oak

MEGAnoob here,
I used to have a smooth running bone stock 1990 NA6, now it's running terribly on a used 90-93 MS2PNP. I Installed all required sensors/gauges (Wideband sensor/gauge, Boost gauge, AIT sensor (in stock airbox for now), and MAP sensor line ("T"ed into FPR line). On the software side, I loaded the 90-93 base tune from https://supermiata.com/megasquirtinfodownloads.aspx (the one with AFM removed obviously). I then calibrated my AIT sensor to the GM settings, and with the weird idle I was able to verify that the base timing is at 10 degrees BTDC. I then turned ON "include AFR target" in general settings. For idle control, I set up my PWM valve @313hz with idle following closed loop algorithm. Valve closed is set to 25.1 and Open at 65.1.

NOW, my problem (foot was never on throttle for any of this) Ever since I started the car for the first time, it raises rpms to around 2000 after engine catches, hangs there, attempts to drop to a normal idle of 750-1100, then shoots back up again to 2000-2100. It then repeats a cycle of violently shooting down to normal idle and shooting back up, doing this process about every 2 seconds. This seems to happen at any operating temperature. I suspected a vacuum leak and replaced all the vacuum lines with fresh new ones (1/8" line from FPR "T"ed to a 3/16", which feeds another "T" inside the car feeding my MS2PNP and my boost gauge with 1/8" line). This did nothing. Also the MAP sensor port coming from the MS2 got loosened accidently during install but I just screwed it back in and it seems fine? Would a vacuum leak even cause this erratic behavior? All other settings unmentioned have been untouched. Wideband, AIT, and boost gauge seem to be working fine. My car was running flawlessly beforehand :/. It's probably something I messed up and would love to know what it is.

Video of problem:

https://www.youtube.com/watch?v=CmfWSBQy9Nc&ab_channel=OakleyWood

Tune and Datalog included

irodd

iTrader: (4)

I didnot check the tune file, just took a look on the log: there is a fuel cut every 2.5sec.
Try to turn off the "Override fuel cut"

nickalltogether

I would set idle to open loop until you are confident in your base values. Same deal with over-run fuel cut as mentioned above. I don't have TunerStudio on this PC, but I would be curious what your timing is doing through all of this as well. The IACV duty looks pretty solid, so rpm changes would most likely be driven by fuel or timing changes in my experience.

oak

The problem happened in open loop mode as well. The timing follows the stock map and advances to high 20s at around 2000rpm if I remember correctly. I might have a vacuum leak at the injector o ring and I'll swap out those this weekend just to rule that out.

curly

iTrader: (25)

Unplug your idle valve. If it still shoots to 2000, you have a MASSIVE leak, not just an o-ring. If not, you just need to tune.

oak

When I took off a vacuum plug,nothing changed. Right now I'm thinking it could be a massive leak from one (or all) of the 30 year old rubber gaskets between the fuel injectors and intake manifold. I've seen some other threads where this caused a bad vacuum leak.

curly

iTrader: (25)

unplug the electrical connection, not a vacuum plug.

oak

Thanks for the clarification, I'm an idiot. I unplugged the idle valve and now idle is smoother, and closer to normal values (750-1500). No fuel cut at idle anymore . Idle still surges though, and I'm getting high 15-16 AFR so I've likely still got a vacuum leak right?

curly

iTrader: (25)

Not necessarily. You need to tune both software, and mechanical. So bypass, throttle stop, etc. Select your entire fuel table and multiply by 1.1. That’ll add 10% fuel, should even put your idle. Once coolant is up to ~180-190, you should be idling at ~1000rpm and 15-30% idle duty. If it won’t get to these figures with a small adjustment of throttle bypass, then at that point I’d start looking for vacuum leaks. You’re running too horribly right now to bother looking IMO.

Martin Y

I had that crazily surging idle symptom years ago after changes meant my idle air control valve was working backwards. Changed the PWM idle valve mode setting to Inverted and everything instantly settled down.

oak

Thanks for the help guys, after some tweaks to the VE and spark tables, I was able to get a much more consistent idle. Still have stumbles and dips, but there's tons of info on this site that'll help me tune that out. No need to ask the same questions twice ! Here's the VE and spark tables as I was able to adjust them tonight, can't do much on weekdays after work because I don't really want to **** off my apartment neighbors any more than I already have with my project car **** .

nickalltogether

Glad you're making some progress with it. Two things:

1- Your VE values are way high. What is your injector size and reqfuel value?
2- I've found that my car idles well with 10 degrees of timing at idle. AFAIK this is also where they idle on the stock ECU. That may be worth looking into for you.

Also, if you're still running batch fuel injection you may find that the car idles better at 13.5:1 AFR instead of leaner.

curly

iTrader: (25)

Nick, no they don’t. If you notice when you jump ten/gnd on a stock car, the idle dips, meaning timing goes down to 10, not up. If you look at spark and Vance on an obd2 car, you’d see idle Figures close to the base maps, 16-18 or higher.

oak

1. I noticed that, haven't actually driven the car yet so I'm wondering what it'll be like during load, where the values are maxed out at 255. I doubled all VE values and bumped up idle ones a bit more to get a 13.5 afr at idle (at operating temp)
temp. Injectors are the blue 230cc, but may be knockoffs installed by P/O that don't flow as well? They would've been installed by a mechanic as none of the P/O were "mechanically inclined". Req fuel is at the base map 12.5.

2. Curly addressed that, spark seems ok, maybe I can bump the two values I changed back to base.

curly

iTrader: (25)

Yeah, didn’t mention it; but you NEED to fix your fuel. Google the fuel calculation, after all the multiplication and additions, MS spits out a PW. You may be idling well with a decent PW, but your fuel table is compensating for an incorrect figure elsewhere, or a mechanical issue such as fuel pump, pressure, or injectors. You CANNOT continue tuning it until this is resolved.

Martin Y

I think your fuelling problem is that in General Settings you have Secondary Fuel Load enabled as Speed Density. I think it should be Disabled.
(If I understand it correctly, at the moment your VE Table 1 value is being multiplied by your VE Table 2 value.)
If that's what it is then when you disable Secondary Fuel Load you will probably find you have to reduce your VE Table 1 values to something sensible again and maybe reduce your Req Fuel too as the current values look really high.

oak

I'll check that out, was gonna do a quick fuel pressure test tonight but one of my injector seals sprang a leak . Now I have to replace that before any further troubleshooting with the engine running . In for a fun weekend boys.

oak

Dude, thank you! For whatever reason the base map I downloaded had VE table enabled. With it disabled the car runs almost like stock, still getting high 1500rpm idle though. No vac leaks, when I pulled a vacuum plug idle got a lot worse. Base timing @10 degrees. Idle control valve is disabled and physically unplugged, should I just plug it in and switch to closed loop and adjust DC to lower rpms? Or is there some other fundamental problem causing my idle to be high?

Martin Y

Try plugging the idle speed control valve back in and, if the revs start wildly surging again, look in Idle Control and change the Valve Mode from Normal to Inverted.

My guess is your ECU has one of Jean's PWM converter boards fitted to raise the ISC valve drive frequency. That gives an inverted output where 100% is closed and 0% is open. When I fitted one in my DYPNP I missed the instruction to invert the Valve Mode and got the crazy revving symptom you saw.

nickalltogether

What's the benefit of the PWM converter board? I have DIYPNP but had never heard of that before. Is it just more resolution in the Idle Valve positions?