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I leaned out my K-Jet by twisting the "CO adjustment" to the left about a 1/4 turn. It ran great until recently, when I started to notice a gas smell at idle.
Turns out the auxair valve and control pressure regulator relay had an iffy ground. The engine stayed on full rich. I screwed it down to the mounting plate and all is well.
Apparently the engine runs well enough under the typically light loads I apply to it at a pretty lean condition, and even with full "choke" on, it ran acceptably, in fact, really well at very high speeds.
Is there a reasonably priced high-pressure control-pressure-regulator setup I could install, along with an exhaust gas temp sensor I could install in the EGR port?
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you need to know what the control pressure is first. if it's too high, the car will run lean, too low and it's richer. then you can twiddle with whatever to adjust it. a reasonable pyrometer for the exhaust is an oxymoron. pryrometer's ain't cheap. good luck, chuck.
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Turns out the auxair valve and control pressure regulator relay had an iffy ground. The engine stayed on full rich. I screwed it down to the mounting plate and all is well.
As I remember it, those grounds are just for the heaters, which are in there to provide a quicker "warmed up" state.
The engine won't "stay full rich" because even without the heaters, the AAV and CPR will stabilize air and fuel mix to "warm-normal values" due to ambient engine heat.
It just takes a little longer, depending on outside temps. In warm weather, the heaters hardly come into play at all, IMO.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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"The engine won't "stay full rich" because even without the heaters, the AAV and CPR will stabilize air and fuel mix to "warm-normal values" due to ambient engine heat."
I am not certain that what you are saying is true. On my 144 I converted it to K-Jet from SU's & I initally didn't bother to hook up power to the control pressure regulator(I didn't bother putting on the AAV either) & the car ran fine but guzzled thur a tank of juice in less than 150 miles! I quickly connected power to it. :)
Cheers,
Paul.
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"I am not certain that what you are saying is true. On my 144 I converted it to K-Jet from SU's & I initally didn't bother to hook up power to the control pressure regulator(I didn't bother putting on the AAV either) & the car ran fine but guzzled thur a tank of juice in less than 150 miles! I quickly connected power to it. :)"
Paul,
I could well be mistaken, but based my comment on doing Pressure Tests from the Kjet service manual, where with pump relay jumpered, the CPR heater coil should bring Control pressure up to normal (warm running) value in about 2 minutes. And then reading the following from Bentley/Bosch FI manual:
"After a cold start, fuel mixture needs to be cut back in one or two minutes, but the engine block might take 10 minutes to warm up to the point where it affects the bimatal arm in the Control Pressure Regulator. To ensure that the mixture is not enriched for too long, an electric heating coil warms the arm when the ignition is turned on. Warm-up needs are different for each car model, so do not interchange regulators."
That seemed to imply to me that engine heat sort of "took over" (the CPR heating) after 10 minutes or so. In any case, I don't deny that the heaters aren't needed. Just that I assumed their effect would be "matched" by engine heat after a few minutes, and that the rich warm-up mix would be reduced when that happened.
Perhaps on your conversion to Kjet, you had to mount the CPR where it didn't get the expected heat from the block?
One thing I do know for sure is that mis-plugging the CPR heater connecter to the Frequency Valve will give you FULL-rich all the time. (BTDT)
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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I had mine mounted on the intake manifold same as Volvo did it.
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I'm not very familiar with B20 Kjet component locations, but from a Haynes picture, that intake manifold position looks like it could be cooler (slower heating) than the later B21 block mount location.
Which could make a non-functioning heater element more noticeable, by extending the transition time to warm control pressure on the B20.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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So if I put in a hotter thrmostat, I might get a leaner mix?
Or does the CPR and AAV stop completely down at less than operating temp? Seems like the temp gauge is alway s abit low. Fuel gauge is okay, so I think voltage stabilizer is okay. I kinda remember swapping one in.
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"So if I put in a hotter thrmostat, I might get a leaner mix?"
No, I don't think so. The AAV and CPR/WUR have basically two fixed "settings"—Cold and Warm or normal running. What can vary is the transition time from cold to warm. The heating elements reduce that time.
Normal engine running temperature has no effect on Control Pressure. Running a few degrees hotter or cooler won't influence the CPR at all, IMO.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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I wonder how much richer it runs at full throttle with the control pressure regulator disconected from power? You could do something wacky like put a switch on your throttle that turns it off as you are nearly at full throttle.
Cheers,
Paul.
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Of course, the best bet is to see what the engine likes in terms of air/fuel on a dyno. Typically, an engine likes the mixture as lean as possible without detonation. Most often, Lean = power, contrary to popular myth.
Per
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posted by
someone claiming to be Rhys
on
Mon May 17 14:36 CST 2004 [ RELATED]
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I am not aware of this myth. My understanding is that a mixture slightly richer than stoichiometric produces best power, and provides greater resistance to detonation. Every modern fuel injection system goes rich during WOT, and aircraft piston engines always go rich during full power operation for these reasons. Aircraft fuel used to be rated at two different octanes depending on rich or lean operation, and the rich octane value is always substantially higher.
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I should have clarified that a bit...rich for rich's sake doesn't create power, you're trying give the engine just enough fuel so it can support its compression ratio and timing.
The combustion of the gasoline isn't what creates the power...it's the oxygen that is atomized with it.
Here's an article on the system that we're just starting to use.
http://www.carcraft.com/techarticles/116_0402_tune/
In short, a dynamometer and a wideband O2 sensor are invaluable for tuning. But, as an aside, our SUs when tuned by ear and smell came out with very respectable a/f ratios on a chassis dyno.
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posted by
someone claiming to be Rhys
on
Tue May 18 19:48 CST 2004 [ RELATED]
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This article supports what I have said previously, that best power is achieved in the 12.8-13.2:1 air/fuel ratio region, which is far richer than the 14.7:1 stoichiometric.
As to the chemistry of combustion, it is indeed the fuel that creates heat, and its combustion is supported by oxygen. No more fuel can be burned than there is oxygen to support that burning. It is the fuel that creates the heat that provides the expansion and the resultant power stroke. Oxygen certainly doesn't require "atomization" as it exists (at the temperature range we operate piston engines in anyways) as a covalently bonded gaseous pair of atoms, hence, O2.
That your engine running with SU's has a good fuel air ratio has everything to do with the needle profiles established over forty years ago, and less with wide band, narrow band, dynomometer testing magic wand waving. Wide band O2 sensors are certainly usefull, but the inherent defects in fuel distribution that are evident in all carbureted engines do not require the extreme accuracy they provide. Wide bands are used to further improve the performance of the most recent generation of catalytic convertors, and are also essential to the ULEV engines that are becoming prevalent. Nonetheless, the English boffins knew what they were doing in their day, and over 600 needle profiles prove that.
Everything acts to support combustion, which is the primary function of the engine, and timing and compression ratio are subserviant to that goal, not the other way round.
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re: The combustion of the gasoline isn't what creates the power...it's the oxygen that is atomized with it.
Well, it's the same oxygen whether it's gasoline or alcohol being burned, so why is gasoline said to contain more btus of power and why does fuel consumption increase burning alcohol?
atomize: to reduce to minute particles or to a fine spray
It might have to be liquid oxygen, then!
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I agree, stoichiometric mixture is best for power with pollution in mind, richer gives more power with disregard to pollution & in piston engine planes you definately want to err on th rich side. :) You can also go a fair bit leaner than stoichiometric at part throttle for economy. With D-Jet & SU cars I try & make it feel a bit wheezy feeling at part throttle, ie, get the highest vacuum possible & then lean it out a little more so the vacuum drops, but not so far that you get misfires.
Cheers,
Paul.
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re: richer gives more power with disregard to pollution & in piston engine planes you definately want to err on th rich side
Mixtures are richened for cooling purposes and to prevent detonation.
One would expect more power to be produced when heat is highest, right? The energy is the heat, right?
A richer-than-ideal mixture simply means some of the fuel isn't being burned, right? How does not burning fuel create more power?
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Stoichiometric means chemically correct. Assuming are fuel is just CH, a stoichiometric mixture would burn like this:
CH + O2 = CO2 + H2O
If you richen the mixture, you can burn extra fuel and the burn becomes:
CH + O2 = CO + CO2 + H2O
Carbon monoxide is produced instead of carbon dioxide when the oxygen is insufficent. Please note my bad chimistry equations are for illustration purposes only. :)
About 10 years ago a friend of mine had a dyno & I spent alot of time there. His gas analyzer was of the older variety that measured CO output & it didn't give a mixture ratio. 3-4% CO was a good range for most engines for maximum horsepower, turbo cars did well with 5-7% CO.
Cheers,
Paul.
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Is there a reasonable priced[$100 or so] wide band oxygen sensor & gauge setup? I would love to know what the A/F ratio is for tuning my D-Jet. I've got a summit racing one, but it has a limited range. Any ideas?
Mike M.
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The cheapest one with an integrated display I found was $320. PLX Devices M300. It agrees with the standalone units at the dyno.
The megasquirt guys are going to release their own DIY board soon. Might be $150ish with sensor.
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I'm sure there are several wide-band O2 sensors out there. The only I know of is ECM, check www.ecm-co.com
I think ~$100 is going to be a stretch, though.
Kåre
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