JhnRX7

My Z has been acting up lately and has started getting really bad lately.

First: Start-up issue

When you first start it cold the air bypass valve is supposed to open causing a high idle for warm up. When I start the z the idle is around 900 RPM and it is ideling relatively smooth. However, if you try and give it gas it will not take any. It wont rev past 1500 RPM without flooring it. (keep in mind when it does this it is like something is holding the motor back, its not stuttering or hesistating at all) After about a minute of low ideling it works its way up to 1500 RPM as it should and slowly drops down as the car warms up as it should. The Air Bypass Valve is brand new.

Second:

While crusing on the highway I have been getting alot of hesistations between 1500 RPM and 3000 RPM. This only happens under light throttle, not WOT.

I checked for the flashing light under the ECU and that was OK. I suspect one of the sensors to be causing some of this. I cleaned all of the connections, but no change. I have noticed one thing that might be a problem: There are 3 sensors on the thermostat housing. The water temp sensor that has a 2 wire connector. The sensor for the gague cluster which has a bullet connector directly on the sensor. And another sensor that has one wire coming out of it which leads to a bullet connector. I am not sure what that last sensor is (i believe it might have something to do with the ignition), but the wire looks like it is about to fall off right where it meets the sensor. I cannot find the name of that sensor anywhere nor can i find where to get a new one.

In general the car seems to be lacking power and the gas mileage has decreased since all of this started.

First off can anyone help me identify that sensor (ill take a picture after work tonight). And would this sensor explain any of my problems.

Any other input would be appreciated.

Thanks

NismoPick

Have you checked the timing? Vacuum lines? O2 sensor? AFM? TPS? Cold start valve? Those would be the main causes of a rough idle. AFM / TPS / O2 sensor / worn plugs, wires, cap, rotor could also cause loss of power.

Indeed... take a pic of the thermo housing so we know which sensor you mean.

JhnRX7

The idle is actually very smooth and consistant. The problem is that for the first minute the car is on, the idle is low and the car will not respond to throttle. It just sort of bogs down when throttle is applied.

I did check the ECU and I got the blinking light so the O2 sensor seems to be working. I actually have a new one on the way right now anyway. Vacuum lines look good, they are all new. Air Bypass Valve (cold start valve) is brand new OEM part. Cap and rotor are brand new. Plug wires look good. I pulled the AFM and the inside is nice and clean and the flapper swings freely, however there is silicone holding the black cover on so it looks like someone has tried to adjust it at one point. I need to check TPS.

Pics will come after work.

JhnRX7

Sorry, I was thinking the cold start valve was the bypass valve not the injector.

The cold start valve only supposed to be activated while the starter is cranking. So if for some reason it continues to fire after the car starts it would make the mixture rich causing the engine to possibly bog down?

I will try and disconnect this and start the car and see if there is any difference.

NismoPick

The cold start valve & air regulator (Air Bypass Valve) are two different things. The CSV sprays fuel into the intake when cold. The air regulator allows more air into the intake when cold. Check the CSV.... it's likely not spraying.

Did you check the actual spark plugs? And yes, the AFM has probably been tampered with if there is silicone around the cover. If they didn't know what they were doing, they probably made it worse than better.


EDIT... ah, I see you figured it out.

JhnRX7

I was really hard to get this picture with the upper radiator hose in the way.

This sensor is located about where the Thermotime switch is, however my sensor obviously looks different. That picture was taken from the fuel injection bible so that is not an 83 thermostat housing.



You can see the break in the wire that I was talking about. that wire continues about 3 inches to a bullet connector.

straight hate

Check the CHTS too if its out it will give you mixture problems. I think that sensor in your pick is the coolant temp sensor. Both of those sensors are going to make you run rich and effect fuel economy. Check your plugs and see if there running rich.

JhnRX7

Just checked the timing. It is dead on at 8 degrees...

I pulled the plug on the CSV before I started it and nothing changed. It started up nice and easily exactly as it always has. It is probably not working at all. Im afraid to pull the injector to test it because it looks like if I try and pull the fuel line off it will break (both injector and line). That will be a weekend job because i need to get to work tomorrow.

...Well back out to the car to check TPS and AFM.

JhnRX7

I have suspected the CHTS as well, but what is the best way to go about testing it... From what I hear this is a part you need to stick to OEM with and it is about $45. I dont want to buy that unless im sure thats the problem.

Unless there are 2 coolant temp sensors, im pretty sure the coolant temp sensor is the one on the right in the drawing. (It looks exactly like the CHTS)

straight hate

Lol, I'll help the best I can I havnt worked on and N/A in over a year now. CHTS, if I remeber corectly you have to pull the sensor out. Boil a cup of water in the microwave(do not submerge the sensor past the conector) while submerging the sensor it should read 17(?) ohms. Cant remeber but if its anything lower its bad.? You really need to check the haynes I think the test is in there if not you need to search for it.
Coolant sensors, I belive there are two one is for the temp dash gauge and the other is the actual sensor...like I said I'm rusty. Dig through the haynes I think the basic test are in there. Anybody got anything else?

JhnRX7

here is the #2 plug. The tip is tan so it seems like the Air/Fuel is ok. It looks a little rough tho, any expert spark plug readers on here???

Also, what range of resistance is acceptable for spark plug wires? I measured 7.8K Ohms on one of the wires (the rest were similar)

JhnRX7

I dont have a haynes, but I just read through the workshop manual for the CHTS and thats basically what they said, I will give that a shot.

My thermostat housing has 3 sensors on it: the one on the right is water temp, the one in the center is for the gauge, and the one on the left is the one i posted a picture of. That is the one that i would love to know exactly what it does.

straight hate

Plug looks normal, clean em' up and put them back in. Crusty are normal, just a little oil. I honestly think you need to look at fuel pressure at idle and while driving, see what its doing. Basics first.

straight hate

Got me man, bleach or nismo might know. Another thing you can try...when you dont have to drive to work in the morning. Drain a little coolant and pull the water temp sensor out. Get a scotch brite pad and clean the corosion off of that sensor, after 25 years they can build up a layer between the sensor and the coolant and quit reading your coolant temp.

JhnRX7

So I just tested the CHTS sensor. It is dead on @ 68 degrees, however as the temp rises it gets more and more inaccurate.

My Readings:

68F = 2.58K Ohm
90F = 2.1K Ohm
100F = 1.6K Ohm
140F = 0.83K Ohm
160F = 0.63K Ohm
176F = 0.49K Ohm
200F = 0.31K Ohm

Is that far enough off to require replacement? ...Its pretty far off at 176F

JhnRX7

TPS checks out OK. There is continuity at idle and WOT.

straight hate

If I'm reading that chart right I would say your CHTS is ok. Resistance will drop as the motor warms, leaning out.

JhnRX7

Thanks for all the help straight hate

straight hate

edit that...I was looking at 140 F= .49k ohms, I was reading it wrong. Has that sensor ever been replaced?

JhnRX7

It looks like the sensor is original. for 176 it says between 0.25k - 0.4k ohms. Mine is at 0.49k ohms. According to that chart I should replace it. I was pretty accurate in my recording, I used a digital temperature gauge in a pot on the stove and as the temp rose I wrote down the resistance at each temp point.

straight hate

You are correct, didnt mean to confuse you. I was reading the wrong temp on the chart. I would says the sensor is toast. Especially it has never been changed I would say that what your problem is. They were a weak link.

straight hate

If you change it make sure to clean that connector out too.

NismoPick

#1... Nice Canon EOS Rebel.

#2... The prob is not likely the CHTS. When that sensor goes bad, you know it (floods / won't start).

#3... Neither the thermotime nor coolant temp sensor are connected to the ecu, so those aren't the cause. The thermotime sensor just activates the fuel rail cooler, the coolant temp sensor signals the dash temp gauge.

#4... Try cleaning the plugs & checking the gap.

#5... Pull the AFM cover off & push the spring while you rev (that may make the engine run better... if so you need to adjust it). Other than that, get to work on the CSV.

straight hate

Sorry for any missleading info, just trying to help.

NismoPick

^^^ No biggie... all suggestions work till we figure it out.