OPS failed again

[fastcat800]

This weekend while pulling I developed the same high speed miss I had six months ago. Yesterday I did the fuel pressure test by opening the water bleed valve and the truck quits. OPS is fried again after only 7K miles. Guess it's time to buy the relay parts and fix it right. I can't believe Chevy could build a truck with such a poor design. The good news is I got 14.9 mpg pulling 6000 lbs at 65 mph. I am very happy about that.

[Kennedy]

I've got the cure on my site. I haven't listed it yet, but I also have the fittings ready to install the Kennedy Lift Pump right where the old one mounts also...

[HowieE]

A diagram and pictures of the OPS mode setup are posted on my web page.
http://mysite.verizon.net/vze54tx9/id13.html

The OPS is just a swith and it is either on or off as a function of oil pressure.
Opening the fuel drain and having the engine die is not necessarily and indication of a failed OPS. Reducing the fuel pressure this way you may have just starved te injection pump for fuel or the fuel pump is just too weak to supply that additional volume of fuel.

[fastcat800]

You can feel the lift pump run when you crank the motor and it was replaced the same time the OPS was last replaced. I am sure it's the OPS.

[fastcat800]

Hey John, I looked at your site under fuel systems and didn't see anything. What are you talking about?

[Kennedy]

Under 6.5 parts/lift pump I have the lift control harness that takes complete control of the lift pump giving prime, OPS shutdown, and manual activation which is particularly handy for filter bleeding. Lift pump is under Dmax parts at present.

Control:

http://www.kennedydiesel.com/categoryresults2.cfm?Category=1&SubCategory=158

Pump:

http://www.kennedydiesel.com/categoryresults2.cfm?Category=3&SubCategory=157

[HowieE]

If you want to test the OPS find the orange and gray wires coming up from the OPS. Skin back a section on each of these wires and put a clip lead across them. This will bypass the OPS. Start the truck and while it is running at idle remove the clip lead. If the truck stops the OPS is bad.

With the factory wiring you will hear the pump during the glow plug cycle because the pump is turned on at that time by the fuel pump relay. Once the engine starts and oil pressure is above 4# the OPS makes and feeds current to the pump. The above test just remove the OPS from the circuit. I am assuming you have greater than 4#s oil pressure in that engine.

[fastcat800]

Howie, my truck runs fine without the lift pump working at all unless you demand a lot of fuel from a hard acceleration or when pulling a heavy load. It will idle all day long with no pump so your test won't work. Easier way would be to test for power at the gray wire out of the switch with the truck running.

[Kennedy]

Originally posted by HowieE:


With the factory wiring you will hear the pump during the glow plug cycle because the pump is turned on at that time by the fuel pump relay. Once the engine starts and oil pressure is above 4# the OPS makes and feeds current to the pump. The above test just remove the OPS from the circuit. I am assuming you have greater than 4#s oil pressure in that engine. Only 96+ trucks run the "prime" cycle at key up. When designing my control, I decided to incorporate this feature as I think it is a good idea. The idea behind this control was to be stand alone and originally was for the Dmax which had nothing for a lift pump. The 6.5 is a natural candidate due to the issues that it has with these switches, and my lift pump should well be the last you'll ever buy...

[woody]

You may want to see if you're using the latest design OPS. As I understand it, GM has updated the design of this switch at least 3 times, the latest being P/N 12555492. This latest switch has lasted 5 years for me, the original lasting 6 mos, and the second design 1 1/2 years.

Just my $.02, good luck,

Woody

[HowieE]

Yes, with the truck running you should see power on the gray wire coming from the OPS if all is well. The test I mentioned above just bypassed the OPS to test the pump.
You are saying your truck will run at idle without the fuel pump being on at all. What is the source of fuel to the injection pump for this all day idle.
It now sounds like you have a fuel pump problem if the engine will run without load but will fail under load. I don't know the factory specks for fuel pressure but I ran my 6.2 for the last 8 years with a Carter 4# pump. If you have a pressure guage I would test the fuel pressure coming off the pump while ideling and then under load.

[JohnC]

Originally posted by HowieE:
You are saying your truck will run at idle without the fuel pump being on at all. What is the source of fuel to the injection pump for this all day idle...The injection pump has an internal transfer pump that is designed to function with positive pressure at its inlet, but can keep the engine running even if the lift pump fails. The quality of running is then determined by the restrictions in the dead pump and filter.

[GMC Hauler]

JK,
Nice option for the lift pump! Do you think that the high volume lines are required for a rig like mine? What exactly is included and involved with R/R of the fuel lines? Have you tried one out on the 6.5? What pressures do you see at starting, idle, cruise, and full throttle?

Thanks

[ 08-20-2005, 10:13 AM: Message edited by: GMC Hauler ]

[rjschoolcraft]

Preparing to install one on my truck now. I have the harness installed already and really like the manual prime feature.

[Kennedy]

The pump is more about volume than psi. It only makes about 4psi, but will mainytain a minimum 1 psi on a Dmax running at 450RWHP. The lines on the 6.5 are pretty small, but I think it will keep up fine. The OE does around .5 GPM where this one is capable of well over 3 gpm based on line size. We will not see that with the small lies that we have.

Flow through restriction (in case it would quit) is nil.

RJ is my test subject and I am quite certain that he will be pleasedwith the results...