Argh! Stupid OPS!

[TurboTahoe]

Hi guys,

Just a reminder that those crazy OPS (Oil Pressure Switches) really don't last long (unless you put in an OPS relay). On the Tahoe, I knew that the Lift Pump was getting on in years (no idea how old it is, but judging from the looks of it, it's been many many years - it has a bunch of dirt and corrosion on it.) Well, I started getting the 'fish bite' symptoms at higher RPM while accelerating (around 2400 RPM). When I got home, I opened the fuel bleed valve, and sure enough, the Tahoe died. Since I put in a new OPS about 3 years ago, I thought to myself that it was probably the Lift Pump. I asked my son to read the multimeter while I lie under the Tahoe (while it is running in Park) and check - sure enough, there is 12V at the connector to the LP, but LP isn't running. I just assumed that the LP was dead, and I promptly ordered a new one from Bill Heath. It arrived in a couple of days, and I stuck it in (note: Bill gives great written instructions as well as those pesky little O-rings that would be hard to find if I just bought the LP from GM).

Anyway, I put the LP in, and then started up the Tahoe, and went to the fuel bleed valve again. Still quits. Oh no! It occurred to me that I didn't even do any diagnostics, I just assumed the LP was dead after my quickie 12V test. I picked up the old LP and applied 12V to it. Purrs away like always. I then apply 12V to the new LP. It also purrs. Well, looks like the 'not that old' OPS is dead - provides 12V to the multimeter, but can't do it under load. ARGH! I go to NAPA, buy their house brand OPS and plop it in. Sure enough, the LP starts running, no problem.

Anyway - the moral of the story is that OPS goes bad quickly, and I need to get cracking on the OPS relay, and that 12V at the LP doesn't mean that it works under load!

Thanks,

Rob

P.S. Although I have no fuel pressure gauge, my seat-of-pants dyno says that the new Health HD LP works great! No skips, no fishbite, no hesitation. Tahoe running great again!

 

[chessie 6.5]

I'm also concerned about the vibration that the ops has to endure from our engines. I'm going to remote mount it with a short section of hp ss hose with proper reusable fittings. This way if it goes bad down the road, it'll be easy to change without standing on my head.

 

[JiFaire]

Good point, Chessie - Leroy sells those 'OPS Extenders' at PMDCable.com, in our vendors section!

Rob, good for you for tracking down the problem... two things can happen with LP issues that make it hard to diagnose...

The first is when the LP sounds like it's working (it's purring) but you have no fuel... this indicates a problem internal to the LP and means you must replace it.

The second (which you had) is when the LP seems to have 12v at the contacts, and still won't run ... it's easy to think the LP is bad, but sometimes, it is getting 12 volts, but no amperage.

In this case, the contacts in the OPS get crudded up over time and won't carry the amperage needed for the LP under load. Aftermarket OPS contacts are much cheaper than the GM ones, and it's a known issue that the aftermarket OPS switches aren't rated for the correct load. At one point, one of the major aftermarket relay companies recognized this as an issue and was contemplating re-designing their OPS - I'm not sure what happened to that idea, but I told Leroy to watch for an 'improved' OPS model.

Putting a secondary relay after the OPS diverts the high-current load away from the OPS and also makes for an easier-to-replace part. If the LP is drawing current straight from the battery (through a secondary relay) then you know it will be getting the juice it needs.

Jim

 

[Turbine Doc]

Vibration thus far has not been a fail mode on mine, and I have one in my truck that is mounted on a 3" long pipe nipple & some elbows to get it out from under the intake where later model truck OPS's are located; my fear/suspicion is that as the aftermarket parts have been migrated to foreign soil manufacture, the quality has also gone to the wayside, even on my 98 with it's GM designed redundant lift pump power routine, I've added relays to both my parallel lift pumps

 

[bobbiemartin]

I'm also concerned about the vibration that the ops has to endure from our engines. I'm going to remote mount it with a short section of hp ss hose with proper reusable fittings. This way if it goes bad down the road, it'll be easy to change without standing on my head.

I remote mounted my OPS. I also have the Kennedy lift pump controller, so I have two oil pressure switches. The factory OPS is still connected and runs through a relay, but is not currently powering a lift pump. Should the Kennedy unit fail, I could plug it in and use it. One of these days I plan on installing two lift pumps, so it will get used in the future. Then I will have a completely redundant system, with two independent oil pressure switches and power supplies.

Steel braided hose runs from block to the sending units.

 

[proth1975]

What size fittings did you use for the block? Did you keep the brass section that the OPS originally attached to? How much hose is OK?

After getting that damn thing out last night, I'd love it anywhere but it's stock location.

-P

 

[bobbiemartin]

What size fittings did you use for the block? Did you keep the brass section that the OPS originally attached to? How much hose is OK?

After getting that damn thing out last night, I'd love it anywhere but it's stock location.

-P

Yes it makes it much easier to get to. I had to lengthen the wires, but since you are cutting some of them to add the relay, its no big deal. I did keep the original brass fitting at the block as it has a restrictor and it allowed me to use a straight hose end. I think its 1/8 pipe, maybe ¼ can't remember. In any event, its the same as an OPS, so not hard to figure out. I suppose you could run any reasonable length of hose, I think my hose is about 18-20". The other end was more of a challenge. I think with the commercial OPS hose extender, you just kind of wire tie up the OPS as best you can. I would rather have them solid mounted, so I made a mounting bracket. It uses a bulkhead fitting and a tee. As I recall, there is an adapter between the bulkhead fitting and the tee. Used a 90 degree hose end to connect to the bulkhead fitting. All those adapters & hose ends start adding up, but I'm happy with the way it turned out.

Here is the way the hose connects to the engine

 

[buddy]

When I did mine the OPS is 1/4" NPT. PMDCable.com sells a steel braided hydrulic hose with 1/4" NPT ends already crimped on. The internal steel braiding provided a ground for the OPS so you dont need another. I originally used a regular grease hose, with 1/8" MPT ends, so I had to adapt to 1/4" MPT and 1/4" FPT and provide a ground to the OPS end of the hose.

 

[proth1975]

When I did mine the OPS is 1/4" NPT. PMDCable.com sells a steel braided hydrulic hose with 1/4" NPT ends already crimped on. The internal steel braiding provided a ground for the OPS so you dont need another. I originally used a regular grease hose, with 1/8" MPT ends, so I had to adapt to 1/4" MPT and 1/4" FPT and provide a ground to the OPS end of the hose.

Wait... The sensor itself needs to be grounded? I just had a shop here fab up a hose (using hydraulic hose)... in case my PMDCable extension didn't show up tomorrow. So, to make it work I need to ground it somehow? It doesn't come through the harness?

-P

 

[buddy]

correct, no ground on the harness, just positive battery input and output and signal output. It needs engine ground. So if the hose was not steel braided (in or out) and the crimp connectors touching the braiding then you can put a ring terminal and some washers (so its tight) between the OPS and the hose connction. Or solder/weld a wire between the hose connections.