Why does it still enrich?

[Helmsy]

OK so some of you might have read the post where this began.

AFR's go Down as RPM's go Up?

I found that I was way too rich under boost ( high 9s).

I have an adjustable wur so I banged in the disc and tightened the 3 screws on the bottom and managed to get it into the mid 10s.

Still not happy with this I decided to install a RPM switch to control when the enrichment happens.

Switch works fine however it still enriches under boost from about 3k. I repeat I have tested the rpm switch and it works fine so why is it still enriching under boost if the wur boost line is inactive??

Banging the disc in and tightening the screws does have an effect however they are in further than I would like them to be and still rich and too early.

I believe it is either a wur issue or possibly the fuel head? I cannot go above ~ 5.8bar system pressure otherwise I get run-on after shutdown. Yes I have the shutdown delay relay but I mean chugging on.

Also I noticed when checking the system pressure it fluctuates somewhat by +- .1 bar. Is this normal?

Any help or ideas will be greatly appreciated as I am all outta ideas.

[RarlyL8]

A vac leak, damaged WUR diaphragm or faulty fuel injectors can produce the symptoms you describe. Any of these things may disrupt proper metering signals. The shutdown delay being activatied is an indication that your injectors may be leaking.
I would first check for vac leaks such as blown o-rings and poped hoses then pull your injectors and test them. Your BL WUR is fairly new so should not be damaged, however, if you have over-adjusted it could be so far off that it will not adjust out. If that is the case you need to send it back to BL.
Tough to diagnose long distance.

[Helmsy]

Thanks Brian.

I checked and tightened all my clamps and hoses and don't believe it is an air leak that is causing this (but I won't rule anything out!).

I haven't really adjusted my wur as far as enrichment goes except for making it leaner on boost. Could adjusting too far for leanness damage the wur? Funny how if I mityvac my wur it seems like it works fine however it still enriches under boost.

I will test my injectors as this could be a culprit.

[911st]

My two cents:

Assuming all systems are functioning correctly, AFR's are effected in part by control pressure.

They are also determined by where the metering plate rides in the metering cone.

The cone is profiled to match stock air flow expectations and is more sensitive to air flow changes at low power levels. Probably so fuel delivery is more accurate in the idle to cruse range.

Modify a 930 so it responds quicker and with higher air flows than expected and it has the potential to advance the metering plate faster than designed, exaggerating the AFR curve.

Even with boost enrichment being delayed.

However, in the upper rpm range the metering plate starts to stall. It is at this point where some release the enrichment delay, lowering control pressure, and allowing the metering plate to advance further.

Assuming a stock Fuel Distributor, you may be able to increase warm control pressure to compensate to a degree. However, with this may come a lean condition on cruse.

While 10.5/1 on boost AFR is not an ideal from a peak power point of view, it is what most car manufactures seem to target for there stock turbo motors.


This dose not mean there may not be something in your case that could be out of spec and a bigger source of your problem.


As to run on, the FD will bled system pressure down to the injectors pop pressure after shut off. That is normal.

A higher system pressure should increase that potential. If the motor runs on in a normal manner that would seem acceptable. If the injectors pop pressures are not closely balanced, the run on will sound more erratic, could be prolonged further, and may sound more like dieseling as only one or a couple out of spec injectors continue to drain down.

[BlkBird]

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[Helmsy]

I contacted BL and he said it is probably due to the system pressure being low however being a euro I believe my pressure should be about 6.2-6.5bar so I am not far out of the range.

I will try a few things over the next week or so.

1. I will try my old stock wur (glad I still have it) and see what happens.

2. I will increse my system pressure and see how I go in relation to enriching and also running-on (dieseling).

3. I will go over everything again and make sure there are no air leaks. I may make up a leak test like I have seen on here before and pressurise the system and look for leaks.

If it still has the isssues with the stock wur and higher system pressure I think it will point towards the injectors leaking/not holding pressure.

I will report back with results....

[WERK I]

Ben,
How old is the fuel filter? How old are the injectors?

Keep in mind your AFR"s are an average of the 6 cylinders. If you are looking for good AFR's and want to sleep well at night, you've got to heed Brian's advice about the injectors. Take them out, test them for consistency across all six. There's an excellent thread started by Stu (stup) when he was tuning his CIS system. injector test
You may have one or two injectors causing your numbers to go way off. Be prepared to make some revised adjustments on your BL WUR after all is said and done.

You have a "running-on" (dieseling) problem? I'm assuming you're aware of the delay in the ignition to turn off after the ignition switch is turned to off. That's pointing to a leaking injector(s).

[9dreizig]

Did you check all of the nuts on your intake ? I've found they can loosen over time and will cause a vacuum leak there as well. Get some carb cleaner and try the spray test, under idle spray it around and see if it effects rpms.. if it does there's your leak!

[Helmsy]

ok so to update I changed out my wur to the stock one and shimmed my fuel head to increase system pressure to 6.3 bar (euro M66). Took a few shim combos to get there too. Gives 2-3 pops on shutdown now.

Went for a drive and no change on the enrichment. Wur pressures are actually pretty good and cruise 14.4 and idle set to ~14.0.

Full boost yielded low 12s which isn't too bad however when I lift my foot off it goes to low 10s for a split-second. Rpms without boost is steady 14.4 all the way i.e. no enrichment. With any boost it enriches from about 2.5k rpm (switch set for 4.8k rpm).

I will be checking injectors tomorrow however i did a flow comparison test about 12 months ago and it was fine. Any other tests I should do on them?

I will also check my pumps to make sure they are delivering the correct amount and not affecting control pressure under boost. I also put the 7k pill in the switch.

[Helmsy]

Oh and by the way it runs a lot smoother and removed about 95% of the slight bucking/surging feeling it has always had. I believe raising the system pressure helped greatly with that.

I'll just have to live with the popping on shutdown.

[9dreizig]

Ben,
I am still maintaining you've got a vacuum leak somewhere, I chased one for literally months!. Did you try the carb cleaner test ? Having just fixed mine I noticed all the popping went away as well when that happened.

[Helmsy]

Todd,

I have done the carb cleaner test and couldn't find a leak. I also tightened everything up. This doesn't mean I don't have a leak tho.

It is only happening under boost so it is probably a miniscule leak that won't show at idle with carb cleaner.

I will pull the ic and change out the orange seals and have another inspection of all hoses and clamps.

[911st]

With the addition of a wide band O2 and ability to capture what is really going on we might just be seeing some of the weaknesses that CIS has always had.


It really dose not sound like there is much of anything much wrong except for the injector pop pressures being different.

When a 930 is modified so it flows a lot more faster and earlier, it just tends to exaggerate the first and last parts of the fuel curve. It gets richer earlier and goes lean later.

CIS is pretty accurate at steady state between idle and cruse air flows.

Start flowing enough air for 125hp or so at 2500rpm and it seems to want to go rich.

I believe it is mostly because of the profile of the metering cone but there might also be a little bit of over swing do to the mass of the metering plate, arm, and pin -- plus how fast the control pressure fuel above the metering pin can be expelled and replaced.

Again, I would check the injectors for equal pop pressure as to the 'run on' and the 'lean after firing or popping as you call it.


I could be wrong.

[Helmsy]

OK so I got ambitious and pulled the injector blocks. I had new ones lying around but never had time to install them.

The old ones were of course cracked. One was worse than the others.

[WERK I]

Originally Posted by Helmsy

OK so I got ambitious and pulled the injector blocks. I had new ones lying around but never had time to install them.

The old ones were of course cracked. One was worse than the others.




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WTH? Did someone try to weld a magnesium manifold with aluminum?

[Helmsy]

I don't know but the main thing is there are no leaks there. Looks like something was there and was grinded off??

Anyway finished up today and changed the plugs out while I was at it.

Took it for a subdued ride to tune afr and bad news is - it's still the same. Enriches early (even with a 7k pill in) and shutdown is horrible.

I can now say that it is likely the injectors or fuel head.

In regard to the shutdown what is a normal shutdown like with the shutdown delay relay. Is it noticeable at all or just normal for 1-2secs after the key is off? Mine doesn't seem normal at all.

[cliveiupfx9]

Originally Posted by RarlyL8

A vac leak, damaged WUR diaphragm or faulty fuel injectors can produce the symptoms you describe. Any of these things may disrupt proper metering signals. The shutdown delay being activatied is an indication that your injectors may be leaking.
I would first check for vac leaks such as blown o-rings and poped hoses then pull your injectors and test them. Your BL WUR is fairly new so should not be damaged, however, if you have over-adjusted it could be so far off that it will not adjust out. If that is the case you need to send it back to BL.
Tough to diagnose long distance.

Now I understand more about it, Thanks for your analysis!

[mark houghton]

Originally Posted by cliveiupfx9

Now I understand more about it, Thanks for your analysis!

Brian, I don't understand your comment:

Originally Posted by RarlyL8
"The shutdown delay being activatied is an indication that your injectors may be leaking".

If we're referring to the ignition shutdown delay relay, all it does is keep power to the ignition for a couple seconds after the key is turned off. Thus, the engine will continue to run and burn any residual fuel as the pressure bleeds down and the fuel lines lose pressure. AFAIK, that relay will be activated each and every time you turn off the ignition key, whether or not the injectors are leaking.

I have no first hand knowledge, since my relay (although present) has been bypassed when the PO installed MSD ignition to a dedicated power source, rather than taking the power from the relay as it should have been. I've never gotten around to re-wiring.

[911st]

Sorry to hear the latest efforts did not improve things. I had my fingers crossed for you.

As noted in post 4 & 14, I suspect your AFR's are not way out of line for a modified 930.

And -- that the only issue is probably unequal injector pop pressures that might be effecting the shut down quality.

Porsche seems to have designed the fuel metering profile to be accurate in the idle and cruse range, to be a bit on the rich side at TQ peak, and to accommodate only a modest increase in air flow over 300hp at peak fuel delivery.

Change its air flow expectation and things can go out of whack and exaggerate the AFR curve. We can trick it it a little by playing with the control pressure's but this only takes things so far.

For reference, with the 94 3.6T Porsche changed the profile of the metering cone, added larger flow injectors, and changed the control pressures to accommodate it's 360hp goal.

Think about it, we are modifying a 300hp fuel delivery system to support 400-500hp.

In the end we may have to live with a bit less than perfect fuel curve.

[Helmsy]

Thanks guys.

I completely agree with 911st that it is somewhat a 'normal' occurence to be seeing the afr curve the way it is once we modify our engines but keep relatively stock cis and dizzy, etc.

I am trying to track down someone who can test my injectors to see if they are the culprit.

Mark mine also had the relay bypassed when I got it and no shims in the control pressure plunger (low system pressure) which leads me to believe they knew of issues before I got my hands on it.

I believe the 'run-on' doesn't seem normal and is more than likely a sign of faulty injectors.