davek9

Mark K, I do not understand how you can "tune" a car with idiot lights?

Why don't you spend the $ and buy an Innovate digital gauge, that way you can actually LOG what the AFR is and stop guessing at it?
Even using actual gauges I've found some are not very fast and w/o seeing the NUMBERS, it's anyone's guess what is going on, right?

I know that you know that O2 sensors don't last forever, they do burn out eventually especially with overly rich mixtures.

From what I read you have checked the Idle and WOT connections back to both ECU connectors and are sure they are good.

I just went through this on my TwinScrew 86.5 and found a broken harness, so I rewired directly from the TPS to the White and White w/ Red near the Firewall before it goes inside the car.

Mine were a little easier to get at

IMHO Dump that idiot light

Edit: and thanks John for that Info on the O2 not relying on the WOT switch, makes sense.

Dave K

mark kibort

Dave what makes you think i have tuned the car with "idiot lights". this engine hasnt lasted 100+ hours of racing on dumb luck..... it's tuned and tuned safely, at the dyno and is very safe by all measures and puts out the hp it should given the stock components.

the gauge , to this point and this is 15 years of use, has shown to be a valuable tool in warning if there was a problem. It has never acted like this and on the dyno, i can see if it is heading down to 12:1 or if its running near 13.5:1. (but not much more than that). and on the dyno, the rations have not changed, nor do i expect them to, because there has not been changes made other than fuel pressure. its a simple device.. its a voltage meter, with lights! so, the O2 sensor is putting out some lower voltage based on a real lean condition, or its broken due to age /or exposure to high temps for too long. (and rich conditions. 11:5 to 12:1 wot)

The fact that the AFR is hunting, or lowering at WOT, in the lean to very lean range, concerns me, but based on performance, i dont seem to feel any issues with power, which would follow the degree of leanness the gauge is indicating.

good idea with John suggesting a WOT switch light, but to

so, now that we have determined the WOT switch is fine, it falls back to the question, do i have a problem or is there a problem with the 02 sensor, or the AFR gauge.

your advice would not help me, if the 02 sensor has a problem. and certainly i dont need to log data, of the 02, because normally, its rock solid at varied temps at the desired air/fuel ratios. it hunts on the hyway, goes lean under decel, and full rich under WOT. (or near WOT)

mark kibort

seems it was doing this at laguna seca too. the mixture looks perfect, and then, its like there is electrical noise that might be altering the voltage that i use to power the AFR.

go to 8min on the video.

or, maybe the throttle is not all the way, WOT, might be slack in the cable.

how much throttle do you need for the mixture to go full rich? i thought i remember it being 90% or something. maybe that is out of adjustment> ill have to see if reallly pressing to the floor changes anything , and the electrical source.

and then the race before, it showed it occasionally, generaly no issues. but watch a lap from 3:10 onward sold light, but at the end of the long back straight, it hits some noise....but generally all blue light when WOT.

mark kibort

Has anyone seen a fuel pump fail in this way, where it is fine in normal operation, but on long WOT duration, the pump starts to not provide the flow needed to support desired mixture levels.

im going to do some tests today and then to the dyno next week for the real tests and verification and correlation of the AFR meter and the dyno AFM readings

IcemanG17

If you are running on the O2 sensor vs open loop it will explain a loss of power AND higher temps....you have been having issues with overheating that never happened before right?

The fuel pump is fairly easy to check......use a pressure gauge on rail, then make sure leak down times are correct vs WSM and a simple flow test of volume vs time.

When I had a fuel pump die on my old street 928.....it would die....and the resistance across the terminals was super high.....it would cool down a fire up briefly and once cool the resistance dropped to normal levels (compared with new fuel pump)...if I remember right the new pump was low...like 1-2 ohms...the old once would spike to 10-12 ohms and not run

While unlikely your regulator could be dying......or the pressure dampers.....

mark kibort

Brian, If you run the o2 sensor at WOT but its open loop mode, that means that its hunting, so you have little chance of knocking or overheating. you only get over temp at a specific range of mixture, very close to stoich. 14.7. much lower, and even though lean, the temps are much lower. (lean of stoich is a common practice in aviation for reduced egt and CHTs)

But, i show the Thunderhilll video side by side on this thread, and there was no hunting issue of the AFR then, so the overheat was the air in the system problem, not fuel ratios.

and, i ran the same temp this year, with the AFR problem and the car has never run more cool.

Im not sensing a power loss when the afr starts acting "noisy", whcih if it was going that lean, i would suspect to feel something.

the fuel check is not as easy as you make it. its generally fine as you can see. mixture is over 12:1. only in the long straights, and the highest RPM does there seem to be a "problem" due to the AFR bouncing around. plus, the Holbert car didnt hold pressure, and that had no effect on mixture levels on the dyno or track. i have a new fuel pump now, which holds pressure for the specified time. the trick is finding out the flow at the rated pressure . tough test to make.

thanks for the ideas though. the best test will try and simulate the hunting fuel mixture under WOT and see if the pressure is dipping on the dyno or if the AFR is hunting and the dyno shows mixture solid, we know its an electrical issue. i can change the power source, which might be "noisy" which can certainly be cause of an erroneous reading, after all, that meter is just a voltage reader.

EDIT: i just checked the electrical connections, and the connection seemed to not be as solid as a connector next to it on the fuse panel, so i changed it. immediately, its showing a little different level of light-up , even with the ignition just turned on. so, i suspect that is the issue. when i run it, ill see.

mark kibort

UPDATE: i just changed the fuse box power source for the AFR sensor,from "rear ac" to "power locks" (i use power from accessories power supplies that are not being used. i usually solder a fuse to the bottom leg and then plug in to an open socket. )
it seems like there is a lot less noise , and when WOT, it seem constant at the rich side of the meter with a constant blue light.. i dont know why that would make a difference as all the circuits get power from the top "powerbar". im thinking it was just a bad connection with the makeshift fuse i had on the positive wire to the AFR.


im still going to the dyno to see if there are any abnormal readings from the wide band O2 under WOT.