Low mpg, fuel pressure problems
#1
07-21-2016, 03:27 AM
Join Date: Jul 2016
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Low mpg, fuel pressure problems
Hello,
I have a '96 stock cummins with no mods and am having problems. When I got it I was getting 17 mpg and was disappointed with that but now it's worse. 15 on the road, 11-12 in town.
I recently started having problems with it after quite a bit of driving, it would lose power and fall on it's face at rpms over 1500, so I put a gauge on and saw that my pressure was starting off good but once the fuel in the tank got hot, it was going down to nothing. I replaced the OFV and it helped but still after it got hot, it would starve. I deleted the heater and prefilter, I ran a rubber hose from the tank to the LP, and I checked the steel lines from the LP to the filter base and the base to the IP. No restrictions found, so I replaced the LP (with an aftermarket one). Now it holds decent pressure at high rpm but drops to 10 psi at idle and it makes the engine run rough with poor throttle response at idle. That's better than falling on it's face when I floor it, but the only way for me to get the pressure up to the specs on the OFV is to get the engine going 1800 rpm. Pinching the return line makes no difference, so the OFV valve isn't causing it. I've ordered a OEM LP to see if I can get my idle pressure back up around 20 where it likes to be. Does this sound like I'm on the right track? I've been pulling my hair out trying to figure all this out.
Would these problems be causing my poor mileage too? I intend to advance the timing (it's stock still, I checked by pinning the pump and the engine at the same time) but before I do any mods I want it back to solid stock performance so that I have a good baseline first. I did adjust the wastegate a bit and got my boost up to 22 psi, but other than that everything is stock still. I have people constantly telling me they get 23 to 25 mpg with their 12 valves, so I see no reason mine can't do the same.
I have a '96 stock cummins with no mods and am having problems. When I got it I was getting 17 mpg and was disappointed with that but now it's worse. 15 on the road, 11-12 in town.
I recently started having problems with it after quite a bit of driving, it would lose power and fall on it's face at rpms over 1500, so I put a gauge on and saw that my pressure was starting off good but once the fuel in the tank got hot, it was going down to nothing. I replaced the OFV and it helped but still after it got hot, it would starve. I deleted the heater and prefilter, I ran a rubber hose from the tank to the LP, and I checked the steel lines from the LP to the filter base and the base to the IP. No restrictions found, so I replaced the LP (with an aftermarket one). Now it holds decent pressure at high rpm but drops to 10 psi at idle and it makes the engine run rough with poor throttle response at idle. That's better than falling on it's face when I floor it, but the only way for me to get the pressure up to the specs on the OFV is to get the engine going 1800 rpm. Pinching the return line makes no difference, so the OFV valve isn't causing it. I've ordered a OEM LP to see if I can get my idle pressure back up around 20 where it likes to be. Does this sound like I'm on the right track? I've been pulling my hair out trying to figure all this out.
Would these problems be causing my poor mileage too? I intend to advance the timing (it's stock still, I checked by pinning the pump and the engine at the same time) but before I do any mods I want it back to solid stock performance so that I have a good baseline first. I did adjust the wastegate a bit and got my boost up to 22 psi, but other than that everything is stock still. I have people constantly telling me they get 23 to 25 mpg with their 12 valves, so I see no reason mine can't do the same.
#2
07-25-2016, 03:27 AM
Join Date: Jul 2016
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
I got the OEM lift pump in and put it on. The pressures looked better but still a bit low at idle. I pulled the tork tek OF valve out and put the old OF valve in and suddenly my idle pressure was 25 psi. I guess there is a problem with the tork tek valve I just got. I wonder why it bypasses at idle but at 1200 rpm or so, it jumps up to 25-30. Strange, but it's staying 25 at idle now with the old OF valve so I'm leaving it for now.
I bumped the timing up. I didn't have the dial indicator, I just pinned the engine and pump, then rotated the engine back about 3/8" on my harmonic balancer and tightened the pump nut. The plate on the pump says it is at 13 degrees, so I think I set it somewhere near 16-17. The guy at the diesel shop told me to turn the engine back 3/4" to one full inch, but I think that would have me in the 20s for timing and I don't want that. It starts faster with less cranking and it really woke the engine up! It runs smoother and much stronger. I hope the mileage will improve too.
I use this truck as a service truck for my business daily, so although I want to punch it up a little, I don't want to go overboard. I'm considering putting 3k governor springs on it and maybe turning the star wheel a bit and whatever else I can do to help it get better economy and power.
I bumped the timing up. I didn't have the dial indicator, I just pinned the engine and pump, then rotated the engine back about 3/8" on my harmonic balancer and tightened the pump nut. The plate on the pump says it is at 13 degrees, so I think I set it somewhere near 16-17. The guy at the diesel shop told me to turn the engine back 3/4" to one full inch, but I think that would have me in the 20s for timing and I don't want that. It starts faster with less cranking and it really woke the engine up! It runs smoother and much stronger. I hope the mileage will improve too.
I use this truck as a service truck for my business daily, so although I want to punch it up a little, I don't want to go overboard. I'm considering putting 3k governor springs on it and maybe turning the star wheel a bit and whatever else I can do to help it get better economy and power.
