Problems with oil pressure switches

[anhipps]

I know this topic has been covered a lot, and I thought I had fixed the problem when I installed the relay to take the load for the lift pump. Unfortunately, the second AC Delco OPS has just gone out in last 4k miles(since the relay). I have checked the wiring that I installed against the diagrams that other have posted, and it seems right.

I am really tempted to put a "T" in and add an separate pressure(non oem style) and try to get out of this failure loop. This the forth bad switch in 17k miles. If anyone has any words of wisdom, caution, something to check, etc. I'd appreciate it. The Switch that I'm thinking about using is a Mr. Gasket 7872. By the way this is on a '93 3500.

 

[bk95td]

I haven't had troubles with the oil pressure switches on my 92 and 93s[no extra relays]. I have had trouble on one of the 95's. It fried a napa ops in a couple days. It also fried a AC Delco ops in a few weeks.
I rewired one of my 94's to run with the key on. I removed the ops out of the lp wiring completely. I have the troublesome 95 on a switch now but plan to change it to the same way the 94 is.
What I did to eliminate the ops was to tee the pink wire going to the fuel heater in the fuel filter.[it's hot with the key on] I ran a short wire to the fuel pump relay on the firewall. I'd have to double check to be positive but I'm pretty shure the trigger wire for the relay is purple/white. I cut the purple/white and attached the jumper from the fuel heater to the relay. I capped the purple /white coming from the harness because it would still be live in "start". This works for me. It does eliminate the alleged"Safety" of the original design in the case of a crash .

 

[buddy]

So your LP stops working or the oil pressure gauge?

I would suspect an issue with how the relay was wired if its failing to the LP. such as you may have accidentally made the relay always on with battery source and just runs through it when OPS porvides power. The wire coming from the OPS need to go to contact 85 or 86 on the relay.

 

[anhipps]

The LP stops working.
I went and rechecked my wiring to the relay. I spliced into the orange(12V) wire going the OPS, this 12V goes to terminal 30 of relay. I cut the wire going from the OPS to the LP and the jumpers are now routed this way:
OPS connector to terminal 86(solenoid power)
Terminal 87 to LP( relay switched power)
This is the way that others on the forum have described their modification and it seems to be working for them. Does anybody see anything screwy in what I've done?

 

[buddy]

That seems good, as long as 85 is grounded. If the relay has an internal diode then you have to make sure you have the 85 and 86 connections correct, so the diode resists flow from power to ground.

 

[orrum]

Grounds, grounds, grounds!!!! If u wanna b a diesel mechanic u gotta have permanantely sooty black hands and u gotta work them grounds, grounds, grounds, I am tellin u its all about them grounds! Ya;ll know about the woodchuck chuckin wood?????

 

[anhipps]

Assuming that my wiring is ok, what else may be killing the op switches. Heat, vibration, voltage back feeding, bad switches? Is any body else having continued problems after adding the relay? Should I be using a separate 12V source to power the pump through the relay instead of the same source that is powering the the relay itself? Has anybody tried using a heavier duty non-oem type pressure switch?

 

[bobbiemartin]

I remote mounted my OPS. The constant engine shaking and high current load of the stock OPS are the double whammy as far as longevity is concerned. I have been using the Kennedy Lift Pump Control Harness for several years and I can report it works very well. Its a little pricey, but IMO worth it. You also need the original OPS for the oil pressure gauge. I wired the original OPS thorough a relay so it still works. Should the Kennedy LP box quit, all I would have to do is get under the truck and connect the original lift pump connector and I'm ready to go. I have a future project planned where I will have two lift pumps, one run by the Kennedy harness, one with the original OPS through a relay. Basically a totally redundant system of lift pumps. I have it pretty well figured out, just need the time now to make all the parts.

You can see the OPS units behind the AC accumulator. One relay is for the stock OPS, the other runs the injection pump. The black box towards the center of the firewall is the Kennedy Lift Pump control box

 

[buddy]

I would use a different relay, or check the coil resistance with a meter between contacts 85 and 86, it should be pretty high, like 40-80 ohms. What is your voltage on the dash gauge typically read and have you checked the voltage on the batteries with a meter while the engine is running? It should be just over 14V, but if you have a bad voltage regulator in the alternator maybe youre getting 16V, and the dash gauge probably reads a little low.

 

[anhipps]

I checked the ground and it is good. The relay reads 84 ohms across the solenoid. The voltage gauge in the instrument panel was showing over 14V, So I thought I might Have found the problem, but......I checked with a meter it shows 14 at idle and 14.2 at 2000 rpm which seems good. So, I am still looking for a culprit.

 

[buddy]

Does your relay have a diagram printed on it, and the coil part have a little bypass circuit with a diode (triangle with line across tip) on it? Usually on the top it would show this diagram.

 

[anhipps]

Yes, I believe it does. What happens if it's hooked up backwards?

 

[buddy]

Well, if it was backwards then you would almost be shorting the OPS output to ground. So if the triangle points from 86 to 85 then the OPS grey wire ouptut needs to go to 85. The coil power needs to be on the side that the triange is pointing at. And the ground towards the base of the triangle, so it resists current flow from power to ground. If its already hooked up correctly, I would try another relay in there as it should not be eating up the OPS. When you read 84 ohms across the coil you must have put the positive meter lead on the correct side, because the other way you should get very little resistance if there is a diode.

I dont know if the diode direction is standard on all relays that have them, such as power should always go to 85 and ground to 86.

 

[anhipps]

I've been thinking back to the first couple of pressure switches that failed and wondering what is common to pre and post relay mod. The first OPS may have been toast when I got the truck. I replaced it and several thousand miles later the new one failed. I have used AC Delco switches each time. Then I added the relay and have had two more pressure switches fail. It almost seems as if the added relay did not improve the problem. The only thing that is common to both situations is the wire coming into the switch and the connector itself, and of course the location of the OPS. But if it was just location(heat and vibration), other people would be having failures after adding the relay. If it is electrical, it would have to be either too high a load or too high a voltage. I guess I'll keep checking things out. I'd rather find the cause of the failures versus just putting in a beefier OPS.

 

[great white]

... Should I be using a separate 12V source to power the pump through the relay instead of the same source that is powering the the relay itself?

Umm, can you describe that a little better?

You're only triggering the relay coil off the OPS right?

It might seem pretty simple and I'm not trying to be insulting, but you're feeding the relay high power contacts from a battery source, not after it passes through the OPS right?

I'm sure you understand the purpose of the relay is to remove high current from the OPS contacts....

 

[anhipps]

I checked the amperage at the ops(powering the relay) and got 0.15A. That seems low enough not to fry OPS. Then I checked the LP run amperage off of the relay. It read 2.2A initial surge and then settled down to 1.4A. I've continued to research the forums and it appears most replacement pressure switches are not rated for more than 1 amp. With 0.15A across the OPS switch, there shouldn't be a problem, but there is. I read elsewhere( http://www.dieselplace.com/forum/showthread.php?t=249105 )someone contacted Wells Manufacturing and they acknowledged that their switches were made to too low a spec and were going to be changing them. Does anyone know if Wells ever came out with a heavier duty OPS?

 

[Burning oil]

I checked the amperage at the ops(powering the relay) and got 0.15A. That seems low enough not to fry OPS. Then I checked the LP run amperage off of the relay. It read 2.2A initial surge and then settled down to 1.4A. I've continued to research the forums and it appears most replacement pressure switches are not rated for more than 1 amp. With 0.15A across the OPS switch, there shouldn't be a problem, but there is. I read elsewhere( http://www.dieselplace.com/forum/showthread.php?t=249105 )someone contacted Wells Manufacturing and they acknowledged that their switches were made to too low a spec and were going to be changing them. Does anyone know if Wells ever came out with a heavier duty OPS?

I did contact wells about this, they have no plans on upgrading/changing the ops.

 

[Turbine Doc]

Use the OPS to run a relay and then the power side of the relay to power the lift pump, probably as much to do with material used in the contacts as the in-rush & sustaining load power current to the lift pump, contacts gettting dirty/melting/pitting over time of operation even the OEM OPS's that are now outsource manufacture are prone to early fails.

 

[anhipps]

TD and BJ,

The truck is set up currently with the OPS triggering a relay and power to the LP running through the relay. This has not kept the last two pressure switches from failing, even though the load across the OPS contacts is only 0.15A.

 

[buddy]

If you have a relay with a diode, I would try one without. I never liked just a diode, a diode and a resistor is cool, or just a resistor, but then it draws a little more current. If it is hooked up properly with the diode opposing current, which is must be if its only drawing 0.15 amps, then I would suggest that the direct short across the coil when it collapses the magnetic field is allowing too much of a spike to hit the contacts of the OPS. The diode only design is known to limit the life of the relay itself, burning the contact, and sometimes contact weld them. So I might try a relay without a diode, and if you like just put a diode with a series resistor on it externally.