Oil Pressure Reading Backwards [Archive] - DFWstangs Forums

: Oil Pressure Reading Backwards


TX_92_Notch
04-02-2006, 05:06 PM
I just got my new motor (306, 1992 Fox) installed and running (finally). The oil pressure gauge is reading backwards.

When I rev the engine a little and it builds oil pressure, the gauge goes down, as opposed to up!

When the key is off, the oil pressure gauge seems to read where it's supposed to, which is f'ed up because there should be no oil pressure, right? Then when started, the oil pressure gauge goes down... behaves exactly like it would if it was working right, just everything is reversed on the gauge. :confused:

I put a new sending unit on it during the motor swap, surely the oil presure is not actually dropping...

Anyone ever had this problem? Any thoughts?

Dacotua
04-02-2006, 06:23 PM
I just got my new motor (306, 1992 Fox) installed and running (finally). The oil pressure gauge is reading backwards.

When I rev the engine a little and it builds oil pressure, the gauge goes down, as opposed to up!

When the key is off, the oil pressure gauge seems to read where it's supposed to, which is f'ed up because there should be no oil pressure, right? Then when started, the oil pressure gauge goes down... behaves exactly like it would if it was working right, just everything is reversed on the gauge. :confused:

I put a new sending unit on it during the motor swap, surely the oil presure is not actually dropping...

Anyone ever had this problem? Any thoughts?

Stock oil pressure gauge on the fox are really innacurate. I gave up on it years ago and installed an aftermarket gauge. My stock gauge barely goes above the red these days.

mustangguy289
04-02-2006, 06:25 PM
Are they electrical gauges or mechanical? im guessing electrical..... maybe check ur wire going to the pressure sending unit...

Fordfans21
04-02-2006, 06:36 PM
disconnect it and get an aftermarket gauge...stock gauges blow

TX_92_Notch
04-02-2006, 10:23 PM
disconnect it and get an aftermarket gauge...stock gauges blow

I may save up and get a full set of Autometer gauges and the dash kit from www.florida50.com

I just put in a 306 and would like to have some more accurate readings.

The stock tach has gone completely haywire as well.

TX_92_Notch
04-02-2006, 10:24 PM
Stock oil pressure gauge on the fox are really innacurate. I gave up on it years ago and installed an aftermarket gauge. My stock gauge barely goes above the red these days.

It's not so much that it's inaccurate. Honestly, it's probably reading accurately, but the needle is moving in the wrong direction.

Turn the key on, the needle goes to the top. Start it, the needle moves down as though it's reading pressure and moving, but in the wrong direction. Give it some throttle, and the needle moves even further down.

Wierdest thing I've ever see a gauge do.

TX_92_Notch
04-02-2006, 10:26 PM
Are they electrical gauges or mechanical? im guessing electrical..... maybe check ur wire going to the pressure sending unit...

Stock electrical. The one reason why I wouldn't think it's the wire is that it worked fine when I pulled the motor out.

All I did to the wire is cut off the stock 90 degree connector and put on a female connector that works with the oil pressure sending unit I bought.

Not sure if that would make a difference?

cobra186
04-02-2006, 10:36 PM
If you bought a new oil sending unit make sure it is the correct unit for gauges. Sometimes the idiots beind the parts counter will give ya' one for the old style "idiot lights" and they do not interchange.

Fordfans21
04-02-2006, 11:13 PM
is it a 2 wire connector? i dont remember...you could have switched the wires by accident. if you want a accurate reading get a known good gauge and hook it up. anyone at a race shop or someone off the board should have one to borrow or "rent"

relic
04-03-2006, 09:16 AM
work behind the dash any? if so, x2 on the wires of the gauge itself. No work behind the dash, try calling up a diff store or Dallas Mustang to see which sending unit is a direct stock replacement, just to verify that they gave you an applicable unit. if it was one for the 'idiot lights' then I'd think the gauge would go up when your pressure either got way low or way hi. Next shot, x2, or 3.. or 4... on the stock gauges suck post. last but not least, might think about not running it till you can verify that your pressure is not actually going down, not a fun thing to do now that you went through all the trouble of swapping that 55K stock block for a fresh 306 long with that heads/cam/intake swap, but it's better to make sure there's not a prob then to find out that there is and you just burnt a bearing....

Just my pair of pennies..

gl with it man, I'm waiting on a billit timing set to get in from Summit so I can bolt everything back together, better than new of course, then I'll be playing the same game.

relic
04-03-2006, 09:17 AM
oh yea, and gratz on getting everthing back together and swapped out.

TX_92_Notch
04-03-2006, 12:03 PM
might think about not running it till you can verify that your pressure is not actually going down, not a fun thing to do now that you went through all the trouble of swapping that 55K stock block for a fresh 306 long with that heads/cam/intake swap, but it's better to make sure there's not a prob then to find out that there is and you just burnt a bearing....

I thought about that... I let it run in the driveway for a few minutes while I was investigating the wiring and sending unit. Never had any overheating problems or interesting sounds. Discovered that the female connector on the wire was broke in half. So I put a new one on and it still did the same thing.

I don't think I'm lacking oil pressure - and the leak at the valve cover lets me know I've got oil to the top of the motor...

It did heat up to around 210-220 at one point, but it was probably an air pocket in the coolant. I added more coolant and it hasn't gone over 200 degrees since. I know that's a tad on the high side... but we'll get that worked out too.

So far I've driven it around the block and about 2 miles to a friend's house. No problems from the motor - I would think it would have done something by now if the oil pressure was actually dropping.

AL P
04-03-2006, 12:14 PM
I've been through this shit before. First thing you need to do is get a mechanical gauge on the thing and check the pressure with it. If it still drops when you give it more rpm then the only thing I can think of off the top of my head is that the pickup on the pump could possibly be too close to the bottom of the oil pan. Did you measure this distance when you re-assmbled the engine? It should be a quater of an inch (.250"). I don't know if you installed a main girdle on the engine but if you did, it is real easy to get the pickup in a funky position.

AL P
04-03-2006, 12:16 PM
I forgot to mention that you could also have a problem where the pickup bolts to the pump itself or where the pump mates to the block. A mismatch at any of these points can cause a leak and make the oil pressure do all sorts of whacky shit. A severe leak at the sending unit will also do the same thing.

TX_92_Notch
04-03-2006, 12:18 PM
oh yea, and gratz on getting everthing back together and swapped out.

It was fun, but a royal pain in the ass at the same time. I put the heads on backwards and had to take them back off. Broke a lower intake and had to replace it. Then dropped a bolt into the lower and had to take it back off. Bolted the long tubes in place and discovered 3 stripped holes... had to pull the motor back out to tap those out. The story goes on and on... definitely learned a few lessons.

I just hope it runs like it sounds. Judging the sound (exhaust note, idle, lope, etc)on a scale of 1 to 10, I'd give it an 11 :D

blackjack
04-03-2006, 12:19 PM
you might of installed your new motor backwards

TX_92_Notch
04-03-2006, 12:22 PM
First thing you need to do is get a mechanical gauge on the thing and check the pressure with it. If it still drops when you give it more rpm then the only thing I can think of off the top of my head is that the pickup on the pump could possibly be too close to the bottom of the oil pan.

I plan to install a mechanical gauge and check it that way. And no I didn't measure the distance. Simply re-used my old pickup and pan with a new oil pump.

I don't know if you installed a main girdle on the engine but if you did, it is real easy to get the pickup in a funky position.

No main girdle...

relic
04-03-2006, 12:49 PM
you might of installed your new motor backwards


lmfao


.... would be a bit difficult.. gotta try that one.....

relic
04-03-2006, 12:54 PM
It was fun, but a royal pain in the ass at the same time. I put the heads on backwards and had to take them back off. Broke a lower intake and had to replace it. Then dropped a bolt into the lower and had to take it back off. Bolted the long tubes in place and discovered 3 stripped holes... had to pull the motor back out to tap those out. The story goes on and on... definitely learned a few lessons.

I just hope it runs like it sounds. Judging the sound (exhaust note, idle, lope, etc)on a scale of 1 to 10, I'd give it an 11 :D


sounds like ya had fun... I've broken of 2 bolts int he stock heads, had to get a set of ported gt-40's and a nice moderate cam from a friend of mine, then broke off one of the bolts off the harmonic puller set.... that was fun.. so now I'm waiting on a timing chain and a harmonic balancer to get here from summit to put all the shite back together.. then I have to douche the thing like 4 times with all the shit that's fallen down into my oil pan while the timing cover's been off... is gonna be fun lol