bd0nalds0n

How much latency is there in the feedback loop between the o2 sensor and the ability for the LH/EZK/whatever to adjust mixture?

I notice that my fuel pressure rises under acceleration, but the car goes lean for a second or two (on the wideband LH-1, bet 15-16:1), esp. under modest/very light increase in throttle. Fuel pressure never falls. At idle, it's around 46psi, and rises to around 50-52. At idle, the car is running bet. 11-13:1. The short-term lean readings actually seem to worsen the higher I crank up the RRFPR, even though the car is running richer and richer at idle as I do so. I haven't tested the fuel pressure using a mechanical guage, so I don't know if the sending unit is properly calibrated, but the fuel pump is brand new.

My question is, is it normal for there to be a few seconds latency in the feedback loop during which the car would either run lean or the 02 sensor would read lean? Should I replace the stock 02 sensor? Do I need to adjust the RRFPR differently?

Right now I'm running 2 o2 sensors, the stock one to the stock computer, and the wideband to the LH1 for diagnostic purposes only. Does the wideband (or a newer "stock" sensor) react quicker?

Some sharing of experiences as a baseline would be helpful. Also, I know one of my knock sensors it out of the loop, so I know I will need to revisit all this once the car is not running retarded in "protect" mode.

Thanks in advance, and I'm sure I will get a lot more excited about the project once I can stop worrying about whether I'm doing something wrong or risking damage through ignorance.

BC

As we saw on mirmar Brian, that LM stays at 14 all the way through "Crap, that van came up fast", so if there is any latency, I would think the 02 would have reacted already - does that make sense?

I really think the Boost gauge will help identify and correlate the lean areas as well.

Tony

I know feed back to the LM-1 is INSTANT, INSTANT enough to see misfires in the igniton system if you record it..
As far as the stock O2 sensor and the speed at which it updates the LH, im not sure. I would imagine though that it also is pretty "instant" as seems to be dipslayed on both my ARM1 narrow band and LM-1 wide band. Perhaps John or Rich, the LH guruus, will chime in


Mine is still way rich and I havent had much time to really dedicate to tuning it properly yet..just taking the time to drive it and have fun for a while. Ive got some air/vac leaks that i need to stop before i go any farther with tuning.
My LM-3 is waiting for me at home, it will allow me to data log boost, injector cycle and a few other things. Once i get the time to figure all that out i will get serious about properly tuning it.

My car idles "ok". but im not happy with it at this point. I really havent ran with my idle stabilzer hooked up since i did the install. I did a few days however, to see if the LH needed it in the loop for feed back during its "learning" phase. After the engine warmed up, it would hunt wildly for an idle...800-1200...up and down. When i un plugged it, it would stop hunting and settle at appx 1000rpm steady idle. I now leave it all unpluged and it starts in cold weather, warm weather and no issues in traffic. As the car warms up however, the idle is VERY lumpy. Like i said, Ive got airleaks and stuff that when factored into it all my be part of the cause.
I plan on plugging t the leaks..running the 30# injectors and see how it goes. if that doesnt work, the 24#s go in.

FYI..be sure you secure the wiring harness in front of the engine or route it in a manner that the crank pulley doesnt rub on it!

keep us updated. PM me as well if you have any questions.

Jim R.

I don't think it should have that kind of delay. There may be a split second delay in response on an aggressive quick full throttle stab of the go pedal, but no more than that. Do you have a A/F guage in the car working off the stock O2 sensor and if so, what does it show in relation to the wide band? I think you should be getting more fuel pressure than you are reading under load, but I'm not too familiar with Andy's setup. Lean is BAD, so be careful until you get it straight.

Good luck with your new toy, I should have my SC'd 928 finished this weekend.

Jim R.

BC

His AFR is almost constant at 14 or above upon heavy accelleration tony. His fuel pressure at cruise is about 50 as I recall, and then when he really got on it it went to 55. I' can only assume the FPR is regulating to 5psi higher as that is what it is seeing?

Tony

Im 40psi at idle and see upwards of 80-90 psi under full boost...that gives me appz 10.4:1 AFR. like i said, rich.
Such simple/basic numbers, yet so EXTREMELY vital. I have yet to get a good answer on what the fuel pressrue should be. Turn..adjust..run...eye on the LM1 ...try again is my only approach. When i figure it out, i'll let you.

BC

Okay. I think that his FP is not rising NEARLY enough.

GoRideSno

Brian,
There is a discussion on my site about the BEGI.

Twin-Screw setup with small pulley (66mm) around 7psi.

First set the atmospheric or "onset" fuel pressure.

The center allen screw (atmospheric fuel pressure setting) should be completely backed out (it'll come out, it's ok) then screw it clockwise 7.5 turns. This is just a reference point and may need to be moved to get the proper fuel pressure at idle with the vacline off the regulator. That pressure is 55psi with the vacum line off of the 2025. Be sure to remove the vac line at the 2025 and plug it so there is no vac leak when setting the pressure.

The proper setting of the rise-in-rate **** is 1.5 clockwise turns from completely backed out as a starting point. Turning the **** clockwise will richen the mixture.

If the LM1 dosen't show a ratio of richer than 13.5-1 as soon as you hit WOT then raise the onset fuel pressure by 5 psi incriments.

If you are leaner than 12.5-1 at WOT then turn the rise in rate screw clockwise by 1/2 turn incriments to richen.

BE VERY CAREFUL an do not do any of this on a street with other drivers.

For the knock sensor wire. You may be able to spot it in broad day light and just fish it out. If not then just loosen the hose clamp at the throttlebody, loosen the belt, loosen the two bolts that hold the snout support together, remover the 8 bolts that hold the SC down. If you still can't see it you can use a clothes hanger to fish it out.

I was so tired monday night when I left that I slept in the car on the way home after driving an hour os so in thick fog. I averaged about 4 hrs sleep Friday through Tuesday night. As a result your and 2 other cars hit the road by Tuesday including a GTS. Would have been 4 but Dave H had a clutch problem that he had to tend to.
HTH,


Andy K

GoRideSno

Brian,
What A/F ratio meter do you have besides the LM-1?
If you have an ARM1 then it should mirror the LM-1. The ARM-1 Updates very quickly. Shane mentioned thet the Sunpro guage he had mirrored the ARM-1 so that one should be fine too. Not all A/F ratio meters update very quickly. This is why suggest the ARM-1 or the Sunpro.
HTH,
Andy

bd0nalds0n

I have a Nordskog that seems to update pretty quickly, but it's pulling from the old 02 sensor not the wideband.

GoRideSno

I am confused. Did you use an 85-86 throttle switch or did you use the one from your S4? If you used the S4 throttle switch then do not drive the car again untill you have installed the 85-86 throttle switch.


I can't think of any benefit. If you follow the procedure I gave you above then your fuel pressure at idle won't change unless you have the vac line off of the 2025. Once you reconnect the vac line to the 2025 the fuel pressure at idle will remain at stock.
HTH and check your messages

Andy K

mspiegle

2 points:

#1, Narrow band sensors react faster than wideband sensors

#2, I notice that instant 1/2 throttle my car will go lean for a second then come back. Instant full throttle is instantly rich. Why? My guess is that instant 1/2 throttle doesn't trip the WOT switch and the ECU doesn't widen the pulse width of the injectors. Instant full throttle gives the wide pulse width right away providing you with a rich mixture instantly.

Tony

Andy, i assume that is all based on 30# injectors?

John Speake

Hi Tony,
There is a delay in the LH O2 loop circuit response. I can see it clearly on my test jig when I input a lambda change from (say) 0.8 to 1.0. I would say a couple of seconds to change the pulse width by about 20%. This is under constant MAF voltage conditions. I think this would also be the case with modest changes of MAf voltage.

When the throttle is hit harder, then there is a overshoot on the injection pulse, giving the equivalent of the old "acellerator pump" that one used to get on some carburettors, to give extra mixture enrichment and more power.

mspiegle

John,
When you the throttle switch signals a WOT condition, is the pulse immediately widened?