - 10:05 pm, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

The car is totally standard other than different wheels.

I can't see there is a problem with the coil pack as it runs very well with the AFM disconnected.
Damian Ware
DieHard
Victoria
UZZ32

Posts: 567
Reg: 10-2005

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Monday, August 20, 2007 - 10:53 pm, by:  Damian Ware (Frozenpod) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Under full load above 4000rpm the ECU determines the amount of fuel to add by using AFM. Unless the mixtures are completely wrong under full load I would suggest the AFM is operating ok.

Below 4000rpm the engine will be running in closed loop off the oxygen sensors but with reference to the AFM and air temp sensor and water temp sensor.

If any of the sensors are incorrect it can cause the ECU make corrections which it thinks is correct that could cause the AFR to be rich or lean. From your description it sounds like it is running lean in closed loop.

As above I doubt the AFM is the problem as if the AFM output is incorrect the engine will run rich or lean but it will adjust itself very quickly and run of the oxygen sensors somewhat ignoring the AFM (depending on how incorrect the output is).

I would be checking the temp sensors and if they are operating correctly. I would also disconnect the oxygen sensors and if possible look into the ECU. A faulty ECU can cause the AFR to be incorrect.

Replacing the oxygen sensors is fairly easy and they are cheap so if you cant find the fault I suggest replacing them.
Jeremy Abram
Newbie
Cambridgeshire
Soarer V8

Posts: 3
Reg: 08-2007

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Tuesday, August 21, 2007 - 04:38 am, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Tomorrow I'm going to check the voltage drop of the wire going from the AFM to the ECU.

Failing that, I think a new pair of O2 sensors will be next, then try a known to be good AFM and lastly try a known to be good ECU.

If that doesn't work, I'll set fire to it!
Jeremy Abram
Newbie
Cambridgeshire
Soarer V8

Posts: 4
Reg: 08-2007

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Tuesday, August 21, 2007 - 06:40 am, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Just ordered two O2 sensors. Seems the most logical thing to change, as they do have an expected max lifespan.
Jeremy Abram
Tinkerer
Cambridgeshire
Soarer V8

Posts: 8
Reg: 08-2007

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Friday, August 24, 2007 - 11:23 pm, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Well the new O2 sensors are in (after much faffing about. One come out very easily, the other I had to re-tap the hole in the exhaust, but they are now in.

But the engine is running exactly the same, missing under load up to 4000rpm but fine above 4000rpm.

Jeremy Abram
Tinkerer
Cambridgeshire
Soarer V8

Posts: 9
Reg: 08-2007

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Saturday, August 25, 2007 - 02:06 am, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

This is me (at the back to the left hand side):






Well that will teach me to over look the fecking obvious!

This afternoon I pulled all the plugs out. In my defence I had been told by the seller that the plugs had been checked and were all ok. Infact the plug gaps ranged between 1.1mm to 1.4mm. They should be 0.8mm. Also the plugs look like they are passed their best. The colour of them is good though, a nice light brown.

Two of them did have evidence of gasses passing between the metal and the ceramic which could be seen as a 'burnt' area of the ceramic where it meets the metal casing. A couple of the HT leads were showing signs of arcing too.

I closed to gaps upto 0.8mm, and now it's running perfectly.

so I'm going to order a set of new plugs and new leads:thumbs:
Gregg Holden
Trader
WA
Soarer UZZ31 Supercharged

Posts: 753
Reg: 08-2005

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Friday, September 14, 2007 - 03:44 pm, by:  Gregg Holden (Xzotic) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Shame I didn't see this post earlier. Had exactly the same problem - Joe "Hollywood" immediately suspected arcing of the HT leads. This was confirmed, replaced and all sorted within a couple of hours.
Adam Peterson
Goo Roo
Western Australia
Bugatti Veyron

Posts: 1167
Reg: 04-2006

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Monday, September 17, 2007 - 12:49 pm, by:  Adam Peterson (President) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Gregg, what about pulsing revs when the car is coasting ?
Thats what mine does at times.
Gregg Holden
Trader
WA
Soarer UZZ31 Supercharged

Posts: 770
Reg: 08-2005

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Monday, September 17, 2007 - 07:44 pm, by:  Gregg Holden (Xzotic) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

No adam no pulsing on coast, however once you ease the throttle when cruising you get the stuttering problem as the leads start to arc. When you rev up past 3000 odd then it goes away but will repeat again anywhere in the lower power band.

If yours is pulsing or surging then may be a different problem (or a combination of issues - HT leads being one of them). You said your HT leads showed signs of arcing - have you replaced them yet?...
Adam Peterson
Goo Roo
Western Australia
Bugatti Veyron

Posts: 1173
Reg: 04-2006

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Tuesday, September 18, 2007 - 11:09 am, by:  Adam Peterson (President) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I havent replaced anything yet. I have only had the car for about 5 weeks and its riddled with problems that is damaging my wallet!
I have already had to spend over $1600 just on cosmetic stuff alone and i still have a lot to go.
It may be spark plugs ?
Plus i dont have a service history either so i dont know whats happening.
Gregg Holden
Trader
WA
Soarer UZZ31 Supercharged

Posts: 778
Reg: 08-2005

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Tuesday, September 18, 2007 - 02:00 pm, by:  Gregg Holden (Xzotic) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Adam had you asked Joe to have a look at it?...
Andrew Ferres
DieHard
WA
'90 C-F Celsior V8, '84 Soarer V8, '91 Supra V8

Posts: 701
Reg: 07-2005

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Tuesday, September 18, 2007 - 07:38 pm, by:  Andrew Ferres (Peewee) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Stock plugs should be 1.1mm, not 0.8mm

0.8mm is for boosted applications, or cars with a weak ignition system.
Matthew Sharpe
Goo Roo
North Island
JZZ31

Posts: 3025
Reg: 10-2005

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Wednesday, September 19, 2007 - 04:57 pm, by:  Matthew Sharpe (Madmatt) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Another victim of "cheap soarer" syndrome.
Ben Kelly
TryHard
Lidcombe
v8

Posts: 226
Reg: 08-2005

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Sunday, September 23, 2007 - 07:58 pm, by:  Ben Kelly (Ace) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

jeremy change the plugs and leads already. then let us know.
Jeremy Abram
Tinkerer
Cambridgeshire
Soarer V8

Posts: 11
Reg: 08-2007

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Saturday, December 29, 2007 - 01:26 am, by:  Jeremy Abram (Jem) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Matthew Sharpe wrote on Wednesday, September 19, 2007 - 04:57 pm:




Not at all!

I changed the plugs and leads back in August and that fixed the problem.

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