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MG TD TF 1500 - CP8200 O2 Sensor Gauge

You may recall from other threads that Jim Northrup has an O2 sensor in his TD with a unique display on his instrument panel. Here's an image of the display. It's made by SunPro and is their Model CP8200. I'm installing one in Lazarus and I'm intrigued by the display. An O2 sensor puts out a voltage signal that goes from 0 (ultra lean) to about 1 volt (ultra rich). The ideal stoichiometric level 14.7:1) is in the vicinity of about half a volt (.4 to .5). I put together an O2 simulator (AA cell and potentiometer) and fed the voltage into one of the gauges to see it respond. I don't seem to be smart enough to figure out YouTube's latest instructions, so I put the video on Ttalk. see http://www.ttalk.info/SUNP0008.wmv. Bud


Bud Krueger

Bud - Thank you - most interesting. The Mark II TD I recently bought has a bung in the exhaust, and I am considering getting a SunPro. Worth it?

Tom Lange
MGT Repair
t lange

For those of us without such knowledge could you explain in layman's terms why I would want one of these in my TD? Sounds interesting...looks cool.
Thanks,
Ed
efh Haskell

Tom, I'm still at the experimental stage. Having the bung in place you're about half way there $-wise. It cost me $40 for an installed bung. I lucked out at finding an experienced s/s welder. I hope to have the system operational within a week. More later. Bud
Bud Krueger

Ed, I'm just a neophyte on this. It's a way of observing your carburetion in terms of lean/good/rich while you're running. The O2 sensor signal is one of the most critical inputs to the computer of modern cars. Guess it's sort of like being able to see the color of your spark plugs while on the go. Bud
Bud Krueger

Ed, you don't really need one on a stock T car. Might be fun to play with though. On the other hand it would be really nice to have on an engine with performance modifications..particularly with a super charger. Running way rich will will thin the oil and foul the plugs. Running lean on a high compression engine is a recepie for burning pistons. With the O2 sensor you can observe whats going on with the mixture through the range of RPMS and any given load. Very handy although I'm not to keen on the " lean-ideal-high" gauge. I'd rather see something that tells me exactly what the mix is...13-1....17-1 .... you get the idea.
L E D LaVerne

Hey Ya'll!
We ran our Magnacharger in our '51 TD with stock 5.12 gearing, and it seemed to run great. Sometimes, ignorance is BLISS!
Once the '50 TD was back on the road, now with MGB 3.92 gearing, it took possession of the Magnacharger. I stuck the air ratio gauge on for some feedback.
I'll give some of the examples what it has come in real valuable for:

1. When first put on the road, it would run rich and start leaning out as speed increased, up to 60mph. About that speed, the gauge would start disappearing lean for a brief moment and then reappear to a bit rich. The faster we'd cruise, the longer it would languish offscale lean. By 80mph, it stayed lean and would bob back up briefly and then disappear. It seemed that the carb flowed only enough fuel for just under 60mph and then couldn't pass any more fuel. That is not good on hot days with the water temp at 230F. It is no fun cruising in crowded rush hour traffic and then get backfiring through the intake! It took about 2 seasons before this fuel starvation was brought under control.

2. I utilized the gauge to adjust the mainjet to the optimum setting. At idle, it is at the richest LED. Starts great with no enrichener and idles very reliably. As speed picks up, it rises toward ideal, one LED about every 15mph. At 80mph, it is running one LED to the rich, right where I want it.
I've experimented with leaner, but it seemed to suffer a bit on takeoff, considering the gearing.

3. Heading for GOF Central in 95F+ temps, I'm sure we were filling up at stations in that part of the midwest that pushed the 15% limits on ethanol. With the recored radiator, water temp was under 200F for the most part, but frequently, cruising 70-80mph, the engine would cut out! One look at the air/fuel gauge show we were completely leaned out to nothing. Within seconds, I'd pull the switch on the backup Facet pump, and in a flash, we're back up. I experimented with this on the way there and back and concluded it was vaporlocking at speed in the heat of the day, with the old, lower pressure pump. It has never repeated this behavior, on numerous day-long cruises, as the temps haven't been that high, since. One of these days, I want to plant a bunch of diigtal thermometers all over the engine compartment, especailly the fuel line & carb, to see how hot it is on the other side of the firewall that burns my feet!

4. We were cruising, again, in rush hour traffic, and everything was running & reading great. I'd bumped the timing up from 25 to 30BTDC, and was keeping a close eye on it. Wife remarked it sure was running good that night. All of a sudden, it started backfiring through the intake, which is quite distressing. I told my wife to just slow down, which alleviated the backfiring in the past, but one look at the gauge showed we were dreadfully lean, so we pulled off at the next exit. With the heavy blower hanging on the intake, the dogs keep coming loose! I tighten them up every month or so, but invariably, they work their way loose (gotta get out some red locktite!). So after popping the bonnet, I see the dog between 3 & 4 is completely loose/disengaged. The other three are also loose... the the blower is sloppy and it is sucking air.
If it weren't for the gauge. I would've assumed the backfiring resulted from the extra ignition advance, and we'd have just kept driving at a slow speed.

5. The LEDs are very responsive and have given me a better feel for the SU. When backing off the throttle, the ratio goes completely lean as it decelerates, then whips right back into the rich and near ideal region instantaneously.

6. The manifolds nuts would work their way loose on the '51, which didn't have the gauge. One day, wife came home, and it was screeching just like a siezed bearing in the blower! The ear piercing, high pitched squeal was coming from the Magnacharger, so I spent quite a bit of time investigating the blower and scratching my head. If I had the air/fuel ratio gauge and the vacuum/boost gauge, I'd have seen instantly it was running lean and focused my attention to the real problem- the intake gasket. The engine had sucked the resilient gasket material off the steel reinforcement, and the sheet metal made a rudimentary reed instrument producing an outrageous tune!

My earliest opinion of the LED gauge was it would be cheap and I'd be disappointed, but I selected it because it was part of the set. I gained a lot of respect for it as a very esnsitive, responsive tool. I can appreciate a gauge with a digital display or a needle may be desirable for more of a steady state situation, but the only thing that can respond quicker than the LEDs would be an oscilloscope. I think my next gauge will be one with both Digital display and LEDs.

FYI, 30 degrees advance with the magnacharger runs fine; usually boost never exceeds 5psi, for what that's worth.



JIM NORTHRUP SR

Jim, That's a heckuva report!

Thanks,
Dave
Dave Braun

Dave,
That little blurb wouldn't even be an abstract compared to your reports.

Your technique for adjusting the float level was the trick that finally resolved the fuel starvation problem. I was almost convinced a single SU couldn't flow enough gas for a supercharged engine, and that's with 2 fuel pumps. I had kept doublechecking the float level with a drill bit for calibration, before then.

Prior to that, the fuel feed seemed to flatline at 60mph and run dangerously lean. The power flattened right out- we'd have to push it to make 80mph. I talked it over with Joe Curto, and tried a steel float needle along with different needle & mainjet, but no improvement. Even gave up on the SU and machined up a new carb manifold to try Harley carbs, which proved to be a disaster. Now it runs up to 80mph+ with power to spare, rock solid at one LED rich.

Without the gauge, I would have assumed it was running exactly as Moss had designed it, and never suspected a problem... and never enjoyed the extra power, either. We ran it for almost a decade on our '51 and now I look back and wonder. With 5:12 gearing, the '51 was never pushed down the highway as hard (did clock 75mph at Michigan International Speedway).

Thank You Dave!

Warmly,
Jim
JIM NORTHRUP SR

Dave,
That little blurb wouldn't even be an abstract compared to your reports.

Your technique for adjusting the float level was the trick that finally resolved the fuel starvation problem. I was almost convinced a single SU couldn't flow enough gas for a supercharged engine, and that's with 2 fuel pumps. I had kept doublechecking the float level with a drill bit for calibration, before then.

Prior to that, the fuel feed seemed to flatline at 60mph and run dangerously lean. The power flattened right out- we'd have to push it to make 80mph. I talked it over with Joe Curto, and tried a steel float needle along with different needle & mainjet, but no improvement. Even gave up on the SU and machined up a new carb manifold to try Harley carbs, which proved to be a disaster. Now it runs up to 80mph+ with power to spare, rock solid at one LED rich.

Without the gauge, I would have assumed it was running exactly as Moss had designed it, and never suspected a problem... and never enjoyed the extra power, either. We ran it for almost a decade on our '51 and now I look back and wonder. With 5:12 gearing, the '51 was never pushed down the highway as hard (did clock 75mph at Michigan International Speedway).

Thank You Dave!

Warmly,
Jim
JIM NORTHRUP SR

Well, it was an interesting experiment, but I don't think I'll be continuing with it. It's probably a very meaningful display for someone with hardware like Jim's but I'll stick looking at the plugs. As Jim mentioned above, the display seems to be insistent upon showing that the engine is running somewhat rich (green LEDs). I took that as gospel and cranked the nuts on both carburetors up 3 flats and went for a spin. Still running in the green LED area. Only time I saw anything in the yellow was between shifts. Got back to the garage and pulled a couple of plugs. The ceramic was virtually white. Way too lean. Maybe it's just the display unit. I wish that I could read the actual voltage of the O2 sensor, but that doesn't seem to be feasible. It's a classic example of the uncertainty principle. The sensor is a very high impedance source. Even putting a very high input impedance voltmeter across the O2 sensor output changes it drastically.

The attached ambient image is a bit misleading in not showing the degree of white on the ceramic. Camera shake makes it bit fuzzy. An image with strobe is much sharper, but it makes the electrode area much too white. Bud

Bud Krueger

Once again I'd like to see a display that gives a true fuel/air ratio. Where did you mount the sensor in the exhaust stream Bud?
L E D LaVerne

Right here:


Bud Krueger


>"Once again I'd like to see a display that gives a true fuel/air ratio. "


http://www.glowshiftdirect.com/White-Elite-Series-Wideband-Air-Fuel-Gauge.aspx?gdftrk=gdfV22417_a_7c1458_a_7c6258_a_7cGS_d_EWT02W

Jim B.
JA Benjamin

"Once again I'd like to see a display that gives a true fuel/air ratio."

I checked on ebay and found a gauge that offers both the LEDs as well as digital readout, for under $20, so I bought it for our Honda CRX that I'm putting motorcycle carbs on. I'll probably check it out on the MG after it arrives.

That gauge also displays system voltage at various times.
JIM NORTHRUP SR

Jim,

Do you have an ebay item number for the gauge you bought?
Dave Ahrendt

Universal 2" 52mm Air Fuel Ratio AFR/Volt Blue Digital LE... (400449048174) for under $20.

For even less $, there's one with LEDs and a needle...
190970603876.

The reason I installed the Sunpro originally is that was part of a set of matching gauges, but the black background doesn't really match the others. Now there's a gauge with a white background that has digital display and LEDs, 221300359328. My offer of $20 is still pending, but it won't break us to pay the whole $25.49, which includes shipping.
JIM NORTHRUP SR

I'm buying one, myself. A concern is the statement about volts reading '8 to 16'. A normal narrow band O2 sensor's output is less than 1 volt. Bud
Bud Krueger

Bud,
That 8-16 Volts is most likely referring to when the gauge switches to read battery/generator voltage. It is a cute feature!

I was going to see if you wanted my Sunpro to doublecheck yours. The thing I didn't like about the Sunpro is the plug won't stay in on the back.
JIM NORTHRUP SR

Jim, the test that I showed in the opening of this thread indicates that the SunPro is sowing what It should for the various O2 sensor voltages. But, thanks for the offer. I found that I had to give a good push onto the connector to get it to click into the gauge. Once in, it ain't common out! I tried.

I had the impression that the eBay gauge was displaying sensor voltage.

I just put back the three flats up that I had put on the carburetors. Heading out to the highway for a run of about 20 miles at 60 mph to see where the gauge reads and how the plugs look. Report to follow. Bud
Bud Krueger

Same plug after going down 3 flats. SunPro showed lowest green (Rich) LED. Occassional blips of top yellow (Ideal) LED. Indication from plug color is that it's still a bit too lean. Bud

Bud Krueger

Bud,
For what it's worth, I yanked out a plug and inspected the ceramic- light tan. These are platinums with very recessed, cold electrode, about a year old/~ 5000 miles, many of them hard miles.

Your "simulation" was very interesting. I assume the O2 sensor wasn't attached. "Applying an external voltage to the zirconia sensors, e.g. by checking them with some types of ohmmeter, may damage them." (Wikipedia- oxygen sensor).

I try to forget one episode with a VOM- diagnosing a nonfunctioning robot "magnetic core memory board" (late 1970's vintage Hitachi/GE) comparing it to a functional board. Instead of getting a 3rd one running.... then there was only 1! Only had $250 invested in the three of them, but made $18,000 renting one out, until the customer's building was hit by lightning, destroying the robot. He turned it in on his insurance, and got $5000 FOR MY ROBOT, then bought a robot of his own with the insurance settlement!

While on the subject of O2 sensors, I might try welding an 1/8" NPT fitting onto an old O2 sensor thread and install an exhaust temp gauge thermocouple in the bung temporarily. Since I'm swapping the engine this winter with another that will have Len's roller lifter cam with "street supercharged" grind, I should record the exhaust temps NOW with the current engine. I'd be really curious to find a drop into exhaust temp due to the minimal overlap of the new cam!
Shall we start a new thread on EXHAUST TEMP GAUGES?

JIM
JIM NORTHRUP SR

Jim, the input for the simulation was just the voltage from the potentiometer. No sensor attached. I've tried measuring the sensor input to the SunPro gauge, but the meter drops the voltage appreciably and the display goes into the red (Lean) range. Bud
Bud Krueger

The Chinese O2 display arrived this afternoon. Did a quick look and saw that it does indeed display the air/fuel ratio as well as red/yellow/green (lean/optimim/rich) LEDs. I can't do a live test at the moment since Lazarus' carburetors are in my basement at the moment getting rehab'd. I'll see if I can do another simulator demo video tomorrow. The image below was taken with an input voltage close to that for a 14.7 a/f ratio. The reading is not the battery voltage. Bud

Bud Krueger

Bud,
I got one of those Dragon Gauge air/fuel ratio meters, too, plus their exhaust temp gauge, and allocated them to a Honda project, as these match the blue interior. Your sentence, "The image below was taken with an input voltage close to that for a 14.7 a/f ratio." is not clear to me. Did you substitute something like a .5 V source in place of O2 sensor?
I didn't read the instructions, but this is what the ad states:
" When powered on digital gauge will read the voltage for 1 minute and switch to Air Fuel Ratio.
It will only switch back to voltage if there is a decrease or increase.

I also scored an air/fuel ratio gauge that halfway matches our MGs gauges. Since I stuck a thermocouple in the oxygen sensor bung, testing for my new A/F gauges and exhaust temp gauges on the MG is on hold due to salt on the roads- mama said so! However, I did a makeshift test on the stove, and it was rather interesting. When energized, this gauge whipped the LEDs around, back and forth, then displayed the battery voltage and ran the LEDs to a corresponding voltage position, for a about 1 second, then registered the air/fuel ratio. The instructions are quite confusing/conflicting on its function as a voltmeter, as translated from Chinese to English. As much as I rely on vehicle voltmeters, I wish they didn't combine these two functions in one meter. The mixed readings may be confusing glancing at it while driving.
I tried using the flash for a clearer picture, but the flames did not appear. I had to hold steady for a long exposure without the flash.
Just one more toy to play with next spring!


JRN JIM

Jim, I used the same AA battery across a potentiometer as the input. That let me dial the various A/F levels. That translation is a real bugger. I'll try to video tape a demo later today. Bud
Bud Krueger

The SunPro CP8500 video is now on YouTube. You can see it at http://youtu.be/ufgNWWzce14 . Hopefully, I'll have the video about the Dragon Gauge Digital up within an hour or so (I hope). Bud
Bud Krueger

Yikes! Here's the video showing the Dragon Digital AIR/FUEL gauge in operation. I've got to learn to work from a script. Ignore the obvious goofs like my forgetting how to read dvm (it's reading about .5 volts, not 5.5). At least I finally managed to figure out how to get something on YouTube. I haven't had a chance to try the Dragon unit in real operation yet since Lazarus' carburetors are on the workbench awaiting a new set of innards. Here you go http://youtu.be/2aHXbRy9cVE Bud
Bud Krueger

I like it! Thanks Bud!
JRN JIM

Good job on the video Bud,

Mort
Mort Resnicoff 50 TD (Mobius)

I'm really anxious to get it tied to a live O2 sensor. With luck my carburetor parts may be on Monday and I'll be able to get the system functioning by the end of the week. It was obvious that the SunPro system was not very accurate. I'm getting convinced that O2 sensors are designed to work into a very specific load for the system function to be satisfied. Bud
Bud Krueger

Bud,

You state the cost of the gauge (which is a very fine price indeed). However, does that also require a sensor? How much are those? I have a bung in the final collector of my 4-2-1 extractor with the hope of using it to dyno tune the engine at some point. I never purchased the parts as it was cost prohibitive at the time. Your comments indicate that things may have changed.

Alex
Alex Waugh

Right, Alex, the gauge is just to display the output of the sensor. A single-wire O2 sensor can be had for under $20. I'll get the model # for you in the morning. Bud
Bud Krueger

It's morning. The Bosch 11027 seems like a decent, basic, single-wire sensor and sells for about $17 at AutoZone. Bud
Bud Krueger

I went with an AEM system. They have a couple of analog versions that fit the TD dashboard style. I plan to install it when I get a new exhaust system.

Their web site is quite informative.

Jim

http://www.aemelectronics.com/wideband-air-fuel-systems-15/analog-wideband-air-fuel-gauge-31/
J Barry

This thread was discussed between 12/11/2013 and 21/12/2013

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.