Sorry to be Redundent - Help

[bhermes]

Great, thanks to both. I feel that it couldn't hurt to have the pressure gauge and the pot. I will start working on both after the 70mph winds go away today. The detail in how to install really helps.

I went to radio shack and the smallest pot they had was 5k. I am a little confused in looking at the resistances in the attachment above about installing the pot I see resistances up to 20k. I guess this is not necessary. I assume that 5k may not give the variance I need. Comments?

Otherwise I think this is a good plan or start.

One other question, if this is a temperature issue or resistance issue causing a call for less fuel inaccurantly will I be able to recreate in the driveway or is driving required. Just want to make sure I go on a nice day in case the car does break down. It usually or maybe always will start after 20-30 minutes either way.

I have also pulled a copy of the EFI Bible and will begin looking through.

Thanks.

[siteunseen]

Mine never completely died, just bucked and jumped like it was out of gas, and would always crank and idle. If your car is stalling out and hard to re crank I'd definitely go get a pressure gauge and the brass fittings. And yeah I can flood mine out sitting in the driveway turning it wide open. I believe the one I bought was this one 1M-Ohm Linear Taper Potentiometer : Potentiometers | RadioShack.com.

[Stanley]

If you want a permanent FP gauge McDaniel has some nice ones, mine is 0 to 10 psi (for the SU's) but pretty sure they have some for Fuel injection. Tempered safety glass good for 250 psi, 2 1/2" face, etc. Mine cost about $60, they gave me the name of a local supplier and I ordered it through them. Hooked it up with a Tee (in my case, attached to the mech. fuel pump), to a steel braided hose with a cloth braided cover good for 3000 psi, local hose place put it together with AN fittings. Run it through the firewall grommet where the AC used to go, hooked it to the gauge with a snap-tite fitting from M-C so I can remove it in about a minute. The gauge is mounted under the glove box with a $10 clamp from autozone.

Like seeing the fuel pressure when I'm driving. That way I don't buy any unnecessary fuel pumps and hopefully will have some advance warning if it gets weak or filters get plugged. Cost 60 (gauge)+50 (hose) + 20 (snap-tite) + 10(clamp) + 10 (Tee and BSPT adapter)= $150. Was going to install an electric pump but I see the mech one is putting out steady 3.8 psi to the SU's so it saved me that money.

Edited November 17, 2013 by Stanley

[bhermes]

In the photo with the gauge added are those 1/8" fittings? Seem bigger.

Went to hardware store and the smallest fitting they had was 1/4". If the lines are 5/16 should I not be getting 1/4" fittings?

Maybe I just dont understand OD vs ID of the lines.

I did get the gauge but thought I may need to go to auto store to get the fittings.

For temperary hook up will 50 psi tubing work? I may just get the right stuff but if I dont.

Thanks.

[bhermes]

The 1M Ohm makes more since than the 1k Ohm.

Thanks.

[EuroDat]

In the photo with the gauge added are those 1/8" fittings? Seem bigger.

Went to hardware store and the smallest fitting they had was 1/4". If the lines are 5/16 should I not be getting 1/4" fittings?

Maybe I just dont understand OD vs ID of the lines.

I did get the gauge but thought I may need to go to auto store to get the fittings.

For temperary hook up will 50 psi tubing work? I may just get the right stuff but if I dont.

Thanks.

I went to my local auto parts store and purchased a 1.5mtr length of fuel hose and hose clamps. Then I found a T-piece to suit at the hardware store. Here is an example BRASS BARBED T PIECE 3 WAY FUEL HOSE JOINER FOR COMPRESSED AIR GAS OIL LPG PIPE | eBay

I was using it in the car for a week or so to see what was happening. The pressure will get up towards 36 psi when the engine under heavy load (low vacuum) WOT.

Chas

[FastWoman]

The gauge:

One of these: Shop Aqua EZ Pressure Gauge at Lowes.com

One of these:

http://www.iboats.com/BRASS-TEE-1-4-FEMALE-THREAD-Seachoice/dm/view_id.927903?cm_mmc=Google_Main-_-Mall+Product+Listings%3AGoogle-_-+%3AMall+Product+Listings%3AGoogle-_-Seachoice&kw={keyword}&gclid=COCNyOS37boCFYWDQgod4i8AVA

Two of these...

Brass Coupler 1 8" Hose Barb x 10 32 Unified Male Thread Fuel Gas Water Fitting | eBay

... all in thread sizes to match the gauge, of course!

The potentiometer: 1MOhm is probably too much resistance. 1kOhm is perhaps too little. Although the 1MOhm will technically work, the adjustment will be extremely touchy and imprecise. Ideally, you should use a total resistance that's roughly twice what you need, so that your adjustments will be roughly in the center of the range. I use a 5kOhm potentiometer, because my desired resistance is in the neighborhood of 2.5kOhm. I could also probably use a 10kOhm potentiometer fairly well, but I wouldn't want to go higher. A 1k potentiometer would be inadequate to adjust my ECU, but others have used resistances that low. I would say 5k would be a pretty safe choice for most people.

If you want to make the installation permanent, I would recommend one of these:

Vishay Spectrol M43P502KB40 Trimmer 20 Turn 5K | eBay

... or one of these...

20pcs 3296W 502 5K Ohm Trim Pot Trimmer Potentiometer 3296W | eBay

You adjust them with a little screwdriver, and it takes 20 turns to move through the entire adjustment range. These 20 turn pots are extremely stable and accurate, and it would be difficult to knock them out of whack.

Edited November 18, 2013 by FastWoman

[jcb]

The gauge:

One of these: Shop Aqua EZ Pressure Gauge at Lowes.com

One of these:

BRASS TEE-1/4-FEMALE THREAD - Seachoice 20891 - iboats

Two of these...

Brass Coupler 1 8" Hose Barb x 10 32 Unified Male Thread Fuel Gas Water Fitting | eBay

... all in thread sizes to match the gauge, of course!

The potentiometer: 1MOhm is probably too much resistance. 1kOhm is perhaps too little. Although the 1MOhm will technically work, the adjustment will be extremely touchy and imprecise. Ideally, you should use a total resistance that's roughly twice what you need, so that your adjustments will be roughly in the center of the range. I use a 5kOhm potentiometer, because my desired resistance is in the neighborhood of 2.5kOhm. I could also probably use a 10kOhm potentiometer fairly well, but I wouldn't want to go higher. A 1k potentiometer would be inadequate to adjust my ECU, but others have used resistances that low. I would say 5k would be a pretty safe choice for most people.

If you want to make the installation permanent, I would recommend one of these:

Vishay Spectrol M43P502KB40 Trimmer 20 Turn 5K | eBay

... or one of these...

20pcs 3296W 502 5K Ohm Trim Pot Trimmer Potentiometer 3296W | eBay

You adjust them with a little screwdriver, and it takes 20 turns to move through the entire adjustment range. These 20 turn pots are extremely stable and accurate, and it would be difficult to knock them out of whack.

Thanks FastWoman for posting this info. I had planed to PM you about what you had used for this upgrade.

My understanding of things electrical is limited so my next question is this. Do you need to use a meter to adjust or can I just use the trial and error method? My car (stock 78/280z ) is sometimes hard to start the first time in the day. Pops back thru the intake and does not want to run. Most times it starts right up. Sorry to ramble on and not intending to highjack the thread. Thanks

[FastWoman]

You don't NEED a multimeter, but this is one of those really cheap and useful tools you should probably have anyway. It will cost you all of $5-$10 at an auto parts store, and it's really handy to stash somewhere in your car, in case you have (or someone else) has electrical trouble. Even if you don't know how to use it, someone else might.

I tuned my engine as follows:

First, I set the idle mixture adjustment screw on the airflow meter (big screw beneath and towards the driver's side of the outlet of the airflow meter, possibly obscured by a rubber plug) to exactly 5 turns CCW from the completely screwed-in position. Is this the best setting? I really can't say. As far as I could tell, the adjustment did little or nothing. Seriously.

Then I hooked up a vacuum gauge to the intake manifold. I disconnected the HVAC control like and connected my gauge to the manifold using that nipple. It's the nipple just forward of the brake booster vacuum hose. Since you have a '78, yours will be configured the same way.

Then I started the engine, and adjusted the potentiometer for the best idle. Note: As idle picks up, you will need to adjust the idle speed back down to the spec 800 RPM with the big screw on the top of the throttle body. (Actually I have mine set to 900 RPM -- engine likes it better.) Next, I let it warm up completely, and I fine-tuned the adjustment to produce the highest engine vacuum. Then I turned the control just a tiny bit to the "richer" side (lower resistance -- which you can confirm with that $5 multimeter!). You don't want to adjust so far that you lose engine vacuum. You just want to be a bit on the "rich" side of that "just right" zone.

Next, I changed out my plugs, and went for a short test drive to ensure the engine responded well. Then I pulled the new plugs and "read" them to confirm I had a good mixture. You mostly need to note the appearance of the insulator. If it's chalky white, you need to adjust for a richer mixture (adjust the potentiometer to a lower resistance). If it's sooty, you need to adjust for a leaner mixture. If it's a nice, warm mocha, you've got it just right.

Before you do ANY of this stuff, you should make certain you don't have any vacuum leaks. You can read about my "yogurt cup test" (note: Yoplait brand fits, but you can really use anything that fits the hole) on post #36 of this thread:

http://www.classiczcars.com/forums/open-s30-z-discussions/40234-purs-like-kitten.html

This thread chronicles how I got my engine running normally AFTER replacing my leaky intake/exhaust gasket, replacing leaky injectors, verifying/refreshing/replacing fuel/intake parts, verifying my vacuum advance wasn't stuck (and replacing my distributor because it was), setting the timing, and adjusting the valves. Tweaking the fuel/air mixture with the potentiometer was really the LAST step in the process.

I'm not saying you can't do the potentiometer modification as the first step in the process. However, you might be putting a bandaid over some other problem -- e.g. richening the mixture to compensate for a massive vacuum leak. Although that might make the engine run better, it still wouldn't make it run RIGHT. You'd still need to work through other possible problems/issues, and you would have to keep re-adjusting your potentiometer every time. So if your goal is to get the engine running RIGHT, you will save yourself a lot of work by doing the mixture adjustment last (and only once).

Oh, and back to the multimeter: I suggest you take a reading on the potentiometer, so that you can note the "just right" resistance in your service log book. This way you'll have a record of how your fuel system changes over time (in case you need to readjust later).

Edited November 19, 2013 by FastWoman

[siteunseen]

Great info! Thank You Fastwoman. Now I can "un-cobble" mine out of the cabin for good.

[jcb]

Fast woman, Thank you so much. Great tutorial for all to read. I have ordered the potentiometer and will check the other items you mentioned.

Thanks again for the reply. JB

[FastWoman]

You're both quite welcome. I hope it all comes out well!

FAIW, siteunseen, although a patch into the wiring harness with a couple of bullet connectors is the least invasive way to add the potentiometer, snipping the #13 wire (as I recall) of the EFI harness and inserting the potentiometer there (under the dash) is perhaps the "better" way. (See towards the end of the thread I linked.) This will keep the potentiometer in a cleaner, cooler environment, where it is likely to be more stable.

Good luck with your engines, guys! :-)