1988 V6 GT Had low oil pressure reading and the guage seemed somewhat irregular. I got a new sending unit (NAPA) and changed the oil and filter at the same time. I changed to Mobil 1 10-40 and assumed I would see pressure increase just because of the change to 10-40. Started and went for a drive. Gauge was quite "jerky" and the longer I drove the lower the pressure. Checked the 88 manual and guage checks OK (pegs when you turn key to run with plug removed from sender).

Got a manual oil pressure test guage from Harbour Freight ($9.00) and as I pulled the sender to check the pressure, the line looked dry. I put at least a foot of string trimmer line down the line and still did not hit oil. Maybe I am wrong but I assumed that the line would actually pressure the guage with oil.

Could this be the wrong oil filer, is the line plugged or does the sender read off of air pressure and not actually oil. Oil filer is FRAM (I know the opinions of FRAM as I read this site every day, but oil was cheap at WalMart) and it is the larger filter so I can get a full 5 qts.

what did the mechanical pressure gauge read?

It is difficult to tell where the problem lies. I would rule out the oil filter as that sounds like a long shot. My guess is that its the gauge. If you have an ohm meter put in on the 100-1K scale in in that range. Pull the sensor connector and start the engine. Now measure the resistance between the center pin and ground. If you are getting 80-90 ohms the oil presure is fine and it would signal a broken gauge. However, if you are not seeing this resistance then something in the engine is wrong. Whats the mileage on this engine?

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87GT - with 3800SC Series III engine, 4T65eHD
87GT - 3.4L Turbocharged engine, modified TH125H
" I'M ON THE LOOSE WITHOUT THE JUICE "

Your oil pressure sending tube should be full of oil...a lot of it actually. If it springs a leak, normally it will be a gusher, because it's right at the outlet of the oil pump. You must have a clogged passage in your block. I have no idea how to check for that or fix it.

Thanks to all for the help. 125,000 miles. I did not actually take a manual reading yet actually hoping that I would hear something pretty simple like the line bleeds down into the pan after sitting for a couple of days (afraid that the actual reading would prove my fears). I will see if I can find a way to clear a plug in the line.

If I can get a flexable wire or heavy trimmer line down the tube is there a danger of doing any damage assuming I can always get the wire back out. Thought I might pull the coil wire and try turning the engine a few times (I can hold a rag and have my wife turn the motor) to see if I can blow out any clog.

Battery in, battery out is a pain for testing. The switch from NAPA does not have the nut on the bottom of the switch as the bottom of the body is all one piece and I don't have a socket that is large enough or deep enough. To hold the line base (19mm) and put an adjustable wrench on the base I need the battery out for clearance.

Any other suggestions: I will test guage and clear line.

One other way is leave the oil pressure sensing unit off. Pull the coil wire off the coil, we do not want the engine to start. Have someone crank the engine over and you standby and watch the oil sensing line (with some rags). If you crank that engine over you should get oil out the sensor line. Be careful and make sure you have enough oil in the oil pan.

The best way is to get the mechanical gauge on it and see what the pressure is.

Jack

[This message has been edited by J Gunsett (edited 03-31-2008).]

If the bypas of the oil filter is messed up it could mess up your pressure reading, But usually it reads really high.
I suspect the line is clogged. You can pull the fitting off the block near the oil filter then take the tube off and clean them out.