handcannon
Well-Known Member
I'm posting this mostly for information for others to hopefully keep them from going through what I did. If this info helps others understand and keeps them from wasting time and money on non-AC Delco OPS's my time and frustations are worth it. If somebody is in the same spot I was in with an aftermarket OPS and is having unexplained problems maybe this will help them.
I got my 94 K2500 Chevy in Feb this year. It was a project as the PO slid on ice and smacked a tree in Dec 09. In early April I was able to finally start driving it. I did a bunch of checking and discovered the OPS was bad, not powering the LP. I went to the parts house to get a new OPS but all they had was a Standard brand item, part number XIP PS245. Being anxious to get a new OPS installed so I could drive the truck I got the Standard OPS and installed it. Then I read in one of the forums I haunt (don't remember which one) that only the AC Delco will hold up over time, too late. I noticed right off that the oil pressure gauge was reading about 15 pounds less than before. No problem I thought, I can compensate for that mentally since I am aware of it.
Fast forward from April to late May. I was in town running at an idle in a parking lot, fortunately not in traffic, when the truck just out of the blue died. It would not restart right away. After a bit of cranking it stumbled to a rough start. My first thought was PMD problems since I had been reading so many posts about that problem, but mine was remote mounted.
Nothing happened for about a week, Then it happened again, fortunately still not in traffic. Restart was the same. By this time I was connecting the hard restart to similar times I have had with my 83 6.2 truck and air in the fuel problems with it. I had also noticed my fuel pressure gauge at times showed 0 PSI. After this time I put a chunk of clear tube on the IP return and sure enough, air bubbles. Also, when I pulled the stock return line off I heard a "boiling" sound, that lasted for about a minute, coming from the fuel tank. Hmmm, vacuum in the tank. I loosened the cap a little bit, drove it some, and checked it. Sure enough, vacuum again. I left the cap loose and drove it some more. No more vacuum.
The third time it died I stopped at the end of my driveway to go to the mailbox. I checked the fuel cap, it was still loose so no vacuum. Somewhere along here I had noticed that with a cold motor I had fuel pressure, but with a warm motor I lost fuel pressure. I had done the OPS relay mod when I origionally changed the OPS and had also wired in a push button to run the LP to bleed air out when changing fuel filters. So with a warm motor I would use the push button any time I had to let the motor idle and had no more problems. It did die one more time, but it was my fault since I forgot to use the push button to keep the LP running.
I then did a temporary wire bypass for the LP. I ran a wire from a switched hot under the dash to the LP fuse on the firewall. This worked, no more dying. However, I soon discovered it worked too good. When the motor was warm everything ran as normal, but when it was cold the motor would not shut off. The OPS would supply 12v when it was cold and this 12v would not shut off with the key, essentially feeding back and bypassing the ignition switch. I could turn off the ignition switch and pull the key when the motor was cold and it would stay running until the OPS warmed up enough for the LP circuit to fail. By this time I had already ordered an AC Delco OPS and was just biding my time waiting for it to arrive.
My conclusions---I was dealing with multiple problems. (1) I need to modify my fuel cap to keep from building vacuum in the tank. (2) My new aftermarket OPS failed less than two months after install. (3) The LP, age unknown, is getting very weak and was having trouble overcoming the vacuum buildup in the fuel tank. (4) Since the LP was not working all the time, the IP was sucking fuel from the tank, creating vacuum in the fuel line. I had been having trouble with fuel leaking from the filter after doing the feed the beast mod, but I thought I had that cured. However, the vacuum in the fuel line created by the IP was apparently allowing some air to be sucked in somewhere around the fuel manager. This showed up as dying when allowed to idle for very long.
I replaced the OPS today with the AC Delco that I ordered. The LP is now working all the time, only at much reduced PSI since it is getting weak. As soon as I can come up with the funds I will be replacing it. Also, I will eventually replace the fuel manager with probably the Racor 230. And I still need to modify the fuel cap to keep vacuum from building.
Because of having a fuel pressure gauge and having done a lot of reading on this forum I had learned a lot about diagnosing these kind of problems. I just hope my post here will help somebody in the future.
Thanks to everybody who contributes questions and solutions.
Don
I got my 94 K2500 Chevy in Feb this year. It was a project as the PO slid on ice and smacked a tree in Dec 09. In early April I was able to finally start driving it. I did a bunch of checking and discovered the OPS was bad, not powering the LP. I went to the parts house to get a new OPS but all they had was a Standard brand item, part number XIP PS245. Being anxious to get a new OPS installed so I could drive the truck I got the Standard OPS and installed it. Then I read in one of the forums I haunt (don't remember which one) that only the AC Delco will hold up over time, too late. I noticed right off that the oil pressure gauge was reading about 15 pounds less than before. No problem I thought, I can compensate for that mentally since I am aware of it.
Fast forward from April to late May. I was in town running at an idle in a parking lot, fortunately not in traffic, when the truck just out of the blue died. It would not restart right away. After a bit of cranking it stumbled to a rough start. My first thought was PMD problems since I had been reading so many posts about that problem, but mine was remote mounted.
Nothing happened for about a week, Then it happened again, fortunately still not in traffic. Restart was the same. By this time I was connecting the hard restart to similar times I have had with my 83 6.2 truck and air in the fuel problems with it. I had also noticed my fuel pressure gauge at times showed 0 PSI. After this time I put a chunk of clear tube on the IP return and sure enough, air bubbles. Also, when I pulled the stock return line off I heard a "boiling" sound, that lasted for about a minute, coming from the fuel tank. Hmmm, vacuum in the tank. I loosened the cap a little bit, drove it some, and checked it. Sure enough, vacuum again. I left the cap loose and drove it some more. No more vacuum.
The third time it died I stopped at the end of my driveway to go to the mailbox. I checked the fuel cap, it was still loose so no vacuum. Somewhere along here I had noticed that with a cold motor I had fuel pressure, but with a warm motor I lost fuel pressure. I had done the OPS relay mod when I origionally changed the OPS and had also wired in a push button to run the LP to bleed air out when changing fuel filters. So with a warm motor I would use the push button any time I had to let the motor idle and had no more problems. It did die one more time, but it was my fault since I forgot to use the push button to keep the LP running.
I then did a temporary wire bypass for the LP. I ran a wire from a switched hot under the dash to the LP fuse on the firewall. This worked, no more dying. However, I soon discovered it worked too good. When the motor was warm everything ran as normal, but when it was cold the motor would not shut off. The OPS would supply 12v when it was cold and this 12v would not shut off with the key, essentially feeding back and bypassing the ignition switch. I could turn off the ignition switch and pull the key when the motor was cold and it would stay running until the OPS warmed up enough for the LP circuit to fail. By this time I had already ordered an AC Delco OPS and was just biding my time waiting for it to arrive.
My conclusions---I was dealing with multiple problems. (1) I need to modify my fuel cap to keep from building vacuum in the tank. (2) My new aftermarket OPS failed less than two months after install. (3) The LP, age unknown, is getting very weak and was having trouble overcoming the vacuum buildup in the fuel tank. (4) Since the LP was not working all the time, the IP was sucking fuel from the tank, creating vacuum in the fuel line. I had been having trouble with fuel leaking from the filter after doing the feed the beast mod, but I thought I had that cured. However, the vacuum in the fuel line created by the IP was apparently allowing some air to be sucked in somewhere around the fuel manager. This showed up as dying when allowed to idle for very long.
I replaced the OPS today with the AC Delco that I ordered. The LP is now working all the time, only at much reduced PSI since it is getting weak. As soon as I can come up with the funds I will be replacing it. Also, I will eventually replace the fuel manager with probably the Racor 230. And I still need to modify the fuel cap to keep vacuum from building.
Because of having a fuel pressure gauge and having done a lot of reading on this forum I had learned a lot about diagnosing these kind of problems. I just hope my post here will help somebody in the future.
Thanks to everybody who contributes questions and solutions.
Don
