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'88 oil pressure

New User
Posts: 32
Joined: 09/12
Posted: 09/29/12 09:36 PM

I purchased my '88 GT a few years back and it always had a problem with low oil pressure. I have changed the oil pressure sensor twice as well as oil grade and types and still the gauge needle almost bottoms or remains half way below the center normal setting.
Any help will be apreciated


Post Reply
Posts: 455
Joined: 04/12
Posted: 09/30/12 08:59 AM

look at the size of your oil pressure switch..

does it look like this???

do you have a harbor freight nearby... you might want to use a tool like this oil pressure test gauge to check the mechanical oil pressure..

Image 12200

ford used aluminum bodied oil pumps and they do wear internally. reducing oil flow.. less oil flow.. less pressure ...

its almost impossible to get the oil pan on a fox bodied car with the engine in...
i have done it on the 83 tbird i used to have..  but it took a significant about of work. if i had an engine hoist at that moment it would have gone easier.. i don't recommend attempting to get the pan down.. its easier to pull the motor..

there is another way to check the oil pump output ... this i usually use a remote starter button...

i unplug the ignition coil.... so NO spark can be created...

i hook up the remote starter switch.. and verify the engine will not start..

i crawl under the car.. remove the oil filter... with a catch pan positioned in the proper area...i then crank the engine with the remote starter switch... this pushes oil out of the oil filter mount..  this is a subjective test... it should have a nice full flow coming out.. not just a dribble..

i also use this same process when i am done installing new oil pumps or the pan ... as its a LOT easier to prime the oil pump this way...  with the filter off... then the filter goes on... from the drivers seat.. crank the engine till you get some kind of pressure indication..  restore the power to the coil... and start the engine..    warning.. once in a while.. you run into one that the injectors were spraying. but with the KEY off. there should be NO power to the fuel injection system..

please use extreme care when installing the oil pump intermediate shaft...  the stock replacement shafts are just fine for street..     the cranking test with the filter off.. verifies the oil pump works before you start the engine..

OH... and for those who want to attempt to get the oil pan off a fox body without pulling the motor..  it involves pulling the motor upward with a transmission support bar.. till the bell housing is bumping the floor pan..    using 3/4 inch all thread with various sizes of washers to compress the lower control arms into the top of the cross member..  then disconnecting the steering coupling and dropping the cross member..   it would be easier to release the lower control arms from the spindles and remove the coil springs.. then the whole cross member comes out.. allowing you free access..  this is just a lot more work..  and then you have to reassemble the suspension also..  

Post Reply
Posts: 455
Joined: 04/12
Posted: 09/30/12 09:11 AM

oh..... ONE MORE THING... before you attempt any of the ABOVE...

please check the grounds... its EASY...

take a digital volt meter.. set it to 20 volt DC scale....   start the engine.. turn on the headlights.

1. test across the battery posts.... 14.1 to 14.7 volts is expected..

2. test from the Negative battery post to the engine block.  0.04 volts is expected

3. test from the Negative battery post to the body...  0.02 volts is expected..

4. test from the engine block to the body.... 0.02 volts is expected..

if you get 0.00 volts DC on these last 3 tests.. change the meter setting to 2 volts DC.. and retest the last 3...

if you get more than the 0.04 or 0.02 volts dc.. then you have a bad ground between those parts.. repair is needed.. taking the ground connections apart and wire brushing them...

since gauges use ONLY ONE WIRE.. the ground side is the other wire...

if you have a bad ground.. and this 2 minute test will prove they are good or bad...  the gauges will be incorrect..  

Post Reply
New User
Posts: 32
Joined: 09/12
Posted: 09/30/12 06:27 PM

Thanks for the help and I am just overwhelmed thinking at how big the task is just to replace the oil pump. The oil pressure sensor looks exactly like the one on the photo.
I have other questions though:

1. what replacement oil pump would you recommend?
2. I don't have a problem with the rest of the gauges, so can I assume that the ground is ok?  


Post Reply
Posts: 455
Joined: 04/12
Posted: 09/30/12 07:44 PM

A1.  just a stock replacement oil pump  is good enough for almost all the applications... do replace the intermediate shaft also.. some pumps come with them...  

A1b   its about 20 minutes including the time to disconnect the coil and jack up the car to remove the oil filter and crank the engine.. to actually take a look at the flow while the engine is cranking...  a friend can turn the key.. saves the cost of the remote starter button...

2...  digital volt meters are CHEEP... the can be had from 7 to about 25 bucks..   i personally aim people at the 20 buck version from harbor freight.. 37772...  its very handy.. its very simple to use..  it does not shut its self off while you are testing..  if it gets broken.. you are only out 20 bucks..

the test i outlined above i can do in under a minute...  i have found so many fords and other cars that have GROUND ISSUES.....

the oil pressure test gauge is handy .. but its 20 or 25 bucks from HF also..

0-4 PSI - Open Ckt
4-8 PSI - 24-36 Ohms
90 PSI - 8.5-17.5 Ohms

with an 88. you are lucky. that you actually have a somewhat working gauge.
the 89 and up models with a gauge.. actually used a reversed pressure switch.. not a variable sending unit..  the later switch is open at 0.. closes at 5 psi... shorts the wire to ground.. but on the 89 model.. there is a resistor in the circuit..  so it brings the oil  gauge up to 1/4 to 5/16 mark...  fooling almost everybody.. rock stable oil pressure..  

Post Reply
Posts: 261
Joined: 08/11
Posted: 10/01/12 06:36 AM

Wayne, you are correct on the pressure switch just "turning on" the gauge, but that's on the 4cyl cars. The 5.0L gauge cluster and sender still read actual pressure (of course no numbers on the gauge face though).

I've replaced a couple of pumps in the car and what I do is remove the upper intake for cowl/firewall clearance, jack the engine up until it is against the firewall/trans tunnel, and unbolt the oil pan. You won't get the pan physically out, but it will be down about six inches and you can remove the oil pump and pickup tube and snake them out between the block and pan. Some of the work is almost by feel, but it can be done. The worst part is getting the block surface clean and the new gasket in place, especially at the rear of the engine. Like I said, not the best route, but it is possible without removing the whole engine or the crossmember, both big jobs for a shade-tree flat-backer...

Mark Houlahan
Brand Manager
Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto
2005 F-150 4x2 4.2L V-6/4R70W Auto

Post Reply
Posts: 455
Joined: 04/12
Posted: 10/01/12 07:28 AM

mark.... do you have one of these around your shop???

Image 11976

they are not always 75 ...

freeze plugs...   motor mounts... oil pans...  engine support while the transmission is out...

on the front wheel drive cars... you can hang the engine and transmission while you drop the entire sub frame..  

so much better that a pipe and chain...  or blocks of wood holding the engine up while the motor mounts are being replaced...  

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New User
Posts: 32
Joined: 09/12
Posted: 10/02/12 10:16 PM

Wayne, thanks for the help  

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