xpress

MY 89 Auto. Just had the dealer replace the sender as the old one always pegged at 5 bar and never moved as soon as the ignition was turned on. Drove the car from the dealer and the gauge looked fine - 4 to 5 bar driving and 2.5 to 3 bar at stop. After about 10 minutes of driving, stopped at a stoplight, the gauge showed 3 bar and then never moved again. Turned the car off, needle went to 0 after about 5 minutes, turned it on and all was fine while driving for a short period - then the needle pegged again at about 3 bars and would not move. Repeated short drives produced the same results. Any ideas would be greatly appreciated - another bad sender? I did not purchase the new sender from the dealer. Also checked "search" and didn't find anything like this issue.

xpress

After driving it awhile, the problem seems to happen when the car is up to temp. and the oil is hot. Any ideas?

GlenL

This happens when the leads are attached backwards. There's a pressure sensor for the gauge and a pressure switch for the idiot light. If you connect it backwards the gauge goes to 5 Bar immediately. Or maybe it was really broken, but reversing the leads would have been good.

It sounds to me like it's showing you what it is measuring. You get good pressure cold and crappy pressure hot.

What oil are you running?

blown 87

I thought the 89 had that one piece three wire set up.

GlenL

In that case ignore my guess on the old sender.

I do think he's got a pressure problem now.

xpress

Oil is 20w 50 . Leads are correct - works fine for awhile then freezes. Time for another new sender?

GlenL

What brand? Organic or synthetic?

With the engine hot, if you turn the engine off and then back on without starting it what pressure does it show? Should be zero with the engine not running.

Mrmerlin

if you turn off the the key then back on you may see the gauge slowly reset to 0 as the pressure bleeds off, this all depends on how fast you can cut the engine off then get the key back on.

Now for whats happening in your car. First look at the connector and the wire harness at the sender, its possible the wires might be damaged, shorting or broken.
If they look OK then remove the plug on the sender and inspect it, if there is oil on it spray if with some brake cleaner. If its dry then you have another choice and i would do this first.
Remove the new sender and install an oil pressure gauge and go drive the car till its warm then have a helper on the gas pedal while you inspect the gauge.
If it goes to 5 bar at about 2200 RPM and then back to 1.5 to 3 bar at idle then the oil system is OK .
You either need a new sender or the gauge is not working correctly, this could be a dirty connection at the pod

xpress

What brand? Organic or synthetic? "Organic"

With the engine hot, if you turn the engine off and then back on without starting it what pressure does it show? Should be zero with the engine not running. "Shows the same pressure that was on the gauge before it was turned off."

Mrmerlin

with that info it sounds like your gauge is not working correctly.
BUT install an oil pressure gauge where the sender mounts to determine whats really happening

daveo90s4

Does your 89 MY have the digital dash? If so you can do oil pressure (and other) diagnostics via the digital dash - not necessarily the full answer but useful for, as I say, diagnostics.

xpress

Mr. Merlin - Could you give me an idea of where I could obtain an oil pressure gauge that would fit. Absent that, I have another sender to swap in. If that still does not work, I was going to remove the Pod to install new bulbs and will clean contacts. Everything works as it should untill the car is run for awhile and the oil and water temp get to normal operating temp. Strange.

Mrmerlin

I dont know where you can another oil press gauge but since you have another sender it could be easier to match up the threads.
. From the info it sounds like a gauge problem, but fitting a OP gauge will let you know for sure

SharkSkin

There may be a piece of crud blocking the tiny hole in the sender... That could account for the reading sticking at 3 and taking a long time to go to zero.

dprantl

I have a similar issue, except not as bad as yours. When cold or warmed up, the gauge works perfect and response is immediate. If it gets to over 95 deg F outside, my gauge becomes very slow to respond. At first I freaked out because I thought that my oil was getting too thin, but then I realized that the gauge dropped just as slowly as it raised. I.e. I could run at 4k RPM for 10 seconds and watch the gauge creep to 5 bar, then shut it off right away. I could then see the gauge creep down at the same speed to 0, slowly. Since the pressure sender is before the oil filter (thanks SharkSkin for reminding me of this in another thread), it is probably some gunk messing the sender up down there. I haven't had time to remove the sender to verify yet though.

Dan
'91 928GT S/C 475hp/460lb.ft