Electronic boost gauge goes wack above 5k RPMs
07-26-2007, 11:05 AM
#1
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Electronic boost gauge goes wack above 5k RPMs
As most of you know I have a pretty trick setup (if I do say so myself) for my AFR and boost gages in the center airvent.
For the longest time I've thought my SCer belt was slipping because I would hit 5-6psi of boost, and then the boost would fall off - sometimes going to vacuum! It was very frustrating because I would tighten the belt and it still seemed like it was slipping.
I recently did some data logging and when I did my run I saw the boost gauge do it's typical thing... DAMN BELT!
or so I thought. I looked at the the data log and WTF! Boost went up to 6.5psi and held...
Son of a @!%^&%!
So I hooked up an analogue gauge to confirm and sure enough... the analogue gauge held as well. I spoke to the manufacturer of the digital gauge and they suggested I put an air compressor to the line and see what happens. So I put 10psi to the line and everything was happy. They also said to make sure it's away from any ignition wires. The sender is already in the passenger foot well, so it's pretty far away, but to be sure I pulled it away from the CE panel. No change.
Then I spoke to DR the other day and he said he used to have issues with electrical components (radar detectors, etc.) freaking out when you hit about 5500 RPM. Ding ding ding... that seems to be where my issue occurring. Every time I get north of 5k RPM, the guage goes wacked!
So here are my questions,
1. What would cause this to happen?
2. I assume it's some kind of voltage drop or EFI. Could I wire in a capacitor that would help isolate it? I don't know the draw, but I doubt it's very much.
3. Any other thoughts or suggestions?
What really pisses me off, is that for the past 9 months I thought I was chasing a belt issue, when I was really chasing a faulty reading on a guage. MFer!
For the longest time I've thought my SCer belt was slipping because I would hit 5-6psi of boost, and then the boost would fall off - sometimes going to vacuum! It was very frustrating because I would tighten the belt and it still seemed like it was slipping.
I recently did some data logging and when I did my run I saw the boost gauge do it's typical thing... DAMN BELT!
or so I thought. I looked at the the data log and WTF! Boost went up to 6.5psi and held... Son of a @!%^&%!
So I hooked up an analogue gauge to confirm and sure enough... the analogue gauge held as well. I spoke to the manufacturer of the digital gauge and they suggested I put an air compressor to the line and see what happens. So I put 10psi to the line and everything was happy. They also said to make sure it's away from any ignition wires. The sender is already in the passenger foot well, so it's pretty far away, but to be sure I pulled it away from the CE panel. No change.
Then I spoke to DR the other day and he said he used to have issues with electrical components (radar detectors, etc.) freaking out when you hit about 5500 RPM. Ding ding ding... that seems to be where my issue occurring. Every time I get north of 5k RPM, the guage goes wacked!
So here are my questions,
1. What would cause this to happen?
2. I assume it's some kind of voltage drop or EFI. Could I wire in a capacitor that would help isolate it? I don't know the draw, but I doubt it's very much.
3. Any other thoughts or suggestions?
What really pisses me off, is that for the past 9 months I thought I was chasing a belt issue, when I was really chasing a faulty reading on a guage. MFer!
Last edited by AO; 07-26-2007 at 11:49 AM.
07-26-2007, 11:14 AM
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Andrew,
Just guessing here, but could you try to run the wire in shielded cable? This won't help if it's a voltage fluctuation issue, but since the manufacturer said to re-route the wire away from the ignition wires it may be picking up inductive current and shielded or twisted pair wire might alleviate this.
It would be easy to test if your issue is consistent and predictable without completely replacing the wire, just run it on the surface like a jumper without actually routing it until you've confirmed it fixes the problem.
Just my .02.
EDIT: Damn you Imre, you beat me to it!
Just guessing here, but could you try to run the wire in shielded cable? This won't help if it's a voltage fluctuation issue, but since the manufacturer said to re-route the wire away from the ignition wires it may be picking up inductive current and shielded or twisted pair wire might alleviate this.
It would be easy to test if your issue is consistent and predictable without completely replacing the wire, just run it on the surface like a jumper without actually routing it until you've confirmed it fixes the problem.
Just my .02.
EDIT: Damn you Imre, you beat me to it!
07-26-2007, 11:33 AM
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I've never heard of any kind of 'flexible shielding' if that's what you're referring to.
I would just run a new wire with the same or thicker wire in a shielded or twisted pair (or both) jumper to see if it works. You should be able to replicate the number of conductors and correct gauge wire with a short length of STP (shielded twisted pair).
I would just run a new wire with the same or thicker wire in a shielded or twisted pair (or both) jumper to see if it works. You should be able to replicate the number of conductors and correct gauge wire with a short length of STP (shielded twisted pair).
07-26-2007, 11:49 AM
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Maybe it's worth putting a scope on a 12V source and seeing how dirty it is, or gets above 5K. Interesting that DR also sees this on his, so this may point to a common issue we all have but don't know about it. Maybe the alternator/regulator starts to freak at high RPM. That could lead to all sorts of issues. What affect does this have on the LH and EZK??
Food for thought at least.
Food for thought at least.
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07-26-2007, 02:17 PM
#9
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Hello Andrew,
It's almost certainly an EFI issue, probably due to igntion HT lead pickup. If you can replace the lead from sensor to unit with some audio screened lead, that may help. Don't use radio coax cable).
If that fails some RF bypass capacitors at the unit may help, connected across the sensor leads . You can also buy clamp on ferrite supressors that may help. You will just have to experiment.
The problem might be RF pickup on the power supply leads, the same techniques apply here.
It's almost certainly an EFI issue, probably due to igntion HT lead pickup. If you can replace the lead from sensor to unit with some audio screened lead, that may help. Don't use radio coax cable).
If that fails some RF bypass capacitors at the unit may help, connected across the sensor leads . You can also buy clamp on ferrite supressors that may help. You will just have to experiment.
The problem might be RF pickup on the power supply leads, the same techniques apply here.
