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I'm just trying to get some advice as I'm getting my tuning together - it's going pretty well so far. I'll eventually be running closed loop, but right now I'm running in open loop trying to get the fueling together. Here's my engine specs:
-88 GMC Sierra
-Vortec 350
-Comp Cams xr258hr cam
-LS6 Valve springs
-1.6 roller rockers
-68#hr cop car injectors
-30 psi fuel pressure
-shorty headers
The fueling everywhere else(up to redline) is looking okay so far, but for some reason if I try to get it to idle at the commanded AFR(14.0), the engine starts to shake and act funky. It idles super smooth if I've adjusted the VE tables so I get an WB AFR around 12 - 13.5, but anything higher than that and it starts to act strange. If I get it above 14.7 it will start to surge. Do any of you have any suggestions as to what might be going on? i'm pretty new at this, so I'm out of ideas over here, lol
Assuming original pressure was at 12 psi bumped to 30 psi, a 68 pph injector will behave like a 107.5 pph injector. Is this all accounted for in your tune? My thinking it's way too much injector that your pulse widths are too short and precise control for a stable idle is hard to achieve. Is your fuel pressure regulator adjustable and can you drop the pressure?
Yep, I used RBob's utility program so it's all taken care of in the tune. My fuel pressure regulator is also adjustable, and I've tried out a few different springs, giving me 16 psi all the way up to 32. I was running 22 psi for a while, but it felt pretty anemic. When I bumped it up to 30 psi, I was surprised to see that the engine really woke up.
Hey guys,
The fueling everywhere else(up to redline) is looking okay so far, but for some reason if I try to get it to idle at the commanded AFR(14.0), the engine starts to shake and act funky. It idles super smooth if I've adjusted the VE tables so I get an WB AFR around 12 - 13.5, but anything higher than that and it starts to act strange. If I get it above 14.7 it will start to surge. Do any of you have any suggestions as to what might be going on? i'm pretty new at this, so I'm out of ideas over here, lol
Okay that's good to hear. I was worried with it being so rich that I might get cylinder wash or something. I guess what I want to understand is why it doesn't want to run well at the commanded AFR at operating temp?
Okay that's good to hear. I was worried with it being so rich that I might get cylinder wash or something. I guess what I want to understand is why it doesn't want to run well at the commanded AFR at operating temp?
Because it is too lean. An engine at idle is barely running, It will generally like a 13.0 - 13.5 AFR during this time. The cam also affects this, as the idle speed should be raised a bit, and sometimes adding additional SA is helpful.
I'm still tuning in open loop at this point, but within a week or so, I'd like to transition to closed loop. Basically if it gets anywhere above 13.5, the engine will start to stumble. If it goes above 14.0, it will start to surge.
Okay thanks for the explanation! This engine stock runs around 550 rpms at idle, so I've raised it to 675. I've also raised the SA and it seems to run smoother.
So if the engine likes 13.0 AFR at idle, should I change the Open Loop - AFR vs RPM & VAC table to reflect this? It's currently set at 13.80 for the idle area. Also, when I transition to closed loop, will the engine try to run at 14.7 at idle, or will it try to run at the commanded AFR in the open loop table?
Whew...thanks so much for pointing at those threads - my head is swirling a bit but I understand a little better now
I spent the past few weeks reading up on all of it and now I'm finally starting to understand everything, but unfortunately, I have more questions, lol. I've been using these tables below to get the engine to run around 14.7 in closed loop, and I'd say I've been halfway successful so far. These are the numbers I have so far:
So with these numbers, while driving, if I'm pulling off from a dead stop, it will hover somewhere in the range of 14.7 on the WB if I'm only using 1/4 - 1/3 throttle. If I'm using 1/3 - 1/2 throttle, the engine starts going lean. I'm trying to figure out why that is.
In combing through the treads, I've noticed a lot of people have the same value in the tables from top to bottom(like above), so I tried that approach. But I noticed on most of the stock truck calibrations, the tables don't have the same numbers as seen below:
Is this maybe why the engine tends to run lean if I'm giving it a little more gas, or do you think it's something else? Btw, if holding the pedal steady at cruising speed, it will also read around stoich, but if I start to give it too much gas (though not enough to go into Open Loop), it will go lean.
The problem is, it's still surging at idle. So far I've increased the SA table at idle, got the IAC counts to 5 - 10 at idle, and I've messed around with these tables below, but I have a pretty poor understanding of how they function to try and control the surging, even reading through a bunch of threads on the topic. Sometimes I think it helps, and then surging comes back. I'm not sure which way to push these tables in either direction - can anyone shed some light on these:
Ah I see, so the car might be reading rich when it actually isn't? Interesting. My cam is pretty mild by most standards - it has around 37 degrees overlap. Will this still cause the WB to read rich when it actually isn't?
Okay great, ill try learning with open loop idle and see how that goes
Okay thanks for the response. As you can tell this is my first build, so I'm just trying to get a handle on everything and truly understand what's going on, since I didn't know what to expect. When I'm done tuning I'm going to ship it down to California, I just want to make sure I have all of my ducks in a row, and that it will pass the sniffer test. I guess because it's a milder engine build, I didn't expect it to like idling so rich.
In open loop, it likes to the idle AFR around 12 - 13.3 or so. So what I did is I put it into closed loop raised the O2 - Idle O2 Window Terms table as follows:
MnR/L - 781.20
Rich - 794.22
Lean - 750.82
At these settings, the truck now runs super smooth at idle in closed loop. I guess what I'm getting at is, is this normal for the engine specs I stated earlier in the post? I've seen engines with bigger cams idling around 14.0 with no surging, so I'm just trying to understand why the engine needs to idle so rich at idle. Right now I have the SA at idle jacked up all the way to 27, with the idle speed set around 675 rpms fully warmed up. I'm also not positive whether an engine idling at 12.5 AFR will pass the sniffer test, even if everything else is running at stoich, since I'm not a tech.
Just trying to learn is all - thanks for the help so far.
When I'm done tuning I'm going to ship it down to California, I just want to make sure I have all of my ducks in a row, and that it will pass the sniffer test.
I thought Communifornia was automatically failing vehicles with modified "tunes" loaded into the computer.
Yeah I tried to study the smog procedures to make sure I wouldn't fail this thing, because while I was away at school they changed the rules . Here's how the OBD I and OBD II tests differ(from my understanding).
OBD I: Visual inspection. Sniffer test. Check engine light test. The visual and sniffer are self explanatory, but with the check engine test they basically just see that the light is working correctly - nothing is connected to the port, since OBD I ins't as intelligent a system anyways.
OBD II: Visual inspection. No Sniffer. Scanner connected to OBD II port. Since they're connecting their scanners to the OBD II port, there's no need to do the sniffer - the scanner tells them everything they need to know, like whether it's modified or not. I think that's why the OBD II guys are freaking out about it - I feel for them, man. When it comes down to it, you can put together a clean running vehicle that passes smog easily, but if all of the parts aren't CARB compliant, you're screwed.
Lucky for me I have OBD I, and everything is gonna look stock under the hood. I've even got the dang a.i.r. injection tubes on this thing, lol.
That's just more Cali tree-hugger BS for emissions in that state. Arizona has almost exactly the same emissions standard, but we don't care if you change the tune with OBDII as long as it doesn't set a CEL light, no roller test. OBDI is a roller test just like Cali and they don't care if you replaced the ECM or anything else, it just has to pass smog test. If you have collectors insurance then you are good to go for life, no testing at all no matter what you did to the motor/tune. I just send in my registration every two years, car never goes to the testing station.
I take it there's a limitation on the miles you can drive with the collectors insurance right?
Yes, most insurance company's have a restriction on miles driven a year which is about 6K. However, my company says you can not use as a daily driver, which I do not. Have they ever checked, no. I pay $300 a year, full coverage including tow, glass coverage replacement and must be kept in locked garage etc with a stated value of the car. Very good coverage and I only drive about 3K a year if that now. You will have to check with the different companies on what they allow the car to be driven and other restrictions. GL
So I'm happy to report I've made some progress over the past few weeks in open loop. Two things really helped me out:
1) Drastically reducing the timing at idle(around 16 degrees in the idle area). Every time I would come to a stop, the engine would surge at idle, and it still has a bit of the rolling idle/surge thing when coming to a stop, but it eventually goes away, which is a huge improvement.
2) Setting the entire Open loop - AFR vs RPM & VAC table to 14.7. This helped me dial in the VE table so when I eventually go into closed loop, it might play better. I can now idle around 14.7 easily in open loop.
The only problem is, when I put it back into closed loop, it still surges at idle. Not only that, but I find the o2 sensor is jumping all over the place and it doesn't seem to move very fast. Every time the o2 swings up or down, I can feel it as I'm driving. It definitely doesn't feel normal. That, and there seems to be a pretty sharp loss of power in closed loop, which I figure wouldn't happen since in open loop I've got the engine to run at 14.7 pretty much everywhere(except WOT)
Do you guys have any tips for transitioning to a closed loop tune, after you've got the open loop tune dialed in pretty well?
Yeah it's been a while, but I was able to stop the surging by doing quite a few things. Here's what I did:
1). Increased the idle speed. My truck runs at 550 rpms at idle, stock. I increased the idle speed to 650
2). Reduced the timing pretty drastically in certain areas. I actually found out one major reason for surging in certain spots was that the SA timing table was too high in certain areas. I decreased the SA in the idle area to around 16 degrees and it helped.
3). Bought a VRFPR. This helps tremendously as you can run a lower fuel pressure at idle, which helped quite a bit with stability.
4). Did a series of open loop VE learns, then hand smoothed the table from there. For whatever reason, I couldn't get the VE tables to be perfectly smooth by just doing VE learns, so after I did quite a few(6 or 7), I transitioned to datalogs, interpolating the data, and then hand smoothing
5). I upgraded my stock o2 sensor to a heated o2 sensor.
6). Transitioned to closed loop and did a series of VE learns, and then hand smoothed the table.
Right now it runs so smooth I can't even get the damn thing to surge if I tried lol
Thanks Ace! I'm going to try your suggestions.
What is a VRFPR? Variable Rate Fuel Pressure Regulator?
In open loop I have a solid idle, once she warms up and switches to closed loop, I get the surge when coming to a stop and while stopped.
I have a lean issue because I see the AE light up in WUD when the surging is active and also from the data log, watching the narrowband O2 go lean/rich. Should I add more fueling via the VE table? Maybe retard SA in the idle areas? How does one do that?
Thanks!
What is a VRFPR? Variable Rate Fuel Pressure Regulator?
Vacuum Referenced Fuel Pressure Regulator. The Aeromotive Universal VRFPR is a good choice, it comes with two different springs for different pressures. Hope this helps.
2nd what Buccaneer said. I've got the Aeromotive 13301 model and it works great. What are your mods btw? What you'll need might greatly depend on that. For example, I thought that my engine needed more fuel at idle(around 13.4 AFR or so) to run smooth, but making those changes actually showed me that it can be stable running around 14.7 at idle.
The advantage of running a VRFPR is that you can run a lower fuel pressure at idle. One of the typical mods us TBI guys usually do is run larger injectors and higher fuel pressure. But at idle, it could present problems running smoothly - the VRFPR fixes that.
You have the EBL flash right? For changing the SA at idle, just go into the SA spark table in tunerpro and decrease the numbers in the idle area.
The heated o2 helps because some guys go with long tube headers, which puts the o2 sensor further down the pipe. Problem is, it can go cold during idle until you start moving again, so the self heated o2 fixes that.
Basically lots of trial and error. You gotta play with things a bit and see what the engine likes - and ask a bunch of questions(Lord knows I did lol).
Thanks. ECM is Flash-ii with PortMod.
New Blueprint crate Engine, Long Block, Chevy, Small Block, 355, SBC, 350 Crate Motor, Cylinder Heads, Roller Cam - kept the TPI set up.
Went with an adjustable FPR, not VRFPR. Dialed in to 47 PSI with Southbay 30# injectors. Used ELB utility to set the BPC.
Engine has mild cam, aluminum heads, hooker headers, no cat, magnaflow muffler. No smog / EGR.
In open loop I'm pretty good at idle, closed loop surges. I think I'm going to start a new bin. I've been slowly learning since I replaced the engine in June and installed the Flash-ii.
There is a lot of useful information in this thread, that's why I'm leaning towards just starting a new tune now that I have a better understanding.
I'll post my BIN here prior to starting my new turn in case its salvageable
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Last edited by 89 GTA 355; 02-11-2024 at 12:17 PM.
Reason: Added datalog
Thanks. ECM is Flash-ii with PortMod.
New Blueprint crate Engine, Long Block, Chevy, Small Block, 355, SBC, 350 Crate Motor, Cylinder Heads, Roller Cam - kept the TPI set up.
Went with an adjustable FPR, not VRFPR. Dialed in to 47 PSI with Southbay 30# injectors. Used ELB utility to set the BPC.
Engine has mild cam, aluminum heads, hooker headers, no cat, magnaflow muffler. No smog / EGR.
.
Note that the FPR on a return-type MPFI system MUST be vacuum referenced. This is not the same as a VRFPR on a TBI setup. In this case, MPFI, vacuum referencing the FPR maintains the same differential fuel pressure across the injector. So there isn't any change in the flow rate.
And of course the BPC - BPC vs VAC table ends up being all the same value. As the injector flow rate stays the same with a change in vacuum.
05-27-2023, 01:21 PM
. Here's how the OBD I and OBD II tests differ(from my understanding).
