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  Soarer Central * Mechanical - V8 * Car slow's down / revs drop suddenly while driving * Archive through December 12, 2009 Previous Previous    Next Next  

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Jengiz Isikli
Tinkerer
VIC
V8

Posts: 30
Reg: 01-2009

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Thursday, February 26, 2009 - 07:47 pm, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Hi guy's and girls.

well lately ive been noticing a random 'thing' that happens when i drive the soarer to and from work every day..

while cruising at perhaps..80/100kms.. the revs will drop in the vicinity of 500-1000 revs.. and the car will feel asif it is majorly slowing down..asif i pressed the breaks. but in actual fact my foot is on the accelerator.

its quite strange.. the car just lunges back and pulls me forwarded as if i have applied the breaks firmly.

then the revs shoot back up to what i had previously..

its very intermittent.. i cant pinpoint WHEN it will happen

the car itself is a 1991 V8 limited soarer..
done roughly 180kms..
engine is all standard.. has had an oil change and filter change within the last month.. ahh.. belts look brilliant, and over all the engine is in top condition.

thats all i can think of.

ive also reset the ECU a while back, and i remember it used to do this before i reset the ecu

ANY SUGGESTIONS would be apreciated.

thanks everyone.
Joe Russell
TryHard
Marlborough
4.0 V8 GT-L(UZZ31)

Posts: 241
Reg: 10-2008

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Thursday, February 26, 2009 - 08:00 pm, by:  Joe Russell (Joe_r) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Check your fuel filter(search here or planetsoarer.com/indexfull), and also how full is your tank when this happens?
I get this under heavy acceleration with less than about 25 litres, I think it is fuel moving away(opposing flow) from the drain/pump due to having no surge tank and no baffles.
Jengiz Isikli
Tinkerer
VIC
V8

Posts: 32
Reg: 01-2009

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Thursday, February 26, 2009 - 08:49 pm, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

tru, i get fuel surge.. i think they call it.

i get that when im lower than 15L of fuel.. i accelerate and my car chuggs asif the fuel lines have air gaps tehehe

but its not my fuel that is a problem, i always cruise at a steady pace when this happens..

i will check my fuel filter, good that you mentioned that i havent diagnosed that recently !
Joe Russell
TryHard
Marlborough
4.0 V8 GT-L(UZZ31)

Posts: 242
Reg: 10-2008

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Friday, February 27, 2009 - 04:30 am, by:  Joe Russell (Joe_r) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Haha its annoying isn't it!
That is even more odd, but I'd still look at the filter, maybe the fuel pump ecu too(again search here) could be a faulty connection/component.
Dave Hart
Goo Roo
Waikato
UZZ32

Posts: 1376
Reg: 08-2005

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Friday, February 27, 2009 - 07:34 am, by:  Dave Hart (Davyboy) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I think you'll find it's the air flow sensor. If the sensor thinks there's a low air mass either from the air flow or from the temperature sensor then it will drop the fuel to keep the air/fuel ratio correct.
The revs always drop never rise except to go back to where they were - is that what happens?
Jengiz Isikli
Tinkerer
VIC
V8

Posts: 34
Reg: 01-2009

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Friday, February 27, 2009 - 09:08 am, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Dave Hart wrote on Friday, February 27, 2009 - 07:34 am:

The revs always drop never rise except to go back to where they were - is that what happens?




YES! exactly rite, it happened this morning aswell, i was cruising on Princess highway, roughly 70kms.. steady.. and out of nowhere asif there was a STRONG wind.. the car revs dropped by 1K.. and the car kinda pulled forward a bit, then the revs jumped back up to normal.

im going to chop up my airbox this weekend and make a BFI, with the air channel under the tail light etc.. using MDF board and so on..

maybe its a restriction in the factory airbox i have now.

but this weekend im going to diagnose a few things on the car, check the fuel filter and make a BFI for the car..

see how it go's.
Joe Russell
TryHard
Marlborough
4.0 V8 GT-L(UZZ31)

Posts: 244
Reg: 10-2008

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Friday, February 27, 2009 - 09:18 am, by:  Joe Russell (Joe_r) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Good point Dave, could definitely be the afs.
Dave Hart
Goo Roo
Waikato
UZZ32

Posts: 1377
Reg: 08-2005

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Friday, February 27, 2009 - 10:07 am, by:  Dave Hart (Davyboy) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I mentioned that because I'm having the same problem.
Someone on this site said to give the air flow and temperate sensor a clean so I did and that's what happened. Found out later that you shouldn't touch them, well not to the extent I did.
After the filter there's also a fine metal grid so be careful not to damage it.
You don't want to know how much a new sensor is.
Jengiz Isikli
Tinkerer
VIC
V8

Posts: 36
Reg: 01-2009

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Friday, February 27, 2009 - 11:09 am, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

ahahah well i think i will leave the afm and temp sensor alone then..

but as said i will check the fuel filter and also make my BFI over the weekend with pictures.

thanks for the support guys.

Greatly apreciated
Joe Russell
TryHard
Marlborough
4.0 V8 GT-L(UZZ31)

Posts: 245
Reg: 10-2008

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Friday, February 27, 2009 - 01:58 pm, by:  Joe Russell (Joe_r) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

You can put stuff like Isopropel alcohol through and it with be fine, it's a very good cleaner.
Don't sniff it though

AFM's work by measuring static air temperature and comparing it to the temperature of the flowing air (using the fine metal grid Dave mentioned) to get an airspeed without impeding it's flow too much, so cleaning the metal grid and temp sensor with an evaporating type alcohol will likely improve the accuracy of it(only if it's dirty obviously, which it will be).
Remember to be gentle
Jengiz Isikli
Tinkerer
VIC
V8

Posts: 41
Reg: 01-2009

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Tuesday, March 03, 2009 - 09:35 am, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

i done my BFI over the weekend, i basicaly cut out the front face of the factory airbox, removed all unnecessary plastics and stuff.

cut it out carefully as i wanted to keep the original clipping and factory air filter.
Tom Jeffries
Tinkerer
South Australia
SC400 V8 GT 2D Coupe

Posts: 10
Reg: 09-2007

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Wednesday, March 04, 2009 - 10:51 pm, by:  Tom Jeffries (Tom_j) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I think i'm having the same problems...
My V8 is fine when i'm driving up to 60km an hour, then (usually on a hot day) and i speed up to 70/80km at some random point the revs cut in and out and it feels as if the car is jerking back and forward.
If i stop (eg at lights) the engine will die.
If i drive like it for too long then stop the engine will die and wont start for about ten minutes.
It smells as if it is running rich. Very frustrating...
As i said usually when the outside temperature is hot which leads my mate to think it is the Air Flow Meter.
Any thoughts?
Tom Richards
TryHard
nsw
V8

Posts: 174
Reg: 08-2005

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Thursday, March 05, 2009 - 08:45 am, by:  Tom Richards (Tomr) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

hi tom,

i would check the 2 coils. you can check with a multi meter which will tell if they are stuffed, but cannot give 100% assurance they are ok.

measure the primary coil (low voltage pins) should be close to 0 ohms. measure from either of the primary pins to the high noltage output and it should be ~12k ohms. if it is higher than ~12k, it is stuffed. this is a 99% check of whether the coil is ok.
Dave Hart
Goo Roo
Waikato
UZZ32

Posts: 1382
Reg: 08-2005

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Thursday, March 05, 2009 - 02:11 pm, by:  Dave Hart (Davyboy) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I take it that you're not getting any alarm messages, if you do then get them analysed.
Jengiz Isikli
Tinkerer
VIC
V8

Posts: 75
Reg: 01-2009

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Wednesday, March 11, 2009 - 10:47 am, by:  Jengiz Isikli (Jengiz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

nope, no alarm messages. no lights on the dash.. nothing. just a random drop in revs
Tom Richards
TryHard
nsw
V8

Posts: 175
Reg: 08-2005

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Wednesday, March 11, 2009 - 11:38 am, by:  Tom Richards (Tomr) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

have you checked the coils?
Adrian Klaebe
Newbie
ACT
single turbo

Posts: 5
Reg: 06-2008

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Sunday, March 15, 2009 - 03:56 pm, by:  Adrian Klaebe (Kedderz) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I have the same problem as what is described here. From the searching I have done, its either;

- blocked fuel filter
- fuel ECU malfunctioning (common for the car to start fine when cold but when warm it will randomly cut out)
- CAS/CPS

If only I knew about the above before I left the car in sydney after just purchasing it! (im from ACT)
Dave Hart
Goo Roo
Waikato
UZZ32

Posts: 1391
Reg: 08-2005

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Monday, March 16, 2009 - 07:22 am, by:  Dave Hart (Davyboy) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

If your top speed isn't affected then I can't see it being a fuel filter problem.
Scott Voravongsa
Newbie
hawaii
sc400 v8

Posts: 2
Reg: 12-2009

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Thursday, December 03, 2009 - 09:46 pm, by:  Scott Voravongsa (Grindin8o8) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

i have the same symptoms. bought a new used maf sensor and problem still occurs. lately on start ups my car would idle rough with rpm needles bouncing from 0-1500 rpm and then die.
Andrew Duaso
TryHard
Victoria
V8

Posts: 461
Reg: 02-2009

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Thursday, December 03, 2009 - 11:30 pm, by:  Andrew Duaso (Andrewd) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

All the above unsolved problems are due to the ISC

I had same issues. Repaired the isc and easy off bam, the problem was gone!
Adam Birkefeld
Tinkerer
N.S.W
V8

Posts: 42
Reg: 01-2006

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Friday, December 11, 2009 - 10:04 pm, by:  Adam Birkefeld (Go_ads) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Sorry to ask a dumb question but what is the 'isc'?
Damian Ware
Goo Roo
Victoria
UZZ32

Posts: 1231
Reg: 10-2005

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Saturday, December 12, 2009 - 09:11 am, by:  Damian Ware (Frozenpod) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

ISC is actually the ISCV Idle Speed Control Valve.

Most of the above problems have nothing at all to do with the ISCV.


Scott Voravongsa wrote on Thursday, December 03, 2009 - 09:46 pm:

i have the same symptoms. bought a new used maf sensor and problem still occurs. lately on start ups my car would idle rough with rpm needles bouncing from 0-1500 rpm and then die.




Sounds like the water temp sensor or ECU is faulty.


Tom Jeffries wrote on Wednesday, March 04, 2009 - 10:51 pm:

If i drive like it for too long then stop the engine will die and wont start for about ten minutes




I have only seen a faulty ECU or fuel pump ECU cause this.

You can try unplugging the AFM for a test as it will start without it.


Joe Russell wrote on Friday, February 27, 2009 - 01:58 pm:

You can put stuff like Isopropel alcohol through and it with be fine, it's a very good cleaner.
Don't sniff it though

AFM's work by measuring static air temperature and comparing it to the temperature of the flowing air (using the fine metal grid Dave mentioned) to get an airspeed without impeding it's flow too much, so cleaning the metal grid and temp sensor with an evaporating type alcohol will likely improve the accuracy of it(only if it's dirty obviously, which it will be).
Remember to be gentle




Leave the AFM alone they use a mirror and photo diodes which cannot be cleaned.

They also do not need to be cleaned and AFM failures are very rare. The car will run with the AFM unplugged so if you think the AFM is faulty you can try that as a test.
Cihan Aday
Moderator
etuner.com.au
JZZ30

Posts: 3097
Reg: 07-2005

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Saturday, December 12, 2009 - 02:43 pm, by:  Cihan Aday (Cihan) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

'Jerking' above 1500rpm between zero and light throttle application could also be confused with deceleration enleanment / fuel cut which is a normal feature used to save fuel. Most noticeable when the torque converter is locked in 3rd, and overdrive gears.
Damian Ware
Goo Roo
Victoria
UZZ32

Posts: 1232
Reg: 10-2005

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Saturday, December 12, 2009 - 03:48 pm, by:  Damian Ware (Frozenpod) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)


Cihan Aday wrote on Saturday, December 12, 2009 - 02:43 pm:

between zero and light throttle application could also be confused with deceleration enleanment / fuel cut which is a normal feature used to save fuel




V8 ECU doesn't have this feature.
Cihan Aday
Moderator
etuner.com.au
JZZ30

Posts: 3102
Reg: 07-2005

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Saturday, December 12, 2009 - 05:22 pm, by:  Cihan Aday (Cihan) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)



Of course it does.

What makes you say it doesn't?

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