Fluctuating clt and rising with rpms

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Spiffy
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Fluctuating clt and rising with rpms

Post by Spiffy »

Hi, I have this issue where the water temp isn't stable, when fully warmed up it will hover around 90* Celsius with fluctuations of 5-10 degrees. And when I give it some gas the indicated temp will start to rise, in the log you'll see it rising as the rpms rise. Up to around 100-110*C then it goes down when rpms drop

Anyone have any idea? Bad sensor or bad wiring?
It's a Bosch sensor. All other inputs are stable. This will lead to unstable injection won't it?
I'm away for the weekend so can't post my log but will do so when I get home tomorrow.

Engine is a Datsun 4cyl with l-jetronic injection converted to ms2

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Matt Cramer
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Re: Fluctuating clt and rising with rpms

Post by Matt Cramer »

Are we talking abrupt spikes for one record, or the coolant temperature gradually ramping up and back down? If it's the latter, I suspect that's what the temperature is really doing - but you're probably past the point where you need warm up enrichment.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Spiffy
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Re: Fluctuating clt and rising with rpms

Post by Spiffy »

Matt Cramer wrote:Are we talking abrupt spikes for one record, or the coolant temperature gradually ramping up and back down? If it's the latter, I suspect that's what the temperature is really doing - but you're probably past the point where you need warm up enrichment.
I'm no expert but it's ramping up and down with rpm's but not smooth like the intake temp for example. Spikes up and down.
Attached is an exerpt from my datalog from my last drive, clt is like this every time.
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Matt Cramer
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Re: Fluctuating clt and rising with rpms

Post by Matt Cramer »

That looks like noise all right. How's the sensor grounded?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
rickb794
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Re: Fluctuating clt and rising with rpms

Post by rickb794 »

Since it appears you have installed an MS2 with a L-jetronic harness, I would recommend carefully going over all circuits especially power distribution and grounding.
Using existing circuitry may not be compatible with MS.

MS pins 15-19 should not be grounded to the body, all 5 wires should be grounded at the motor.
With the MS unplugged there should be no continuity to ground on pins 1, 2, & 7 on the harness side of the DB37.
Power for the system should be direct from the battery through a main relay not the car harness.
Coil, fuel pump, injectors, and O2 sensor should be powered via the fuel pump relay.
Injector impedance is another concern, check it.
Non-resistor plugs cannot be used and low resistance wires are not recommended.

Much is covered in this post. http://www.msextra.com/forums/viewtopic ... 01&t=65757
And Section 3 of the hardware manual.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
Spiffy
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Re: Fluctuating clt and rising with rpms

Post by Spiffy »

Looking at the wiring scheme in the service manual it appears the coolant temp sensor isn't grounded via the ecu like the other sensors.
I'll have to physically check it to verify but regardless it's part of the same wiring harness so ground should be at the engine, but I'll have to take a closer look at the wiring harness. Maybe I'll just have to run a new ground for it

https://drive.google.com/file/d/0Bz5x7m ... sp=sharing
rickb794
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Re: Fluctuating clt and rising with rpms

Post by rickb794 »

Spiffy wrote:Looking at the wiring scheme in the service manual it appears the coolant temp sensor isn't grounded via the ecu like the other sensors.
I'll have to physically check it to verify but regardless it's part of the same wiring harness so ground should be at the engine, but I'll have to take a closer look at the wiring harness. Maybe I'll just have to run a new ground for it

https://drive.google.com/file/d/0Bz5x7m ... sp=sharing
A lot of OEM harnesses ground to the body, this is not recommended for MS.
Power from OEM harnesses is often noisy.

Some coolant sensors do not have a signal return and ground to the motor, I have used them successfully.
It is usually pretty easy to find an alternate sensor if the need arrises.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
Spiffy
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Re: Fluctuating clt and rising with rpms

Post by Spiffy »

Just a little revisit of this one, haven't done anything yet just wondering if placement of the sensor could contribute to the temperature rising?
The sensor is placed in the head just underneath intake runner 3 on the intake manifold. I wonder if I moved it to the thermostat housing like other cars if that could help?

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turbogrill
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Re: Fluctuating clt and rising with rpms

Post by turbogrill »

What sensor is it? Some of the standard sensors are a terrible match with megasquirt. Megasquirt has a 2.2kohm pull up, some sensor has the interesting operation point at a much lower ohm.

So a change in temperature will correspond to a tiny change in voltage. When you increase the rpm you typically get more noise.

With a properly matched tempsensor youncan ground to engine ground. (Sensor ground is prefered if possible).
Spiffy
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Re: Fluctuating clt and rising with rpms

Post by Spiffy »

I did a thing the other night and swapped the sensor for a straight 330 ohm resistor, this gave me a solid 84c water temp, until I started the engine and got driving. Then it started to fluctuate and rise with rpm. So it's likely a grounding issue.
I also heard that old Volvos suffer from this, they also use a ljetronic system. So I'm gonna cut the ground wire and rewire it to sensor ground and hopefully that will work.

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rickb794
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Re: Fluctuating clt and rising with rpms

Post by rickb794 »

Just be sure there is no continuity to ground at the sensor ground wire with the harness unplugged from the MS.

See 3.2 in the manual.

Some sensors may not have a sensor return (ground path) and use the motor (often these are early EFI or gauge sensors), if these cant be made to work swapping to a 2 wire sensor is in order.
You don't have to use all the same brand/model sensors as long as you are able to calibrate.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
Use only these manuals other manuals may cause brain damage or worse.
turbogrill
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Re: Fluctuating clt and rising with rpms

Post by turbogrill »

Autometer 2252 is a decent match for megasquirt. I used Autometer 2385 and engine ground, that was not a great combo. Temp would raise 10 F or so with RPMs. Switched to Autometer 2252 with engine ground and much better, but will rewire to use signal ground.

Autometer 2252:
At 212 F, 1 Farenheit is 0.015v, 0.01v noise would be 0.6 degrees

Autometer 2385 (common sensor)
At 210 F, 1 Farenheit is 0.003v, 0.01v noise would be 3.3 degrees

So with the second sensor you are much more sensitive to noise.
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