Problem Putting 100k Pot/resistor For Richening Fuel On 83 280zxt

[Guest jjohart]

Hi, I just went and bought the appropriate linear adjustable potentiometer and bullet connectors for doing the adjustable fuel enrichment tweak discussed here and elsewheres. I and my shop mechanic found that the instructions for how to wire it (to a "coolant temperature sensor") does not exist for my car, as the only sensor is a thermotime dual ended single plug. The instructions note the correct wires for said pot are bullet connectors coming out from that c.t sensor, which is pictured immediately next to a thermotime sending unit. I've got nowheres to go on my FED/Emission controlled car, which apparently only uses an engine cylinder head temp sensing probe. Am I mistaken in assuming that folks that have wired this up have older cars (ie., 280Z,etc?).

John

P.S., here's a link to Atlantic Z's instructions, which are really quite well done, if you've a 78 or earlier Z!

http://www.AtlanticZ.ca/zclub/techtips/tempsensorpot/index.html

[Guest SpyderZ]

This is my opinion: The instruction in that link should work only for cold start only. When the car warm up and under cruise it uses the AFM signal. For your need I suggest you to use the signal from the AFM. It's pin 32 and 34 that you want to add the resistor. Note when you add the resistor between these 2 pins you have to disconnect the inputs from the AFM's potentiometer side. I've been thinking of doing this for 280ZXT also but I only want to do it under boost. There are a couple ways you can accomplish this: 1. Use the hobble pressure switch to trigger this circuitry to switch your input from AFM to your variable resistor. 2. Use the kick-down switch from the automatic trans car and mount it on top of your gas pedal so that when you floor it it will trigger this circuitry to give you more gas. In any case the hook up is follow:

Get a 5 prongs relay. Connect 12V to pin 85 of the relay. Connect your (-) trigger input to pin 86. Cut the wire that goes to pin 34 of the AFM. Note now you have 2 ends, 1 to the AFM (Call this A) and 1 go to the ECU ( call this . Connect A to pin 87A (NC) of the relay. Connect B to pin 30 (common) of your relay. Now connect pin 87 (NO) of the relay to your variable resistor and the other end of the resistor go to pin 32 of the AFM. Note: if you hook up this way you can give it more gas under certain condition and you can choose it. Also you can adjust your AFM to lean it way out to run bigger injectors as well. I did not do this for my car yet but I accidentally find out that my car was running way rich when I had the AFM disconnected. With this setup you are essentially almost disconnect the AFM. Please let me know how it turns out. When I have time I will definitely do this to my ZXT.

[technicalninja]

I posted a fairly detailed explanation for this mod a while back. Use search function. Your cylinder head temp sensor (on side of cylinder head near #5 plug) takes the place of the earlier cars CTS in the thermo housing. It works on the same principles and as I remeber it has the same resistance map as the earlier sensors. Adding the adjustable POT in this circuit will allow some linear tailoring of your fuel curve. This mod only helps curve after car is fully warmed up as the resistance curve of the sensor itself is not linear. you also need a 1000 ohm VPOT not a 100K ohm as you posted. Mine ended up needing about 600 ohms (10.5/1 N/A).

[Guest jjohart]

So, from what you've said, the fellow above your post who said it (the pot) would only affect cold start is wrong?

I hate to be a splitter, yet again, but on another site, Atlantic Z, there's a fellow, Blue, who says the engine temp doesn't matter, it will increase richness across the board, but less so in cold temp. Being that I've a turbo Z, and yes in your earlier thread, there was some variant opinion on this tweak's effect on the turbo (not sure if more or less efficacy)..but please read his post(s), with all due respect...seems like there's not one clear answer about the HOW MUCH this thing does, particularly since I'm not really crazy about leaning out my AFM to compensate for this swithcy thing, my car is lean as hell already, thanks very much!

John-BTW, we've a Patriots day holiday here in Massachusetts..is there a Texas day, to remember the Alamo, or something?

[Guest jjohart]

oops, ok, here is A.Z chatter on their forum:

http://www.atlanticz.ca/forum/viewtopic.php?t=583

[Guest bastaad525]

I dunno if I'd do that mod to the AFM... if you're boosting enough that you're running lean, no amount of modding or bypassing the AFM signal is gonna affect that. Stock fuel injectors at stock fuel pressure are maxed out at 10 psi of boost at 5000rpm and above, no amount of tweaking the AFM not gonna fix that. If you want a way of adding extra fuel only on boost for relatively cheap get an RRFPR like the one I'm using from B.E.G.I. - It ups fuel pressure on boost only, no need to tweak the AFM or anything else, and with a good pump can provide enough fuel to support 14psi of fuel w/o running lean (I did this with stock injectors and a MSD fuel pump).

 

 

Unless you're looking to mod the AFM to run LEANER? this would make more sense since the stock EFI runs REALLY rich between 3-4k when boost first comes on.

[technicalninja]

jjohart is correct as the added resistance of the pot is always applied to the circuit. The reason it doesn't effect a cold engine as much as a warm one is that the curve of the cts/chts (coolant temp sensor/cylinder head temp sensor) is not a linear one. Per Nissan SM (77 and 82) the resistance values are

-22F=20-30k ohms

14F =7.6-10.8k ohms

50F = 3.25-4.15k ohms

68F = 2.25-2.75k ohms

122F= .74-.94k ohms

176F= .29-.36k ohms

 

For those who are wondering the small k after the value stands for 1000.

 

So a cold engine should have between 3000 and 10,000 ohms of resistance (depending on outside temp)while the same engine fully warmed up will show 300 ohms. Add 500 ohms to 5000 and the change is minor. Add 500 ohms to 300 and the change is much more pronounced.

The added resistance does effect the fuel curve across the board.It just doesn't effect the cold mapping nearly as much as it effects the warm mapping.

I agree with Bastaad525 as to the afm mod. Any enrichment mod which relies on a one time change to the curve that doesn't take into account RPM or load is a poor idea. Might work for some but count me out.

The cts mod this post was about can provide a mild increase in fuel output but is best suited for N/A applications as increasing boost vastly increases airflow and the cts mod doesn't have a snowballs chance of keeping up with the fuel needs. The cts mod also doesn't add much to cold operation so on a 10.5-1 N/A you should let it warm up before hosing it. Good advice for any engine.

The rrfpr with an improved fuel pump is the first step to increasing fuel for a turbo. This mod has no effect on normal driving situations and only changes fuel flow as boost increases. It is simple and reliable but does has a price tag somewhat higher that the .99 cents that I pay for my VPOT at RadioShack.

 

Hope this helps

Rick

[Guest bastaad525]

Truth be told, for the amount of money the average RRFPR will cost you you would probably be better off just going with a used set of the Ford SVO 370cc injectors, though it is a compromise as you will have to mess with the AFM to get it to drive normally around town, but should set you back less than $100. The RRFPR was $200 but I like that it didn't affect off boost driveability at all and was very easy to tune for the amount of fuel I needed on boost.