Engine test stand

[Dave WM]

I was going to replace the WTS with the pot, not put it in series, that way I can adjust from 0-5k ohms, the WTS will have no effect this way, but I can adjust and see what happens.

I did NOT check the leaking FPR vacuum line recently but will again, since I could have missed it.

I was looking over the AtanticZ tips on grounds, since I have only a partial setup. I could not see any grounds in the wiring diagram off the EFI harness itself, so nothing there is grounded. I did notice on my car the AFM is grounded but I don't see any electrical reason why. It does not appear to have any electrical connections to the case, but I will ground it anyway.  there was a EFI ground noted on the tips section but that seems to be for a secondary harness that controls non EFI functions (there was a temp gauge, and a water temp switch for dist advance or EGR from what I could tell). The EFI harness (the big one) had NO eyelets that would require grounding.

The Battery IS grounded to the engine block (the only thing I can ground to) by connecting the negative starter cable to the batter and the starter bolt that fastens to the engine thru the adapter plate. The only things that would use the ground that I can see would be the therotime (not using it), the spark plugs, and the fuel pump (not using the switch off the EFI for that at this time).

Since the AFM has a huge part to play in fuel mix, I will connect a ground wire from the mount bolts to the engine block for what its worth. I could see it if somehow it was electrically connected as part of a voltage divider like a pot that uses the case as the center lead, but that does not seem to be the case here. But it cant hurt and I am running out of ideas.

could not pickup any new plugs today, apparently they are not a stocked item at most of my local part stores. So will take some more time and see if I can get the relatively new ones super cleaned up, and order some new ones to test later.

I suppose I should ground the case of the EFI as well, installed in the car it is after all ground thru the mount screws.

 

 

 

Edited April 28, 2019 by Dave WM

[Dave WM]

another ground issue. I was looking over my grounds, on my 75 cali car (one set of coils on dizzy) I have a R and G wire from dizzy to term block. The term block connects to an engine harness which I presume goes around the front of the car, eventually working its way back to the passenger side compartment mounted ignition module. One this term block I found a ground wire from the same green wire to the AFM ground point. So on side of the pickup coil is grounded? there is nothing in the FSM showing a ground on the pickup leads. To further complicate maters the ground lead does not look factory (to new a looking eyelet). So I don't know if this was added or a fix for a broken lead.

Lastly on my alternator I have a huge black earth lead connected to the earth bold on the alternator. Why is this? should the case of the alternator not be a sufficient enough ground? or is it not reasonable to relay on all the mount bolts to provide a good ground in this case? The black wire goes into the wire harness so I don't know exactly where it ends up, I presume as a connection somewhere near the starter negative lead that goes back to the battery.

[Captain Obvious]

IIRC, there are no ground connections to the EFI harness other than the large wire that leads directly over to the battery. All the other connections (other than the thermotime) are derived inside the harness from that one single ground.

I don't think the distributor pickup is supposed to be grounded in any way. In fact, in an effort to prevent noise pickup from any other sources in the car, it's twisted pair to reduce antenna loop area. I haven't looked at in depth though. On my 77, that terminal block does not connect either side to ground. Don't know for sure about 75.

I also believe the electronics portion of the AFM is floating and not grounded inside the case. So if they ground the AFM case, it's most likely another interference prevention technique. Faraday cage. Grounding the ECU case as well would do the same thing. All the electronics inside are floating with respect to the metal shell, but it can help to reduce outside interference from things like the ignition flyback.

In the end though... I doubt any of that is the root cause of the problems you're having. Sounds like it's getting better though!!! Step by step!

[Dave WM]

yep, CO that was my thinking, I kept reading about the importance of grounds, being I had none I wanted to look into it, and just could not see it. The distributor ground is a real bugger, but like I said it did NOT look factory.

[Dave WM]

more progress. hooked up the fuel pump to the fuel pump relay, getting rid of the power strip to clean up the wiring. Alt is working fine 14-15v, so no more dead battery and good voltage supply for everything else.

It pretty much will fire right up, then chug chug very loud. Throttle it up and down until it catches and the idle shoots up, runs smoothly and seems fine (also MUCH quieter), will run like that for a long time (smooth). I can make it start chugging again IIRC it was a combo of altering timing and resistance of the WTS and idle screw then it will drop down in rpm and resume chugging (sometime with a backfire out of the tail pipe as well).

I am starting to think its a low idle timing issue/ignition issue, so next up will be the timing light. I wonder if it could be a weak spark at low RPM? one thing I noticed on the bench was there was a critical speed the distributer needed to spin to fire the coil. Like the signal from pickup was too weak, spin it faster and all was ok. Perhaps ZH resistor may come into play here.

Edited April 28, 2019 by Dave WM

[Zed Head]

Sticking advance mechanisms in the distributor?  Vacuum or centrifugal.

Air gap might be affected by RPM.

[Captain Obvious]

3 hours ago, Dave WM said:

I am starting to think its a low idle timing issue/ignition issue, so next up will be the timing light. I wonder if it could be a weak spark at low RPM? one thing I noticed on the bench was there was a critical speed the distributer needed to spin to fire the coil. Like the signal from pickup was too weak, spin it faster and all was ok. Perhaps ZH resistor may come into play here.

I'm not a timing expert, but I wonder if you would even see much of an impact at no load condition even if the advance mechanisms (centrifugal and vacuum) were working at all. I mean, on the road under load, you'd be losing lots of power and would certainly notice it. But under no load conditions, I'm not sure you'd see much impact. I can't easily disable my mechanical advance, but maybe I'll try disconnecting my vacuum advance and seeing what happens.

As for the distributor signal to the ignition module... The VR is just a changing magnetic field cutting through a coil. The faster it changes, the higher the induced current and the higher the voltage that could be generated in an attempt to push it.  So yes... The output voltage is proportional to the rotation speed. That said, however, it has to work well enough at starter cranking RPM or the engine would never even start. And I'm assuming your starter spins a lot slower than even a low idle speed.

[Dave WM]

thanks CO, I am just grasping at straws. I cant get my head around why the plugs foul so quickly, yet leaning the mix via the pot in place of the WTS causes the engine to run more poorly.

I am going to try it again and just let it run out of gas (2 gallons). the chug chug chug throttle up catch and run normal is really odd to me. The best running resistance was about 2.5k even after warm up. If the injectors were dirty or partly clogged needing the richer mix, how could I get such obvious fouling? Next run will include a color tune plug installed as well.

 

[Captain Obvious]

Remember that engines don't want to run slow and they hate running at idle. They also hate running cold. So it wouldn't be unusual for it to run poorly until it warms up. But once it warms up, it should be much more robust. And once the engine warms up the WTS should be about 250 Ohms. So if it runs better at 2.5K even after warm-up, then there's something going on.

If it wants a higher resistance on the WTS, then it sounds like you're running lean. But for confirmation, you should be able to do some quick and dirty tests to see if it's rich or lean. I know you already know this stuff, but just in case:

I assume you've got some of the vacuum connections on the intake manifold blocked off with rubber caps? Like the brake booster connection? You can pull the cap off a tiny bit to manually modulate some additional air into the intake manifold and see how the engine reacts. If the speed goes up and it steadies out, then you're probably running rich. If it get's worse and starts to misfire, you're already lean and making it worse by letting extra unmetered air in. Move slowly though... A little bit of air here can make a big difference.

You can also adjust the mixture by moving the AFM position around, but same thing... A little motion there can make a big difference. It's squirrely.

Have you ever taken a measurement on the ATS? It should be reading about 2K Ohms at your ambient this time of year.

[Dave WM]

finally something new to report..

there are 3 wires from the distributer, to small rings and one large ring.

I have been connecting one small and one large, tried today, same thing struggle to start chug chug etc... so I connected the 2 small rings, started right up with normal sound, no chug. tried the other small and the large in the past but never just the 2 smalls.

would throttle up etc.. and this is with the WTS hooked up as it should be. I had to stop for work, did not want to run it un attended.

The ign module I am using did not have the setup for the multiple inputs from the distributer. I just had assumed it was a large ring and a small ring.

will try it again from a cold start later with the current setup.

Edited April 29, 2019 by Dave WM

[Dave WM]

started right up no need to monkey with WTS.

Think ZH was on to something about the signal to ign module. Going to have to hit up Jeff to see if he has a tach laying around, I would like to know I have that part of the circuit working right. I don't want to just assume I have the resistor hooked up right. Curious about the RPM anyway as I would like to see if its idling correctly.

Will get video later, but it started instantly from a warm start. I am reading about 40 ohms on the water temp gauge sender which I have previously check as 185 on the gauge. Jeff, I will be hooking up that oil pressure and water temp gauge later.

Edited April 29, 2019 by Dave WM

[Zed Head]

Here's the diagram of the distributor dual pickup wires.  Looks like if you connect the two outside wires, Green and Red, (Edit - I screwed up here. The out side wires would be Red and Brown)m to your module you could get double voltage pulses maybe.  Not sure.

The easy way to check that you have two correct wires might be to measure resistance.  If you're on one pickup coil you'll see ~720 ohms.  Green is the shared wire, red and brown are the independent wires.

Edited April 29, 2019 by Zed Head