CALLING ALL ELECTICAL GENIUSES

Tom Kelly

Active Member
I am reaching out to all you electrical gurus for help. I can’t think of anything else to try.

I have a Speedhut digital boost (only) gauge in my 86. It came with the car when I bought it. It worked fine for years. This Spring I made some changes including the installation of an AEM A/F gauge, changed to an LT-1 MAF with translator and added a powerlogger which also upgraded my scanmaster to 2.2.

At about that time, or soon after, my boost gauge started acting up. It went through some weird phases but here is what it does now.

First start of the morning: Works fine. Initializes properly and settles on “0”. In operation it reports boost numbers consistent with the scanmaster (v 2.2 reports boost and vacuum)

Subsequent starts: Gauge immediately goes to “Sender error” and stays that way. No function at all.

All starts: If you just turn the key on but don’t start the car it initializes normally and settles on “0”. If this is a “subsequent” start as soon as I start the car it shifts to “Sender error”

I have replaced the sender and sender harness. Speedhut has replaced the circuit board twice. None of these have changed anything.

I have tried resetting everything after that initial start by disconnecting the battery for an hour. No change,

I have tried disconnecting the gauge after it has gone to sender error and then reconnecting it. It just goes right back to sender error.

Speedhut has advised me that the gauge ignores vacuum/boost conditions when initializing. They say all it looks at is the 5 volt signal.

Maddeningly it works the first start of the day all the time.

What am I missing?
 

salvageV6

Daily Driver
I'd make sure the power source which I assume is +12 to it stays on at all times when cranking and starting the car.

Assuming a new/known working gauge doesn't fix it.

What clears the sender error? Any wiring installation diagrams for it?
 

Tom Kelly

Active Member
I'd make sure the power source which I assume is +12 to it stays on at all times when cranking and starting the car.

Assuming a new/known working gauge doesn't fix it.

What clears the sender error? Any wiring installation diagrams for it?
I had the same idea. I asked them to "loan" me a working gauge to test. No dice. They told me that the gauge looks for a 5V signal and will then initialize properly. Otherwise it goes to sender error. I would keep exploring the voltage during cranking but it works perfectly first start of the day every day. And not at all the rest of the day. I am trying to figure out what is different from the first start to subsequent starts. Even when I reset the whole electrical system by killing the battery for an hour. It still doesn't work on all but the first start.
 

No disintegrations

Well-Known Member
If the wiring is nicely zip tied and routed just for shits cut as many as you can and let the wiring just hang like a mess. The wire may be reading a radio signal from another wire. If this fixes it then try routing it away from the previous route.
 

dynoman

Well-Known Member
Is the boost gauge connected to the terminal on the powerlogger ?? Does the powerlogger & boost gauge share the same sender ?? If so , separate them and try .
 

Tom Kelly

Active Member
Is the boost gauge connected to the terminal on the powerlogger ?? Does the powerlogger & boost gauge share the same sender ?? If so , separate them and try .
The scanmaster gets it's boost reading from the 3 BAR MAP sensor. This is separate from the sender to the boost gauge. That sender is connected to the vacuum line just outside the vacuum canister. Depending on boost the 5V signal is adjusted and that's what the gauge is reading when initializing. With no boost the signal is 5V. That's what the gauge looks for when initializing. Under boost the signal reduces depending on level of boost. On the other hand, the output from the AEM a/f gauge is also sent to the powerlogger/scanmaster input module via one of the connectors on the gauge..
 

No disintegrations

Well-Known Member
We should of things that are different from the first start of the day. The engine bay will be its coolest. Cool temps are helpful for substandard wires. Perhaps a corroded connection somewhere.

So it has to sit all night in order to work again?
 

Tom Kelly

Active Member
Did you touch or reroute any of the boost gauge wiring during the A/F gauge install ?
Yes it has to sit all night to work again. The new A/F gauge now sits next to the old boost gauge. I changed from a 2 gauge A pillar pod to a 3 pod. They share a common 12V and ground with the fuel pressure gauge. All of the wires and connections are good (the original wiring I inherited was a mess; all redone by professionals; it worked fine for years). No corrosion at all.
 

87GNALKY

Active Member
Long shot WAG here... but ground your multi meter to the neg. battery terminal (use a lead wire if the length is an issue to get all the way to the Batt. and put your posi mult meter lead on the ground point of the gauge ground.. The screw or whatever it is grounded to. If you have positive voltage or even just a small bit of posi voltage on that posi lead, you have a problem. That means that you have a posi backfeed of some type negating the required amount of ground that your gauge is looking for. Yes.. I have seen posi voltage run to what people believed was just a damned old dirty ground under a door jam screw and completely negate the effects of having a -12, -6, -5 volt point of negative contact. Not likely, but if you are chasing ghost already, may as well do the simple stuff first.
 

salvageV6

Daily Driver
Error Messages: - This error indicates that there is no Sender/Sensor connected to the gauge or that there is a grounding issue with the Sender/Sensor. -

This error indicates that the Easy Touch Bezel™ is not properly insulated. This error also occurs if you are touching the bezel when the gauge is powered on

I would check the bezel for proper positioning and check the wiring to the sender itself. I would put a good digital voltmeter on the sender voltage signals using their ground.

Same with the +12 feed.
 

87GNALKY

Active Member
Error Messages: - This error indicates that there is no Sender/Sensor connected to the gauge or that there is a grounding issue with the Sender/Sensor. -

This error indicates that the Easy Touch Bezel™ is not properly insulated. This error also occurs if you are touching the bezel when the gauge is powered on

I would check the bezel for proper positioning and check the wiring to the sender itself. I would put a good digital voltmeter on the sender voltage signals using their ground.

Same with the +12 feed.
Like I stated. Looks like a grounding/ lack of grounding issue. If you have even 1 volt of + trnsmitiing to the grounded point, then you only have a -4 volt ground which will eliminate the required +5 volts needed. You are on the right track though..
 

salvageV6

Daily Driver
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....
 
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