Flow Testing Results of OEM CIS Injectors

I understand that after replacing the injectors it is required to adjust the mixture at the fuel distributor with the use of a exhuast gas anylazer. I thought that the K Jet ECU has fixed values and therefore can't signal to the fuel distributor to make changes to the fuel mixture. If the mixture is set at the factory and the anti tamper plug has not been touched, then why would one need to tweek the mixture after injector replacement? Would this be due to the +/- 20% error variation found when testing?

 

K Jet has no ECU. The ECU in the system only controls the frequency valve based on the signal from the O2 sensor. That component only modifies the base setting in steady state situations. The base setting is established via the main mixture screw and has primary authority over mixture.

 

Ok, just mispoke about the ECU, actually a signal processor. So if the base setting has never been manually adjusted then why would one need to fuss with it after installing new injectors? I have read many threads that comment on how after replacement of injectors one ends up with a rough idle(usually lean) and perhaps reduced performance until a new base setting is established. Maybe I'm wrong about that and in fact the new injectors are actually "failing"? Just trying to get to the logic behind this.

 

I have been working on them professionally since they still had carbs and I have never heard that. Maybe those guys had more experience, I don't know.



Changing injectors can have an effect on mixture and it should be checked. Besides making the car run properly is what the desired goal is. Why even consider one of the most important adjustments in that process? I cannot even concieve of leaving the job half done.

If I put a new tire on your car would you consider it advisable to check the pressure?

 

Thanks. Good analogy.

 

As usual Steve explains it simply and correctly.

Brian, I agree that 95% of the time glowing headers are ignition related. However I must relate a personal experience. My Mondial had glowing headers, but only in light driving/idling. Around town and such. Not glowing cherry red and visible in daylight, but if you opened the engine lid at night, they were definitely glowing. I checked the mixture and instead of being around 13-14:1, the car was running 40:1 at idle and down to about 20:1 at light throttle. Not sure how the car even ran that lean, but it did! Verell and I tweaked the K-jet with a gas sniffer and no more glowing headers. Extreme lean running will produce glowing headers, believe me!! So my advice to climb is to put a gas analyzer on it. It probably needs new injectors and a k-jet tweak. Very simple operations both. Here's my fuel injector tutorial with thanks to Bertocchi.

http://www.birdmanferrari.com/service/injectors/injector_clean.htm

By the way, the injector cleaning and mixture tweak made the car run a zillion times better. It starts SO easy now.

Birdman

 

What is the ratio for a 1980 injected USA spec 308?

I've taken a can of fuel injector cleaner and put the straw right into the injector tip and let each injector have it. I Used 3 bottles of the stuff between the 8 cylinders. No i couldn't see the pattern but i feel they were cleaned. The cans would stop spraying after 2/3 of the can was emptied since the propellant at that level couldn't keep the injectors open. All the injectors had this resistance to the lessened force of the can.

 

I'm not an expert on mixtures, but 14.7:1 air:fuel is the "ideal" stoichiometric ratio. Right around that number is where you want to be in general. If the headers are glowing due to being lean, it will be way way off. Not a little off. If the mixture is in the ballpark, the glowing is timing like Brian said.

 

Thanks

 

I know this sounds kinda clueless but i'm sick of driving an igniter around..

Is the ratio adjusted by turning the mixture dial on the throttle body in-between the black air hose and the plenum? That is if i took it to a garage that had a gas analyzer could the knob be turned 'till the ratio was was 14.7:1?

Oh, and 36mm on the crank pulley to turn with a breaker bar in clockwise direction?

 

You said it yourself "Headers". He has glowing "Header" as in one.


Fuel system problems will effect both equally. Cam timing and ignition strike individual banks.

Auto diagnosis 101.



If you hear hoof beats do not look for Zebras.

 

Waste of time.

Address the symptoms.

 

I'll check cam timing next then do the gas analyzer if timing is good.

 

There are threads on how to adjust the CIS mixture but you wouldn't go there till you knew the cam timing was right.

Once you know the cam timing is right then you need a gas analyser you know you can trust.

Before you do a mixture adjustment make sure any and all vacuum and CIS air hoses are secure and not leaking.

Adjustment needs a 3mm Allen key & the adjuster is on the CIS head under a cover screw. Clockwise makes it richer, anti-clock to lean it off.

Make sure you have the thing idling at near enough 1000 - don't trust the tacho (mine is at least 100 off at that speed) , use a meter. As you make an adjustment the idle may change & so you may need to reduce/increase it between adjustments back to 1000 to get an accurate reading (use the air idle screw).

In between each adjustment you need to block off the cover screw hole or replace the cover screw to get an accurate reading because air leaks in there & will distort the reading.

Adjust in tiny increments, its very sensitive & always make the last adjustment going clockwise (richer).

When you are done you should be able to drop the idle down to 850-900 ish using the air adjuster screw under the throttle body.

...but as Brian basically said - check your cam timing first.

 

Keep in mind that while 14.7:1 is the theoretical ideal for combustion, it isn't necessarily where you want your car to be. A little richer than ideal may provide better power, a little leaner fewer emissions. It's actually a pretty complicated matrix for best mixture, which is one reason why modern cars have complicated fuel maps.

 

I missed that detail!

 

But if you only have ONE glowing header, it's not the mixture! The mixture affects both banks equally! Like Brian said. Sorry for the confusion.

 

Hey Climb, my advice, which is worth less than what you pay for it is:

1. Be absolutely positive sure that you have only one glowing header. If the front one is glowing too, I would suspect your mixture.

2. If it's just the rear header, you probably have a cam out of time, because there isn't really anything to be "adjusted" in the GTSi ignition system. The crank sensors are fixed, the ECUs have no timing adjustment and neither do the distributors. It either sparks at the right time or it sparks not at all.

When mine was doing it, I first thought it was only the rear bank because that's the one you can see. The front is pretty well hidden.

Birdman

 

I see.

Gotta try to get a view of the front bank somehow.