When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I recently purchased a new aeromotive 13301 vrfpr for my truck, to try and get a more stable idle in closed loop. It's been working great, except ever since I've installed it, I've been getting this weird lean spot at a TPS percentage between 10-15, and rpms 1400-1700. I've been running the heavier spring between 25-30 PSI, and no matter what, if I don't jack up the VE in the spot you see below, it will go super lean. I'm using EBL, btw.
I figured it might be AE, so I richened up the AE quite a bit, it still goes lean unless I push up the VE table in that section. I also tried to go with a static fuel pressure of 30 PSI, and it still goes lean in that area. Have you seen anything like this before? This seemed to happen only after I installed the vrfpr.
Did you change the BPC - BPC vs VAC table to match? Have you checked the actual fuel pressure at various manifold pressure points? Is the VRFPR vacuum line connected to a full time port?
Yep I adjusted the BPC - BPC vs VAC tables both for the vac referenced tune, and the static fuel pressure tune. I've got an electronic autometer fuel pressure gauge on one of the side ports of the vrfpr, and it runs right into the cab where I can monitor the fuel pressure while driving. When I'm holding the pedal and it's going lean, the fuel pressure seems to hold steady.
For the vacuum ref line, i've got it connected to the port on the furthest left...I believe the two on the far left and far right are manifold vacuum, right? The bigger one in the middle is for the PCV valve, and the smaller port at the bottom(ported) is for the evap canister. Please correct me if I'm wrong. I'm running the 454 tbi btw.
I'm using it because I'm running 27-30 PSI fuel pressure, with 68hr injectors. It was almost impossible to get it to idle at 14.7 in closed loop.
Using the vrfpr, I was able to for the first time to get at stable idle (I almost didn't think it would ever happen, lol) - it's just this little weird issue I've got to get a handle on.
Ah i gotcha. What problem were you trying to solve?
It's funny, back when I was using the regular tbi regulator with the 30 psi spring, the fueling looked pretty good, except steady was a problem. Now that I've got the vrfpr, it's got a great idle, and great fueling from 2000 rpms on up, but 1300-1700 rpms go totally soggy.
I had a SBC 400 with a 224/234 cam, ported CFI Intake, headers/exhaust, and other mods in an '83 CFI TA running of the stock, 305 ECM/tune. I got it running pretty good w/just bigger injectors, fuel pressure and base timing, but it would stall from flooding if you pushed in the clutch at at right about 1200 RPM on decel. Basically, if you pushed in the clutch right at the bottom of DFCO, injectors would come back on full force, and flood it and stall. Clutch at a higher RPM, it would stumble and recover....at a lower RPM (after injectors had come on more gradually) and it would be fine. 1200 RPM? Flood and die.
I added the VRFPR as a countermeasure to that problem and it was effective at eliminating that problem. A side benefit was better idle (which had been too rich before) and really good highway fuel economy. But my thing was all f'd up and like I mentioned earlier, it was more of a band-aid that worked, than a good solution. Tuning the ECM would have been a better final solution, but this worked pretty good.
You can "tailor" the effectiveness, or the level of influence that the VR FPR has by changing injector sizing and pressure to mitigate or enhance the influence of the vacuum, on the fuel delivery.
Oh wow, I'm surprised you got it to run even that well without a proper tune! My truck ran like a turd with the stock tune, but with the magic of the EBL software, it's starting to turn out real nice. The VE learn stuff if pretty cool especially if it's your first build and you don't have a solid handle on the ins and outs of tuning yet, which I definitely don't, but I'm getting there.
Oh wow, I'm surprised you got it to run even that well without a proper tune! My truck ran like a turd with the stock tune, but with the magic of the EBL software, it's starting to turn out real nice. The VE learn stuff if pretty cool especially if it's your first build and you don't have a solid handle on the ins and outs of tuning yet, which I definitely don't, but I'm getting there.
It took time, and I think the key was that the tq curve (and thus, the fuel curve) was the same shape, as the stock tq curve, only more of it. It idled like stock, had great throttle response and drivability was good, went mid 13's, and got as high as 25 mpg on a road trip, so all in all...it was "good enough", just tuning things mechanically.
Hey everyone,
I figured it might be AE, so I richened up the AE quite a bit, it still goes lean unless I push up the VE table in that section. I also tried to go with a static fuel pressure of 30 PSI, and it still goes lean in that area. Have you seen anything like this before? This seemed to happen only after I installed the vrfpr.
Pictures attached:
Ace17, any chance the fuel system is hard plumbed? That is from the feed into the TBI and the outlet to the VRFPR ?
There is something else that I've run into. There is an easy test for it.
So the feed line going to the TB is a ptfe line with a hard line attachment - same with the return line coming from the TB going to the vrfpr. The return line going from the bottom of the vrfpr back to the tank is 6an braided nylon fuel hose. i've attached photos of the parts of the ptfe fuel lines that are hard.
OK, need to add about 4 feet of rubber hose. Either between the feed line and the TBI (best) or the TBI outlet and FPR. Can use regular fuel line, no need for the expensive stuff. Can also coil it so that it takes up less room.
Basically the rubber hose will become a fuel pressure pulsation damper. See if that does the trick. If so can then do something more permanent.
I totally removed the hard/ptfe line from the fuel filter, all the way up to the throttle body, went driving around, and that lean spot is all but eliminated! This thing pulls so hard now, it's crazy. Now it's got me wondering, what's the ratio of hard/ptfe to rubber line you think I or anyone should have on a vehicle?? I think this might explain why my tune recently has been going in circles.
To be honest, I don't know how much 'give' or damping is required. I ran into this accidentally, only to have my findings backed up a day later by another tuner.
Many port injected vehicles run fuel pulsation dampers, including the '90 - '92 MPFI Camaro & Firebirds.
I started running Viton lined -6 Pro-Flo 30R9 Braided Hose. About 2.5' on the TBI inlet side, and about a foot on the outlet to FPR side. This hose is soft (and doesn't weep fumes!). This is what made the difference.
It looks like a FPR could be used as a damper, and also be adjustable to the fuel pressure.
That was a wicked good point to bring up, RBob. The CFI has a Pulse damper in the front/first TBI, the single 2bbl TBI doesn't so that feature has to be implemented elsewhere in the system. The soft fuel line is a simple, effective solution.
Yeah it's pretty wild. I'm still in the process of tuning, but for the longest time, I just thought I hit a bottleneck at 4400 rpms. Not that I have a radical cam or anything, but I thought it would pull at at least to 5k, only it never did, no matter how much fuel I threw at it. I just accepted that maybe my intake just didn't flow that well or something.
Did some driving today, and it's pulling past 5k for the first time ever, lol.
Thanks again for all the help everyone!!! And for future viewers who may ever read this forum post...don't overlook hard fuel lines if you're having weird tuning issues
So the feed line going to the TB is a ptfe line with a hard line attachment - same with the return line coming from the TB going to the vrfpr. The return line going from the bottom of the vrfpr back to the tank is 6an braided nylon fuel hose. i've attached photos of the parts of the ptfe fuel lines that are hard.
Is this braided line to hardline crimp connection something you did custom?
I've been looking for a way to bring flexible line from the bellhousing to the throttle body but all the AN to hardline fittings make me nervous.
Nope, I bought the fuel line kit on Ebay a number of years ago. So the feed line for example, is basically a hard metal line from the pump to the fuel filter. Then from the fuel filter, it changes to a stainless steel braided ptfe line all the way up to the throttle body, which changes into that hard line attachment.
What I did, is bought 10 ft of standard rubber fuel hose, a 6an female to 3/8" straight barb fitting(to stick in the fuel filter side of the rubber hose). another 6an male flare to M16x1.5(since this is the size of the fuel filter outlet), and for the hardline crimp connection near the throttle body, I cut the crimp off and connected the rubber line straight on. On the other side, I needed to make a hard line to rubber line connection - these below are easy to use and work well:
These AN fittings ARE pretty intimidating at first, because there's so many of the dang things(styles, sizes, etc). But after about of week of studying your fuel system, and buying a few of the wrong AN fittings (like me ), you'll get it pretty quick.
11-13-2023, 05:20 PM
- it worked!!
), you'll get it pretty quick. 