New lift pump voltage and OPS issues

[Big Green]

I've looked a number of the other threads on this topic but didn't really see the answer I was looking for.

I've replaced the lift pump and the OPS within the last 5k. Recently, I've had issues with what feels like it's running out of fuel under heavy throttle. So I did the old 'open the filter drain petcock' test. Engine died, so no fuel pressure at run. Then tested for fuel pressure at crank. Fuel pressure was good and I bled the filter and restarted it.

So, checked for voltage at the lift pump. At crank I'm seeing 12v so no issue. When it's running however, I'm only seeing 4-6 volts (and no fuel pressure).

The question is, how much voltage should I see while it's running? It would seem that 12v should be present but I need to know for sure.

During my search for the voltage question I ran across several referances to a OPS saver, basically a relay that is installed between the OPS and the pump. The OPS just trips the relay and then it an additional power wire that runs to the relay. Has anyone bought/built/installed one? How did it work?

Thanks
Big Green
'95 6.5td
KD chip & exhaust, gear drive, gauges, and a host of other goodies

[Robyn]

The voltage should be 12V or better depending on other factors.

The oil pressure switch takes over the duties of the relay when the engine is running.

Your OPS is probably toast.

Replace the little critter and your issue should go away.

You could do the trick with the relay as you found.

The contacts in the OPS are a tad skimpy and over time the contacts burn out and thus the low voltage your seeing at the lift pump.

For now I would just replace the OPS (Simple task) and get it off and going again.

Robyn

[DickWells]

Hi: Yup, I've installed my own relay, way back in 99-00. Trouble is, I'm in Brownsville, TX with an 04 DM, and the ole Burb is in VT! If memory serves, the hot line to the lift pump was white w/black tracer, but not sure. You'll find it in the BIG Ole connector up at the rear of the engine, on the fire-wall. But, knowing that you need to know for sure, you'll need a wiring diagram, and some more info. IIRC, that wire was used to trigger the relay? Sooooo, I'll bet Robyn, or someone with better knowledge will step in here and put you straight. Regardless, you'll need to go directly to the battery, or fuse/power/dist center to pick up a hot feed to power the pump through the relay. I added a whole fuse buss to the top of the power/dist. cover, because I got sick of those chintsy fuse-tappers every time I wanted to add a circuit!
Seems to me that if you have a multi-meter in the feed wire to the pump while the pump is running, you'd only read partial voltage anyway, since the pump is using juice at the time. I'm just an old farm boy, and can't talk electricity, anyway! Right or wrong, guys and gals? Maybe I'll learn something today, too.
Good luck.
Dick:)

[Big Green]

Thanks for the replies so far.

I've replaced the OPS before although I have to say that I'm more than a tad disappointed with this one since it probably has less than 5,000 miles on it at most. All of the others were easy to diagnose since the voltage just went to zero at the run. The low voltage is what has me stumped on this one.

Really, I've dabbled in electrical design a time or two but it's not my expertise. I'm more of the mechanical type guy (designing airplane stuff). There is a buddy that fixes/repairs/rebuilds old pinball machines and he has volunteered to help design/build the relay.

The one thing that I do want to make sure that any relay set up would have and that is a push button on/off so that I can run the pump with one hand while bleeding the filter with the other. What a pain having to get the wife or daughter to come out to the shop in her slippers and robe (because we all know that nothing ever fails when it's convenient).

I'm starting to wonder if there would be a market for a kit for just this.

Thanks
Big Green
'95 6.5td
KD chip & exhaust, gear drive, gauges, and a host of other goodies

[DmaxMaverick]

The OPS relay is a good upgrade, and will usually relieve you of the OPS-LP issues commonly seen. Kennedy does sell a complete kit. It's pricey, but works as advertised, with an accommodation for one-hand filter priming (you can essentially put the prime switch anywhere you need/want).