Unplug the coolant temp sensor

[eco]

I have heard more than once that unplugging the coolant temperature senor would leave the computer in open loop. That makes sense since the computer looks to that sensor to know when to get into closed loop. Simple enough. I have also heard that leaving it unplugged and staying in open loop is a good thing from a performance standpoint because the motor is run at a richer air:fuel ratio. This makes sense too because in closed loop the air:fuel ratio hovers right around ~14.7:1. I am not sure where it is in open loop, but it is richer. With a gasoline engine, peak power is made with an air:fuel ratio of 13:1.

I have never heard of anyone testing this out. Would anyone be willing to give this a try? It's easy enough to do - unplug it, go for a drive (5 miles or so), then plug it back in.

In this mode, the O2 sensor does nothing. The TPS, MAP/MAF, air temp sensor and the stator would be running the motor which in theory is suitable. I have seen hot rods with custom EFI systems with just these sensors. If you have MAF, you could tune for power at 13:1 and switch to 14.7:1 for economy - this could be done with an air adjuster an the O2 would be helpless to over ride the adjustment.

Anyways, I am curious about the viability of keeping the computer in open loop and I doubt if I am the only 8-9 generation owner that would like to know more about this. So, lets give this a try.

 

[Lost]

Where the heck have u been ????

Excellent question.I'd like to know myself.
Hey you could throw a switch on it .. That way if in traffic it would not load up .

How that van coming???.

 

[Bob Ayers]

It will throw a CEL, coolant temp sensor out of range........

 

[Skandocious]

It will throw a CEL, coolant temp sensor out of range........

Yes but will it still operate properly, and in open loop? That is the question

I do believe Paul said that you can buy chips/programmers that allow you to force the computer into open loop.

 

[eco]

Hmmm, unplugged ECT = infinate resistance....cold temp = high resistance....cold temp = open loop. Or maybe a resistor could be wired onto the end to take the place of the sensor.

Where the heck have u been ????

Excellent question.I'd like to know myself.
Hey you could throw a switch on it .. That way if in traffic it would not load up .

How that van coming???.

I have been working alot of hours and working on the van. It's almost done. I should be ready to fire up within the next couple weeks. I started out the year over $12,000 dollars in debt (credit cards, taxes) and I have gotten that down to about $200 and I should have it all paid off within the next couple weeks.

Lost - Go to your truck, unplugg the coolant sensor, take it for a spin and tells us how it went.

 

[Bob Ayers]

The PCM will probably go into "Limp Home Mode", where it will run bad, and get terrible MPG.

 

[Bob Ayers]

Yes but will it still operate properly, and in open loop? That is the question

I do believe Paul said that you can buy chips/programmers that allow you to force the computer into open loop.

GEEEZ, if open loop is all you want, WOT will give you that, without screwing with any sensors!!

 

[d-kuzmen]

If your truck uses a IAT sensor it still may go into closed loop, if it doesn't see coolant temp come up but air temp is warm it may use that for an input. Not 100 % on this though.

 

[eco]

The PCM will probably go into "Limp Home Mode", where it will run bad, and get terrible MPG.

Thats what I am thinking would happen. The computer would see the infinate resistance then go to limp mode.

But, lets say you find out what the resistance is at the sensor at 80 degrees (or what ever temp that is more than 50* but less than 185*) then wire in a permanently installed reistor to take the place of the sensor. It wouldent be in limp mode anymore. Heck, not even a CEL. Since there is no timer on these rigs to say "hey we should be in closed loop by now" or "hey the coolant should be warmer than 80* by now" so I don't see how or why there would be a problem.

These rigs have more performance in open loop, but they burn more fuel. They run slightly richer and they have a slightly more aggressive timing curve. As the motor warms up, the fuel injector pulse width becomes less as does the timing. Another bonus is that the O2 sensor is out of the picture which gives the user 100% control of the AF ratio. With MAF and an IST "air adjuster" you can set the AF ratio to 13:1 for power or 14.7:1 for economy.

What do you think?

 

[Fellro]

Limp mode as well, of a sort. The O2 also sets it's own loop, as the engine temp takes too long to achieve temp for the O2, and with the newer heated O2 sensors, that time is also much shorter. Coolant temp may also affect converter lockup though. Some systems wait for the engine to warm up before engaging the lockup clutch.

 

[F 150Cobra]

my coolant sensor was bad once... i broke it lol.. and the truck ran horrible no power at all

 

[eco]

my coolant sensor was bad once... i broke it lol.. and the truck ran horrible no power at all

When it was broken, it was basically unplugged, right?

 

[eco]

Limp mode as well, of a sort. The O2 also sets it's own loop, as the engine temp takes too long to achieve temp for the O2, and with the newer heated O2 sensors, that time is also much shorter. Coolant temp may also affect converter lockup though. Some systems wait for the engine to warm up before engaging the lockup clutch.

If the computer does not see 185* at the ECT, it is not going to reach closed loop.....period. Not gonna happen. If it isn't in closed loop, the O2 is out of the picture.

As far as the torque converter, that may/may not (I don't know) be an issue with the computer controlled transmissions, but not a c6 or AOD.

 

[Bob Ayers]

Thats what I am thinking would happen. The computer would see the infinate resistance then go to limp mode.

But, lets say you find out what the resistance is at the sensor at 80 degrees (or what ever temp that is more than 50* but less than 185*) then wire in a permanently installed reistor to take the place of the sensor. It wouldent be in limp mode anymore. Heck, not even a CEL. Since there is no timer on these rigs to say "hey we should be in closed loop by now" or "hey the coolant should be warmer than 80* by now" so I don't see how or why there would be a problem.

These rigs have more performance in open loop, but they burn more fuel. They run slightly richer and they have a slightly more aggressive timing curve. As the motor warms up, the fuel injector pulse width becomes less as does the timing. Another bonus is that the O2 sensor is out of the picture which gives the user 100% control of the AF ratio. With MAF and an IST "air adjuster" you can set the AF ratio to 13:1 for power or 14.7:1 for economy.

What do you think?

First off, there is a timer in the PCM to see how long it takes the coolant to come up to operating temp, so it will throw a CEL with a fixed resistor at some temp value like 80 degrees!

Why are you trying so hard to wreck a system that is designed to make the engine as efficient as possible???? You wanted open loop, and I've already said you get that at WOT (Wide Open Throttle)!!

 

[Fellro]

If the computer does not see 185* at the ECT, it is not going to reach closed loop.....period. Not gonna happen. If it isn't in closed loop, the O2 is out of the picture.

As far as the torque converter, that may/may not (I don't know) be an issue with the computer controlled transmissions, but not a c6 or AOD.

If the coolant temp regulated the O2, why even make heated O2 sensors? The whole point of a heated O2 is to speed up the time the O2 can get into closed loop. The coolant sensor does not determine that time. Exhaust gas heats the O2, not coolant. The computer will go to a preset value for the coolant, but still close the loop for the O2.
And, yes, I know the C6 was never made with lockup, but since you didn't disclose the trans, I put that out. You could have also said the 5 speed doesn't have a lockup.
Besides, if you want to stay in open loop, why not just unplug the O2? Or put in a cooler thermostat, or remove it altogether, or run a restrictor plate? By staying in closed loop, you make the fuel mixture off from optimum, so do it if you want, but the engine will not realistically have any better performance, most likely worse, and will not be as efficient.

 

[Bob Ayers]

The coolant sensor does not determine that time. Exhaust gas heats the O2, not coolant. The computer will go to a preset value for the coolant, but still close the loop for the O2.

Not true:

P0125 - This means that the engine coolant temperature (ECT) sensor indicates that the engine has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine.

 

[Skandocious]

By staying in closed loop, you make the fuel mixture off from optimum, so do it if you want, but the engine will not realistically have any better performance, most likely worse, and will not be as efficient.

Roger I will also say --- the truck does definitely perform better when in open loop. I'm not sure about the newer rigs but the richer fuel mixture in these trucks makes a world of difference. Mike made a thread about this discussion a while back... Less efficient -- yes. Less power -- no.

http://www.fordtruckfanatics.com/forum/showthread.php?t=3532

 

[Bob Ayers]

Roger I will also say --- the truck does definitely perform better when in open loop. I'm not sure about the newer rigs but the richer fuel mixture in these trucks makes a world of difference. Mike made a thread about this discussion a while back... Less efficient -- yes. Less power -- no.

http://www.fordtruckfanatics.com/forum/showthread.php?t=3532

Chris, let me repeat my previous post! It will go into open loop when you are WOT, so why mess with anything????

If you stay at WOT, you are going to get $hit for MPG any way!!!!

 

[Skandocious]

Chris, let me repeat my previous post! It will go into open loop when you are WOT, so why mess with anything????

If you stay at WOT, you are going to get $hit for MPG any way!!!!

I saw that in your post and chose not to address it. Since you've now addressed me directly, I'll answer Yes, WOT will enrich the fuel and put the computer into "open loop" (notice the quotes). I put it in quotes because it's not exactly the same as the open loop when the engine is cold. It is taking readings from more sensors than the cold-state open loop. Refer to the chart below to see what I'm talking about:

As you can see from the chart --- cold start open loop only takes readings from RPM / ECT / ACT --- while WOT open loop takes readings from those + MAF/MAP/KS/VSS. As seen in the third column, it also controls spark with a load vs. RPM algorithm.

EDIT: I'm going to eat my words... I just read some more about the above chart and the computer enters "cold drive-away" state as soon as you throw her in drive, which makes the computer poll from more sensors... Perhaps it would be most beneficial to get a programmer which allow you to put the computer into "warm-up / idle" open loop --- I'd think it would offer the most performance... Dunno....

 

[Bob Ayers]

I saw that in your post and chose not to address it. Since you've now addressed me directly, I'll answer Yes, WOT will enrich the fuel and put the computer into "open loop" (notice the quotes). I put it in quotes because it's not exactly the same as the open loop when the engine is cold. It is taking readings from more sensors than the cold-state open loop. Refer to the chart below to see what I'm talking about:

As you can see from the chart --- cold start open loop only takes readings from RPM / ECT / ACT --- while WOT open loop takes readings from those + MAF/MAP/KS/VSS. As seen in the third column, it also controls spark with a load vs. RPM algorithm.

I guess you missed the MAXIMUM for fuel enrichment for WOT......The input from the other sensors will help you, not hurt you, because emissions are ignored!!!