Oil Pressure Dropping To 0 Under 1500rpm-???

Discussion in 'Fox 5.0 Mustang Tech' started by BKM48198, May 31, 2014.

  1. I finally got my engine in and fired today, I put together an Explorer 5.0 with my old Mustang cam, the gt40 heads with TFS spring kit installed and the 96 Explorer intake. I t starts and runs but has an exhaust leak on the pass. side at the header, it runs and idles fine but when I let it get under 1500RPM the oil pressure drops to zero on the stock gauge, it did also get a new oil pump, pick-up tube, and oil pan, checking the dipstick it shows full of oil. Any idea why the pressure drops?
  2. faulty stock gauge? Gotta install a real gauge and go from there
  3. I had to take care of a header leak today, then looked for gauges, 2 were too small and the one I had that fits is missing the housing it came in, I tried it and it showed about 12 psi when the stock gauge showed zero, only showed about 30psi at 2000rpm, I'll get a good gauge or an adapter for the other gauges I have and try it again after work tomorrow if I get a chance, I might be working 12 hr shifts again this week. :(
  4. When you installed the oil pump did you put the gasket on the pick up? Verify the pick up reached down far enough into the sump?
  5. before you put a new gauge on, try a new sending unit. they go bad fairly regularly.
  6. As long as you have 10 psi per 1,000 rpm, you are good
  7. I bought it new from NPD and did put in the gasket but did not verify it went down far enough, both the tube and pump should have been OE replacements not a higher volume oil pump, when it starts it does show pressure at idle but after it warms up it drops. I put an old gauge on it that showed about 12-15 psi when the other gauge dropped to zero, I think I'll try a thicker oil and new filter, it has 5-w30 in it now and that might be a bit too thin for an older motor. The shortblock had about 100,000 miles on it but everything looked good and it had good compression so I didn't replace anything inside it other than the cam.
  8. It also has low vacuum also, I think the valves might not have been adjusted properly so I am going to take the upper plenum and valve covers back off and check the valves, could that cause the oil pressure to be low? After looking at some videos on youtube I think all the valves need another 1/2 to full turn.
  9. I don't think your valve timing has much of anything to do with it. Try a new sending unit. They are cheap and easy to install and like said they are prone to failure over time.
  10. I had an old one and tried it already, it does the same thing but it is old and both spin around on the threaded part that bolts on, both could be bad. I didn't think the lash would have any effect on the oil pressure but could on the low vacuum, since I will have the upper off I will check it out good and look for anything that could cause a vacuum leak. I'll get another sending unit and try it after the valves are checked.
  11. What's the skinny on the bottom end? You build it? Another shop build it? Is there a drop in oil pressure under load?
  12. It was out of a 96 Explorer that was hit in the back quarter panel and totaled, had about 100,000 miles on it, when I took it apart everything looked good and I was told it ran good before it was wrecked. I cleaned it up, installed my Mustang cam and put TFS springs on the GT40 heads after the machine shop was done cleaning them, the valves were a little dirty but cleaned up and didn't look bad so I reused them. It runs and sounds good after replacing one of the BBK headers that was leaking, I haven't taken it out on the streets yet, just fired it up Saturday afternoon, let it run 5-10 mins to heat up and bake in the paint, did that a couple times and kept the RPM's up so the oil pressure didn't stay low long. I did a VERY low budget build but wanted the new oil pump, pick-up, and pan, and a good set of Fel-Pro gaskets, bought the 1 piece pan gasket also because I couldn't find one in a set. The crank broke on my OE motor 2 years ago and I just picked up a craigslist mustang motor and put it in then it started smoking last fall. It might be good still and just need head gaskets. I might take that block to the machine shop and turn it into a 306 and swap it next year......my wife has MS and her Dr appointments and meds are more important than spending a lot of money on my car, so until I hit the lottery my funds are limited.
  13. 100k should be nothing for these motors unless the oil was never changed. I swapped to an autometer gauge just to avoid this exact issue. I would say for giggles go to your lps abd get a cheap mechanical gauge. Hook it up. You should see 20+ psi when hot. 50 or so under load. If that's not the case you have bearing issues or your pump is squirting oil between its mating surfaces.
  14. The miles didn't bother me and being in an Explorer I hoped it didn't get the abuse it would have in a Mustang, I had a 96 Explorer that had 228,000 miles on it until the oil pump went out on me while in the left lane on a freeway, by the time I could get over and off the road it seized up, the heads off that motor went on my sons Mustang about 5 years ago, the last time I had to deal with installing a set of heads. I took the intake and valve covers off tonight and found 3 were loose enough to unscrew by hand, so they need to be set properly. I pulled the fan and shroud to get access to the crank so after work tomorrow I will try to set them again. Then I'll check on a mechanical gauge, and keep my fingers crossed.
  15. I am seeing some similar issues with oil pressure and the stock gauge. I have a mechanical gauge under the hood and it shows a good 50 PSI. The OEM gauge inside the car runs at two marks up from the bottom red mark and occasionally bounces around. I swapped the oil pressure sender for another one I had laying around and that didn't change anything. The fact that both senders would spin by hand even when they are wrenched in tight makes me believe that it is a grounding problem. The fix may be to use a hose clamp on the sender body to clamp down a wire that gets the other end grounded to the engine block.

    If that doesn't work, then the fuel gauge anti-slosh module may be bad. I believe that it's secondary function is to supply regulated voltage to the fuel quantity and oil pressure gauges. That way the gauges always work correctly even if the voltage from the alternator/battery isn't what it should be.
    #15 jrichker, Jun 3, 2014
    Last edited: Jun 3, 2014
  16. That sounds logical, I'll run a wire and try grounding the sender housing, I just got in from re-adjusting the rockers on the car tonight, hopefully they are set properly this time. I didn't get to start it because I swap the battery between my Mustang and my truck after the last battery I bought died over the winter, probably because I didn't keep it charged. If I get time I'll swap them around tomorrow night and also try the ground wire and go from there. If that doesn't help I will change to a thicker oil and another new filter over the weekend and go from there.
  17. Undercut your mains and rods. I delt with the same exact thing. I had a mech. gauge.
  18. @BKM48198
    I added a ground wire for the oil pressure sender, and it didn't change anything.

    The next possible culprits are the wiring , dash connectors,and the anti-slosh/instrument voltage regulator module.

    My gas gauge hasn't worked correctly for months, so I guess it's time to fix the spare anti-slosh/instrument voltage regulator module that been sitting on my electronics workbench for a very long time...
  19. Are you the one that had the write up on how to rebuild the anti slosh module? I had it on my computer but the kids dropped it and ruined the screen.
  20. That's me - actually I copied in from someone else. For sake of making it simpler to find, here it is...

    Copied from DrBob

    I worked on an 88 Mustang today that had similar symptoms. Short version, I took the “anti slosh module” off of the back of the instrument cluster and replaced the electrolytic capacitor. Fixed it for $1.39 with a part from Radio Shack.

    In an attempt to help other folks, here’s the long version.
    Remove the “anti slosh module” located on the back of the instrument cluster. There was a single Torx screw holding mine to the cluster.

    Find the electrolytic capacitor. It will be the largest, 2 wire component on the board. The capacitor may have a red or blue plastic wrapper on it. Mine was red.

    The wrapper should have printing on it. Look for printing that looks something like this:

    The “100uF” tells you this is a 100 micro Farad capacitor. The “+25V” tells you the capacitor is rated for 25 Volts. Yours may be different. You may use a higher voltage part but don't use a lower rated voltage part. If you use a lower voltage part the capacitor might open later on down the road or it could be as bad as catching fire.

    If you can’t find the printing you’ll need to remove the part. You have to anyway so nothing wasted. However pay close attention to the way the capacitor is oriented on the board.

    One end of the capacitor will be bare metal with a wire sticking out. The other end should have some sort of insulation over it with a wire sticking out. The bare metal end is the negative end while the insulated end is the positive end. Pay attention to which end is connected to which hole on the board.

    Get a replacement part. I got mine at Radio Shack, $1.39. Here’s the info:
    100µF 35V 20% Axial-Lead Electrolytic Capacitor
    Model: 272-1016 | Catalog #: 272-1016