Lean/Rich compromise

[930turbo]

My 3.0 '77 has an unusual mixture problem that I can't seem to over come. If I adjust the idle to proper mixture, the mid-range acceleration goes way lean until boost, then it absolutely flys!. If I adjust the idle to too rich, the acceleration is good but the boost power is soggy, as if too rich. That being said, it appears my CIS is delivering a range that can not be adjusted to achieve all the correct mixture delivery. It's as if ther eis a dip in delivery that can't be overcome. Any suggestions?

[kellcats521]

Your warm up regulator is not working correctly.

Look into:
1) having it rebuilt
2) modifying it to enable small adjustments or,
3) sending it to someone who modifys them [Brian Laesk (sp) is one who does this IIRC]

Do a search on what the warm up regulator really does - it is a significant part of the turbo fuel system.

[930turbo]

My WUR is already modified for cold-start adjustment. It's an original NOS 022 in perfect condition. I'm considering a change to the later 054 with boost enrichment (and a delay circuit) but I am concerned with adding too many variables and adding another degree of tuning difficulty. I know the car is capable of an ideal idle, mid-range drivability and gobbs of power, just not all at the same time. it's a little frustrating.

[RarlyL8]

The 054 is a good unit but it sounds like your present unit needs adjusting.
To do this correctly you need dyno A/F information or use an LM-1; something that will give you readings throughout the operating range of your engine. You will then see exactly what you are dealing with and the changes resulting as you tune.

[NathanUK]

The more adjustability the better, as long as like Brian says use a wideband AFR meter.

I would send it off to Brian Leask and get his RPM solenoid setup too.

[GaryR]

AFAIK Brian has not released his RPM solenoid yet. In his email to me on 1/31/07:

"The RPM controlled solenoid kits are finished. I am putting the finishing touches on the documentation at the moment, and hope to have it finished this weekend. I have not determined an exact price yet, but they will most likely be in the $250-$300 range. I will be accepting cashier’s checks in the mail or PayPal electronic funds for payment."

[930turbo]

I discovered a failed rear fuel pump and thought I had it all figured out. After replacing the pump, the mixture issue still exists. It's still rich @ idle, lean under part-throttle and rich under boost - so rich, it limits by total boost to .7 bar with a 1.0 bar spring. If I adjust the CO to so lean it will not idle and barely runs, it will get all 1.0. I'm stumped.

[GaryR]

Originally posted by GaryR
AFAIK Brian has not released his RPM solenoid yet.

An update - he HAS released the solenoid kits and I actually received #1 a couple weeks ago but the car isn't ready for it yet. Another month or so....

[gumba]

What does the RPM solenoid do?
Harold
'79 930/DP935

[RarlyL8]

The RPM solenoid will block the boost signal to the WUR until a preset RPM.

You cannot adjust your boost enrichment or off-idle inrichment with the idle mixture screw. Those areas must be adjusted at the WUR. If you do not have an adjustable (modified) WUR you cannot fix your problem.

Do you know what your fuel pressure is during these events? If not that is where you need to start. Get a fuel pressure reading and an A/F reading throughout the RPM range. Purchase or modify your WUR to be adjustable and then tune away. Start by optimizing your idle CO; everything else will move from that point.

[930turbo]

The WUR has a boost enrichment function built in from the factory. The problem with this design is, the enrichment comes in as soon as boost appears at about 3000RPM. The mixture does not need enrichment until about 4000RPM, which creates an over-rich condition between 3-4K RPM. The additional soleniod is normally closed, blocking the boost signal from the WUR until the desired engine speed - 4000RPM - thus eliminating the over-rich transition.

[RarlyL8]

The stock 930 WUR tends to run rich on boost in stock and mildly modified engines. Optimal A/F ratio is ~12.2:1 above 0.4bar. Does your engine hit 0.4bar at 4000rpm in every gear? Probably not. That is where the extra tuning will help, both for more power and better fuel economy. It is not required but there are advantages to be had.

[930turbo]

I conducted an experiment today. I disconnected and plugged the MAP line to the waste gate to see if my car was capable of generating more than .7 bar unregulated, it does not. With the wastegate disabled, I still get no more than .7 bar boost. My O2 sensor is indicating .970 volts under full boost which should be reasonably close. Is it possible the turbo itself is failing? It doesn't smoke or make any unusual noises. Is there anything else that would limit the boost/power output? I'm still stumped.

[magic930]

Maybe the Blow Off valve is stuck open.

[WERK I]

Originally posted by 930turbo
I conducted an experiment today. I disconnected and plugged the MAP line to the waste gate to see if my car was capable of generating more than .7 bar unregulated, it does not. With the wastegate disabled, I still get no more than .7 bar boost. My O2 sensor is indicating .970 volts under full boost which should be reasonably close. Is it possible the turbo itself is failing? It doesn't smoke or make any unusual noises. Is there anything else that would limit the boost/power output? I'm still stumped.

Did you plug the vent side of the wastegate, too?
If you didn't, you should, but be extremely careful. Boost spikes happen very fast!

[NathanUK]

Make sure your headers are not leaking so that the turbo is getting bypassed.

[RarlyL8]

It sounds like your engine itself is not capable of flowing more than 0.7bar at this time.

Do you have a cat? Is it or your muffler blocked?

[930turbo]

The engine is fresh. It has made 1.0 bar on occasion. I replaced the fuel distributor with an 037 from a 3.3. Does this unit deliver more fuel per deflection than the original 018 from the 3.0. In other words, are the fuel slits larger? Today, my Fluke meter hit 1.009 volts from the O2 sensor and still at only .7 bar. That's way rich. The mixtuer goes progressively richer as the air-flow demand increases.

[WERK I]

If you are way rich, you may not reach 1.0 bar because the exhaust temps are down. Boost is a function of exhaust gas velocity AND temperature.

[RarlyL8]

What else have you done to your fuel delivery system?
The fuel head and WUR are a tuned unit when working optimally. Yours is out of synch. An excessively rich condition will not only cool the exhaust as stated by Dave, but it will also effectively extiguish the spark. Your engine is drowning in fuel.