Rally dash oil pressure gauge issue.

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Dartswinger70

Dartswinger70

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I did spend some time searching on this but didn't find anything quite like my issue. When I turn the ley to "run" the oil pressure gauge goes to high, but when I start the car up, it reads "low". Any thoughts? Also where is the ground for the cluster? is it a separate wire that runs to chassis ground? Or should i run a ground to a chassis ground? I had read about grounding the cluster, but the other gauges work, I am now thinking i should check wiring and the sender. Ant thoughts on troubleshooting, where to start?
 
Yeah I am going to trace wires at some point, it sounds backward or a reverse wired or polarity issue.
 
Pull the wire off the sender (near the distributor) & see what happens.

Also, do you have a ground wire from the engine to the frame?
 
Yes I do have a ground to the chassis. I also have the bulkhead connector off that goes to the wiper motor ands to the reverse switch on the transmission. I'm not sure if that has anything to do with it. I have to make repairs to that harness. I just now thought of that. I have a new underhood harness,but the bulkhead connector back to dash is original
 
Reads like the sender is for a oil lamp and not a oil gauge. Oil warning lamp sender is either open or closed to turn the lamp on and off. A closed lamp sender can kill a good oil gauge.
 
RedFish said:
Reads like the sender is for a oil lamp and not a oil gauge. Oil warning lamp sender is either open or closed to turn the lamp on and off. A closed lamp sender can kill a good oil gauge.
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Is there a way to tell by looking at it? it looks like my old one, like a bell with a flat male blade tab on it. That may be the issue i put a new sender in when I ovehauled the engine about 13 years ago. I still have the old one, i may throw it in to see what happens.
 
RedFish said:
Nope. A sender for a gauge is larger and has a round button on top for a contact. A connector that does look like female spade terminal slips over that button.
for Mopar Oil Pressure Sending Unit 383-340-440 ACCURATE Plymouth Dodge Chrysler | eBay
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I think I know what you mean, it does sound like I have the incorrect sender then. I have a male blade connector standing straight up. I will look into it. I think I bought that at Rock auto, they are generally good but things like this do happen, they forget about the rally dash even if you enter in "Swinger 340 LOL! I will have to hope the gauge survives. i don't have the car on the road, still getting it in paint so it hasn't seen much time running.
 
Thanks in advance It did work with the old unit I had in my 318 when I had it on the road years ago. i think this may be it, I will look at the 318 and compare the two senders.
 
Just a story to share. A fellow service tech was working on a Ford Ranchero. All day he was feckin with this thing and I hadn't had time to talk with him before beer thirty. He said the temp lamp would slowly get brighter and brighter as if the engine was running hot. Turns out that a parts yard motor had been previously installed. His whole day, sending the radiator out for flush, replacing water pump, etc.., was all about a wrong sender application. One sender is either open or closed. The other starts at little to no resistance, then resistance increases to lift the gauge needle. Same wire attaches to both. One is powered by switched 12 volts. The other is powered by a gauge voltage limiter. the engine had came from a vehicle with temp gauge instead of warning lamp.
 
RedFish said:
Just a story to share. A fellow service tech was working on a Ford Ranchero. All day he was feckin with this thing and I hadn't had time to talk with him before beer thirty. He said the temp lamp would slowly get brighter and brighter as if the engine was running hot. Turns out that a parts yard motor had been previously installed. His whole day, sending the radiator out for flush, replacing water pump, etc.., was all about a wrong sender application. One sender is either open or closed. The other starts at little to no resistance, then resistance increases to lift the gauge needle. Same wire attahes to both. One is powered by switched 12 volts. The other is powered by a gauge voltage limiter.
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I think that's the problem, and I hope the gauge survived, I wont know until I actually get out to the garage but i thank you I would have spent time tracing wires scratching my head etc.etc. Like said it did work before I tore the car apart.
 
Well... even if you did correctly identify your application as 340 Swinger at Rockauto, they don't separate the base model Dart from a specific year model 340 Swinger with the rally instrument panel. Their computers can only do so much.
 
RedFish said:
Well... even if you did correctly identify your application as 340 Swinger at Rockauto, they don't separate the base model Dart from a specific year model 340 Swinger with the rally instrument panel. Their computers can only do so much.
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Agreed. And knowing me I bolted it in and went with it even though it wasn't exact. i am mostly to blame LOL! I do recall the style you described, and I have the old one so ill throw it in and hope the guage made it.
 
These thermal gauges operate on heat that is generated by changing resistance values. Temperature gauges tend to live longer due to engine rarely running hot for any length of time. engine stays cool, gauge stays cool. Oil gauges experience more heat.
The fuel gauge is the problem child. A full tank of gas generates a lot of heat, plus the heat from the voltage limiter is also inside your rally fuel gauge. They are now 52 years old. A solid state regulator that doesn't supply so much voltage at switch on can extend their life but they will be slow as molasses. Good luck with all of them.
 
I did have the incorrect sender in. I found my old one in my 318,and put it in. same deal only now the sender dopesnt go to high with ley on. I did an ohms test with engine running and it is 70 ohms and gauge reads low. I hooked up a snap on oil pressure gauge and I have 45 psi at idle. i am going to try a sender before going after the gauge. I seem to think or read that 70 ohms will real as "low" so I am thinking the sender is not working correctly.
 
I purchased a new sender ,still no workie...however at least i have the correct sender, onward from here...I am going to resistance check the wire next, does anyone make the gauge if that is the culprit? It does max out when grounded though so I dunno...
 
I have a test box I made that I can send you if you want. It checks empty half and full. I made it for the fuel gauge, but the oil pressure works the same way.

EA34A483-9970-43A5-8A7F-F73F60A1F264.jpeg
 
The new sender could still be bad. The new Chineseium parts are crap.
Do you have an ohmmeter? If not Harbor Freight has them cheap (sometimes free).

Measure the sender to ground with the engine off. Should be about 80 ohms.

Measure the sender with the engine running. The reading should be lower, maybe 20-60 ohms.
 
Mike69cuda said:
The new sender could still be bad. The new Chineseium parts are crap.
Do you have an ohmmeter? If not Harbor Freight has them cheap (sometimes free).

Measure the sender to ground with the engine off. Should be about 80 ohms.

Measure the sender with the engine running. The reading should be lower, maybe 20-60 ohms.
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Thanks Will do. I plan on shooting wires tonight or tomorrow. I do have an ohmmeter and I agree about todays knock off parts .It was a Standard brand unit although I realize that doesn't mean it isn' t Chinese. Truth is they don't want us keeping these cars around much longer I don't like the look of aftermarket gauges but will go that route if I have to I suppose. It just seems these a body dashes look better clean without things bolted to them.
 
Dartswinger70 said:
I did an ohms test with engine running and it is 70 ohms and gauge reads low.
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Sorry I didn't see your post before.
Yes 70 ohms should read low on the gage.

I've plotted some of this out on a graph. Ohms is the side axis.
Its a work in progress...
On the graph is two sets of info.:
1 Engine running, dash gage in response to known resistors, along with specifications that have been kindly shared from repair manuals.
2 Sender resistance in response to my car's old NAPA - Echlin oil pressure sender.
If that makes it confusing, I can digitally erase that later.

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It's my opinion that that parts suppliers began substituting because they did not have the correctly calibrated ones.
Based on the test of the gage in my '67 I also think the spec I have from the '85AMC Jeep SJ shop manual is probably slightly different than Chrysler's 1960s spec.

Oil Pressure Gage and Sending Unit Revisited
 
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I did some digging into the Chrysler parts books and IMO it is clear that the original oil pressure senders were not superceded by the ones with the later part numbers.
If it was acceptable to substitute the 3488 609 sender for the 2495 222 sender then there would have been no need to have them called out to be used with the matching pre March 1971 and post March 1971 oil gauges.

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I homed the gray wire from the sender to the round printed circuit connector. It was 0.8 then I cleaned the female side of the bulkhead connector Ingot the ohm reading down to 0.5 on the 200 ohm scale which is the lowest my meter goes. That seems "Ok" to me as it's still 0 ohms or more specifically 1 half ohm. Are these gauges serviceable? Should I go into the dash and pull the gauge? Is there a way to test the guage?
 
I have no gauge movement at all when the car is started and running and the last I tried touching the sender wire to ground it moved all the way to high
 
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