Strange Coolant Temperature Sensor problem ***and overall wellness thread!

[FunkySwerve]

I've recently purchased an E30, the coolant temperature sensor was disconnected. Didn't pay it any mind, assumed it'd be an easy fix. Well, it hasn't been for me!

On top of this I've recently failed smog emissions by a small margin above the max(NoX).

I'm not quite sure if this has anything to do with it, but I'd like to get it squared away nonetheless!

In one of the pictures you will see the coolant temperature sensor that is unplugged. Well, I can't seem to find the wiring to it and in addition to that, it has a 325e yellow sensor on it as well(????).





The block is a 2.5 for sure as it's stamped, could the head and cylinder block been changed? Or even the sensors were swapped out for some reason? Either way I'm not finding the connecting cable.




Thank you in advanced!

[betsy325e]

1. That 2.5 in the photo is stamped on the head, not the block. You're confusing me.

As for switches as if they were from an Eta:

The one farthest towards the front of your car is the thermo-time switch. Not the temp. sensor. People disconnect these when they get cold start valve issues, like a valve that won't close, etc. After the first 8 seconds of start up on a cold day this connector ain't doin much of anything. Def. ain't doin anything if you haven't got a cold start valve on the manifold anymore, which it looks like you haven't.

Second two spade connector is the coolant temperature switch -- closes at such and such degrees (I think 112, 120F, can't remember) letting the idle control module in your car know the car is warmin' up. There should be two shitty little spade connectors for this somewhere in that harness. With the swap done these probably ain't doin' shit if they changed over from motronic 1.0. Not too familiar with the engine management on "i"s, but I want to say they got rid of the coolant temp switch.

Take a peek in your glovebox and see what sorts of #s you got on your ECU or just count the number of pin connections. Also look for a black/green/blackwithgreentapeonit box up in the glove box under the dash and see if the previous owner removed it.

Based on your other pictures your temp. sensor to dash (brown connector 1-prong) and coolant temperature sensor (whitish brown, closest to firewall) are connected. Those you'd obviously still need. So everything seems good.

Also, you've got what looks like a 3.0 bar (for an "i") instead of the 2.5 bar (eta) FPR in the photo.

2.5 head swap to a m20b27 eta block is pretty standard fare.

[101]

^^^ what betsy325e said.

Someone probably swapped the thermostat housing at some point with one from an eta. Those first two sensors are for an eta only (thermo time switch and 45'C idle control module switch) and will not have any wiring in the "I" harness.

Forget about them - or if it bothers you - you can remove those sensors and order brass plugs to install instead. And then sell the removed sensors and maybe the idle control module to me at a reduced price in return for this sage internet advice.

Make sure you have the remaining two sensors connected to the correct plugs. One has one wire and one has two. Ask me how I know.

[FunkySwerve]

Thank you guys for taking the time to respond! So I'm assuming this wont affect my NoX emissions much? Lol

Forgive me I'm still new to these things, the E30 I bought previous was very clean and require little work at all.

Just to piggy back on the subject, here are my smog test results:

[101]

Kalifornia smog testing. You have my sympathies. I did find this on the interwebs. Interesting reading!




NOx can be formed by many component failures and system malfunctions - anything that allows the combustion chamber temperature to exceed 2300 degrees Fahrenheit. For example, if the cooling system is utilizing pure water, it will absorb combustion heat and obtain its boiling point rapidly, leaving an air pocket around the combustion chamber. The air pocket will become a hot spot allowing for the combustion chamber temperature to rise. Equally bad is 100% antifreeze, which forms a blanket around the combustion chamber, keeping heat in and allowing the combustion chamber temperature to rise.

Rust surrounding the cooling jacket surface will create the same blanket around the combustion chamber. Poor flow through the radiator, as a result of a blockage or poor circulation, or a partially closed thermostat or limited flow from the water pump, will prevent the high temperatures from escaping through the cooling system. This temperature increase will cause preignition, allowing the oxygen to prematurely oxidize the hydrogen, reducing the available air and fuel during spark ignition. As a result, oxygen will be limited to complete the oxidation of the hydrogen and formation of carbon and oxygen into carbon dioxide will be limited. In this case the gas meter will read high HC, low CO, low 02, low C02, and high NOx.

As the piston rises during the compression stroke, the opposite force of compression in the upward direction and the downward force created as a result of preignition will cause the piston to rock, slapping the piston skirt against the cylinder wall, causing a knock. As a result of an engine knock, we should see the scanner knock reading indicate yes, with a command to retard ignition timing. The secondary ignition scope should have a higher than normal firing line. With excessive preignition, the early flame front comes in contact with the spark ignition flame front. This will result in high HC, low CO, high 02, low C02, and high NOx. The horsepower of the engine will suffer as well.

A lean condition as a result of a false signal from the oxygen sensor, an out-of-calibration MAP sensor, plugged injector, low fuel pressure, low fuel pump volume, or a vacuum leak will cause NOx as well. Under these conditions the oxygen will oxidize the hydrogen and the carbon, creating extreme combustion chamber temperature. This acts much like a cutting torch used to oxidize the carbon atom of the metal. As the temperature climbs the nitrogen atoms will separate and form with the oxygen atoms to create NOx. As the oxygen is used to form NOx, the oxygen will be used up, causing a lot of hydrocarbons to be unused.

The gas analyzer will read high HC, low C0, high 02, low C02, and high NOx. The secondary ignition scope should have a higher than normal firing line, and longer than normal spark duration. The scanner would read zero to low oxygen sensor voltage and a lean condition. As a result of running lean, the additional HC from a richer mixture is not there to absorb the heat. Therefore, the CO molecule needed in the catalytic converter to cause the catalyst to reduce minor levels of NOx to nitrogen and carbon dioxide will not be created. In no way will a catalytic converter reduce excessively high NOx levels.

Carbon build-up on top of the piston or on the cylinder walls may also cause preignition. This would give similar results to the cooling system issue. The carbon build-up could be as a result of running extremely rich for any length of time. Therefore, when repairing high CO emissions failures, always assume that carbon has formed. This type of carbon can even be caused by oil consumption, which will also cool the combustion chamber temperature. Carbon on the throat of the valve will absorb fuel, causing a lean condition and giving a similar result as to the previous lean condition. This type of diagnosis may require a borescope to visually inspect pistons, cylinder bores or valves. To repair this, a chemical top end cleaner may help. If the vehicle is not running rich, the gas analyzer will read high HC, low CO, high O2, low CO2, and high NOx. The reason for the high O2 is that the carbon will assimilate a lean ignition misfire. The scanner would read low oxygen sensor voltage. The secondary ignition scope should have a higher than normal firing line, and a possible appearance of second firing line in the spark line.

A worn or slipping timing belt can certainly increase internal temperatures. If the timing belt or timing chain has excessive slack, the cam timing will be retarded. The camshaft will be behind the crankshaft resulting in the camshaft lobes not opening the valves in the proper relationship to the piston. The intake valves during the intake stroke will open late, causing the air to continue entering the cylinder later than required. As a result, the compression pressure will increase at the top of the compression stroke and temperature will reach its maximum later on into the stroke causing a longer oxidation period which results in extreme combustion temperature. As a result of late intake valve opening, the vacuum will be low, causing the MAP sensor to see a load adding more fuel, causing high CO. The gas analyzer will read high HC, high CO, low O2, low CO2, and high NOx.

If the base timing is advanced too far, the spark plug will ignite the air fuel mixture early, causing the combustion temperature to rise as the compression stroke continues, causing NOx to form. With a very early flame front in the compression stroke, as a result of advanced ignition timing, the temperature created as a result of early oxidation will cause the temperature created during compression to rise extensively.

The exhaust valve seating surface is not just to seal the cylinder airtight, but to provide a means of removing heat from the valve and disbursing it to the cooling system. An exhaust valve that is improperly seated will not transfer heat. As a result, the valve and its seat will rise in temperature, causing preignition. This will result in high HC, low CO, high O2, low CO2, and high NOx.

So as you can see, excessive NOx is caused by high internal temperatures. Unfortunately, there are any number of factors that can increase combustion chamber temperatures past the magic 2300 degrees. Fortunately, with your trusty five gas analyzer and a little reasoning ability, you're in great shape to isolate the problem, replace the faulty components or make adjustments as needed, and send the motorist on their way with a better performing and lower polluting vehicle.

[jlevie]

I'd like to add a bit to 101's excellent post.

You have high HC and high NOX. I'd start by attacking the high HC problem, which could be due to:

Excessive fuel rail pressure from a bad FPR.
Sticking/leaking injectors.
Misfiring from bad/wrong plugs, bad ignition wires, rotor, and cap.
Misfires from an upset in the A/F ratio.
Misfires from an engine running cold (or the DME thinking that it is).

My actions would be to tee in a pressure gauge on the rail supply line and zip tie the gauge to the cowl vent or wiper. The see what happens at idle and while the car is being driven. If the pressure is off, replace the FPR with an OE or OEM part. Then I'd pull the injectors and send them to RC Engineering for rebuild and flow testing. I'd replace the ignition wires rotor and cap with OE or OEM parts and install a fresh set of NKG ZGR5A plugs. I'd also check or replace (with OE or OEM) the engine cooling temperature sensor. The AFM could be bad, but I'd consider that last. Oh yeah, adjust the valves and verify cam timing and run compression and leak down tests.

You should also verify that the engine is reaching normal (80C) temperature and possibly replace the thermostat. And have a smoke test run to check for intake leaks. If the O2 sensor has 100k on it, replace it with an OE or OEM part. The sensor is a scheduled maintenance item that needs to be replaced every 100k.

Once the high HC problem is fixed, the high NOX problem might go away. Whether it does depends on what was causing the high HC and how long the engine has been running rich. If the NOX problem doesn't go away the catalytic converters need to be replaced. Excessive HC can destroy the catalytic converters pretty quickly.

The upside to all of this is passing the emissions test and finding that the engine runs a lot better. It will be well worth what it will cost.

[FunkySwerve]

Thank you all for the detailed responses! I'm going to start working on the above listed, little by little through out the week. Again thank you for taking the time to reply.

On the subject: I know what a bad distributor and rotor looks like, what do good ones look like?

***Also: my coolant temperature gauge isn't working, possible maladies?

[jlevie]

The coolant temp guage could be a bad connection to the PCB in the cluster, a bad SI board, a bad sensor, or a fault in the engine harness.

[FunkySwerve]

The coolant temp guage could be a bad connection to the PCB in the cluster, a bad SI board, a bad sensor, or a fault in the engine harness.

Does that effect operation of the vehicle? In what ways?

[jlevie]

Does that effect operation of the vehicle? In what ways?

No. There is another sensor that furnishes engine temperature data to the DME.

[FunkySwerve]

While inspecting the sensors on the thermostat housing I found this:


The colors don't correspond, should I be concerned/does it need to be switched and spliced?

[101]

I don't get too hung up on the colors. I've seen coolant temperature sensors in brown, blue and white, and the corresponding connector in both blue and brown.

Does the sensor test correctly? It has varying resistance depending on the coolant temperature. If not, or if the sensor looks to be original, I'd replace it. It's a $9 part and a 5 minute job.

[FunkySwerve]

I don't get too hung up on the colors. I've seen coolant temperature sensors in brown, blue and white, and the corresponding connector in both blue and brown.

Does the sensor test correctly? It has varying resistance depending on the coolant temperature. If not, or if the sensor looks to be original, I'd replace it. It's a $9 part and a 5 minute job.

Thank you again 101! Yet again, I have another question: before the car was sold to me I was told the transmission seal was leaking. It has been leaking slowly since I've gotten it so I know this to be an issue. Is this something I can do myself or so I have to submit myself to the will of overpaying to get it done?

[101]

automatic or manual?

front or rear seal (or other?)

If its a front seal, that's going to be a transmission pull. If its a rear seal, You'll need to remove the exhaust system, the heat shields and the driveshaft. I've not done a transmission seal job myself, so perhaps others can chime in with their thoughts.

[jlevie]

What 101 said. Which end of the transmission is leaking. If the rear, the leak could be from the output shaft seal or the selector shaft seal. Both of those can be replaced w/o removing the transmission.