Oil pressure guages going dead under partial throttle

[CManT1914]

Like it says, I replaced my braided lines running to my oil pressure lines tonight. I have a 8.5" long 4AN line running to a 1/4" tee-fitting, where the factory oil pressure unit sits on one side. On the other side, another 12" 4AN braided line runs to the AM unit, sitting next to my fuse box. I had to lengthen the factory wire for the unit by about 3 inches. They work fine at idle, and at cruising, but under acceleration or revving, they both go dead. WTF?! I have no idea why this is happening. It can't be electrical, because they are wired seperate. It can't be a blockage in the lines, because then they wouldn't work at all. My friend said tonight it sounded like I had a vacuum leak because of the way the car was idling (it was idling a little rough after initial startup, but I had the battery disconnected for about 2 hours). Would a vacuum leak cause oil pressure loss under throttle? I am stumped, these damned oil pressure gauges are pissing me off. Any help is appreciated, thanks.

 

[CManT1914]

ttt

 

[mackey]

It really sounds like the place you grounded them isn't making much contact.

 

[CManT1914]

It really sounds like the place you grounded them isn't making much contact.

Well that's what it seems like, but the stock gauge does it too. I have never messed with the wiring for the stock gauge, except for extending the lead wire. They both do it at the same time and everything. When I extended the wire on the stock sending unit, I didn't reuse that rubber insulated boot if that matters. I simply put a spade connector on the end and slid it over the terminal and dropped a nut over the top of that. I don't see how that would effect anything, but I'm gonna pull the wire off the stock unit tomorrow and see if it still does it I guess. I don't know what else to do.

BTW: How fragile are the sending units? My friend dropped my autometer sending unit today, and I was like DUDE WTF?!!

 

[HISSIN50]

Vac would not make a difference.

I thought about what Mac said and that was a thought I had initially too, though it does not fit for what you are seeing I dont think.

I think his point was that the sending units have to be grounded. Usually this is accomplished via the threads themselves (you old set-up did this via the sender threads themselves). I will sometimes put a ground wire on the sender body itself, if I have doubts. For example, if your sender was mounted with rubber lines running to it, the gauge would not read since the sender is not grounded. The sender is like a fan switch in that it just becomes more or less resistive in the ground path (which is its threads into the block). You can test this all real quick with a wire with alligator clips. clip into the sender body or Tee, etc, with one clip, and then put the other clip on a decent ground and see if the gauge reading changes. I am not sure it will.

But I cant think of anything that is not mechanical that would cause this issue. Your oil level is not low, is it?

Sorry to not have more info. Good luck Chris (and thanks for the kind words about the ashtray panel dealie on the other thread).

 

[CManT1914]

Vac would not make a difference.

I thought about what Mac said and that was a thought I had initially too, though it does not fit for what you are seeing I dont think.

I think his point was that the sending units have to be grounded. Usually this is accomplished via the threads themselves (you old set-up did this via the sender threads themselves). I will sometimes put a ground wire on the sender body itself, if I have doubts. For example, if your sender was mounted with rubber lines running to it, the gauge would not read since the sender is not grounded. The sender is like a fan switch in that it just becomes more or less resistive in the ground path (which is its threads into the block). You can test this all real quick with a wire with alligator clips. clip into the sender body or Tee, etc, with one clip, and then put the other clip on a decent ground and see if the gauge reading changes. I am not sure it will.

But I cant think of anything that is not mechanical that would cause this issue. Your oil level is not low, is it?

Sorry to not have more info. Good luck Chris (and thanks for the kind words about the ashtray panel dealie on the other thread).

How would I ground the sender unit itself? What are some mechanical issues that could cause this problem?

EDIT: I noticed the sending units are contacting various metal pieces (like what I think is an A/C line), would this cause them to short or anything?

 

[HISSIN50]

As long as the sender connection is not touching metal, it should be ok.

You can use aligator clips on a piece of wire and clip it to the body of the gauge sender and then clip the other end to a clean ground.

I once used a long stretch of bare wire, wrapped around the sender (near its base, way away from the gauge's connection) and then zip tied to keep the wire in place and tight. . The other end just goes to a ground you like.

I would just do the aligator clip thing (takes 30 seconds to hook up) and see if it makes a difference.

I find it strange that your old OP gauge alone never did this, but now it (and your new gauge) go to zero.

A lack of oil volume can cause no pressure at WOT, as can a misadjusted oil pickup. I doubt either are your issues. I am wondering if for some reason Oil is not making it up to the senders at WOT or that something shifts and you lose the gauge ground at WOT.

I would try grounding the sender and go from there Chris.
Good luck.

 

[CManT1914]

I tried relocation them today to make sure they weren't touching anything they shouldn't be, and now they are both completely dead. WTF?? I'm about to rip them out (the AM one anyway) and throw it in the god-damned trash can.

 

[HISSIN50]

Chris, what happened when you put the ground on the sender? W/O a ground, the gauge will be dead. And dont sweat it - it sounds like a gauge issue and not your motor. I would be happy about that. It will work out. Hang in there bud.

 

[CManT1914]

Chris, what happened when you put the ground on the sender? W/O a ground, the gauge will be dead. And dont sweat it - it sounds like a gauge issue and not your motor. I would be happy about that. It will work out. Hang in there bud.

I haven't tried grounding it yet. I don't have any tools at my house. I'll take a look at it tomorrow though. I'm not real worried about it anymore, all that crap will have to come out when I do my heads/cam swap anyway. If nothing else, I'll redo it all then when it's actually fairly accessible, lol. Thanks JT