EFI Fuseable Link

[woldson]

Bump. Any progress?

[zmaster]

still scratching my brain....so not really. But the car is completely painted so all the bodywork is complete (Pics coming tomorrow in one of my old threads and going on photobucket), and the car is put back together. going to my house tomorrrow morning to finish, and figure this out the problem

[zmaster]

I started my car, and kept the fuel pump switch that I wired in turned on, and I set the fast idle screw to let the motor idle at 850 RPM's, then I checked the fuel pressure guage, and it was reading about 4-8 PSI Is that supposed to be correct, or should the fuel pressure after the fuel filter be higher??? If it is supposed to be between 4-8 psi, then I guess I temporarily fixed my problem.

 

I have had no luck in tracing wires, because I don't want to screw something up. I know I should open my Haynes manual, but I don't have it with me otherwise I would.

[woldson]

Fuel injection is more like 35psi. With the car able to run, Iam guessing that the gauge is off. (guessing)

Hang in there you've made alot of progess and learned along the way.

[zmaster]

If I keep the car off and turn the switch to the fuel pump on the fuel pressure stays at 38 psi on my guage? but when the car is running the guage slowly drops and stays at 4-8 psi, and the car seems to run good It backfires a little, but it runs and idles at 850 rpm's

[mom'sZ]

38 psi is about what it should be in the condition you describe. (bypassing the relay and straight hot wire to pump) But dropping to 4-8 when the car runs is not right. This brings up a good point why it is bad to bypass the relay and saftey switch in the AFM. The only time the fuel rail should see that kind of pressure is when it is running under full load. I'll explain. In the fuel rail there is a pressure regulator which bleeds off excessive pressure. The regulator works off of engine vacumn. When the engine is idling, high vacumn causes a lot of the fuel pressure to return to the fuel tank. When the engine is under a high load (low vacumn) the regulator allows higher fuel pressure at the rail. The fuel injectors deliver more fuel under higher pressure for a given pulse time. In this way, the regulator adjusts the mixture slightly for various conditions, less pressure at idle, more pressure under full load. When you run the pump wired straight up without the engine running, there is no vacumn to allow excessive pressure to bleed off. Normally wired (stock) this condition would only happen for the brief moment that the key is in the start position.

My guess is there is something wrong with the pump. If it is wired straight up and develops full pressure, yet drops to 4-8 when the car is running, it is not working right. When running (idling) it should drop some, maybe to 20-25 but not to 4-8. My guess is if you attempted to run the car hard it would cut out or at least run really lean. 4-8 psi may be adequate to keep it running at idle / low load.

[zmaster]

heres a thought... what if there was less than a gallon of gas, and the pump was pushing air into the fuel line too, would that cause a pressure drop like that? I only have a gallon of gas in the car right now so I was wondering if that would also be a problem. Monday I am putting more gas in the Z.

[zmaster]

I am thinking out loud Right now so bear with me it is confusing even to me.......

 

If I am able to keep the fuel pressure at 36-38 PSI and get the car to run. Will the AFM or whatever controls the pulse of the injectors be able to keep the car running and still be able to pulse the injectors to the RPM's of the car. Because one thing controls the injectors, and something else will control the fuel pump correct? So what I am basicaly trying to say is if I keep 36-38 psi in the fuel line, whatever that controls the injectors will still control them like normal?

 

I am even confusing myself right now.

[m4xwellmurd3r]

the system for controlling the fuel pump is seperate from the system running the injectors, so yeah, if you hard wire it like you have it'll run like normal. Also, if your sucking air into the pump that'll cause it NOT to be able to pump to its full output, and that would cause that pressure drop you're seeing. Put 5 gallons in the tank and see what happens.

 

the afm/water temp sensor/ecu controls the injector pulses, and the system that controls the fuel pump running on/off is seperate (you can hardwire the pump and it'll still run fine, though it's not reccomended you do so if your fuel pump relay is functioning correctly)

[zmaster]

that is EXACTLY the answer I was looking for. Thank You. I will be putting 2 more gallons in on monday, so I will see where that goes, and if the fuel pump is going out...which I doubt I have a few extra pump laying around my garage. One more thing if the fuel pump relay is working correctle, but not sending the voltage it should, and I hard wire the fuel pump in what would I be risking...maybe a fire?

 

I have one more question. If my car runs lean would I be able to pass emmissions better?

[woldson]

I have one more question. If my car runs lean would I be able to pass emmissions better?

 

Not really, proper fuel air mixures create more complete burn=less emmissions. (amoung other things)

[m4xwellmurd3r]

It depends imo.

Running leaner CAN lower the HC and CO% but at the same time, will shoot NOX through the roof. a leaner engine that can still produce a complete burn will reduce emissions, but raise nox.

 

Check to see how the pressure is after putting in more gas. The relay can only send as much voltage as it's being given (12 volts from the battery in this case) if it's not sending enough volts, there's a grounding issue, or a corrosion issue. I'm gonna guess that after putting gas in it it'll have the right pressure. If not, you can try hard wiring it and see if that fixes it.

[zmaster]

ok thanks...the corrosion shuld e at the cnector unde the seat, and what color is the fue pump wire under the drivers seat?...I traced the wire from he fuel pump, mine is green, andI loos it as soon as it goes into the car?

[zmaster]

i have another question...Where isthe needle suppsedto be for the oil pressure? I let my car idle, and get to operating temps about 190, and I nticethe ol pressure guage is 1/4 of an inch mabe a few more hairs ast that of the 0 mark. what should he oil pressure be. heres something else too, the needle is about 3/4 of an inch to the left ofthe 0 psi line when i start my car, and slowly goes up and moves the whole1/4 of an inch past the 0 psi mark so should I count from where it starts to where it stops ? If not then I am thinking i need a new oil pump.

[zmaster]

I put more gas in today about 3 gallons, and that fixed my fuel pressure issue, the car runs at 32 to 34 psi, and it is now holding the fuel pressure also. It wasn't before. Now my fuel pump is making a loud noise like it is going out, and when i start my car, and switch on the fuel pump it starts to make the car run really rich, I have black, and a little blue smoke when i rev the engine.

 

I thought if I bypass the relay to the fuel pump, and keep the pump on, the fuel injectors, and everything else would stay normal, and make the car run right? But then why is my car running rich.

 

I am starting to think I am WAY WAY WAY over my head with this car.

[mom'sZ]

Zmaster:

Like I said in the other thread, I think now that you fixed your fuel pump issue, it sounds like the water temp sensor is bad. They are only 15$ at any auto parts store, as they are used on numerous models, thay are always in stock. Somewhere I have a link to a picture, I will try to find to show you what it looks like and which one it is. But it is located in the thermostat housing below the water inlet. (where the upper radiator hose enters the engine) The symtoms you describe make me almost positive this is the issue you have now (lots of smoke ect.)

As to some of the other stuff you mentioned, for your benefit and others, like m4xwellmurd3r said, the fuel pump is a whole seperate system. It runs or it doesn't run. When it runs, it runs full pressure. Your pressure sounds about right now. The regulator (mounted in the center of the fuel rail, with a vacumn hose running to it) varies the fuel pressure to suit different conditions, but it is a purely mechanical device and not effected by the wiring or ECU ect.

Oh... don't run these cars out of gas, they are really tough to get to prime after they run out.

Again as m4xwellmurd3r said, the only thing that controls the pulse of the injectors is the ECU. The ECU decides how to set the pulse from inputs from the various sensors. There are only a few, most are quite rudimentry. The water temp sensor tells the ECU how hot the motor is, but it only tells the ECU if the temparture is below 60 degrees F, to compensate for really cold conditions. The AFM tells the ECU how much air the motor is ingesting. The AFM is the main sensor that tells the ECU how much fuel to send. There is an air temp sensor built into the AFM that varies the mixture to match air temp. There is also a throttle position switch. It is really only two sets of contacts, which tell the ECU the throttle is almost closed, almost wide open or somewhere in the middle. This is to lean the idle, richen wide open throttle, or just act normally. The air regulator act to bleed extra air into the sytem to raise the idle on warm up. The thermotime richens the start up, it has a little heater built in and after a given time (thus the name) shuts off. It a super simple system so it is easy to work on. Once it works right it will be reliable for years. It provide good power and fuel economy. For a stock L-6 or near stock, you can't do better. It's been a long road but I think you almost there and now you know how the whole thing works. Good SHOW!!

[mom'sZ]

Here is a link to a screen capture of the factory service manual showing the water temp sensor. The thermotime is there as well. I think the water temp sensor is the smaller of the two.

here is a pic of the temp sensor

here is a pic of the thermotime

[zmaster]

Thank you I guess I really have come a long way from knowing ABSOLUTELY NOTHING about z cars to knowing what I have learned, and it all thanks to this site for my knowledge.......but there is one thing i think i should add... the water temperature guage was working properly it was reading 190 degrees, I will still change the temp sensor and i hope that is the problem, the only other thing i could think of that may possibly cause this problem is the ecu, or maybe the thermotime,

but i really don't know and understand the function of the thermotime switch?

[mom'sZ]

Zmaster:

The water temp gauge is seperate from the water temp sensor for the ECU. The gauge and it's sensor are in the regular wiring harness for the rest of the car. The temp sensor for the ECU is in the fuel injection harness, which is a whole seperate harness. Follow the wires back through the bundle if you don't believe me. The sender for the gauge is also in the thermostat housing. It is the little one with only one wire attached with a slid on connector. Just because the gauge still works has nothing to do with the fuel injection. Believe me on this one, I've had this sensor go bad and it does exactly what you describe. Smoked like crazy, won't barely idle and only cleaned up/ran half a$$ decent if you rev the engine. This is because when the sensor goes bad, the ECU goes full rich just to be safe and not burn up the motor.

The thermotime switch is a cold start device to richen the mixture when you first start the motor. The EFI bible explains it better but it works something like this. When you first start the motor, juice is sent to the thermotime switch. Juice flows through the switch to the ECU and the ECU richens the mixture for good cold start/run conditions. As the current continues to flow a bi-metal switch in the thermotime switch begins to heat up. As it gets hotter it eventually breaks contact and stops sending juice to the ECU, telling it to stop enriching the mixture. In this way, if you start the car cold it enriches the mixture, then if you run it for a while, then shut it off, then go to restart it quickly (say you run inside the store and come right back out) the motor is still hot and does not need this enrichment. So, because the thermotime switch is still hot, and the bi-metal not making contact, the thermotime does not send this signal to the ECU. Engine heat also keeps the switch from making contact. This way, if the motor is first started cold, it gets enriched. But if it is started, shut off, started again ect, it only enriches until the engine is hot. Hope this makes sense. It's called thermoTIME because it only enriches for a given period of TIME.

[zmaster]

thats exactly what my car is doing, i turn the fuelk pump on and its like it gets too rick and floods out. I didn't know the guage was seperate. thank you for your help, i will update when i get a new sender.