Problem with setting CO%, it just doesn't go up....or down!

[CanisLupus]

Hi guys!
Been reading the MK2 board for a while and finally decided to register, to hopefully help some folk out and to get to the bottom of a problem I have been having this last few weeks!

First to the car I have a 1987 Jetta MK2, 1.8 GTi, PB engine code, Digifant II system. I have had the car now for 3 years, and the reason I love it so much is because it has been in the family since my Grandad bought it 25 years ago! After him my Aunt had the car for a good 5 years, but unfortunately she bought another car and left the poor Jetta to rot under some trees for about a 1 1/2 years. Until I picked her up Have still got a lot of bodywork to go through one day, but I have been using the car as a daily for the past 2 years and she does run very good. I have done quite a few upgrades (nothing non stock worthy though) and replaced quite a lot during these 2 years. If the list is relevant I can post it up later.

Basically my problem in a nutshell:
I can't get the CO% set properly. According to the past 2 years MOT sheet, she is running at 0.12%-0.15%. When I changed my cambelt + a lot of other things a few weeks ago I finally wanted to tune the motor in properly. Timing marks are all aligned, Advance is at 6 BTDC @ 2500rpm. Thanks to rubjonny's excellent guide here too, the next step is idle & CO. Idle is no problem, but CO% does just not want to change!

What made me post today is I have just come back from the garage down the road where we tried 2 weeks ago to set the CO% with a sniffer. As nothing happened when you turn the screw (CO% wise, turn to much the car does sound different and becomes lumpy ect.) we came to the conclusion the AFM is somehow faulty as it does not adjust. I bought another one in "good" condition from fleabay which arrived yesterday. So today I have been to the garage to set it up and again....nothing changes. My CO% was today 0.15%, and turning the adjuster does nothing, apart from make the engine sound different and more lumpy ect. I have a Bently manual here also which describes the procedure just like Rubjonny does, so everything has been done (Blue temp sender off (yes change it idle, works fine and got replaced), block inlet hose at PCV & rev 3x above 3k to but ECU in service mode.).

Any ideas what the problem may be? I can only think of an air / vacuum leak somewhere. The garage also thinks this may be the case. I have replaced all vacuum hoses 2 months or so ago. And renewed most of the rubber hoses around the engine bay. There are 1-2 older ones but they look fine, no cracks / splits. The only thing I can think of is manifold gasket or the gasket at the throttle, but I have had the throttle off and the gasket was sound then. Manifold itself looks ok, I can't see any craks or splits but it is hard to see behind the whole thing cause there isn't much room.

One thing which has puzzled me since replacing the vacuum hoses though...My MPG counter and the average roadspeed counter on the MFA have NEVER since I've had the car worked properly. The MPG never goes over 17ish and the average roadspeed never really beyond 30ish. As far as I know the MPG comes from the vacuum, I'm not sure if the same is true about average roadspeed. But this made me change the vacuum hoses in the first place, and there is no change in this display, making me think that there is a leak still somewhere possibly or the dash is broken? I work out my MPG and I get 35mpg, which is amazing. I even managed 47 when travelling from Wales to Dover and back last year (90% motorway), which too was just great value.

Well sorry for the long post, I have probably missed something, I just want to know if anyone has any ideas on this, cause it is slowly giving me a headache. Forgot to mention that I daily the car and she drives just fine. gets a little stuttery when off the throttle at low speeds (guess thats the digilag), acceleration is good though, and everything seems smooth.

Thanks!

[Thom89]

Not really my department, but welcome to the mk2 section, I'm sure help will arrive shortly

Thom

[Dolly]

far to much to read. Go to the section at the top of the page with the guides theres a rather good one for sorting out 8v's

[CanisLupus]

far to much to read. Go to the section at the top of the page with the guides theres a rather good one for sorting out 8v's

I thought giving as much info possible would answer questions which needn't be asked in the first place I have checked the guide sections, and probably read most of them, as I said this is also going by Rubjonny's guide.

Basically, CO% doesn't adjust and is on a constant 0.15%. AFM got swapped yesterday, still no difference. All adjoining vacuum hoses and most hoses going to inlet have been replaced. Garage thinks it must be a leak somewhere. I can't think of any other places other than inlet manifold / throttlebody and possibly injector o-rings. Just asking if any of these may be a possibility or if someone has experienced the same and may a different place to look.

And cheers Thom

[Mr Blue]

Have you got a gas blow torch? Run the engine and open the blow torch (not lit) around the pipes and inlet. Any change in revs will identify a leak.

I had this co2 adjustment problem and it was a timing issue. Double check the marks.

[CanisLupus]

Have you got a gas blow torch? Run the engine and open the blow torch (not lit) around the pipes and inlet. Any change in revs will identify a leak.

I had this co2 adjustment problem and it was a timing issue. Double check the marks.

Hm sounds like an idea. I havn't got a torch, though know some people who do, could give that a go. I got some carb cleaner somewhere, could try that first also. Timing is spot on, tripple checked that before I put everything back together. Same with the Timing advance. Thanks.

[mikemk4gti]

I was going to say the same, you could also use something like carb cleaner as its flammable.
If the engine changes when you turn the adjuster then it must be doing something?  Is there another garage where you could try their co2 meter?

[CanisLupus]

I was going to say the same, you could also use something like carb cleaner as its flammable.
If the engine changes when you turn the adjuster then it must be doing something?  Is there another garage where you could try their co2 meter?

Yeh, doing something it is...just not what I want *g*  Well some good news has come from this, looks like I found my leak. Spraying down under the injectors made the idle shoot up. The only thing down there is the intake manifold I think. Spraying directly onto the injectors made no difference so I guess the o-rings are ok so only thing left is manifold. To much rubbish in the way to see anything, but likely cause would be gasket? Seems like I'm gonna have a fun weekend at some point.
Thanks all for the help, will update this when I get round to looking at it one day.

[Mr Blue]

there you go, intake manifold gasket. A torx set with the allen key bits.