2.0 plenum issue, Can it be removed while in the car? Options

[robkammer]

Hi Fellas: I do not have a CHT gauge, nor an AFR gauge. Or a fuel pressure gauge either.
This engine has been a 2056 since way before I bought it in 21. Ran fine, not lean for the thousands of miles I've driven it. At full temp yesterday it settled into a nice idle once I adjusted the idle screw on the TB. I want to check the timing again just to be sure,
Does the CHT control anything other than the AAR? And what would an AFR tell me?

[emerygt350]

Hi Fellas: I do not have a CHT gauge, nor an AFR gauge. Or a fuel pressure gauge either.
This engine has been a 2056 since way before I bought it in 21. Ran fine, not lean for the thousands of miles I've driven it. At full temp yesterday it settled into a nice idle once I adjusted the idle screw on the TB. I want to check the timing again just to be sure,
Does the CHT control anything other than the AAR? And what would an AFR tell me?

The factory CHT in the car for the fuel injection is of course controlling the 'extra richness' needed for cool engine temps. The AAR is entirely its own thing and is just a 'idle up' adjustment that should close very rapidly. It is literally equivalent to the step idle on an old choke system on a regular car. Does nothing but open the throttle (without actually opening the butterfly, instead it is a vacuum leak elsewhere).

The CHT and gauge that we are asking about is normally a ring placed under the #3 cylinder spark plug and run to the cabin for a gauge like a Dakota Digital CHT. This tells you how hot the heads are getting by monitoring the hottest cylinder (3 is hot due to the cooling design on the passenger side bank).

The afr gauge tells you how lean the car is running. You want it lean at cruise and rich at WOT. The values people tend to shoot for is 12 - 12.5 at WOT and 16 or so at cruise (some people like being richer at cruise, some don't). All of this affects performance and more importantly heat.

Prolonged head temps above 400 can result in dropped valve seats, burnt valves, and pinging from lean mixtures destroy your engine.

Without the CHT you don't know how hot the heads are getting (the oil does not respond very quickly to increased head temps so your heads can be over 420F in a minute or two and your oil can still be 140F).

Built motors with higher compression (even a 2056) can result in excessive head temps pretty quickly.

Some people prefer the stress free no gauge approach. I like to get in front of things before they go south.
This is right after start up so the AFR in the lower right is still waiting for a signal it likes from the O2 sensor.

[Jack Standz]

Hi Fellas: I do not have a CHT gauge, nor an AFR gauge. Or a fuel pressure gauge either.
This engine has been a 2056 since way before I bought it in 21. Ran fine, not lean for the thousands of miles I've driven it. At full temp yesterday it settled into a nice idle once I adjusted the idle screw on the TB. I want to check the timing again just to be sure,
Does the CHT control anything other than the AAR? And what would an AFR tell me?

"Ran fine, not lean for the thousands of miles I've driven it."

How do you know this? How do you know if it's not running lean? (Yes, there are ways, but just curious how you know).

Also, not saying that you are incorrect, but would suggest (like Emery said) an AFR gauge will tell you if/when you are running lean or rich. And a CHT gauge will give you the information you need to prevent damaging those heads from overheating.

Many 914 owners run without an AFR gauge and/or a CHT gauge. However, running a modified Type IV motor (even a 2056) changes how your motor performs and what it needs to live a long life. Until you get it running right, keep an eye on head temps and your fuel/air mixture.

[robkammer]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

[emerygt350]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

I made that console gauge setup custom for my stuff. The original 3 gauge face is safely stored away.

The cht sensor for the gauge needs to be on the plug for accurate and immediate readings. The location of the djet sensor is deliberately distant so it does not change as quickly and will not read as hot as the plug. You need to know what the valve seats are experiencing so the plug it the right spot.

The MPS is how you tune it to match the motor. However, you can cheat it by simply adding resistance to the wire leading from the cht. It works but not as well as tuning the mps.

[robkammer]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

I made that console gauge setup custom for my stuff. The original 3 gauge face is safely stored away.

The cht sensor for the gauge needs to be on the plug for accurate and immediate readings. The location of the djet sensor is deliberately distant so it does not change as quickly and will not read as hot as the plug. You need to know what the valve seats are experiencing so the plug it the right spot.

The MPS is how you tune it to match the motor. However, you can cheat it by simply adding resistance to the wire leading from the cht. It works but not as well as tuning the mps.

Well, Everything I've read says to NOT mess with the MPS. Adding resistance is a bit beyond my comfort zone, especially since Radio Shack went away.
I've spent way more time with this car than I ever expected. We have no local gurus to help. My buddy took his 914 to our go-to guy, and he had it for almost 2 years and it's still not right.
Any advice will be be appreciated.

[robkammer]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

I made that console gauge setup custom for my stuff. The original 3 gauge face is safely stored away.

The cht sensor for the gauge needs to be on the plug for accurate and immediate readings. The location of the djet sensor is deliberately distant so it does not change as quickly and will not read as hot as the plug. You need to know what the valve seats are experiencing so the plug it the right spot.

The MPS is how you tune it to match the motor. However, you can cheat it by simply adding resistance to the wire leading from the cht. It works but not as well as tuning the mps.

Well, Everything I've read says to NOT mess with the MPS. Adding resistance is a bit beyond my comfort zone, especially since Radio Shack went away.
I've spent way more time with this car than I ever expected. We have no local gurus to help. My buddy took his 914 to our go-to guy, and he had it for almost 2 years and it's still not right.
Any advice will be be appreciated.

[rjames]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

O2 sensor typically gets mounted on the collector before it enters the muffler.
Others have mounted it elsewhere. Where you put it may depend on your exhaust setup.

For the most part, adjusting the MPS is the how you change the mixture. Tangerine Racing makes a toolkit that isn't expensive to make ajusting it easy.

[Jack Standz]

Thanks. I typically pull the plugs at each oil interval to check the burn. Where would I mount the O2 sensor to feed the AFR? I would consider doing a stealth install for the gauges, but not mess with the stock console setup. Could the cht ring be mounted under the cht sending unit rather than the spark plug? And finally, maybe, if the motor was to run lean or hot, how would I tell the ECU to change the mixture?

I made that console gauge setup custom for my stuff. The original 3 gauge face is safely stored away.

The cht sensor for the gauge needs to be on the plug for accurate and immediate readings. The location of the djet sensor is deliberately distant so it does not change as quickly and will not read as hot as the plug. You need to know what the valve seats are experiencing so the plug it the right spot.

The MPS is how you tune it to match the motor. However, you can cheat it by simply adding resistance to the wire leading from the cht. It works but not as well as tuning the mps.

Well, Everything I've read says to NOT mess with the MPS. Adding resistance is a bit beyond my comfort zone, especially since Radio Shack went away.
I've spent way more time with this car than I ever expected. We have no local gurus to help. My buddy took his 914 to our go-to guy, and he had it for almost 2 years and it's still not right.
Any advice will be be appreciated.

OK, you asked for advice.

The obvious answer to your question is: Find a better "go-to-guy". Two years working on your buddies 914 and didn't fix the problem? Really? Suggest he become your "never-go-to" guy.

[emerygt350]

I am about 6 hours from you, otherwise I would love to help. Adding the resistor is super easy, that is what Porsche did with the 73 2.0. Rather than make a new ECU they put a a 1.7 ECU in it and put a 250ohm resistor inline with the cht. 10minutes and a couple of quick connects and you are ready to go. The other thing they did was put a spacer in the mps and then tuned it for the larger displacement. This is the kind of stuff that is very easy to do

To tune the mps you need the awesome kit from tangerine (it's just a plug with a hole in it and a cool little screwdriver tool) and an Afr gauge. My O2 sensor is mounted on the inlet on cylinder 4 into the muffler. I didn't want to mess up my nice heat exchangers.

That said, at this point it would be helpful for a good description of how it is running. What is the warm up behavior? How long before it is off the cold circuit and idling at 950? How does it perform in acceleration and at cruise? What mpg are you getting at cruise and what are you getting for normal town driving? Does the idle hunt? Where is the pot set on the ECU?

[robkammer]

Thanks Emery: Car starts instantly and idles well for 2 minutes, then starts to stumble but does not die. Any throttle tip-in will cause it to want to quit unless I open it pretty wide. Tried to drive it and it is not driveable. To experiment, while it's running I unplugged the CHT and it was like a kill switch. Would not restart but I could smell fuel.
The head temp was right about 110F , and the CHT resistance was also about 110 ohms.
The CHT is new, but I do have the old one if it makes sense to swap. I'm surprised at the hard fail caused without the CHT in circuit and the reliance on the sensor. This must point to something, but I can't find it on any documentation.
I need to make the tool to remove the sensor if it makes sense.
Stumped.
6 hours away? If you're willing I could do that.

[FlacaProductions]

Have we confirmed fuel pressure? The starting ok and then and ok idle - for a while - and then dying with accelerator tip-in makes me wonder about a dirty/clogged fuel line/filter...gunk settles overnight but gets stirred up and sucked into a filter at start. Rinse/repeat.

[emerygt350]

The car will not run without the signal from the CHT. The injectors just won't fire at all so that is normal behavior.

It does sound a like an air fuel mixture issue.

[robkammer]

My thoughts also. Just ordered a gauge from Summit. My filter is a few years old and worth looking at, but it ran fine before I pulled the engine. Now a search for a filter will begin. I seem to recall the filter has two nipple sizes and it was difficult to source when I put in the car in 21. Hopefully it still has a part number on it.Have a nice weekend.