correct value for warm CHT reading (ohms) Options

[brant]

so my CHT reading was 76 ohms - hot (at 180F oil temp)
I'm reading 2 different things.. on the Brad anders site


one saying that a warm reading should be below 100 ohms
but then the table shows this: for 210F

Sensor Temp = 39 deg. F Temp = 61 deg. F Temp = 210 deg F

0 280 130 003 6.10 K ohms 2.94 K ohms 199.3 ohms
0 280 130 012 NA 2.85 K ohms 191.2 ohms
0 280 130 017 3.63 K ohms 1.74 K ohms 124.7 ohms



I'd love some input from Djet folks about what numbers you see on a warm motor?

brant

[JamesM]

so my CHT reading was 76 ohms - hot (at 180F oil temp)
I'm reading 2 different things.. on the Brad anders site


one saying that a warm reading should be below 100 ohms
but then the table shows this: for 210F

Sensor Temp = 39 deg. F Temp = 61 deg. F Temp = 210 deg F

0 280 130 003 6.10 K ohms 2.94 K ohms 199.3 ohms
0 280 130 012 NA 2.85 K ohms 191.2 ohms
0 280 130 017 3.63 K ohms 1.74 K ohms 124.7 ohms



I'd love some input from Djet folks about what numbers you see on a warm motor?

brant

I believe the discrepancy may be due to (among other things) what can be easily measured on the bench vs installed in a car. The 210 readings were provided because that is a temp point that can easily be measured with the sensor off the car using boiling water

however:

1. The sensor resistance curve doesn't stop at 210 degrees
and
2. Our heads get a lot hotter than 210 degrees in practice.

So take a resistance reading off a sensor installed in a car on a fully warmed motor you are most likely going to see less resistance than the stated 210 deg value, and is going to vary a bit depending on the current temp of the motor.

Also, not sure what the factory tolerance was but I have always seen some level of variance when measuring both CHT and MPS sensors (the two main influencing variables on mixture for d-jet) even across identical part numbers.

Another point of note is that with a single wire sensor the ultimate reading is also dependent on the resistance over the motors ground path which can vary while the car is in operation.

I didnt hang on to the data but I measured every CHT and MPS from my collection with Eric to get baseline data when PMB was putting together their MPS rebuild program, the results were interesting...

They install modern ECUs now (IMG:style_emoticons/default/biggrin.gif)

Bottom line, if you want consistently accurate fueling go with a modern setup.

[brant]

James,

super glad for your input.

I may be chasing nothing.
my plugs look a bit lean
and so far everything is testing spot on
car actually drove great (to santa fe and back to colorado for the RT66)

but my CHT gauge quit working and I pulled the thermo coupler to check it at the event.
noticed that plug was a bit lean... so pulled the other plugs and they are all the same.

I'm going to put the Innovate on it today and see what the actual AFR's are running at warm...

I'm guessing I might have to re-tune the MPS
however, it tested great last night and I see no reason for the car getting "leaner" as the plugs showed.

I will see what the AFR's look like
just seemed like the most likely thing could be a failing CHT sender... but it tests good hot and cold so maybe not....

[JamesM]

Usually when I have seen issues with CHTs or MPS failing things go RICH

Leaky MPS reads as higher load= rich
Increased resistance or BROKEN wire on the CHT circuit = rich

The CHT circuit SHORTED to ground could possibly cause a lean condition, but if that was the case you would most likely notice your car running like complete crap during warmup.


I have never been to confident in my plug reading beyond an engine being obviously rich or lean, Wideband is a good idea for accuracy however you may have a hard time getting the full picture with an instantaneous reading off a gauge as its most likely going to bounce around a bit, I prefer full datalogs to see what is going on over wider operating conditions, but either way should be better data than looking at the plugs

For some reason my gut is saying something with the fuel especially given it sounds like nothing else has changed and its running without noticeable issues....

Gas with any ethanol in it you want to run a couple points richer. Winter/summer blends can burn differently from each other as well as can different brands depending on the additives.

Have you checked your fuel pressure? Unless you have already opened up your MPS, bumping up the fuel pressure a bit may be an easier/safer way to get it slightly richer as MPSs can be a bit touchy, especially if you want to get it back to your prior settings.

Thats a bummer about the head temp gauge. I was going to say if its running good and the head temps are in a safe range I probably wouldn't worry about it. D-jet tends to float around a bit depending of if a fly happened to fart in your engine compartment on any given day (IMG:style_emoticons/default/tongue.gif)

My purple 1.7 car still has d-jet, I run it with zero gauges of any sort as to not obsess about how its running, otherwise I would probably go insane.

[brant]

I'm in agreement with everything you said.
I was re-reading anders last night... and he did say occasionally the CHT will fail with a ground and go 30% lean....

so that was the idea I was chasing.
but 76ohms hot sounds like it could be within tolerance.

I checked timing, fuel pressure, MPH-vacuum, and CHT(hot/cold) last night and everything was perfect. I thought about bumping my fuel pressure as one solution. But decided I needed to see the AFR's before I made any changes. In the past I had tuned this MPS and the AFR's were spot on. I even tuned a 2nd MPS at the same time, and may need to dig that one out of storage to do some more testing


unfortunately... I had a few beers in my wrenching last night.. so put off road testing until tonight...

should know more soon
and possibly, I'm chasing nothing... other than a plug that as you pointed out... is hard or inaccurate to read anyways.

[brant]

New Bosch sensor
New calibration

Fine at idle
Mid to High 12’s from 3k to 5900 rpm

A bit lean. But not much..? At light throttle... highway cruising 80-90mph steady for multiple miles
13.7 to low 14.0. It starts out better but steadily climbs over a mile or two...to that number

I’ll have to research more
What is your goal for steady light throttle?

Oh. And my head temp gauge is now working for no apparent reason
I took the thermo ring out last night for visual inspection. Now it works

[JamesM]

WOT numbers sounds pretty good, especially if you are still holding in the 12s under load at 5900RPM

Are you running a stock cam? All my stock cam cars are done making power well before 5900.

When im tuning Megasquirted cars I usually have the AFR targets set mid 12s under load and mid-high 13s cruise, though i have suspected i could probably lean out the cruise area a bit more. I usually try to keep it out of the 14s unless in overrun but with the thin, hot, dry, air in salt lake I try to error a little on the rich side to help the head temps.

If your head temps are good I would say your numbers are fine.


Around here with my 2.0 d-jet cars (that do have temp monitoring) its not uncommon
for me to see 380-390 (depending on the day) at the #3 plug pushing it on the freeway.

My cam'd high compression 2056 Megasquirt car usually runs ~50 deg cooler

[914_teener]

Stock dizzy?

[Montreal914]

When im tuning Megasquirted cars I usually have the AFR targets set mid 12s under load and mid-high 13s cruise, though i have suspected i could probably lean out the cruise area a bit more. I usually try to keep it out of the 14s unless in overrun but with the thin, hot, dry, air in salt lake I try to error a little on the rich side to help the head temps.


Around here with my 2.0 d-jet cars (that do have temp monitoring) its not uncommon
for me to see 380-390 (depending on the day) at the #3 plug pushing it on the freeway.

My cam'd high compression 2056 Megasquirt car usually runs ~50 deg cooler

Thank you for the data, (IMG:style_emoticons/default/beerchug.gif)

[brant]

Stock dizzy?

this motor was Jason's from AZ
he had it built... and when I bought it from him it was a full Djet motor
he told me the shop had put a "mild" FI cam into it, but don't know which one
I don’t think it would be a raby cam. Probably a webcam

the cam absolutely runs out of lift at 5900
I never typically shift above 5600 as there is no reason
but I rode it out... for the purpose of seeing what the AFR did.

its stock dizzy... all stock injection... the only modification is to the ignition with a Hall Effect, pick up... and a crane/highwire (?) CDI type box.

I'm betting the slightly lean highway condition is the reason I get 32MPG @85

but that I can improve on it some...
I also now believe that my plugs are fine... and yes I might be seeing a tiny bit of a lean condition on the highway.. but doubt the plugs can even show much difference

brant

[brant]

Thank you again .. james , everyone, world.
Good to run ideas past others

[brant]

WOT numbers sounds pretty good, especially if you are still holding in the 12s under load at 5900RPM

Are you running a stock cam? All my stock cam cars are done making power well before 5900.

When im tuning Megasquirted cars I usually have the AFR targets set mid 12s under load and mid-high 13s cruise, though i have suspected i could probably lean out the cruise area a bit more. I usually try to keep it out of the 14s unless in overrun but with the thin, hot, dry, air in salt lake I try to error a little on the rich side to help the head temps.

If your head temps are good I would say your numbers are fine.


Around here with my 2.0 d-jet cars (that do have temp monitoring) its not uncommon
for me to see 380-390 (depending on the day) at the #3 plug pushing it on the freeway.

My cam'd high compression 2056 Megasquirt car usually runs ~50 deg cooler

Absolutely not trying to be negative

I hope you have a cooler on those cars
Those are pretty high head temps. I typically run 300 max. But have seen 340+ a hair
(On the track worse)

I have a long standing theory. That the Djet cars that were kept running.. over heated their cylinder heads... and dropped valve seats with the gas changes. Thus the negative stories.

[JamesM]

WOT numbers sounds pretty good, especially if you are still holding in the 12s under load at 5900RPM

Are you running a stock cam? All my stock cam cars are done making power well before 5900.

When im tuning Megasquirted cars I usually have the AFR targets set mid 12s under load and mid-high 13s cruise, though i have suspected i could probably lean out the cruise area a bit more. I usually try to keep it out of the 14s unless in overrun but with the thin, hot, dry, air in salt lake I try to error a little on the rich side to help the head temps.

If your head temps are good I would say your numbers are fine.


Around here with my 2.0 d-jet cars (that do have temp monitoring) its not uncommon
for me to see 380-390 (depending on the day) at the #3 plug pushing it on the freeway.

My cam'd high compression 2056 Megasquirt car usually runs ~50 deg cooler

Absolutely not trying to be negative

I hope you have a cooler on those cars
Those are pretty high head temps. I typically run 300 max. But have seen 340+ a hair
(On the track worse)

I have a long standing theory. That the Djet cars that were kept running.. over heated their cylinder heads... and dropped valve seats with the gas changes. Thus the negative stories.

Na no cooler, they are bone stock. Around town driving they are fine and dont ever see over 350, they only get up into the pucker temps if im pushing them pretty hard for extended periods at higher speeds on hot days so I just try and drive mindfully. I dont like them being that high but every stock d-jet 2.0 i have ever had runs similar temps around here. Temps were better when i lived in California and usually stayed closer to the 325 range, I just think the Germans didnt design these things to be driven at a sustained 85+ MPH in 100+ degree weather at altitudes where you only have 85% of the cooling air density. its pretty much worst case scenario for air cooled sports cars around here. Haven't been able to blow one up yet though so I just keep pushing them as is. After having abused type 4s for 20 years I have come to the conclusion that well built/maintained ones are a lot more durable than people give them credit for.

These readings are all from VDO gauges though so who knows how accurate they actually are. In the process of swapping them out for Dakota Digital ones.

Was really happy to see the temps my built 2056 runs at, have read for a long time that the stock d-jet cam runs the heads hot but I was still surprised to see the difference though given how much more power the 2056 is putting out.


You may be right about the gas killing motors, or at least accelerating their death, it absolutely makes a difference at least from what I have seen. Nearest corner gas station to my house sells 88 Ethanol free so i almost always run that however its noticeable when I don't, especially if I drive further up in the mountains. Started having vapor locking problems a few years ago seemingly out of the blue and eventually figured out the gas I put in the car had a lot to do with it. Ethanol free, no problem. Standard pump gas though when i would get over about 10,000 ft elevation would almost always without fail start boiling the fuel in the lines. Wound up relocating the pumps so I could go on longer trips and not have to worry about finding good gas.

[914_teener]

Stock dizzy?

this motor was Jason's from AZ
he had it built... and when I bought it from him it was a full Djet motor
he told me the shop had put a "mild" FI cam into it, but don't know which one
I don’t think it would be a raby cam. Probably a webcam

the cam absolutely runs out of lift at 5900
I never typically shift above 5600 as there is no reason
but I rode it out... for the purpose of seeing what the AFR did.

its stock dizzy... all stock injection... the only modification is to the ignition with a Hall Effect, pick up... and a crane/highwire (?) CDI type box.

I'm betting the slightly lean highway condition is the reason I get 32MPG @85

but that I can improve on it some...
I also now believe that my plugs are fine... and yes I might be seeing a tiny bit of a lean condition on the highway.. but doubt the plugs can even show much difference

brant

My thought was this Brant:

The stock dizzy, and I'm assuming yours still uses the trigger points to fire the injectors,makes a huge difference with regards to wear and alignment of those things as far as injection pulse goes. That'd be my experience.

I too , am surprised that yours still makes any power at or even near 5900K


With regards to compression...according to Raby he never recommended to go over 8.5:1 when running D-jet, so I don't know what yours is. That what I remember hearing. Not to mention heads.....they are the heart of a T4 and its weakest link.


In any case, I eventually ditched the stock dizzy for reliablilty sake. No more points and no more trigger points.

Car ran like a top after I got the mixture right. I saw variations up to 9k feet when driving in the local mountains but not at sustained speeds up there on the top of the Mogollon plateau like you do.l

I don't know what you can do other than that and or a potentiometer on the CHT lead.

Those be my .02.

[brant]

Stock dizzy?

this motor was Jason's from AZ
he had it built... and when I bought it from him it was a full Djet motor
he told me the shop had put a "mild" FI cam into it, but don't know which one
I don’t think it would be a raby cam. Probably a webcam

the cam absolutely runs out of lift at 5900
I never typically shift above 5600 as there is no reason
but I rode it out... for the purpose of seeing what the AFR did.

its stock dizzy... all stock injection... the only modification is to the ignition with a Hall Effect, pick up... and a crane/highwire (?) CDI type box.

I'm betting the slightly lean highway condition is the reason I get 32MPG @85

but that I can improve on it some...
I also now believe that my plugs are fine... and yes I might be seeing a tiny bit of a lean condition on the highway.. but doubt the plugs can even show much difference

brant

My thought was this Brant:

The stock dizzy, and I'm assuming yours still uses the trigger points to fire the injectors,makes a huge difference with regards to wear and alignment of those things as far as injection pulse goes. That'd be my experience.

I too , am surprised that yours still makes any power at or even near 5900K


With regards to compression...according to Raby he never recommended to go over 8.5:1 when running D-jet, so I don't know what yours is. That what I remember hearing. Not to mention heads.....they are the heart of a T4 and its weakest link.


In any case, I eventually ditched the stock dizzy for reliablilty sake. No more points and no more trigger points.

Car ran like a top after I got the mixture right. I saw variations up to 9k feet when driving in the local mountains but not at sustained speeds up there on the top of the Mogollon plateau like you do.l

I don't know what you can do other than that and or a potentiometer on the CHT lead.

Those be my .02.

great 2 cents!
and I know I've never adjusted the trigger points.
they have to be 50 years old by now
so a very good idea of something to check

did you go with the blue tooth/fancy new distributor that everyone is using?

brant

[914_teener]

Stock dizzy?

this motor was Jason's from AZ
he had it built... and when I bought it from him it was a full Djet motor
he told me the shop had put a "mild" FI cam into it, but don't know which one
I don’t think it would be a raby cam. Probably a webcam

the cam absolutely runs out of lift at 5900
I never typically shift above 5600 as there is no reason
but I rode it out... for the purpose of seeing what the AFR did.

its stock dizzy... all stock injection... the only modification is to the ignition with a Hall Effect, pick up... and a crane/highwire (?) CDI type box.

I'm betting the slightly lean highway condition is the reason I get 32MPG @85

but that I can improve on it some...
I also now believe that my plugs are fine... and yes I might be seeing a tiny bit of a lean condition on the highway.. but doubt the plugs can even show much difference

brant

My thought was this Brant:

The stock dizzy, and I'm assuming yours still uses the trigger points to fire the injectors,makes a huge difference with regards to wear and alignment of those things as far as injection pulse goes. That'd be my experience.

I too , am surprised that yours still makes any power at or even near 5900K


With regards to compression...according to Raby he never recommended to go over 8.5:1 when running D-jet, so I don't know what yours is. That what I remember hearing. Not to mention heads.....they are the heart of a T4 and its weakest link.


In any case, I eventually ditched the stock dizzy for reliablilty sake. No more points and no more trigger points.

Car ran like a top after I got the mixture right. I saw variations up to 9k feet when driving in the local mountains but not at sustained speeds up there on the top of the Mogollon plateau like you do.l

I don't know what you can do other than that and or a potentiometer on the CHT lead.

Those be my .02.

great 2 cents!
and I know I've never adjusted the trigger points.
they have to be 50 years old by now
so a very good idea of something to check

did you go with the blue tooth/fancy new distributor that everyone is using?

brant

Yea...I did. Pricipally because I couldn't find a non-leaking advance canister and didn't want to waste $110 bucks on a new set of trigger points.

I was having similar symtoms as you are now. I never did install the new thermister for the CHT that McMark used to make. I think 914 Rubber sells them now though.

Missed you on the ole R66. No 914 on that trip for me. I'm getting old so I took a water pumper instead.... (IMG:style_emoticons/default/slits.gif)