Running rich all the way

[shlim]

Hi, I just replaced all the O seals for the fuel injectors and replaced the airflow meter with a good used one (with the fuel/mixture screw still sealed).

Now the car idles and runs well but the CO is at about 2.95% and does not go down even when the car is revved. In fact it's pretty stable at 2.8-3.3%.

I've also changed the fuel regulator, damper and fixed a couple of vacuum leaks at the same time as the O rings.

Help ! It's not possible to adjust the CO down any further with the mixture screw and besides, it's a very strange charateristic, to have the co not go down at higher revs.

This is a 85.5 944 euro-specs ie no O2 sensor nor cat nor altitude sensor.

Any ideas ? I guess if I pried open the airflow meter and messed with the spring I could get the mixture down at idle but it wouldn't explain the O2 not moving down at higher speeds.

Any advise would be much appreciated.

shlim
85.5 944

[Eduardo Castrejón Elbjorn]

Shlim:

Do you tell us that with your old maf you run stoichiometric all the time ?
Why you change the maf ?, if you return to your old maf you run ok ?

2.- what do you use to measure air fuel mixture ?

3.- I read In a bosch fuel management book that you always run rich at wot. Also the o2 cars run rich at wot.
(buy this book,is very useful and tecah you to understand, to fix and to tune, by Charles O probst.

Don´t worry to run rich at wot, but adjust your maf to run stoichiometric at your more useful rpm band.
To run leaner you need to counterclockwise the mixture control screw.

Hope this helps
good luck !

[shlim]

Re: -.1

The old MAF's mixture was good at about 0.75%. I swapped it out because I had rough idle. However, that was also with 2 leaking fuel injector O rings and with the old fuel regulator and accumulator (so I don't know if the old MAF is the culprit for the rough idle).

I can't get the new MAF to go down below 2.95% at idle but I checked again today and the CO does go down when I revv - goes up when idling...so at least that's a relief, don't know what happen the other day.

The CO was checked with one of those professional machines, at my mechanic's workshop. Inconvenient though... else, I'll swap out the MAF back and forth !

I found 3 vacuum leaks - including one major (brake servo vacuum connection), 2 at the fuel regulator and accumulator (basically the Y connector had hardened). Fixed them but no difference to the CO. At least my brakes now feel like they're assisted.

Now, should I rip off the cover of the MAF and fiddle round with the spring ? I presume I should tighten the spring ? For leaner ? Is this an easy to do ? And obvious ?

The funny thing is that the car now idles and runs sweetly, I'm just afraid that my plugs will eventually foul up.

shlim
85.5 944

[Eduardo Castrejón Elbjorn]

http://temp.corvetteforum.net/c4/vette_91//maf.jpg

see this.
I don´t know why I can´t acces to this server from here, but copy and paste in a new ( your webprogram )

[shlim]

Eduardo, thanks for the image but I can't bring the CO mixture down using the conventional method of adjusting the screw at the side of the MAF. That's why I was suggesting tightening the spring.

shlim
85.5 944

[shlim]

FR,

aah... that sounds promising. Where is the switch for the DME to lean the mixture ? I couldn't find any instructions from the workshop guide.

shlim
85.5 944

[Eduardo Castrejón Elbjorn]

In the passenger side, cockpit up the pedals, is a box (ecm or pcm ) the case tha have the chip or eprom to control the motronic.
Have a knob or a position screw to retard or advance the timing .
I don´t remembers what every position means , I don´t remember where I saw this, here but was an url to a 944 site.
You need to use search option
Good luck

[Eduardo Castrejón Elbjorn]

I already found it !
But I don´t believe that this is the solution for you.
Hope helps.
( I need to type because I can´t acces to the url and I can´t use my webpage because this forum can acces to apache server, then I type and post a scanned table )

Aside from chips, small adjustements DME
There is a provision on the motronc cars (944 and 911) to make small adjustements to the fuel mixture (imjection pulsewidht) and the ignition timing in order to compensate for the quality of fuel available in your particular country or region.

There is an board mounted eight position rotary switch accesed through the little hole in the back side of the DME box. These adjustments can be made without opening the cover of the dme box, unless you have a california vehicle, which will probably have a metal plug over the hole instead of a plastic fitting. The switch has a triangular-shaped recess in which to insert a special adjustement tool- I just whittle down a golf tee to make mine.

The switch has detent positions so you can count the clicks to tell where you are set. All the dme boxes I´ve ever seen have been set on position #1, so I call that the stock position. The adjustements can be found in the following table:

[shlim]

Eduardo,

thanks for the info. I will check that out once I can access my DME - I had my car re-carpeted and the guy glued the carpet down the side of the car and didn't make a slit down the vertical carpet - will need to get him to rectify this first or I'll be tearing the carpet off to get to the DME.

There is probably one other thing I didn't check (also because of the DME being inaccessible - and that is the engine heat sensor II (already checked sensor I). If that's not working - it'll be running rich as well (according to the workshop manual check through the pins at DME connector). Do you know if this is the same sensor that provides the dashboard temp ?? (that seems to be accurate enough, judging by when the fan comes on and off).

The airflow meter was taken off a Californian car (had to drill out the metal plug) and is running on a UK non-cat car, so I'm not use if there is some pre-configured setting that's causing the incompatibility.

Anyway, the car seem to run fine - I managed to get an indicated 137mph on the highway. is still zippy.

Anyway, I need to build that airfuelmixture meter. Can I stick the O2 sensor up the exhaust pipe or do I need to install it somewhere up the manifold (in which case I need to drill ?). I do not have a cat so the reading should be accurate at the tail, although it might not be so hot and the O2 sensor might not be accurate. Any advise on building and installing the meter ?

shlim
85.5 944

[Eduardo Castrejón Elbjorn]

Fr Wilk:

Thanks to clarify this, this will be useful for me too !

can you please post the url of the 944 faq because I can´t acces.

Regards