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Author Topic: Struggling to find a balance  (Read 3854 times)

captain slow

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Struggling to find a balance
« on: February 01, 2015, 10:59:09 AM »

Hello all, first time poster here!

So i've got a super nice E30 with the following mods:
M20B25, 60k miles
Miller PSIK
Miller tune selector
BBTB (I believe it's 3", but cannot confirm)
Dinan intake manifold
Euro spec cam
Euro spec pistons (iirc, 9.7:1)
Bavauto long tube headers
Single/custom 2.5" exhaust, high flow cat
Stock injectors (as far as I know)
Miller Adjustable FPR
Euro spec plugs gapped to 0.032"

So, here's the story!

Since I bought the car back in July, I've always noticed that it idles a bit weird.  First off, it idled around 900 rpm and I noticed a slight miss, almost a gentle cough from the engine when it idled.  This has always bugged me.  I scanned the chip to evaluate the tune it had on it and found that it was running a 19lb injector tune.  I studied the records and found no evidence that the injectors were ever upgraded but the car does have an adjustable FPR.  After getting familiar with all the ins and outs of the car, cleaning the ICV and ensuring I'm not chasing a possible vacuum leak, I thought to myself that the issue may be some fuel starvation.  I attempted richening the mixture very slightly (1/4 to 1/3 turn) and found that it didn't really help anything.  Today, as I was buttoning up the car from an oil change, I noticed that the car seemed to be running rich (brown/blackish smoke, an abundance of steam) so I elected to assume the car had stock injectors and turn down the FPR as far as it would go.  Immediate improvement!  Car is idling much better and doesn't cough or hiccup under load.

Another problem that was occurring with the old FPR setting was on cold starts, the car didn't high-idle whatsoever.  Idle would start at 1,200-1,500ish right at startup but immediately drop to 900, where it would remain indefinitely. I haven't had an opportunity to start the car cold yet since I've messed with it but it should be noted that it was happening.

Now, I'd like to ensure the tune is matched to the car's mechanical setup before I get it on a dyno and it gets properly tuned.  Is there a tune out there that is well-matched to my setup?  It's currently on the 19lb injector tune with the high flow exhaust and intake, but I'm not certain that's right for me since I'm running such low fuel pressure (relatively speaking, of course).  Is it OK to run the 19lb tune on stock injectors or am I messing with the ECU's/chip's potential?


Obviously, the solution here is to swap over to 19lb injectors, but I will have to wait for those as some other issues are coming first :)

Any help from the collective would be greatly appreciated!
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millerperformance

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Re: Struggling to find a balance
« Reply #1 on: February 02, 2015, 09:09:52 PM »

Here is how injectors and tunes work. If a tune is scaled for 19# injectors and you are using a SMALLER injector than the tune is intended for, you will have all sorts of problems. Reason is, base fuel is calculated from the load equation. The equation consists of Mass flow, The injection constant and RPM. Stock, the injection constant is 1, for a higher flowing injector, 1 is reduced by a percentage roughly in accordance to Stock Size/New Size... In the case of 19's, 14/19.

When fuel is scaled like this, the base injection calculation is compensating for the higher flow rate. Meaning, base fuel is being UNDER calculated by ROUGHLY 25% Obviously one can alter the fuel values BACK UP to make up for the lack of initial fuel, but other parameters that you do not have access to through the WAR Chip will never be right and you will always be fighting weirdness to varying degree under different conditions. It may even become intermittent.

Turning the fuel pressure DOWN to have the car run better leads me to believe that you are using something HIGHER than 14# injectors to begin with. As this would only compound the 25% deficiency state above. If you were using 14# injectors and turned pressure down as low as you can go (which I would assume is under 43.5psi) the car should run absolutely terrible. What is the actual fuel pressure you are at?

Trying to fight a mechanical unknown or inefficiency with a tune will never yield the intended results. If you have the WAR Chip, and 14# injectors, try running the STOCK Config PSIK tune. Obviously it is meant for a stock car, but if you are not going to upgrade to 19's and you are in fact running stock 14's right now, you will have a much better starting point and will not end up hating the product since you will not be fighting a miscalibrated setup/hardware combo.
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captain slow

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Re: Struggling to find a balance
« Reply #2 on: February 20, 2016, 10:40:09 PM »

Thanks for the detailed reply and apologies that I didn't get back to you for a year!  I ended up caving in and pulling the injectors to do some detective work.  I was sick of trying to fine tune the FPR to compensate for some unknown injectors.  As it happened, I was running single pintle 14# stock injectors!  I pulled the adjustable FPR and threw in the stock one, and replaced the single pintles for some true 19# rebuilt injectors.  Once the car is warm, it idles superbly.  I've noticed that since this change, the car hates off throttle idling when cold.  The car will almost stall, then catch itself, almost stall, catch itself again, then return to a normal idle.  This only happens when the car is stone cold.  Once it's even slightly warm, the issue goes away.  This leads me to believe it's either the temperature sender or a vacuum leak.  Another thing that should be noted is that if I reset the ECU (unplug battery), the car idles fine when cold, this issue only presents itself after adaptions have completed.  I'm taking it to the shop (once I'm back from Afghanistan in May) to have them do a vacuum test and check the vitals.  I do, however, have a question or two for you...

I took the car to the track (mid ohio) in August of 2015 and noticed a few things I'd like to fix before next year..  Chief among which is a stall/stutter/hesitation in the middle of the rev range, around 3500-5500 RPM.  It pulls fine until 3500, then the torque all-but disappears and reappears with a vengeance at 5-5500 RPM to redline.  I'm using your off the shelf PSIK/19#/Exhaust tune, for what it's worth.  Obviously I will want to eliminate the possibility of mechanical faults to the best of my ability, so I will ensure the car is free of any vacuum leaks and is producing strong spark before I proceed with any tuning or chasing any mechanical faults.  My first question is, does this sound like a mechanical fault or is it a result of the wrong spark plugs, or poor tuning? I'm on stock plugs at the European spec gap (.0032) due to my European spec engine. Otherwise the car performs great, it held together fantastically through 4 sessions, but as the temperature rose, the problem presented itself more and more.

My next question is, if I decide to take it to a shop for a dyno tune (if you think it's worth it), do you have any recommended shops in the Cincinnati/Dayton Ohio area that you've worked with in the past?  It'd be nice to work with someone who is familiar with your program if at all possible.
« Last Edit: February 20, 2016, 10:41:51 PM by captain slow »
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