High idle and poor gas mileage
I have a 1981 280zx non turbo that is idling at 1500 RPMs no matter what the temp is outside. It is also getting 8 MPG right now. This just started two weeks ago. I replace the cap and rotor, fuel filter and fuel pump relay a week ago due to an unrelated issue.
Is there anyway to test the thermo timing switch before replacing it. If I unplug it the problem consists and I tried using a jump wire between the two wires but no change.
Does anyone else have any Ideas. Funds are super tight right now and I dont want to buy any uneeded parts.
Thanks,
Steve
Is there anyway to test the thermo timing switch before replacing it. If I unplug it the problem consists and I tried using a jump wire between the two wires but no change.
Does anyone else have any Ideas. Funds are super tight right now and I dont want to buy any uneeded parts.
Thanks,
Steve
- Status
- Not open for further replies.
1 - 15 of 15 Posts
I think you should search CHTS (cylinder head temperature sensor) instead.
Also, check to see if you're running rich with an Air/Fuel Ratio gauge or spark plugs or something. It's 99% chance that you are, but you should check anyway to help rule out leaks, etc.
Also, check to see if you're running rich with an Air/Fuel Ratio gauge or spark plugs or something. It's 99% chance that you are, but you should check anyway to help rule out leaks, etc.
Tell me why you think that. I would like an honest answer,no flames please.AKZX said:I think you should search CHTS (cylinder head temperature sensor) instead.
OK, got that.black said:Coolant temperature sensor is for temp gauge.
Cylinder head temperature sensor is for EFI. It dose not get wet.
Next question.......is it possible to have low coolant temp
and still have the correct head temp?
Well it directly effects EFI, so it can effect idle and gas mileage. Right now, my CHTS is going bad (as I discovered testing per FSM) and it's giving me around 13 mpg, which sucks, and it's also doing all kinds of crazy stuff with my idle. So I'm no expert, I've just seen that it's a really common cause of weird problems like this and I've experienced similar issues.dreamteam said:Tell me why you think that. I would like an honest answer,no flames please.AKZX said:I think you should search CHTS (cylinder head temperature sensor) instead.
Sorry I can't give a better answer, I'm still new at this stuff
I pinched the cold start valve fuel line and I can feel fuel running threw it but there is no change in RPM when it is pinched at idle. I just got the FSM so Im going to start digging into the CHTS. Thermo time is also ok.
Check all vacuum lines for cracks. Sounds like a vacuum leak.
Air flow through the intake controls RPM, that's why opening the throttle increases RPM. So a vacuum leak or stuck throttle blade are possibilities.
Advancing timing will increase RPM also. Check your static timing and/or your timing advance mechanisms. Described in the FSM.
Increased fuel without extra air will usually lower RPM. So a bad CHTS or thermotime switch (which only affects the CSV which only opens at starting anyway) are unlikely sources for your problem. If you feel fuel "flowing" through the CSV line you have super-senses.
Advancing timing will increase RPM also. Check your static timing and/or your timing advance mechanisms. Described in the FSM.
Increased fuel without extra air will usually lower RPM. So a bad CHTS or thermotime switch (which only affects the CSV which only opens at starting anyway) are unlikely sources for your problem. If you feel fuel "flowing" through the CSV line you have super-senses.
BGM,coolant temp sensors are for efi on early models like my 78 but,on later cars it is called a cylinder head temp sensor. Does same thing just in a different position and they both get wet.
The chts is supposed to be wet? I pulled mine and its dry. It tested fine. But i did have to test it in water. Is this supposed to be part of a cooling jacket?coolhand said:BGM,coolant temp sensors are for efi on early models like my 78 but,on later cars it is called a cylinder head temp sensor. Does same thing just in a different position and they both get wet.
I pinched the cold start valve fuel line and I can feel pulsing running threw it but there is no change in RPM when it is pinched at idle. I still felt the pulse and no RPM change with the sensor unpluged. Thermo time ohm load also tested ok. Pinching the intake on air regulator and did nothing to RPM.
CHTS tested within range per FSM. 105F water tested at 1.3 ohms. I lost no coolant when I pulled the sensor and it was dry.
Throttle valve swich tested between 000.2-000.5 with throttle closed and no load then throttle was open.
Running fuel pressure is 32psi
41 psi at 0 inHg Should be 36-37psi
37 psi at 5 inHg Should be 33-35psi
36 psi at 10 inHg Should be 31-32psi
33 psi at 15 inHg Should be 29-30psi
30 psi at 20 inHg Should be 26-28psi
If I put 25 inHg while running the car idels at 900 Rpm
Could 4 psi cause this problem? I seem to doubt it and Auto zone wants $70 for it. Not that I would buy it there. I read a spec that it should be 36psi vacuum while running. How can I test this? Any other ideas?
Thanks
Steve
CHTS tested within range per FSM. 105F water tested at 1.3 ohms. I lost no coolant when I pulled the sensor and it was dry.
Throttle valve swich tested between 000.2-000.5 with throttle closed and no load then throttle was open.
Running fuel pressure is 32psi
41 psi at 0 inHg Should be 36-37psi
37 psi at 5 inHg Should be 33-35psi
36 psi at 10 inHg Should be 31-32psi
33 psi at 15 inHg Should be 29-30psi
30 psi at 20 inHg Should be 26-28psi
If I put 25 inHg while running the car idels at 900 Rpm
Could 4 psi cause this problem? I seem to doubt it and Auto zone wants $70 for it. Not that I would buy it there. I read a spec that it should be 36psi vacuum while running. How can I test this? Any other ideas?
Thanks
Steve
I thought the chts got wet,it is in the head in the water passage is it not? If I am incorrect,my bad but,they are both for efi. I went and took a look at one of my p90 heads and ,no water passage.
Sorry I should have been more specific. Those are the readings of the pressure regulator.
1 - 15 of 15 Posts
- Status
- Not open for further replies.
ZCar Forum
A forum community dedicated to Nissan and Datsun Z car owners and enthusiasts. Come join the discussion about performance, modifications, restorations, troubleshooting, maintenance, and more!
Full Forum Listing
