oil pressure gauge • The Dodge Challenger Message Board

by **MLMFLCN** » 06 Jul 2008 22:57

Hello,

Out driving my 72 Challenger today, ran great. Oil pressure has always shown about 35 - 40 punnds at idle and about 75 when driving. Got home cleaned some things up. Fired it up again to take it around the block one more time, and the oil pressure gauge shows nothing. The gauge is getting juice as it "pops" when you click to run mode. Gauge and sending unit are both new, as is literally everything under the hood. Tach is on the same circuit and it was working fine. Oil pressure gauge shows nothing, sits at 12 pounds, regardless of idle.

Any way to check the sending unit and the gauge?

Thanks

- rich

by **MLMFLCN** » 07 Jul 2008 1:45

one more item, may help...Checked for a good ground at the sending unit. The "fat" part of the unit seems to be grounded fine (really bright on the prick tester), but the actual piece that the lead to the gauge attaches is very dim. Checked for voltage at the piece where the lead attaches on the sending unit, and it shows 7.5 volts, with the key in the run position (engine off).

Seems to me the ground may be the issue. Replace the sending unit? Thanks,

by **dave-r** » 07 Jul 2008 6:42

If the connection to the top of the sending unit is good then I would first suspect the sending unit as being the fault.

by **Eddie** » 07 Jul 2008 14:26

Rich make sure the ground is good on that unit. Did you try to slightly unscrew it and then retighten it? If there is paint on those threads and it's not making a good ground it will show as bad or intermittent problems. But then again it could be bad too! Bad grounding is the majority of all electrical problems. :thumbsup:

by **dave-r** » 07 Jul 2008 14:44

As I slowly (very slowly at the moment) fit my "Painless" full harness kit on the car I am checking all the grounds with an ohm meter to make sure I have a good connection between everything.

The test leads on the ohm meter have more resistance in them than anything grounded on my car so far. :mrgreen:

by **Eddie** » 07 Jul 2008 14:49

by **Eddie** » 07 Jul 2008 15:05

Another thing I just saw was the grey wire with a rubber plug at the end of the lead plugs into the back of the gauge behind the instrument panel. It's probably a long shot but it might be 'loose' at that point. I dont know off hand if you can reach that wire? The grey wire comes off the steering column harness and goes up into the gauge cluster area. I believe it should be 12 volts with key on engine off.

by **MLMFLCN** » 07 Jul 2008 17:35

Hello Eddie,

Thanks for the reply. The ground on the "fat" part of the sending unit shows really bright on the prick tester, but the "stud" piece where the sending unit connects to the wire lead is very weak. I checked the voltage on the stud, with the key on / engine off, and it shows only 7.5 volts.

The gauge is an autometer unit, so getting to the gauge is easy (just kind of hanging/zip tied in the car at this point).

- rich

by **Eddie** » 07 Jul 2008 17:57

MLMFLCN wrote:Hello Eddie,

Thanks for the reply. The ground on the "fat" part of the sending unit shows really bright on the prick tester, but the "stud" piece where the sending unit connects to the wire lead is very weak. I checked the voltage on the stud, with the key on / engine off, and it shows only 7.5 volts.

The gauge is an autometer unit, so getting to the gauge is easy (just kind of hanging/zip tied in the car at this point).

- rich

Then it can only be one thing, and I think both you and Dave diagnosed it correctly! :thumbsup:

(Bet it caused a puckered condition for a split second though) :lol:

by **Jon** » 07 Jul 2008 21:03

More like heart failure. :rage:

by **MLMFLCN** » 08 Jul 2008 10:37

I'm just sorry I recovered the driver's seat prior to this! :tears:

by **MLMFLCN** » 08 Jul 2008 23:53

Alright, changed out the sending unit, and that was not it. Seems so unlikely that the electric gauge failed (Auto meter, less than a year old). Any way to test this? Checked the hot and the ground at the gauge, and they all seem fine.

Engine runs so well, I can't imagine it is anything mechanical. Plus the gauge registers nothing, if there was a mechanical problem, seems it would register something , right? Plus, it just stopped working, which should mean electrical.

Any other thoughts?

by **Eddie** » 09 Jul 2008 0:08

Rich, do you have a D.V.O.M.? You could try a continuity test through the gauge itself. If you dont get a 'beep' or "audible" you know it's got an internal short. Test the gauge at the leads going into the gauge itself.(It's an electrical gauge with 2 wires going into the back of it correct? I dont the resisitance the gauge would have at various readings so that is why I suggested continuity.

by **Jon** » 09 Jul 2008 0:49

We have seen more then a few wiring problems on your car lately. I'd say shorts either in the wiring or possibly went ithrough the gauge.

by **MLMFLCN** » 09 Jul 2008 14:00

That's what I am hoping for. Would this wreck the gauge?

by **MLMFLCN** » 10 Jul 2008 22:41

Did an oil and filter change today. Pulled out the distributer and dizzy, spun the oil pump counterclockwise with a drill with the plug out for the oil sending unit. Within 3 seconds, oil was bubling out of the sending unit hole.

Bought a cheap mechanical gauge, and hooked it up. Fired up the car and retimed. Took about 1 minute for the neoprine tube to fill (20-50 weight oil and a tiny, tiny hose). Gauge never registered anything. Ran the car about ten minutes.

Should I buy another electric gauge (since I may have fried the old one)? Motor runs so good, no hesitation, no smoke, no nothing. I don't know what to think.

Any other thoughts?

by **MLMFLCN** » 10 Jul 2008 23:09

PUlled a valve cover off. The backside is pretty dry, but there is oil pooled near the valves in the side of the head. Valvetrain was quiet while running too.

Anything else physicall you can test (short of having a working gauge :wink:

) to see if the engine REALLY has oil pressure?

Thanks

by **MLMFLCN** » 11 Jul 2008 0:31

Decided to pull the pan to see what is going on. Aside from the pickup, anything else to look for?

by **Jon** » 11 Jul 2008 3:57

Have you tried running it with a valve cover off to see what comes out of the rockers? I would think if there is significant oil there the pump and or relief valve are good.

by **MLMFLCN** » 11 Jul 2008 9:39

I did try that Jon. There was oil pooled in the head, but I could not see anything else coming through up to the valvetrain.

Would you think it is the pump, spring, or pickup at this point? Is this a pain to change out while the engine is inside the car? Was simple on my engine stand. Any tips on the installation of a new pump (i.e. - do you need to remove the dizzy from the top of the motor to facilitate removal of the pump?).

Thanks,

Rich

by **Jon** » 11 Jul 2008 13:43

I have never done one in the car either. Looking at my 340 it would appear removing the steering link would be necessary. If the pan clears the K-frame then it shouldn't be to difficult. Otherwise you may need to jack-up the motor a bit or drop the frame.

As long as the pump drive realigns with new pump they should be able to stay put. Definitely would get new pan gasket too.

Did you replace the pump at your rebuild?

by **dave-r** » 11 Jul 2008 14:51

Changing oil pump?

Big block = easy.
Small block = rather you than me. :roll:

by **Eddie** » 11 Jul 2008 15:14

MLMFLCN wrote:I did try that Jon. There was oil pooled in the head, but I could not see anything else coming through up to the valvetrain.

Would you think it is the pump, spring, or pickup at this point? Is this a pain to change out while the engine is inside the car? Was simple on my engine stand. Any tips on the installation of a new pump (i.e. - do you need to remove the dizzy from the top of the motor to facilitate removal of the pump?).

Thanks,

Rich

You did turn the engine by hand to ensure the oil got to the top end Rich? The engine must turn to line up the cam bearings feed hole to get oil to the valvetrain. Just spinning the oil pump without doing so will restrict the oil flow to the top end. Get a good, mechanical gauge. Keep it for future testing. You must find out your true working pressure. :thumbsup:

by **MLMFLCN** » 11 Jul 2008 18:15

Thanks all. Jon, I did put a new pump in with my rebuild. Not sure what caused the failure.

From looking at the pump (once I get it out of the car), what should I look for to identify what failed? With the new pump, any steps to prep once it is installed?

It was a Melling High Volume. Go with the same again?

Thanks,

by **MLMFLCN** » 11 Jul 2008 18:22

Eddie,

I did not turn the engine this last time while priming, but I did do it last fall when firing for the first time. Should this be done any time while priming?

thanks

by **Eddie** » 11 Jul 2008 18:40

It sounds like you have determined the pump failed? I would use a Melling Hi-Volume, but Sealed Power is also good too. You also checked the intermediate shaft? To prime it you can pour some oil into it right before bolting up to the block to help 'seal the rotors internally. But most will probably spill out before getting it all the way on. :lol:

I wouldnt worry about it though because you should prime the new pump with a long hex shaft,)M.P. priming tool). BTW, Rich sorry to hear of this :frown:

by **MLMFLCN** » 11 Jul 2008 19:12

Thanks for all the great tips.

Eddie, I will do what you have said here too. I can see myself cursing trying to keep all that oil in. I have heard of using vaseline? Do you guys recommend this? I can't imagine mixing anything in the crankcase can be good. :s008:

I guess these things just happen, still would like to know what the oil pump failed. :worry:

by **MLMFLCN** » 11 Jul 2008 19:13

I did check the intermediate shaft, and I do have the priming tool too. Shaft looked fine. Thanks again.

by **Eddie** » 11 Jul 2008 20:05

I would just prime it without the intermediate shaft in and the hex tool. When it 'catches' you will know! I'm sure you've done this before. :frown:

We use Red Transmission Assembly grease on auto trannys,(O-rings, seals,& bushings) but that stuff is just vaseline,(petrolatum jelly), colored red. It doesnt hurt anything but then again tranny fluid has 10 times the detergent in it. I dont think you would need it however.

by **MLMFLCN** » 12 Jul 2008 1:54

pulled the pump out tonight...real easy. Looked like the spring may have locked up and been fully extended, as the valve was not sliding very easily. May have caught a small burr from the original start up. Does that spring really compress when the motor is running to allow the oil to flow? Seems like a pretty stiff spring. I imagine that when the spring is compressed, it allows oil to pass through the pump. My sense is that the spring was not able to, and therefore, severly limited the flow of the pump.

How easy should that valve slide in the bore? I oiled it up, and it still was not really easy to move. I remember when I was installing the lifters in their bore, with 20-50 weight on them, they spun really nice. Probably not the same thing, but it looked liked the machining was kind of the same.

I think this was the problem. Off to summit racing in the morning, installing a new high volume melling tomorrow. Hope that's the ticket.