Adding a resistor to the fuel temp thingy

[Guest Anonymous]

I was hanging outside plaid panty (another type of 7-11 for those of u who dont know what a plaid pantry is) and a guy who i later found out to be a race car mechanic from Portland International Raceway started explaining how i can put a 65 ohm resistor on a wire leading from the water temp thingy (he pointed it out to me and i can't remember exacaly what it was so sorry for reffering to it as a thingy ) and it should give me a few hp by fooling the computer into thinking the engine was a little cooler than it was. Is anyone familiar with this procedure?

[BLKMGK]

This is a common "band-aid" that folks try to do to fool the computer into doing things they think will make more power.

 

Here's what's going on - the ECU will have a circuit much like the choke on a carb. When the engine is cold it runs things a little richer to help it start and run better till it warms up. As it gets warmer it backs the fuel off in relation to the engine heat and will go "closed loop". In closed loop it will modify the fuel delivered while cruising in order to meet emissions. I'm NOT sure how sophisticated the older Z ECUs were but if they've got an O2 they probably do this. Anyway, what you're talking about doing is fooling the computer into thinking the car is colder than it is. As a result it'll run richer, may not go into closed loop, and may even run a totally different ignition program. At WOT this might even get completely ignored depending upon the ECU - I'm not sure.

 

Will it make more power? Maybe. IF it does it will be because the car needed more fuel. If that's the case then perhaps finding a more controlled way to add fuel would be "better". Now possibly the ECU was poorly programmed and the warm up loop provides more power but most OEM ECUs are programmed pretty well for stock setups. Is there some reason why you think it needs more fuel right now?

 

Some other common "band-aids" include: Moving the air temp sensor further away from the intake or actually hanging it inside the engine bay where it gets a reading not related to actual intake air temp. Monkeying wih the MAF meter - if you've changed injectors or fuel pressure this isn't actually so bad but I have some issues with doing this on Mustangs that might also apply to Zs. Ask me if you care and I'll explain Bypassing cooling lines to things like throttle bodies (Mustang guys do this). Changing base timing, not really a bad thing but it's a wholesale change everywhere. Changing fuel pressure - not super bad if the car has decent closed loop corection but at WOT you need to have it just right and warm up could suck. FMUs or rising rate regulators that change fuel pressure more than 1:1. Disabling primary O2 sensors (why?!). Hrm, I think that's all I can think of over and above fiddling the water temp sensor. Most of those changes have other side effects that aren't good and canwill effect other aspects of the car like warm up or driveability. Be very careful making changes like that - at least the resistor can be removed if it runs really bad but I think if you do this you'll find some aspect of the car has changed that you won't like - most likely mileage. You might also burn out a caalytic converter but that's mostly a guess.

 

'Zat help at all?

[BLKMGK]

If you do it and it runs better than the car probably needs more fuel and I'd work on fixing that problem the right way rather than fooling the computer. The problem with fooling the computer is that it usually has unintended side effects.

 

I'll give you a "for instance" that may not apply to Zs. On Fords with bigger injectors folks buy a "retuned" MAF meter to run the new injectors properly. Hell, I've got one too. This is a BAD move. Why? ECU is tuned for 19lb injectors, when it sees X voltage from MAF it thinks X amount of air is blowing into the motor. As a result it gives X amount of injector pulse and X amount of timing. Terrific right? Now, put in bigger injectors and a "retuned MAF". What's that do? They REDUCE the amount of voltage linearly such that X amount of air now puts out a LOWER amount of voltage. The ECU thinks the air is lower and reduces the injector pulse - which is fine since that's the correct fueling for the bigger injectors. See the problem yet? You've just screwed your timing curve! The computer is now running the timing curve for a lower amount of air. (sigh) Try explaining this to a Mustang guy - most of them just don't get it because they do NOT understand how the EEC is working. The "smart" way to do this is to change the bytes in the computer that spec out injector size but for some reason I've only ever seen one tuner talk about doing this and his vaporware hardwaresoftware has yet to hit the street. As a result I've got a modified MAF and a custom chip that has hopefully taken care of the ignition issues as well as fueling. Heck, the EEC is so sophisticated that moving the position of the MAF nearer or closer to the TB changes things. The EEC actually "knows" the distance and makes tuning changes based upon the distance it expects the MAF to be from the TB. Amazing what the OEMs have to do to get driveability and emissions just right isn't it?

 

When you fiddle the MAF on a Z, as I believe some do, you MAY also be changing timing so be careful and take small steps. I don't know very much about the Z ECU so I can't say for sure (shrug). Anyone ever looked into this? How does the ZXT ECU do timing?

 

P.S. WOT timing may not reference the MAF on the Mustang - I've seen differing answers on that. Retuned MAF may only hose the part throttle ignition curves, I'm not sure.

[Guest Anonymous]

Wow thanks BLKMGK. I was mainly wondering on how much i should put into the guys advice. I'm most likely not going to do anything with it but if I do it would just be for the sake of doing it and seeing how it works out but ill end up putting things back.