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OPS relay question on a 98 6.5

G

great white

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Just seeking clarification:

Is the OPS relay modification nessesary on a 98?

I seem to recall some comments how the problem had ben rectified by GM by 98 with a factory relay setup...

true or false?

:smile5:
 
Yeah I think what he is trying to say is the OPS takes over after the glow cycle. I'm gonna fix that problem with the Raptor. it comes with the whole wiring harness, relay etc. It'll be an easy swap now with my fuel lines changed over to Push lok and my custom fittings just came in to adapt to the FSU. :D
 
Was told by gmctd that ops circuit is redundant ,parallel circuits,one thru ops but also one thru pcm & relay .
 
I don't know, but IMHO, that doesn't make sense or is at least useless : if we consider GM choose the option of feeding the lift pump through the OPSfor security purpose, having a redundant circuit controled by the ECM bypasses the OPS and bypasses the security setup itself.

Though, feeding the OPS in parallel with the OPS would not need the interaction of the ECM : just wire a relay, hot when key is on, and let it feed the LP...
 
OK.

The reason I asked was to find out if I needed to add a relay and take the "high" power requirement away from the OPS to reduce the possability of failure in the contacts.

So, do I need to install a relay for longevity and reliability or not?
 
if you want to nothing wrong with adding relay, bad OPS will not leave a OBD-II truck stranded, as a FYI the plastic in the OPS over time gets brittle, so IMO it's good to change @ 50K just as preventative measure, the little mylar diaphragm in the OPS also wears out over so many cycles as well.
 
Doc Recall you & Gmctd doing some tests to demonstrate there being 2 circuits . Good info.
 
OBD1, 92-95, lift pump only runs on OPS after startup, the 94-95 LP relay is only controlled by ign switch in start position while cranking, 92-93 LP relay also controlled by glo controller during WTS. OBD2 96+ always has power from the LP relay in the fuse center which is controlled by the PCM during WTS/crank/operation.
 
So, if OPS broke, we still get power to LP on OBD-II ?

I don't understand the goal, especially as the OPS feed circuit is thought to "offer" security ... Why bypassing it through a second parallel circuit ?
At least the ECM circuit works on a special routine ?
 
matuva said:
So, if OPS broke, we still get power to LP on OBD-II ?

I don't understand the goal, especially as the OPS feed circuit is thought to "offer" security ... Why bypassing it through a second parallel circuit ?
At least the ECM circuit works on a special routine ?
Click to expand...

Yes you still get power, have to lose both OPS & PCM, I suspect as a way for GM to insure PMDs don't die from reduced cooling via IP reduction of fuel flow to the IP. GM IMO added the PCM control path for redundancy of existing OPS path, which would cost more to remove by design than adding in the backup circuit. All conjecture on my part
 
The PCM will know if the engine dies, because it will lose the RPM signal from the CPS, so it will still shut off LP just like OPS when engine died and loses oil pressure.
 
The PCM controls the relay coil to run the lift pump, the line going back to it is a lift pump power so it will throw a DTC if you dont have battery voltage on that line. This is OBD2 specific. no lift pump power DTC in OBD1 and no PCM control of LP.
 
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