What is the OPS' Role in LP operation on OBDII?

[GM Guy]

hey guys, My old man and I are dicussing (arguing) whether or not the OPS needs changed on an OBDII rig when changing the LP. I bought a new OPS and LP (doth delco from rock auto) and was wanting to stick them in, and my old man is convinced i need to send the OPS back. It is my truck and my money, but his shop and parking space, so I do need to at least hear him out:rolleyes5::hihi:

so I am asking you guys, what role does the OPS play in a OBDII truck (this one is my new 99 chassis cab, btw)

also, does the intake need pulled to get the OPS, or will the Lisle 13250 socket get it out of there? If the intake needs pulled, I see it as a fine time to do a FTB install.

feel free to link to a thread, and delete this one, but I didnt find anything during search, so that is why i created a new thread.

 

[ak diesel driver]

takes both OPS failure and PCM failure for lift pump not to work. Last discussion I heard was basically gm didn't want to spen the bucks on a harness change so just added the pcm feature

 

[jrsavoie]

The lift pump and the OPS can go bad independantly of each other>

Did you run voltage directly to the lift pump plug to check the lift pump?

Why do you think the OPS is bad?

 

[GM Guy]

i dont, it is just I am following advice of replacing as a pair, but that advice is probably more useful for OBDI I bet.

Basically, I bought the truck at a Richie Brothers Auction (rbauction.com, big constuction auction company) for 1650 bucks. In the yard, I did not hear the pump, felt it, nothing at all, dead. so we drove the truck home to NW KS empty, so hopefully getting 16mpg, we weren't making the Injection pump suck it too hard. last fuel stop, I did hear something, felt it, and it was quivering a little, but overall weak. I guess it could be a ground that a couple hundred miles may have helped make cure via road vibration, but it looks kinda old, so I figured replacement was in order, and overall a good idea. I also figured if I have the intake off for PMD removal& relocation (it is still good, at least it was for the trip home) and routing of lines for FTB mod, I might as well replace the OPS as Preventive maintenance.

so the OPS does not have anything to do with running the LP on ALL OBDII 96-00 6.5L trucks? is that correct?

If so, according to Rock auto's compatability chart, it will fit all other 6.5L and 6.2Ls, so I guess it goes to the 95! (if I ever get going on that damn thing... )

 

[ak diesel driver]

it's not that it doesn't do anything it's just if it fails the ecm will take over. redundant at least that's my understanding

 

[jrsavoie]

I'm not certain how to bypass the redundancy to test the OPC.
You can test for voltage coming out but it can have the correct voltage but not enough amps to run the Lift pump.
You'd have to figure out how to isolate the power going to the lift pump so the OPC was it's only source.

I thought on the newer vehicles the OPC powered a relay that runs the lift pump. And on those vehicles the OPC's lasted near forever?

I'd hot wire the pump and see how much fuel flows out the drain.

Sounds like you got a good deal.

I must not have been to an auction in a while. Ritchie quit sending me auction flyers

 

[Turbine Doc]

FAQ Library cover OPS troubleshoot & operation http://www.thetruckstop.us/forum/showthread.php?6872

 

[Turbine Doc]

The lift pump and the OPS can go bad independantly of each other>

Did you run voltage directly to the lift pump plug to check the lift pump?

Why do you think the OPS is bad?

correct can go bad independently but so long as one remains other will let it run, so to test pull relay and PCM power will stop and lift will run on OPS only, pull both and pump quits. One thing about the OPS IMO it is a service life item the mylar diaphragm goes bad or body gets brittle, mine snapped off at slightest touch it was just barley hanging together since you have it I'd change it, I don't think OPS socket will make it under the intake, it might, I pulled my intake and put a long pipe nipple & elbow on it and moved it where I could get to it

 

[GM Guy]

I'm not certain how to bypass the redundancy to test the OPC.
You can test for voltage coming out but it can have the correct voltage but not enough amps to run the Lift pump.
You'd have to figure out how to isolate the power going to the lift pump so the OPC was it's only source.

I thought on the newer vehicles the OPC powered a relay that runs the lift pump. And on those vehicles the OPC's lasted near forever?

I'd hot wire the pump and see how much fuel flows out the drain.

Sounds like you got a good deal.

I must not have been to an auction in a while. Ritchie quit sending me auction flyers

as far as ritchie, bring a wad of cash, in case they lost your info. cash is the only way to get into the auction quickly the first time through.

we did miss out though, we were not thinking about parts, and we let a 96 go with exact specs, more miles, and a hard starting blowby equipped 6.5L with a growling 5spd one go for 500 bucks.

 

[GM Guy]

TD, I did read the article in the library, but it wasn't clear to me, but your post on this thread here pretty well spelled it out, at least I think it did: On OBDII the ECM operates the LP via relay. upon failure of the relay, the OPS will then run the LP in the same way it did on OBDI, direct, no relays. Is that correct?

If the above is correct, to test the OPS, of course you do as above, pull the relay. but to do vice versa would test the relay, correct?

So basically if all checks out, I just bought an OPS for another 6.5L, and that I should just change the LP?

I figure even if the lp tests out good and it was a corroded ground, then I can at least use it as the transfer pump, as IIRC the transfer pump on dual tank trucks is the same as the LP. I am kinda wanting a new LP on the suppy.

 

[jrsavoie]

So there OPC's on the new trucks do not go to a relay enroute to the lift pump?

It still goes directly to the lift pump from the OPC?

So it would be a good Idea to do the OPC relay ad on these vehicles as well?

 

[TurboTahoe]

TD, I did read the article in the library, but it wasn't clear to me, but your post on this thread here pretty well spelled it out, at least I think it did: On OBDII the ECM operates the LP via relay. upon failure of the relay, the OPS will then run the LP in the same way it did on OBDI, direct, no relays. Is that correct?

If the above is correct, to test the OPS, of course you do as above, pull the relay. but to do vice versa would test the relay, correct?

So basically if all checks out, I just bought an OPS for another 6.5L, and that I should just change the LP?

I figure even if the lp tests out good and it was a corroded ground, then I can at least use it as the transfer pump, as IIRC the transfer pump on dual tank trucks is the same as the LP. I am kinda wanting a new LP on the suppy.

This is my understanding as well. Being a belt and suspenders kind of guy, I replaced the OPS, Relay and Lift pump all at the same time on the 99 'burb. Relay and LP were piece of cake (LP is kinda messy, but pretty easy - I did have the tank pretty empty, and I parked on an incline with back of truck pointed downhill - with wheel chocks!)

No way I would have replaced the OPS without a crows foot wrench. They didn't have a 1 1/16" crows, so out came the Dremel tool with a grinding wheel, and using the new replacement OPS as a model, was able to get a perfect fit. This allowed me to lay across the engine bay (with foam protecting my chest) and the fuel manager pushed out of the way - took me almost 45 min to get that OPS out and the new one in, but I have had no failures at all since doing that about 4 years ago. I do agree that an in-cab fuel pressure gauge and/or at least an in-line one on the IP input line would be very useful.

-Rob