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Discussion Starter · #1 ·
While driving the truck I can be on throttle cruising at let's say 12k at the rail. If there's a stop sign coming up I'll let off throttle and the rail pressure will stay at the cruising pressure (12k in this example) and then start creeping up (so demanded is about 4-5k and actual will be anywhere from 10-15k usually) before it will finally start falling off to match the demanded pressure again. This problem has been happening since owning the truck but it has recently gotten quite a bit worse. Before it was hit and miss, it did it sometimes but not often. Recently its been happening almost constantly. The trucks been throwing a fuel pressure regulator code for some time now while not showing the usual lope at idle symptom, so I got a new Bosch one in and the problem has still been getting worse since then. This morning I started my truck to drive to work and immediately at startup the actual rail pressure was about 20k and wouldn't fall off, it was just hovering there. After a few seconds I noticed the truck sounded a little off, almost more of a mechanical sound at idle similar to an LB7 and then the idle got a little rough so I shut it off. Started it again, this time pressure was right where it should be, matching demanded at about 5k but then started slowly creeping up to 17k until I just shut it off again. I didn't have time to check anything under the hood or check for codes because I needed to get to work so I left the truck at home but I will be scanning for codes when I get off work.

I just joined the forum to post this so haven't made a sig yet but here's the basics :
2005 LLY with a 68mm drop in and 35 over injectors, FASS 165, Starlite tunes
 

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Discussion Starter · #2 ·
Just remembered, my one theory is the harness for the fuel pressure regulator. When replacing the regulator, we noticed the wiring to it was a little beat up and it had obviously gotten exposed to quite a bit of heat in its lifetime. Also, the harness has a 3 pin plug on one end and a 2 pin on the other. I stripped all of the messed up heat shrink off the wires and found that the extra wire that doesn't run all the way thru the harness is just a bare wire the whole way thru, no insulation on it whatsoever and it just runs about halfway thru the harness and doesn't go to anything. I taped it all back up because I couldn't get a replacement same day but is this likely my issue? I already ordered a replacement thru DHD and it should be here friday.
 

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Had a similar problem with pressure being real low or none at all. Shop replaced the fuel regulator and still very low. Finally they talked to someone at GM and they said if you replace the regulator you have to replace the rail as well because old and new do not match up precisely. Not sure if it was a load of crap but it fixed the problem and the shop didn’t rape me on the labor because they had my truck for 3 days trying to figure it out
 

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Discussion Starter · #4 ·
Had a similar problem with pressure being real low or none at all. Shop replaced the fuel regulator and still very low. Finally they talked to someone at GM and they said if you replace the regulator you have to replace the rail as well because old and new do not match up precisely. Not sure if it was a load of crap but it fixed the problem and the shop didn’t rape me on the labor because they had my truck for 3 days trying to figure it out
That's interesting, I've never heard of needing to replace the rail with the regulator
 

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Me either but it fixed the problem. They tore my truck apart 3 times doing this and doing that and finally got a hold of a GM tech that told them that. It’s a shop I go to regularly for all my cars and trust them. They only billed me for the labor rate to replace the rail and not all the time they actually spent searching for the issue.
Actually worked in my favor because when they had it torn apart I did new water pump, hoses, and belts
 

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Discussion Starter · #6 ·
That's interesting, I've never heard of needing to replace the rail with the regulator
Did they use a Bosch regulator? Also if my issue started after the regulator it'd be something to look into but it's always been an issue. As far as I can tell the only thing replacing my regulator fixed/changed was the cel. Interesting to note tho
 
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