Potentiometer

[rcb280z]

6 minutes ago, Zed Head said:

The engine won't spin so there won't be any spark.  

Let me try and rephrase. 

Will the injectors fire fuel in either of the 2 instances, 1- disconnecting starter solenoid wire and turning key to start position. 2-manipulating afm flap with key in on position.

Sorry I didn't make myself clear the first time. Or does it just pressurize the fuel rail?

 

Edited January 18, 2018 by rcb280z

[Zed Head]

Those two things will only power the fuel pump.  The ECU won't fire the injectors unless it sees spark,or coil discharge, on Pin 1, the wire from the coil negative terminal.  If the coil gets power, then the power shuts off, there could be one spark, from breaking the coil circuit.  But the ECU needs to see three sparks before it will open the injectors.

[rcb280z]

1 minute ago, Zed Head said:

But the ECU needs to see three sparks before it will open the injectors.

Oh yeah that's right! Thanks ZH for clarifying. 

[Captain Obvious]

As Zed Head already mentioned, the (normal) injectors won't fire because the ECU won't see any ignition cycles. However (seems there's always a however, doesn't it?)...

If the engine is cold enough, the cold start injector will fire using the wire off the starter technique. Depends on how cold the thermotime switch is. The AFM manual movement doesn't have that drawback. So if you're used to just moving the AFM vane a little bit with the cover off, then using that method is just fine.

One more thing though... All that said, if you have a fuel pressure gauge installed already, you should already know if you've got pressure in the rail even after sitting overnight. Just look at the gauge.

[rcb280z]

1 hour ago, Captain Obvious said:

you should already know if you've got pressure in the rail even after sitting overnight.

It does bled off. As a matter of fact it bleeds down to "0" in about 3 hours. Keep in mind I have an aftermarket fuel pump and no I don't remember witch one. Installed it about 18 years ago. But its bled off for several years now. It's been doing this for a little while now (a year?) and I've now decided I want to fix it. There are times it fires right up and others not. The fuel pressure gauge pressurizes in about a second so I know fuel is getting there quick. So when it does start the way its supposed to in the morning I'm guessing there is maybe residual fuel in the cold start injector, just enough to start the engine and at that moment the fuel rail has pressurized enough to keep the engine going, maybe?

Today is one of those days that it worked perfect. I heard the cold start injector fire, click sound, and within a split second the engine was purring away.  There is another member that suggested I look into the ignition switch. Guess I can do that next. Just hope I stay motivated to keep plugging away at fixing it. I'm curious as to what it could be. All the resistance readings are good, as you verified as well. So I'm baffled. 

[Captain Obvious]

My check valve holds sometimes and other times it doesn't. And I do notice a difference in starting times. So that could be what's getting you too.

Get into the habit of checking the fuel pressure gauge before you try to start it and see if you've got a correlation there.

[rcb280z]

That sounds like a plan.

[SteveJ]

With seeing many threads about losing pressure because of the check valve, I have to wonder if anybody has tried a check valve like this:  https://www.amazon.com/Airtex-CV8000-Check-Valve-E8120/dp/B001NKS48G

[rcb280z]

1 minute ago, SteveJ said:

With seeing many threads about losing pressure because of the check valve, I have to wonder if anybody has tried a check valve like this:  https://www.amazon.com/Airtex-CV8000-Check-Valve-E8120/dp/B001NKS48G

I did actually try one similar to it and it didn't hold the pressure. But I never found out if "it" was the cause of the bleed off. I clamped the return line and the pressure bled off. I pulled the fuel rail and pressurized it to watch for dripping injectors and saw none. Same thing with cold start injector. 

IIRC Fastwomen had a thread out on it several years back. I can't find it though.

I may just start over and run all the tests again. It baffled me when clamping the return line and CSV line that the pressure bled off.

[siteunseen]

 

[rcb280z]

Thats weird, I searched for that exact thread and got nothing. Thanks Cliff.

[rcb280z]

I remember now. When the aftermarket check valve failed I figured it was due to the return line pressure getting too high. Looks like all these aftermarket check valves are low pressure ones.