Oil pressure dips to zero for split second when shifting into reverse

Mstng93SSP

You have a nice rear end there Dave.
15 Year Member
Nov 29, 1999
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My 1993 mustang does something that is driving me a little nuts. It has a fresh built 306/AOD running a PimpXS megasquirt system. Car runs good, idles fine and generally has good oil pressure. I have the stock oil "gauge" and an autometer analog oil pressure gauge installed. When at idle, in Park and I shift into Reverse the idle drops slightly as would be expected but the "stock dash oil gauge" drops to dead zero for a split second and then right back to normal. Looking at my autometer gauge it has a very very slight fluctuation when this happens, but it shows good pressure. It kind of feels like the gauge thinks the engine is about to stall, but it isn't. I know I shouldn't have much faith in that stock dash unit but it bugs me that it does this. It seems like when the RPM dips below say 850 it has this effect on the gauge. It never stays at the zero for more than a split second. Anyone have any idea what might be happening?

Thanks

Chris
 
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Mstng93SSP

You have a nice rear end there Dave.
15 Year Member
Nov 29, 1999
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Yes I was thinking the same. It's almost like the signal gets interrupted for a split second. It doesn't really worry me, but it irritates me if you know what I mean......
 

stanglx2002

CT Material here
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Jul 7, 2005
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I have chased oil pressure sensor issues on the factory cluster for a long time. You could try replacing the factory sending unit, but the issue maybe the factory pcb inside the factory cluster. With the clusters getting older the parts on the cluster are now starting to go bad and not just the sensors.

This is a big reason why I swapped to a digital dash over trying to fix the factory one or having a lot of aftermarket gauges. I would for sure trust the aftermarket gauge before the factory any day.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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The dip in rpms causes a similar dip in voltage. At the same time the oil pressure fluctuates and the oil pressure gauge reacts to all this but can't keep up giving the exaggerated needle drop.
 
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2000xp8

SN Certified Technician
Aug 8, 2003
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My guess would be when the reverse lights are triggered it causes a voltage issue.
Similar to the way that when i used to turn on my headlights the temp on my factory gauge would go up.
 

Mstng93SSP

You have a nice rear end there Dave.
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It's not the reverse lights, it has done it once or twice when putting it in drive as well. I have a few spare clusters, I am going to try a different gauge and see if it still does it.
 

Steel1

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Aug 18, 2017
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I'm no expert but 15 psi on a new build would concern me, now if it was 100k+ engine I would feel differently.
Just for reference my 2yr. old 393w build runs about 30-35 psi hot idle with a standard oil pump, I know it's not apples to
apples comparison but I would think yours would be similar.

Probably has nothing to due with the brief drop in pressure on the stock gauge though.

Like I said I'm not a professional engine builder and don't know what bearing clearances you have so take it with a grain of
salt.
 

Mstng93SSP

You have a nice rear end there Dave.
15 Year Member
Nov 29, 1999
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Mililani, Hawaii
@Steel1 thanks for your input. It was a 100% gauge configuration issue. I had run a pipe up from where the sender screwed in, made a T so I could run the factory and the pro comp gauge both. Apparently it was too much because I removed my pipe and T and screwed the pro comp gauge directly in to the sender location and oil pressure improved greatly. This is hot idle. I am good with 20psi hot idle.
20201026_111611.jpg
 
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