Fluctuating Oil Pressure

Jul 6, 2003
I've resently made my 77 fj40 a daily driver. I've been doing a bit of highway driving with it. I'm running a stock 2F(suposedly rebuilt a couple years ago...) weber carb, 32" swampers and stock 4 spd tranny. For some reason the oil pressure gauge is all over the road. Sometimes it'll be just a bit above the low of the two range marks. If I floor it, the pressure plumits. Then it won't usually come back up. I drove 3 hours averaging 60-65mph and the entire time the gauge was all over the road. Unfortunately I have no tach so all I have to judge the engine's strain up and down hills is my ear. On that same trip I had drivin' for about an hour and a half. The pressure was really low. I stopped for gas and checked the oil. I immediately got back on the highway and went the same speed. This time the pressure was just a hair above the low of the two range marks. It's never been over half way between the marks except in the mornings. My questions are (finally):
1. Has any one had similar problems?
2. Is it a. the engine (please say no) b. the sender unit or c. my gauge?

Also because of this problem I'm getting custom gauges. What ohms does the fuel gauge need? and better yet is there a website with this kind of little spec/info so I don't have to ask?

Jun 13, 2003
Dont freak out. At start you should be close to the 2nd mark. After warm up in the middle. When good and hot at or just below the 1st mark at idle with it jumping back up to mid range at speed. Get a pressure gauge an test your pressure. Look in the OEM manual and see what you get pressure wise. 40 series oil gauges seem very accurate and reliable in general. If it is low I would drain the case and run 2-3 series of ATF through it to clean the crap out. If still low then look at the pump.
Jul 5, 2003
Central, Utah
The factory toyota book is probably your best bet. Here, I'll tease you a bit. You asked about fuel gauge.
F = 17ohms + or - 2.1 = 31mm from top gskt ht. + or - 2mm
1/2 = 45ohms + or - 4.5 = 114mm from top + or - 2mm
E = 120ohms + or - 6.5 = 183mm + or - 2mm
You probably don't find info like that in a Chiltons. I keep a few different books on my favorite vehicles because invariably no one book has it all.
Jul 22, 2003
Perth Western Australia
I recently had a rapid drop in pressure according to the gauge and as dd113 says its best to borrow/hire a pressure gauge that plugs into where the sensor goes and I got a good reading.At that time I wasnt sure whether it was the dash gauge or sender so I consulted an auto electrician who said the only way you can ascertain whether it is the gauge or sender is to connect a hydraulic pump which simulates engine pressure but his was broken.The price from Toyota was astronomical but I found out that the sensor is common to other toyotas such as corolla and cressida and I found a new non original for 1/5 th of toyotas.Plugged it in and everything has worked properly since.Before you start pulling anything apart check the wiring to the sensor underneath the filter.
May 15, 2003
Electric pressure gauges are not known for being very accurate. (especially factory electric) They can vary as much as 20lbs. It also depends on how close the sender is to the pump. I have a portable pressure gauge I use for just something like this. It looks like a big tire pressure gauge, but I couldn't even tell you where to get one.

I would recomend the wiring first, then go to a garage and find out the accurate pressure. It'll at least make you stop wondering.

Also autometer has a universal fuel sender that works with their gauges. I've heard it's not an exact bolt in but not too hard to make it work.

Check out Jegs or Summit

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