Fuel pressure - idle issue

I made my regulator adjustable and have set my pressure at 11 PSI, the same as before I modified the regulator. I have done a couple of scrubs to my VE table prior to the regulator mods, and except for idle I have a pretty smooth running vehicle. I wanted to raise my fuel pressure up to 15 as I have read this is generally a preferable pressure. If I do this will I need to redo data collection and VE table tuning all over again? 65 PPH injectors if it matters. Just had them cleaned and tested too. I did not get very good data back from the local guy that ran them through his machine. One injector put out 90cc the other 110cc. But he could not give me a rate for that volume. He just put them in the machine and ran the program. It sets the pressure and runs the injectors at different rates. When it's done, those are the volumes of fuel in the graduated cylinders.

At idle, I have a subtle bobble and some steady vibration that I have been unable to isolate. Is it possible a higher fuel pressure will have any positive effect on idle, or is the higher pressure just for higher RPM operation?

All I want for Christmas is a smooth idle. I just hope I don't have to work on it until Christmas to get one.:mad1:

Quote:

---

Originally Posted by Sammy_Johns

I made my regulator adjustable and have set my pressure at 11 PSI, the same as before I modified the regulator. I have done a couple of scrubs to my VE table prior to the regulator mods, and except for idle I have a pretty smooth running vehicle. I wanted to raise my fuel pressure up to 15 as I have read this is generally a preferable pressure. If I do this will I need to redo data collection and VE table tuning all over again? 65 PPH injectors if it matters. Just had them cleaned and tested too. I did not get very good data back from the local guy that ran them through his machine. One injector put out 90cc the other 110cc. But he could not give me a rate for that volume. He just put them in the machine and ran the program. It sets the pressure and runs the injectors at different rates. When it's done, those are the volumes of fuel in the graduated cylinders.

At idle, I have a subtle bobble and some steady vibration that I have been unable to isolate. Is it possible a higher fuel pressure will have any positive effect on idle, or is the higher pressure just for higher RPM operation?

All I want for Christmas is a smooth idle. I just hope I don't have to work on it until Christmas to get one.:mad1:

---

I would try a second set of injectors. That is close to 20% difference in flow rate. 20% is a HUGE fueling difference between cylinders. I like to see no more than 2-3% difference between injector flow rates. The lower the number teh better off you are.

Higher fuel pressure tends to help atomization. If you raise the pressure, adjust your BPWC. After adjust the BPWC you may see you need slight tweaks to your VE tables, but it will not be a huge difference.

Most stock TBI pumps will not pump 15 PSI, just FYI.

Replaced my injectors with rebuilt ones from RB Remanufacturing. I did not have them tested, so I don't have data that says they have less difference in flow than the original ones, but the symptoms did not change, so I am assuming that is not root cause for now. I got my fuel pressure up to 13 psi compressing the stock spring almost all the way. Good enough for now. Maybe I'll get a new spring someday.

Attacking the idle issues from a different angle - When I set my base timing and idle (~500 RPM, 5°BTDC) I came up with 500 RPM based on 100 RPM less than the 600RPM @ 55C shown in the IAC - Desired C/L Idle speed table. My vibration smooths out at higher RPMs. 700-750 is pretty smooth. I shouldn't have to run my idle that high, though should I? How do I determine what a good idle speed is for my setup in both Park and Drive?

Secondly, I have read mush about AFR at idle and stoich at idle or other conditions. I have been unable to find how to view AFR in TunerPro. I have an entry for Autoprom1 WB AFR but it never moves. Probaly cuz I have no WB o2 sensor? Can you level set me on how I know what my AFR is for any given condition please?

Well, there's definitely a difference in the C/L Idle tables between the stock motor and the cop car. The ASDU table is what is in my bin at this time. The cop car idle table seems pretty high. Maybe I'll try bumping the base idle up and use the values from the table in AUML in my bin ans see how that works. Local emissions test allows idle for my year van up to 1200 RPM, so I've got room in that respect. Generally speaking do hotter cams require a higher idle? Cuz that's about the only difference between a cop engine and stock as far as I have read.

Attachment 7650Attachment 7649

That cop car data is no good. I would think you have the wrong adx file for that bin or that bin is just bad.

You need the wideband to measure the AFR. There might be a patch so the code will transmit what it thinks is the AFR but even if it does that, it won't necessarily be accurate.

What's with your project? Is it a stock engine or some modifications. Without any details it's rather hard for anyone to make recommendations. But, generally speaking the idle can be smoother with a little more rpm.

Yes, wrong adx. Sorry, rookie move. The idle info in the cop car bin is defined with Target RPM (AC on) = 563 RPM, (AC Off) = 550 RPM, so that’s not far off of where I am.

I have a 1987 G20 Van. The original motor spun a bearing 12+ years ago and I replaced it with an LO5 out of 1990 Caprice cop car. The cop car motor has a roller cam (or so I have read) .

.05” duration --> 202/207
1.5:1 lift --> .413/.428
lobe sep --> 114.5°

The cop car had a ‘8746 ecu with AUML which I ran in my van for years with many drivability issues. When I decided to try and tune this thing properly, I got a 7747 from a 1990 G20 in the JY and started tuning with ASDU. My current bin has the EGR and air pump turned off. (Also mechanically disabled). I have smoothed the VE table. I had a lot of vibration with the 8746 with AUML as well. That did not change when I swapped in the 7747.

I noticed a difference in the VE table from AUML to ASDU. Of course my ASDU VE table looks smoother, but the overall values seem quite different. Would it be worth trying the VE table from AUML in ASDU?

I also just noticed that my Initial SA scalar is still set to 0 and should match what my dist. is set to. I will change that. Does ECM provide further SA at idle after the initial setting?

My latest log is attached. Any feedback is appreciated.

I would apply the[bpw-spark advance patch] and get a data log with a few minutes of idle at the end then post you data log and bin file. it looks like your bpw needs raised a little to lean it out just a little.

When I first swapped in this motor I paid a lot of money to a mechanic to get this thing running good. Gave up after a couple visits and just put up with drivability issues for years.

You guys have helped me get this thing running 3x better for nothing. I got more to do, but I really appreciate the info available on this site and the folks who have personally helped me out.

...And I'm not just saying that to get you to look at my log file and bin :)

Idle time is at the end of xdl.

Sincerely, THANKS!!
:thumbsup:

try this bin if you want I change the bpw from 135 to 132,see if the blm goes up from 108. changed the idle speed to 550 and the enter an exit stall saver a little.