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 Post subject: MK1 erratic rpm VAF?
PostPosted: Sat Mar 09, 2013 1:10 pm 
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Joined: Sun May 06, 2012 3:07 pm
Posts: 60
Location: Elkridge, Maryland
Hello again everyone. So I replaced my starter the other day and afterwards the car ran great. I drove it 180 miles to my dads place and had no problems the whole trip. So I get in the car to go somewhere in town and the thing is running like crap. The turbo light flashes but the boost gauge is reading steady. When the turbo light is flashing the RPM on the tach will jump around but the clutch is not slipping. Im thinking its the VAF. Could anybody point me to some pictures or instructions on how to clean this sensor? You have to cut out the plastic at the bottom and then re seal it after cleaning the inside, correct?

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1988 Chevy Sprint Turbo
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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Sat Mar 09, 2013 4:06 pm 
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Island Inbreeder
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is this what you referring to.?
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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Sat Mar 09, 2013 6:17 pm 
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Location: Elkridge, Maryland
No, I mean the actual electrical contacts for the potentiometer.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Sun Mar 10, 2013 10:46 am 
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Location: So Cal, USA
The plastic cover is sealed for a reason, there is no need to clean the contacts.
In fact, there are none really other than the actual physical wiring contacts
which are pretty much inaccessable anyway.

The 'wiper' needle does not make contact on the circuit board,
but rather rides above the contacts.
Attachment:
mafopen.jpg
mafopen.jpg [ 111.52 KIB | Viewed 4341 times ]


This would not be the root of your problem, it has nothing
to do with the RPM display or the Turbo light. If it makes you feel
better, than you can check the wiring harness connector to make sure it's
clean, tight, and locked on to the VAF.

The Turbo light is triggered only by the ECM.

Quote:
When the turbo light is flashing the RPM on the tach will jump around but the clutch is not slipping


Give us more info.

When does this happen? Is the RPM jumping around, or is the gauge needle jumping and RPM constant?

I would check some basics..Check for a vacuum leak, hoses, oil dipstick, oil cap....Check around
where you repaired the starter you could have damaged some wiring or vacuum hose or
even knocked loose a coil or plug wire.
It very likely related to your recent repair.


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 2:30 pm 
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Joined: Sun May 06, 2012 3:07 pm
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Location: Elkridge, Maryland
Yeah Ive done the usual checks. Vacuum lines are good. No fluctuations on the vac/boost gauge and a steady 22in/hg while at idle. When the problem occurs the rpm needle on the tach is jumping but the engine itself is not. If revving the engine slowly it will build to 2k without trouble then it will not pass 2k. It does this on accel. When decelerating and watching the tach once you get down to about 2600 the rpm needle will be going pretty erratic from 1500 to 3k rpm reading and the turbo light is flashing but the car is decelerating smoothly. Theres no problem at all after 3k rpm the engine runs great and the rpm is accurate on the gauge. I figured the issue has to be something to do with the recent repair but its odd the car made it 180 miles up mountains before the issue occurred. I had thought I saw a thread on here a while ago about a flashing turbo light and people instructed to clean the contacts on the VAF but the search feature did not help me find it. I know the turbo light is a comparison of mass airflow to crank signal so the car has to have a crank sensor which could be the problem but I could not find the info on where that is located either. Thanks for the help!

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Last edited by groovysomethin on Mon Mar 11, 2013 3:25 pm, edited 4 times in total.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 2:35 pm 
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Joined: Sun May 06, 2012 3:07 pm
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Location: Elkridge, Maryland
If the contacts dont actually touch in the VAF then how is the signal voltage actually being modified? Is there a hall effect type device or some kind of magnetic sensor? Of all the VAF sensors Ive ever learned about there is a mechanical contact somehwere inside that is sweeping across a potentiometer to change the resistance that signal voltage is passing through, but maybe this one is just different than most?

EDIT: after reading your reply again Jamal, Im led to believe you were saying any of the actual parts that are modulating the signal are inaccessible anyways, so unless I have an outright VAF failure then that is most likely not the cause.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 3:26 pm 
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Location: Elkridge, Maryland
By the way I am an ASE master certified tech so Im not just a do it yourselfer. This car has me stumped and the lack of easy to find information doesnt make it any better.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 4:23 pm 
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Quote:
the car has to have a crank sensor


There is no crank sensor. This is OBD 1 or even Pre-OBD-1


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 4:27 pm 
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so what runs the tach? haha, apparantly I have no Idea how this particular car works :lol:

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 4:42 pm 
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groovysomethin wrote:
By the way I am an ASE master certified tech so Im not just a do it yourselfer. This car has me stumped and the lack of easy to find information doesnt make it any better.


.
awesome could you take a picture of the top of your engine I think I can help
Just want to see what "your" engine looks like
so I don't send you down any rabbit holes you don't need to go
your tach is electronic so I'll stop there and ask for a picture .

(I've seen a few Turbo sprint) just want to confirm My suspicions......Thanks ....jv&s
.
.
.
.

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t3 ragtop wrote:
the 3 banger isn't at all a "grenade." it's a tough little son of a bitch doing a big job. respect it.
suprf1y wrote:
I didn't save anything.Vehicles are to me, like little boys are to Tommy.Toys to be abused for my own personal pleasure.
jrjd wrote:
"Driving a Swift GTi is like driving a bike in your house".


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 5:11 pm 
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Location: So Cal, USA
Quote:
I have no Idea how this particular car works


It works by majic and witchcraft :razz:


Need to get yourself the manual, the supplement, and the turbo supplement
and a couple other rags out there. Don't bother with the Haynes crap.
Do some reading, and throw everything else (OBD-2) you've learned out the window
and go back to your basic fundamentals on this one. It's actually very easy,
there are a few things that aren't explained in the manual, that no one has
quite figured out exactly how it works. And it's virtually impossible to
tap into the computer with the one diagnostic port unless you have the
manufacturers diagnostic computer.

Many things are backwards too, like the scale on the VAF.
Where voltage on another car may be High to Low, ours is
Low to High (or reverse that, I can't remember which now, I
just know it's the opposite of most others that's why only
the MR2 mafs work and only a few others as upgrades.


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 5:19 pm 
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Joined: Sun May 06, 2012 3:07 pm
Posts: 60
Location: Elkridge, Maryland
Sure thing, sorry for the blurryness.

http://i.imgur.com/NADKdZY.jpg

http://i.imgur.com/wWtKPOj.jpg

also heres a video of the car trying to rev past 2k slowly. You can see the tach flake out a couple of times as well but it seems like it gets to 2k and cuts the fuel.
http://www.youtube.com/watch?v=ELfDHqfQ ... e=youtu.be
This is a cold start btw thats why the rpm is 1600 at idle. It will try to idle down to around 900 like normal but its running so rough it doesnt like being that low right now.

JamalSpelling wrote:

It works by majic and witchcraft :razz:



Hahaha, It seems that way! Could you point me to a working link to the suppliments and relevant manuals?

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 5:44 pm 
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.http://i.imgur.com/wWtKPOj.jpg
.
.
thank you for that
.when Phil n ed shows up he's going to say the same I'm about to tell you
but not in around about way I say it.
.
the tach run off a wire from your coil (brown w blk stripe)negative side

here's your biscut .........
your having ground issues.!
on your intake ( the silver box ontop) that says EFI

in this picture you can see two 10mm bolt on the side with about 6 black wires (2 0n 1) and 4 on another
these are ground wires for your sensors (O2, knock, TPS, and injectors) I'm missing some I know it.!

Anyway these need to be realy CLEAN and tight and also UP SIZE your ground wires
From battery to body/ battery ground to transaxle
engine to battery ground/ engine to body
look under your dash at your ECM refresh that ground
and this goes without saying your battery terms should be clean tight and solid
.
because you live were you do and the age of the car this should be #1 before any troubleshoot continues
don't put this step off...it's just that important on the MK1 Turbos
.
I'll go try to find the turbo supplement.......jv&s
.
no supplement found broken links.... sorry.....jv&s
.
.
.
.
.

_________________
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t3 ragtop wrote:
the 3 banger isn't at all a "grenade." it's a tough little son of a bitch doing a big job. respect it.
suprf1y wrote:
I didn't save anything.Vehicles are to me, like little boys are to Tommy.Toys to be abused for my own personal pleasure.
jrjd wrote:
"Driving a Swift GTi is like driving a bike in your house".


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 5:57 pm 
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Joined: Tue Feb 13, 2007 10:28 pm
Posts: 1175
Location: So Cal, USA
Pics are kinda blury, but judging from the vid...

I would say to inspect the intake hose for cracks in the bellows or other leaks,
then check the underside of I/C hoses for leaks (they rub sometimes)
and check the I/C for a leak, since it has broken mounts no doubt
it's going to rub a hole in the tank when it rattles on the bracket..
that zip tie doesnt look that secure.

Then of course, I'm sure you've checked the obvious...
Inspected Cap/Rotor and pulled the plugs?


Yeah I know that's not gonna fix yur problem but the Vid sounds
like it's running bad.


JV's Talking about this....Pay attention to what he said, very important!
Attachment:
grounds.jpg
grounds.jpg [ 119.59 KIB | Viewed 4312 times ]


Lot of rust in there, you basically need to check everything.
Look hard enough you'll find some bad wires.


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Mon Mar 11, 2013 6:19 pm 
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Joined: Sun May 06, 2012 3:07 pm
Posts: 60
Location: Elkridge, Maryland
Yeah I was going to slowly start just cleaning up wires and doing normal tune up stuff. The Ic was down very tight before I started looking for the problem with the vehicle. Ive got a very soft rubber pad under the IC (just over the steel bar under the IC ) to prevent any rubbing issues and It will boost to 8 psi without any sounds or signs of leaks. Im going to take another video of how well it runs on the highway tomorrow and post it here. But for now thanks for all the input :thumbsup:

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Wed Mar 13, 2013 10:11 am 
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Joined: Sun May 06, 2012 3:07 pm
Posts: 60
Location: Elkridge, Maryland
Was not able to get around to doing the video yesterday but I checked the grounds and there seems to be quite a bit of corrosion working its way up the wires from where they are crimped the the eyelets. I also found alot of botched looking wiring jobs that are using crimps I might want to re do. It looks like the car came with ac from factory and someone just went to town while removing it or something. It looks as if the car has had a hard life before I got it. Ill update again once I get the materials I need to fix these grounds.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Wed Mar 13, 2013 11:14 am 
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Updated the Mk1 supplement thread with a link to my webserver. Download to your heart's content. :D

viewtopic.php?f=32&t=22574&start=25

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Good stuff for sale!

viewtopic.php?f=15&t=42901&start=0


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 2:11 am 
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CJDavE wrote:
Updated the Mk1 supplement thread with a link to my webserver. Download to your heart's content. :D

http://www.teamswift.net/viewtopic.php? ... 4&start=25



.
.
Good stuff thanks Dave


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 12:37 pm 
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Location: Elkridge, Maryland
CJDavE wrote:
Updated the Mk1 supplement thread with a link to my webserver. Download to your heart's content. :D

http://www.teamswift.net/viewtopic.php? ... 4&start=25




Thank you very much kind sir!

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 4:39 pm 
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Location: Elkridge, Maryland
Ok well we can check grounds off the list. Re did all the grounds with good soldering jobs and new eyelets. absolutely no difference. In fact it may be even worse now :huh: . Any more ideas? The car will hardly idle at all anymore and the tach will be going from around 1500-2k but the engine is about to stall in reality (probably around 500-700 rpm). If I rev the engine it will rev up fine but then one it starts settling down at about 1200rpm the tach starts going crazy( it reads 1500-2k in a very jittery/jerky fashion) but the engine will actually be struggling to idle. I re did the low voltage wires to the coil as well because the tach runs off of the coil but that didnt change anything either.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 5:22 pm 
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Take the vaf off, turn it on its side, and shake it up and down. Make sure the door isn't flapping around, weak door spring.

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 7:14 pm 
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1987TurboSprint wrote:
Take the vaf off, turn it on its side, and shake it up and down. Make sure the door isn't flapping around, weak door spring.



Yup sure does flap around. not super easily but its not hard to make it flap. Is there a fix?

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 7:58 pm 
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Read here

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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 10:12 pm 
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before you start with the spring Make a mark were the spring is set
if you don't you'll wish you did
.
on a personal note *** I have never been able to properly adjust the door spring first time ( it's alittle tricky)
.
check all your little vacume hoses they may look good but give them a pull see if there good
.
stay with it you get it....jv&s

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.

t3 ragtop wrote:
the 3 banger isn't at all a "grenade." it's a tough little son of a bitch doing a big job. respect it.
suprf1y wrote:
I didn't save anything.Vehicles are to me, like little boys are to Tommy.Toys to be abused for my own personal pleasure.
jrjd wrote:
"Driving a Swift GTi is like driving a bike in your house".


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 Post subject: Re: MK1 erratic rpm VAF?
PostPosted: Thu Mar 14, 2013 10:58 pm 
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Posts: 1175
Location: So Cal, USA
yeah, one little slip and you loose the factory setting, got to mark it first.
even so, if the wheel goes flying, you could still be off 360'
Need to make sure theres at least some tension.

still think its vacuum related, you got a leak somewhere.
you didnt put a breather on it did you?
cracked rubber seal on oil cap or dipstick?
or even loose bolts on the intake.

time to do a compression check, cracked valves are very common


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