CIS mixture tweaking Q

Here's a question for all you CIS experts out there. My buddy's car, K-Jet Basic same as mine, ran 'er on the dyno last night. After fixing a bad distributor, we got stuck on trying to dial the mixture in. It was stuck on full rich, PIG-rich, at around 10 mid-run. By leaning out way bigtime, we got it up to around 11-flat mid-run, but still no-where near the low 13's my car runs.

However when messing with the setting at idle, I had NO problem getting it so lean that it was off the charts for the tailpipe wideband sniffer (over 19.0).

What could cause this condition? It's got a new/fresh rebuild warm-up regulator on there, so that should be fine.

What about the fuel delivery pressure? Based on advice from others, we'd bumped it up to the top end of the acceptable spec (don't remember the value). I'm wondering if that might be flowing too much, despite the control pressure being correct (verified with the proper gauges)?

Any help, suggestions, etc are appreciated...

Is there a WOT switch that could be closed all the time?

Assuming you've gone through it with the gauges, and all the control and system pressures are "right", sure sounds like the frequency valve is stuck open, as Loop suggests.

Look for a failed water temp switch or WOT switch' they both control the same circuit to the Lambda controller. In fact, as a test remove the Lamda ECU and see if the problem goes away...

Vaughan,

You say CIS basic and K-Jet. CIS basic as I understand it, is really mechanical injection, no lambda box, no WOT switch, no freq. valve. Still uses a warm-up regulator, etc.

The K-jet my old Rabbit GTI had was what was referred to as CIS-lambda (O2 sensor). Had all those things above that the CIS basic did not.

Based on what you described, I'm inclined to agree w/ Dick and Greg, I'd start by looking at what's going on w/ the freq. valve. Either it's bad, or you may have a short in the wiring for the WOT switch that's got it running in open-loop mode all the time (instead of just at WOT). Something else you may want to look into, if that's not the problem, is the cold start injector and the thermo time switch circuit (part of the warm-up regulator). My guess would be the freq. valve or the WOT wiring (check that first).

Correct, these are CIS-basic cars... we doan need no steekin' Lambdas! ;)

Over on the 924 forum, the suggestion was thrown out that too-high fuel delivery pressure would cause this... and it's definitely high! I think, unless there are any other ideas out there, that we're going to try dialing this back for our next test day, put it where my car is (which was never adjusted), and see how she goes. My car was recording mid-to-low 13's for AFM on the dyno...

Depeneds on what you mean as high. CIS is usually in the 75-80PSI range by design.

I forgot, it was some time ago, but I wanna say something like near 5.5-6.0 bar... ;) so yeah, in that general ballpark... but I measured it on my car to check, think it was more like 4.5bar/65psi...

Its my understanding that dropping the fuel pressure on a CIS-Basic actually increases the amount of fuel delivered. The fuel pressure is what "holds the door closed", so its opposite of what you would think.

I suspect that the fuel pressure is dropping during the pull (plugged filter, weak pump, cruddy warmup regulator) causing it to dump more fuel in. I have some really nice pressure transducers that I've been itching to use on the dyno, we just need to work out the plumbing :D

BTW, you Porsche guys drink a lot of :birra:

Kendall

Kendall's correct, to a point: the "control pressure" is what opposes the pin in the fuel distributor; it's regulated by the, dah dah!, control pressure regulator. However, low system pressure can result in low control pressure

I found this drawing on Da Web:

http://home.hiwaay.net/~langford/CIS.html

This is why I wrote "[a]ssuming you've gone through it with the gauges, and all the control and system pressures are 'right'..." If you don't have the CIS gauges, and you haven't done all the basic checks, anything you do from now on is simply chasing your tail. Without the proper gauges there is basically ZERO chance of properly troubleshooting a CIS system.

Spend the coin for the right tool; it's not that expensive and will save you a TON of grief:

http://www.napaonline.com/NOLViewer/Pages/...2614&ShowPics=1

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Its my understanding that dropping the fuel pressure on a CIS-Basic actually increases the amount of fuel delivered. The fuel pressure is what "holds the door closed", so its opposite of what you would think.

I suspect that the fuel pressure is dropping during the pull (plugged filter, weak pump, cruddy warmup regulator) causing it to dump more fuel in. I have some really nice pressure transducers that I've been itching to use on the dyno, we just need to work out the plumbing :D

BTW, you Porsche guys drink a lot of :birra:

Kendall
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They don't call us PUB Racing for nothing!! :026:

What you're describing is control pressure, as Greg points out; I'm talking about the system pressure. Yeah, we've got two fuel pressure regulators! :D

Warmup regulator is new, as is filter, and pump has no issues putting out that pressure (pushing 6 bar) - unless, as you're suggesting, it's old and weak. Too bad, we could've run the gauges on the dyno to confirm - yes, thanks, Greg, I do have them! - but didn't plan for mixture problems, only ignition...

We'll check again, but I'm 99% sure the control pressure is fine - it's only governed by the WUR (warm-up regulator aka control pressure regulator).

Since control pressure is from 1/4 to 3/4 of the system pressure, it has no problem bleeding the pressure down as needed - but it does make sense how the system pressure being too high could result in incorrect fuel flow, same as the control pressure being too low, since the fuel metering is completely determined by the pressure differential between the two. So you should effectively be able to bump your whole fuel curve up or down by re-shimming the system delivery pressure regulator (in the fuel dizzy).

Oh well, just goes to show you can never be too organized or prepared for a dyno session!

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So you should effectively be able to bump your whole fuel curve up or down by re-shimming the system delivery pressure regulator (in the fuel dizzy).

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Messing with the main (system) pressure will do nothing good. Been there done that doesn't work!If anything shim it up to about 90 to 100 psi and then find a way to accurately regulate control pressure. The stock WUR will not do it right. What was your control pressure anyhow?We have a bolt on system that works flawlessly and would sell you one for $250.

Sure, swapping in an adjustable regulator, gauge, and lines should be pretty straightforward - biggest PITA would probably just be getting the right match of fittings. But I still don't understand why changing system pressure (with contact control pressure) won't have any impact on fuel delivery?

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Sure, swapping in an adjustable regulator, gauge, and lines should be pretty straightforward - biggest PITA would probably just be getting the right match of fittings. But I still don't understand why changing system pressure (with contact control pressure) won't have any impact on fuel delivery?
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It doesn't work because control pressure changes with it. We have hours upon hours of dyno time playing with this. example: altering control pressure a mere 4 psi increased the horsepower of a limited prep 1.6 8V motor from 106hp to 128hp! The correct air fuel ratio is critical and the only way we have found to adjust it without hurting power somewhere on the curve is by ACCURATELY controlling control pressure. The system we use connects directly in place of the stock WUR.

Leaving side legality issues with using non-standard and modified CIS...I agree with what Jeff is saying.

Look at that drawing link I posted above. Note that the control pressure regulator's (CPR's) job is to regulate the pressure at the top of the pin, thus control its rise. A higher control pressure will resist the pin rise more, causing less fuel to be delivered to the injectors; a lower control pressure will allow the pin to rise more, allowing more fuel flow.

The input pressure to the CPR is system pressure. I *believe* the CPR is not a true "pressure regulator" where it controls fluid pressure to a *specific* output number; instead I believe it is a ratio regulator, meaning the output (control) pressure is a ratio of the input (system pressure). So, if you double the system pressure you also double the control pressure. As system pressure rises the actual delta pressure is increasing, but significantly less than the rate of increase in the system pressure.

System pressure is controlled by a spring in the CPR. Shimming the spring increases system pressure.

So, the whole system is a self-correcting mechanical computer (which bodes well for you guys vis-a-vis the new ECU rules. The new rules state that "computers" can be modified or replaced, or something like that. This system is a mechanical computer...) - GA

Neato system.

OK - yes, I think Greg's got the key point in that the WUR seems to not function as a true regulator, only a ratio regulator.

As for legality - might as well discuss it here. Last I heard, fuel-injected cars are allowed to use adjustable fuel pressure regulators. GCR ITCS section D.1.a.6: "Adjustable fuel pressure regulators are permitted."

Greg (and any other rules nerds monitoring): are you aware of or can you find any rules that might contradict this?

PS - there is a way to make the stock one adjustable, though perhaps not the most convenient while installed!

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...fuel-injected cars are allowed to use adjustable fuel pressure regulators...[/b]

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Good point. I was not thinking as broadly as you are. Given that the CPR *is* a fuel pressure regulator, and there's no limitation to WHAT "fuel pressure" you're regulating, I now agree that there's no problems with modifying the CPR or the fuel distributor's system pressure regulator.

In fact, taken REAL broadly, the whole damn system is one big pressure regulator, including the popoff pressures at the tip of the fuel injector (he says, with an evil, scheming grin on his face...) - GA

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As for legality - might as well discuss it here. Last I heard, fuel-injected cars are allowed to use adjustable fuel pressure regulators. GCR ITCS section D.1.a.6: "Adjustable fuel pressure regulators are permitted."

Greg (and any other rules nerds monitoring): are you aware of or can you find any rules that might contradict this?

PS - there is a way to make the stock one adjustable, though perhaps not the most convenient while installed!
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I've had my car teched and passed with this regulator system on because as noted the ITCS doen't specify WHAT fuel pressure is being regulated.

Yes you can make the stock WUR adjustable, but what we use is cleaner, easier, cheaper and rebuildable.

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Messing with the main (system) pressure will do nothing good. Been there done that doesn't work!If anything shim it up to about 90 to 100 psi and then find a way to accurately regulate control pressure. The stock WUR will not do it right. What was your control pressure anyhow?We have a bolt on system that works flawlessly and would sell you one for $250.
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Jeff- Can you send me info on that CPR setup? kendall at jonestechnicalgroup.com

Kendall

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I've had my car teched and passed with this regulator system on...[/b]

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You talking about your annual inspection, or did you get protested? If the former, that check has ZERO credibility (or supportability in a protest situation) as to the legality if items on the car; that's an annual safety check only.

If you want de facto and de jure proof of legality of a mod you've made, you need to follow the process specified in GCR 8.1.4 (p GCR 65 in the latest version). Otherwise, its legality is still up to argument.

Personally, as I noted above, I believe it can be done legally, and I'm sure the board here would be tickled pink to get into debating its legality. However, given your circumspect discussion of this "system" you've installed, I'm guessing you want to keep it proprietary; ergo you should make any potential customers aware that they are proceeding at their own risk.

Greg

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Jeff- Can you send me info on that CPR setup? kendall at jonestechnicalgroup.com

Kendall
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Ditto! I'm at vaughan (at) vaughanscott.com - cheers!

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You talking about your annual inspection, or did you get protested? If the former, that check has ZERO credibility (or supportability in a protest situation) as to the legality if items on the car; that's an annual safety check only.

If you want de facto and de jure proof of legality of a mod you've made, you need to follow the process specified in GCR 8.1.4 (p GCR 65 in the latest version). Otherwise, its legality is still up to argument.

Personally, as I noted above, I believe it can be done legally, and I'm sure the board here would be tickled pink to get into debating its legality. However, given your circumspect discussion of this "system" you've installed, I'm guessing you want to keep it proprietary; ergo you should make any potential customers aware that they are proceeding at their own risk.

Greg
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My impression is that it's nothing particularly special as far as implementation; all you're doing is bleeding pressure off one port and dumping it back to the return line to the tank. I suspect that, once you price out a decent regulator and gauge, then add the expense of compliant stainless braided hoses to plumb them in, with the right stupid metric fittings, any profit would be modest, and worth the effort to figure out all the bits.

I'm still gonna go home and, especially since the gauge is still plugged into my car, play around with the system pressure and watch the control pressure. I'd really like to see this in action, to improve my knowledge of how the system works. I think we've finally reached the point where we can stop struggling to just get the systems working properly, stock, and now look at modifications/tuning.

The CPR (cntrl pres rgl) is a straightfoward/normal regulator whose pressure is a function of the pressure of the internal spring and the augmentation of the bi-metallic strip that the spring reacts against it. If you arrange a threaded rod to react this spring base at the bimetallic end, you have made it adjustable. You can improve it's position and arrange a controlshaft into the cockpit. If you make the CPR adjustable, you'd better install a pressure guage in the side of the circuit that has the larger banjo bolt, or you'll drive yourself crazy trying to know whats going on if you have a (mixture) problem. (also, if you have a significant fuel starvation problem, you will see it-when system pressure reaches control pressure, the contol pressure will be system pressure; since injector pop off {operating} pressure is 35-37psi, and the metering pressure drop accross the metering plunger is only 1.5psi, CIS will fuction with lower system pressures until they get quite low. When you see a stable control pressure start diving, this is indicating fuel starvation. You will notice how control pressure jumps around when you suddenly accelerate as the airflow plate jams up the metering plunger and momentarily influences pressure in the circuit, and you will quickly see what is normal.
However...I still can't think of a scenario that would explain the huge fatness top end on the dyno; with CIS the problem is usually leaness. Is it possible you had an instrumentation issue? Unusual as most problems will drive a wideband to read erroneosly lean (exh air leak, misfire, etc).
A simple and super reliable way to monitor system and control pressures: take 14mm and a 13mm headed banjo bolt; drill !/8" hole thru middle of both, then counterbore that hole from the top w/ a 5/16" bit just enough to stand a short (3/4")piece of 5/16" steel tubing in it; braze the tubing to the banjo; put the 14 in the CPR, the 13 in the cold start valve and connect 2 100psi guages w/8mm fueline and miniclamps.
Good luck-I'm curious what will be the answer here! phil

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The CPR (cntrl pres rgl) is a straightfoward/normal regulator whose pressure is a function of the pressure of the internal spring and the augmentation of the bi-metallic strip that the spring reacts against it. If you arrange a threaded rod to react this spring base at the bimetallic end, you have made it adjustable. You can improve it's position and arrange a controlshaft into the cockpit. If you make the CPR adjustable, you'd better install a pressure guage in the side of the circuit that has the larger banjo bolt, or you'll drive yourself crazy trying to know whats going on if you have a (mixture) problem. (also, if you have a significant fuel starvation problem, you will see it-when system pressure reaches control pressure, the contol pressure will be system pressure; since injector pop off {operating} pressure is 35-37psi, and the metering pressure drop accross the metering plunger is only 1.5psi, CIS will fuction with lower system pressures until they get quite low. When you see a stable control pressure start diving, this is indicating fuel starvation. You will notice how control pressure jumps around when you suddenly accelerate as the airflow plate jams up the metering plunger and momentarily influences pressure in the circuit, and you will quickly see what is normal.
However...I still can't think of a scenario that would explain the huge fatness top end on the dyno; with CIS the problem is usually leaness. Is it possible you had an instrumentation issue? Unusual as most problems will drive a wideband to read erroneosly lean (exh air leak, misfire, etc).
A simple and super reliable way to monitor system and control pressures: take 14mm and a 13mm headed banjo bolt; drill !/8" hole thru middle of both, then counterbore that hole from the top w/ a 5/16" bit just enough to stand a short (3/4")piece of 5/16" steel tubing in it; braze the tubing to the banjo; put the 14 in the CPR, the 13 in the cold start valve and connect 2 100psi guages w/8mm fueline and miniclamps.
Good luck-I'm curious what will be the answer here! phil
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