No charge light comes on at low RPMs

[manoa matt]

Well, as it turns out while checking the wiring and wanting to install a volt meter I discovered that the oil pressure idiot lighty and the battery idiot light had been switched in their housings within the tach.

So my alternator and charging circuit is OK, However now I have a bigger problem, low oil pressure at idle.

I've researched some previous posts and low oil pressure seems to be a prevelant problem at idle after the car is warmed up and the oil thins out. I did recently change my oil but I'm using the same weight (15W-40 as recommended) I did however change brands from Walmart to Shell Rotella T.

When I changed the oil I also changed the oil pressure indicator light sensor, as the old one was leaking from the spade terminal. I had four used sensors all of differing makes, and the one I installed also leaks at the spade terminal, but at least it is warning me of the low pressure. Of the three spare sensors, two of them have the same resistance from the spade terminal to ground, while the other one is considerably higher.

I also have two spare oil pressure gauges, and one gauge pressure sender. The gauge sending unit is installed and over the weekend I hooked up both gauges and could not get a pressure reading for either gauge. I also tried a resistance test for the gauge sender Mark Allison described in a previous post. The sending unit does not have a resistance measurement, so I figure it is at fault.

I think for the time being I will install a mechanical oil pressure gauge (which should be more accurate than the electronic) and monitor the pressure at idle. If all is well, then at a later date I will get the electronic sending unit to keep all my gauges Fiat

Does anyone know at what pressure the oil idiot light comes on at? Does 6 psi sound about right?

Any other recomendations ???

Matt

[mbouse]

don't know the minimum pressure for the light to come on.

my service manual calls for lubrication pressure to be at 50 to 70 psi at 212 degrees F. that is for a 1975 + engine.

I'd like to ask where you are getting those pressure indicators, if they are all leaking. are they oem fiat?

[So Cal Mark]

he did mention the sensors were all used. Normally they get removed because they're not much good anymore. Most warning lights come on around 5psi. Installing the mechanical gauge is a good idea to find the exact pressure.

[mbouse]

http://store01.prostores.com/servlet/mi ... cia/Detail

brand new $8 for a oil pressure light sending unit

[manoa matt]

Three of my sensors have a brown plastic housing, i believe that the brown ones are OEM Fiat

Mike, I've seen the one you provided in the link, I think it is either a Niehoff or a GP Sorenson aftermarket sensor. I can get that white sensor for $5.25 at Checker, but it is special order.

Here are a few I found: http://www.partsamerica.com/ProductList ... h%2fSender

Here are a few Napa parts numbers: ECH OP6068, BA 2010353, ATM 1431012

International Auto has two different ones, not sure what the difference is: http://www.international-auto.com/index ... p&pid=2544

No local stores have the sensor in stock, and I've cross checked the parts numbers for other cars and that yields nothing "in stock" Unless I want to visit a Saab dealership, yeah right. I'm going to order a new rear sway bar from vicks and will lump the sensor onto that order.

One thing is that BOTH Fiat and aftermarket sensors are prone to leak oil around the plastic housing and spade terminal.

I'm not so much worried about obtaining the sensor, or if its OEM or not. Its the low oil pressure that I am worried about, but I'll figure that out tonight or tomorrow when I install the gauge. I did not replace any of bearings on the block or the piston rings when I did my rebuild as there were no noises and everything seemed tight. The oil pump was not broken and the pickup was clean.

[mdrburchette]

Wow, we were beating our heads on the wall trying to figure out that alternator light. I sure hope the oil pressure light is nothing serious!

[mbouse]

yeah, i forgot about the freight expense to aloha land.

i get the oil pressure idiot light to pop on when i am revving too low (500 rpm).

when you were at 2500 rpm, what other things were happening that might lead to the oil pressure sensor to miss seeing oil? were you turning hard, stopping quick, accelerating madly? cuz now we gotta revisit the entire issue all over seeing how it is a different indicator than we previously thought.

[manoa matt]

I remember chasing all the wires up to the gauge connections, but I don't think I checked the gauge wiring itself, I should have caught this mixup earlier. Anyway, I installed a mechanical oil pressure gauge last night, didn't get a chance to test drive because I finshed at midnight. Started it up this morning before work and let it idle for about two minutes. The pressure was about steady at 40 psi on a cold start up, rembember cold here is 70 deg. The light does not come on untill it has been warmed up and driven for some time.

The gauge comes with a clear nylon hose about 5 feet long that goes from a fitting on the oil filter mount up to the gauge. Oil was forced up the tube about 4 feet and stoped about one foot from the gauge. I only ran it for about two minutes, so I don't know if the oil will go all the way up to the gauge, or if it will just compress the air that is left in the tube. I'm wondering if I need to bleed the air out of the line. But PSI should be the same wether its due to air or oil pressure.

The day the light kept comming on, I was just doing stop and go driving around town. Nothing too fast or to hard, but the longer I sat in traffic the more the light kept comming on. It would stand to reason that as the car sat in traffic the engine temp kept rising and kept thinning out the oil.

I'll try to test it out and monitor the oil pressure tonight as I drive around. As long as I have sufficient pressure at idle after warm up, then I don't care about the light. Out of my 4 sensors I could find the sensor that has a slightly higher pressure threshold so that the light stays off at idle.

Matt

[mdrburchette]

According to my 72 owner's manual the oil pressure should be 64 to 85 psi. It also states that it is not uncommon for the light to come on when a warm engine is operating in normal conditions at low rpm. Don't know if this is the same for later model cars though.