CALLING ALL ELECTICAL GENIUSES

87GNALKY

Active Member
Just re-read your post, put a check valve in the rubber line so it only reads boost no vacuum, the ball holds vacuum which may cause initialization error on subsequent startups, there's probably none left when the car sits overnight if it leaks out, easily verified by operating the vent lever after sitting overnight.

Make sure the ground is alone on that gauge as well, not shared by other gauges or lighting etc.

Plenty of good tests to do....
Yes Sir! Your test subject will be ready and narrow your diagnoses in a few hours for sure. Happy hunting. Very interest as, the phantom issues resolved; are great stickies for the forums..
 

Tom Kelly

Active Member
I never assume.... especially on the internet.
[/QUOTE7
I had thought about the vacuum issue and thought maybe the exact same thing about retained vacuum (after a fresh start) preventing initialization but Speedhut tech help told me that the gauge ONLY looks for 4.5-5.0 volts to initialize correctly. The presence or absence of vacuum in the line doesn't matter. I appreciate the ideas to check and I ill get on that. I have been laid up on crutches with a broken leg for awhile so it may take me a bit. I will report back when/if I get a solution. I understand the grounding issue but am skeptical as if it was grounding why would the fresh morning start always work. That's why I tried disconnecting the battery for an hour to try to simulate the fresh morning start with no electricity left in the system except fresh juice when I reconnected the battery. I thought if coolant temp was the issue ( a relay somewhere?) I tried waiting for the temp to go back to under 100 degrees. The baffling part is why does the first start ALWAYS work fine.
 

dynoman

Well-Known Member
I am wondering where the 5V signal originates in a 12V system. Stupid question?
From the gauge itself. That's why I said to completely separate the gauge from shared power & ground sources ( run power & ground straight from battery )
and reroute the sensor harness just for troubleshooting purposes .
 

Tom Kelly

Active Member
So can I test for the 5V at the sensor end of the harness by disconnecting it from the sensor and putting the positive probe in the connector?
I
 

Tom Kelly

Active Member
Still thinking. If the gauge itself sends the 5V to the sensor then what does it look at when verifying the signal from the sensor. The boost signal? Without boost going on I imagine that return signal should be 5V also. If the gauge is looking to that signal and somehow it is not 5V (as would be the case under boost) then maybe the sensor is sensing boost at the critical moment of start? I wish I understood exactly how it works so I wouldn't be grasping for this.
 

salvageV6

Daily Driver
If you get a nice steady 5 volt signal on the red wire with sender removed using the red and black harness ground wire to the sender to measure from, then you need to test the white wire and red wires with the sender connected using the harness black wire as your ground reference for each reading. To do that most likely you will have to open the harness and probe the wires nothing that can't be fixed easily enough with electrical tape then harness tape.

You need to ask the manufacturer what should be seen on the white sender wire at proper initialization, or measure it yourself with that test setup on the sender harness wiring in both working and not working conditions and note the differences if any.

You also should ask them what they mean by "grounding problems" that could cause the sensor error you are getting as noted in their directions. If the black wire from the gauge to the sender is supposed to be isolated from the battery/chassis car ground completely, it can be measured with an ohm meter, all power OFF to the gauge and measure on the ohms scale between the battery ground and the sender black wire.

Is the sender metal? If so perhaps making sure it isn't grounded by anything other than the harness.

Assuming the main ground and power to the gauge have been isolated as suggested last week.....
 

Tom Kelly

Active Member
Thanks. I'll give it a whirl when I can get out there again. But in my mind I keep coming back to what is different on the first start when it always works fine. I know that it's the pressure in the vacuum line during boost that pushes the diaphragm and reduces the 5v signal. What if there is pressure in that vacuum line (I know.... it's a VACUUM line) but what if somehow after the first start there is pressure in the line during startup. That could push the diaphragm and reduce the signal. It must be only on startup as if I just key on without starting it works fine all the time. That's why I can't understand how it can be any of the normal suspects. Would a grounding problem be this consistent?
 

87GNALKY

Active Member
Thanks. I'll give it a whirl when I can get out there again. But in my mind I keep coming back to what is different on the first start when it always works fine. I know that it's the pressure in the vacuum line during boost that pushes the diaphragm and reduces the 5v signal. What if there is pressure in that vacuum line (I know.... it's a VACUUM line) but what if somehow after the first start there is pressure in the line during startup. That could push the diaphragm and reduce the signal. It must be only on startup as if I just key on without starting it works fine all the time. That's why I can't understand how it can be any of the normal suspects. Would a grounding problem be this consistent?
Give this a try if all else fails, Your A/f gauge is also looking at variable voltages. I haven't read through every post but the A/F voltages are going to change especially after a cold start. If that guage is robbing your boost guage of critical + or - it may cause your boost to read incorrectly. I would try unhooking the A/F sensor from the down-pipe. (You will have to re-calibrate before screwing it back in) no big deal though.. You could have a heated sensor completely interfearing with the voltage as you are sharing the power source. Like I said, haven't read all the post but this is about when the issue started best I can tell.
 

Tom Kelly

Active Member
Give this a try if all else fails, Your A/f gauge is also looking at variable voltages. I haven't read through every post but the A/F voltages are going to change especially after a cold start. If that guage is robbing your boost guage of critical + or - it may cause your boost to read incorrectly. I would try unhooking the A/F sensor from the down-pipe. (You will have to re-calibrate before screwing it back in) no big deal though.. You could have a heated sensor completely interfearing with the voltage as you are sharing the power source. Like I said, haven't read all the post but this is about when the issue started best I can tell.
That's brilliant. The sensor is cold the first start and warm thereafter. It's like someone said earlier....put the boost gauge on its own wiring. I just couldn't think what was different. The a/f sensor could be what's different. I'll act on that. Thanks for the tip.
 

87GNALKY

Active Member
That's brilliant. The sensor is cold the first start and warm thereafter. It's like someone said earlier....put the boost gauge on its own wiring. I just couldn't think what was different. The a/f sensor could be what's different. I'll act on that. Thanks for the tip.
Your welcome brother. I hope this fixes it. I actually am a network engineer for a living so electronics are where I like to focus. However, it is still a long shot... But just maybe you will find that a heated O2 sensor does jack around with the voltages and cause you some issues..
 

Tom Kelly

Active Member
Your welcome brother. I hope this fixes it. I actually am a network engineer for a living so electronics are where I like to focus. However, it is still a long shot... But just maybe you will find that a heated O2 sensor does jack around with the voltages and cause you some issues..
Your welcome brother. I hope this fixes it. I actually am a network engineer for a living so electronics are where I like to focus. However, it is still a long shot... But just maybe you will find that a heated O2 sensor does jack around with the voltages and cause you some issues..
I'm trying to think his all the way through. Is the heated/cold a/f sensor theory consistent with the fact that it ALWAYS works when I just key on and don't start the car. Since there's no exhaust, then no signal?
 

87GNALKY

Active Member
I'm trying to think his all the way through. Is the heated/cold a/f sensor theory consistent with the fact that it ALWAYS works when I just key on and don't start the car. Since there's no exhaust, then no signal?
As soon as the key is on, the sensor starts heating up. So I don't know exactly if that could be the issue. Just looking at all the possibilities with a "ghost in the machine"..
 

Tom Kelly

Active Member
As soon as the key is on, the sensor starts heating up. So I don't know exactly if that could be the issue. Just looking at all the possibilities with a "ghost in the machine"..
Yeah the only way is as someone recommended earlier. Separate the gauge completely from all others and run the harness outside the car. What a pain it was to run al those wires. But I don't see any other way. The problem DID start with the installation of the A/F gauge (among other things at the same time)
 

salvageV6

Daily Driver
Maybe when cranking and starting the gauge loses power, first post I made covered that I believe. Assuming it initializes fine every KOEO.

What testing have you actually done so far?

Thinking worked great for Einstein, testing and experiments are what proved out his theories.
 

Tom Kelly

Active Member
This is true about thinking ..However I am laid up on crutches for the past and future several months and it's hard to do anything so I have been trying to use my noodle to figure it out to the extent I can. I'm optimistic that the THEORY about A/F gauge interference is gonna pan out. That's because it could explain the key on successes and first start success. So my actual EXPERIMENT will be to merely disconnect the 12V from the A/F gauge rendering it useless and see if the Boost gauge works after that. Just sometimes, thinking can lead to the right experiment. I appreciate all the input I have gotten. It shows that many heads are better than one.
 
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