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The air bypass in the AFM isn't meant to be used as an idle adjustment... it adjusts the airflow across the whole scale. It's a bad idea to employ it for any type of fuel tuning. Get a real fuel controller or go stock... you're just going to melt something.

Just for my own edification.... Just how does opening something to atmosphere FIX a vacuum leak? :nuts:

EVERY MKIII runs closed loop 90% of the time... '86.5, '87 and earlier are no exception.

You can't use Vf to tune. P E R I O D. It serves as a rough guide at best. And you can't even use it a a rough guide for open loop operation.

Heated O2 sensor? Sure, why not? Just use a relay triggered by the fuel pump relay and with it up for 12v. You can't just wire in a wideband O2 sensor though.... just narrowband.

Quote:

Originally Posted by cre (Post 100492)

The air bypass in the AFM isn't meant to be used as an idle adjustment... it adjusts the airflow across the whole scale. It's a bad idea to employ it for any type of fuel tuning. Get a real fuel controller or go stock... you're just going to melt something.

I didnt adjust the idle bypass, I played the toothed wheel setting. In the stock form the VF showed it was adding fuel to the short term trims, in the 3.5 to 5v region. So I richened it one tooth and brought the VF into the 2.5 area with brief operations plus/minus of that.

Just for my own edification.... Just how does opening something to atmosphere FIX a vacuum leak? :nuts:

My vacuum leak was the small hole I said drilled in the filler cap. If not and manifold vacuum is present in the crank case, my front and rear main seals vibrate like a harmica, sounding like a worn out throwout bearing. Thus creating a small vacuum leak post AFM. Now with the crank case vented to atomoshphere and the vacuum line plugged top the intake, the leak is gone.

EVERY MKIII runs closed loop 90% of the time... '86.5, '87 and earlier are no exception.

OK, so there is no O2 swing at idle. It does run a constant 15.5 tho on the wideband, just no corrections. Figured with the narrow band cooling at idle, they would not use an unheated O2 for idle closed loop. Only thing I can think of is, Im running the later model coolant temp sensor (since its a 90 Cressida harness) and maybe the earlier sensors had a different resistance. Ill look up the checks for those and see if the ohms reading is the same between each.

You can't use Vf to tune. P E R I O D. It serves as a rough guide at best. And you can't even use it a a rough guide for open loop operation.

I know I cant use it as an open loop feedback...Im happy with the mid 12's the map is giving me. Why cant we tune with the VF? With a wideband installed and seeing what the ECU is doing with short term trims, if its maxed out rich or lean, I dont see a problem using it for tuning since we dont really have any other way of knowing. I thought I would get to it before the ecu learned and stored it into longterm, only to lose it if the battery dies?

Heated O2 sensor? Sure, why not? Just use a relay triggered by the fuel pump relay and with it up for 12v. You can't just wire in a wideband O2 sensor though.... just narrowband.

I have some spare heated narrowbands. Ill look into installing in a few weeks. Im going to see how this setup will run on a day to day basis as is. Im aware of the wideband operation. I have a Turbo Volvo with 500whp. Its running a DSM ecu and is tuned with ECMLink. Whats neat about that is it will take the wideband input and I can determine switch voltage and actually run stoich at 15.5 and gained almost 5mpg over the stock narrowband.
Im running the Wideband on the truck just for feedback only.

message quoted internally.

I haven't the patience for everything in this build that I disagree with or that could be handled much more practically and provide greater reliability and response... Perhaps someone else will step in.

Vf is indicative of many things and there's actually a LOT more in that signal than just fuel trim feedback. Hook it up to an oscilloscope if you have one and check it out. It's also not a reliable indication of AFR as a narrowband isn't really capable of providing reliable information about your AFR. The narrowband is essentially disregarded in open loop operation and Vf represents changes made for other reasons... The only thing you know is that it's making changes that it 'thinks' need to be made; This could be because of detected knock, an OX signal that isn't within spec (for a narrowband signal that means it has to be at the correct frequency with relation to injector and spark timing and within 400mV and 500mV), or due to learned information from driving conditions four weeks ago or any other of three dozen reasons. Vf is unreliable except for situations where you're trying to get one of the more advanced piggyback EMS dialed in as close as possible so they'll live together in piece and it's still not what I'd call trustworthy. (I just re-read your response concerning tuning with Vf) I'd really not rely on it while the TCCS is in it's initial learning mode... it doesn't even know what it's going to do next yet in this state.

In the stock location the narrowband should not cool at idle to such a degree as to skew readings notably. If it is cooling to that degree you may want to invest in insulating your header as that heat's probably ending up in the engine bay and the gasses in the exhaust piping are ending up cooler, denser and thus slower moving than is preferable.

Adjusting the tension spring in the AFM causes a non-linear shift in the measurement of airflow. The vane bypass creates a linear shift, IIRC. In both cases you adjust the entire scale and can not just tweak idle or whatever. Closed loop operation helps as the ECU corrects the shift you've caused, but it's limited in response time, how much it can correct and so on. But again I recommend you do it right and get a fuel controller. You may also screw with your tip-in/out response as the plate is prone to bouncing now due to the unanticipated loss of tension (only really an issue if you make a significant adjustment). I'll grant that one or two teeth either way isn't going to create a significant shift but it isn't without possible side-effects.

Opening the crank case to atmosphere allows more pressure to build within, water vapor and corrosive hydrocarbons to accumulate in your oil (reduced oil and bearing life), reduces the efficiency of your oil seals and piston rings, etc... Fair trade off just to HIDE another problem? FIX the real problem.

Anyway, good luck with the project and have fun with it!

Thanks for the reply Cre. With the one tooth adjustment on the wheel and a slight turn in on the idle bypass, everything is still in check. Truck runs great (except for a bad cold start injector) and I'm pleased with the responce and power, read that as low end tq, that this motor has now. I'm still unsure if I have an NA or turbo intake cam, so in a while ill pull the cover and measure lobes.

But for a truck that's 4500lbs, geared 4.88 with 36 inch bias ply tires and duel transfer cases, it go really good.

Thanks for all the help.

I'd love to try that short end gear in a MA61 with a 7M-GTE swap.... :bigthumb:

I'm glad it's all working well for you!

EDIT: What's up with the CSI?

I hope its just a bad unit. It looks crusty on the stem. I bought an NA intake off Ebay, so I know nothing about it. The cold start wiring works afaik since it would lite right off on the Cressida stuff. A friend has a V6 csi that Im going to swap out (plugs and hose the same, just have to woller the bolt pattern)

Truck takes like 15 seconds for it to fire up in the morning, but with a little heat, or even the time between lunch and works end, it will fire right up Seems to just be a cold soak. I do have a fuel pressure tester plumbed in, and in all cases, the pressure has bleed off, but builds instantly.

If the V6 fails to give good results, i trim down the turbo csi, plug the end and drill some squirter holes on either side.

That MA61 would be a hoot with a gear setup like that!