AFM Wiring zxt/zx/z

[yellowoctupus]

I was going to put an 81 zxt afm on my 78 280z supercharged engine (stock ecu), but can't figure out if my wiring will be ok. My 78 afm has 7 prongs, however the stock harness only uses 5 of those. I have a 80zx afm that only has those 5 prongs, and my 81zxt only uses 4. By my wiring diagrams, it looks like it misses the reference voltage postive side! (obviously I'm wrong here somewhere!) What's wrong with this picture?? Can I just plug it in to my harness as is, or do I have to make a switch somewhere or something....?

[BRAAP]

Supercharged with OE N/A EFI? The turbo AFM is the least of your worries my friend. First you will need larger injectors to keep up with the added air flow the supercharger brings to the table. After that, getting the EFI to map the fuel in relation the air flow? You can get it to run, maybe even run OK at cruise, but it will NEVER be anywhere near optimum with flat spots and serious lean AND rich mixture issues throughout the rev range that can not be tuned out. The excessively lean mixtures can and will cause engine damage in very short order under boost conditions, especially with a blower!

 

With the L-6’s propensity to be hyper sensitive detonation, especially under boost, and adding to that this is supercharger boost which creates a hotter intake charge than turbo boost, (exaggerates detonation that much more)? I’m sorry but this a recipe for the quickest most destructive L-series blown head gasket/destroyedL-6 I could think of, outside of C4 attached directly to the side of the engine of course.

 

I'll be the first to say that you if want to supercharge your L-series, you really need to ditch the OE EFI and go aftermarket fuel control, whether it be megasquirt etc, or even a carburetor is huge step in the right direction of the OE N/A EFI! The OE EFI will NOT support nor allow you to tune for the supercharger, PERIOD! Fab some plumbing and run a single SU carb and you will much better off.

 

Sorry if this is not what you want to hear, but trust me, OE N/A EFI is about as far from correct regarding matching the appropriate fuel flow to the air flow a supercharger will induce, as you can get. In the long run, it will cost you more money in blown engines and poor fuel mileage than it would be to just start out with an appropriate EFI system or even a carb.

[yellowoctupus]

Yeah, I know it's not ideal, I'm just cobbing it together to make sure all the belts etc work, then switching to my MS later (of which I'm still a little intimidated about, need to do more learnin' etc). I'm running brown top 250cc zxt injectors and the zxt fuel regulator (I have an adjustable if need be as well) so they shouldn't freak out and run way lean hopefully.

[BRAAP]

Good start with the larger injectors.

Might be best to just leave the N/A AFM for now.

 

 

Disclaimer;

Use this information at your own risk. For off road use only, this intended merely as guide to help and is in no way the definitive approach to tuning the OE EFI. Batteries not included, some assembly required, lack of torque has been to cause cancer in the state of California and wings to sprout on the trunk/hatch lids of FWD cars. Your mileage may vary.

 

 

 

I'll through out a couple tidbits that should help you in your tuning. This applies ONLY to the OE Datsun Z car N/A EFI! This does NOT apply to the Turbo EFI, aftermarket EFI or any other OE EFI.

 

 

The parameters you have available to mess with in “tuning” the OE EFI are,

1) Adjusting the water temp signal to fool the ECU into leaning or richening the mixture. This is a global change and a WOT will add or subtract fuel linearly across the entire RPM band!

2) Adjusting the spring tension of the AFM. This will affect the delivered fuel with it in the range the AFM is operation. It is more sensitive at cruise conditions vs WOT. More on that later.

3) Micro switch on the throttle linkage somewhere that will add or subtract resistance to the water temp circuit at a particular throttle setting. Sorta like an extra TPS that kicks in at different throttle setting, generally at full WOT! I have only had to use this one car before. This is really more of a final WOT fine tuning tool.

4) The Air Temp sensor in the AFM. This is has the same affect on fueling as water temp sensor, just not as aggressive as the water temp sender. I really never mess with this one as the water temp generally gives me the control I need.

 

 

 

A couple of the components and how they operates/ ECU interprets their signal, and how that affects the fueling over the engines rev and load range.

 

AFM;

The AFM’s involvement is as a modifier to the base fuel map which is preset in the ECU and not adjustable. The ECU also uses the AFMs “over swing” when the throttle is stabbed for acceleration enrichment, much like and accelerator pump on carb. The AFM also has and air temp sensor which the ECU uses to help adjust fueling requirements for air density changes due to temp changes. I.e. colder air is more dense than warm air therefore requires more fuel. The flapper it eh air stream is just measuring the “Volume” of air, not the density. The AFM can not measure density of the air due to pressure changes, (altitude or otherwise), or humidity. Also, at WOT, the AFM tops out or is fully open between 4000-4500 RPM. So above that RPM point, the AFM has NO influence on the fuel mixture whatsoever, other than telling the ECU it is fully open!

 

TPS;

The TPS is 2 position switch. One position is idle, the other position is WOT, though it really kicks in at approx ¾ throttle and stays in through WOT. In between that, both switches are open. The ECU uses the TPS understand the demands from the driver which will be one of three things.

1) The throttle is closed

2) The throttle is part way open for cruising conditions.

3) The throttle is open past ¾ and the driver needs more power!

 

With the throttle closed at idle, the ECU richens the mixture a tad.

With throttle just off the closed position yet below the ¾ open threshold, the ECU leans heavily upon the AFM’s input to determine correct fueling. Above ¾ throttle, the ECU leans more on it is own preprogrammed fuel map with the AFM’s input is not so influential.

At elevated RPMS when lift off the throttle and it closes, the ECU will completely turn off the injectors if the RPM is above 3200 RPM and turn them back on at 2800 RPM. Saves a little fuel and helps with emissions tremendously. (some have found that if you pressure wash the engine bay and water gets in the TPS connector, the closed throttle signal stays shorted so the ECU thinks the throttle is closed and acts as violent rev limiter shutting off the injectors and turning them back on at the 3200 and 2800 RPM points described above). Essentially, the TPS is just switch telling the ECU the throttle is closed or open and when to bias the fuel map more heavily off the AFM’s input or its own internal map.

 

Water Temp Sender;

This is just a resister that changes its resistance based on temperature. The warmer the temp, the less the resistance. At room temperature, the Water temp sensor will measure between 2000-3500 ohms. The engine at operating temperature, the water temp sensor will measure between 200-350 ohms. The ECU interprets a cold engine with more resistance and will add fuel accordingly, like choke on carb. The ECU does so linearly across the entire rev range at all loads.

 

 

 

Here is my tuning procedure for the OE EFI. This only works for the OE EFI on N/A engines. Do NOT use this method for your supercharged set up. You will have to sneak up on your tune at WOT and use a wideband O-2 sensor. If you do not have a wide band O-2 senor to use for tuning this, your flying blind and the chances of blowing your engine are very good!

 

 

I start by tuning WOT above 4500 RPM first, warm engine of course. For any other EFI system, you should NEVER tune WOT first! That is just asking for trouble. The only reason this works with OE EFI is generally the fueling requirement are already pretty close to ideal and are safe, i.e. not overly lean or rich etc.

At WOT above 4500 RPM, I will modify the water temp signal till the mixture is where the engine wants it. I use a 1k linear taper variable resistor in series tithe water temp sender covered elsewhere on this forum.

After the ideal water temp resistance is established I will place a fixed resistor at that value in series with the water temp sensor.

 

Next I focus on WOT form 1500-4000 RPM and adjust the AFM spring. Before I make any change to the AFM, I witness mark the OE setting of the AFM with scratch awl. Once that is set, I will tune part throttle 1500-4500, holding the throttle steady as the RPMs rise and note the fuel mixture. I’ll do this at varying throttle settings form just off idle to almost ¾. Hopefully the cruise AFM adjustments will be close. If not, I will have to make a compromise in the AFM adjustments between ideal WOT and cruise, below 4500 RPMs.

 

Then final tuning is the idle. Adjusting the CO mixture screw in the bottom of the AFM to get a smooth clean idle.

 

 

With the supercharger, tuning WOT first is dangerous as you’ll have no idea if the mixture is too lean at WOT above 4500 which could be dangerous allowing detonation, blowing the head gasket or worse, the engine.

 

 

Hope this helps.

[yellowoctupus]

Thanks for the HUGE list of tuning tips. Gotta remember to print this off and stick it with my Datsun Fuel Injection book. I wonder why it's so necessary to have the TPS at al when it's relying so heavily on AFM inputs. I understand why its there for emissions (deaccelerating etc), perhaps the AFM signal is too bouncy at low RPM's, but I wouldn't have thought it'd do much for WOT.

[Challenger]

Amazing post braap!! I vote that this gets stickied somewhere.

 

Little comment. You mentioned about the TPS shorting out. I beleive I had this issue a while back after it started raining. Got in my car and Id start to accerate and if I remember correctly at around 2000ish rpm the engine would completely cut out, kick back in, cut out, etc. This sounds exactly like the fuel injectors just turning off intermittently. Really makes sense now. Cleaned out the TPS and it ran fine, barely made it home, would go past ~30mph.

 

Also regarding the head temp. Isnt it backwards that the resistance gets larger with a cooler sensor? Isnt a cold conductor a better conductor? AKA superconductors at close to 0 K.