Blown Beast

It sounds like your stock O-2 is shot...I would replace it. Remember to disconnect the battery when you make big changes to fueling...the comp. does learn the new changes and needs to be driven for a while in between. (allot of people will disagree with me on this but I have found this to be true on my car) It sounds like you have an LM-1 (great device) I idle at 15:1 when cold and 14.7:1 when warm. cruise is 14.7 on the freeway. WOT is 11:1 - 12.5:1. Off throttle will spike to 16:1. Hope this helps. If you are up in my neck of the woods (Newport Beach, home/Anaheim, work) give me a call and I will lend you a hand. 949-510-1785 Rob

Jim_H

http://www.splitsec.com/

BC

My point here is that under WOT, that meter should never get above 13.

Am I correct?

Jim_H

http://www.toponemall.com/utroligfea.html

bd0nalds0n

Rob: What kind of fuel pressure do you have at idle, and what does it rise to under boost? Can I get some other input from the SC guys re: their own fuel pressure? I think given Tony's rich condition it may not be the most representative of baseline.

mark kibort

scot good one, but you left out highest heat produced at 14.7:1 range. at stoich, thats where detonation occures. however, at very low power settings it could be efficient to run here, certainly its what the 02 sensor helps to do (keep the average in the 14.7 :1 range) as you go leaner, you loose power dramatically, but the EGTs CHTs also go down. this is why real lean is not bad, and doesnt do any harm. (but you have a bunch of lost power) usually, real lean mixtures only result in missing/sputtering. as mixtures pass through stoich (14.7) it doesnt take long for bad things to happen. this is why, as Jim says, its best to be on the rich side, and that makes sure any one cylinder is not having any heat or pinging issues. all it takes is one bad injector to make one cylinder fail ,while all the others put out enough richness to keep the driver in the dark.

Mk

BrianG

ALso, Check the WOT switch for continuity. Your numbers might not be all that bad except for the WOT which looks dangerously lean for WOT. Don't forget that on the '85-86 cars there is a switch that tells the computer that things are at WOT, the TPS input is overridden, and the switch sends the computer to full-rich condition.... Obviously yours is not setting that last bit.

bd0nalds0n

I'm going to check in the morning. I think it's a 3 pole connector, a ground, I assume, and one showing idle (closed TB) and one showing WOT, does this sound right? Also, is there anything that would disable the WOT loop if the knock sensors are not connected? I didn't know whether "safe mode" closes off other loops/pathways. Need to get the knock sensor back together. Thanks to all for the advice and I'll keep updating.

John Speake

Hi Brian,
You are correct about the throttle switches.

The knock sensor circuits only affect ignition advance at high loads.

Sometimes the LH ECU can develop a fault where it does not recognise the WOT (or idle) switch inputs. This can be confirmed with a diagnostic tester.

Tony

Thats very true...what i have is a baseline for my own adjustments, not anyone elses.. Like i said i have some airleaks i have to plug first and how they may be influencing things, i dont know. Im not lean i know that and you should be able to get more fuel pressure than 55psi under boost.

BrianG

Thanks John... I didn't realize that this was potentially an internal LH issue. Is it something that you see often?

Could you provide us a list of common LH failure issues that don't result in the sudden death of our cars, just so we can be aware of the issues that might LOOK like wiring harness issues, but actually be LH failure modes?

Rich9928p

LHs have many failure modes, some die quickly, some die slowly and fail on an intermittent basis which frustrates owners and can rack up a large bill when a mechanic tries to locate the problem. The most common symptoms of a failing LH injection module are:

- Fuel injection valves click when the ignition turned is on and engine is not running

- Engine will not run at idle

- Air-fuel mixture is too rich (this can damage catalytic converters)

- No fuel pump operation, but the fuel pump operates when its relay is jumpered

- The engine will not rev higher than 3000 RPM

- A/T cars: no idle speed regulation when switching between drive gears and neutral or park

- Engine will not start, spark plugs are dry and the ignition system produces spark.

I added a new Diagnostics page for "No-Start" trouble shooting tips at my website www.electronikrepair.com .... you'll find a lot of useful information there including the pin-out of the LH and EZK connectors.

John Speake

Hi Brian,
Rich has mentioned most of them, I would add WOT non-op. Aircon idle compensation not working.

It's quite noticeable that after repair for a show stopper type fault (fuel pump non-op) the owner will say "the car has never run better". This implies that it is quite common for some of the other functions have died before the "big one".

As many of us have never driven another 928 that is known to be A1 condition, it's very hard to know if your car is running 100%.

For example, every time I put the diagnostic tester on a car, I would say that at least 75% of them have a knock sensor or Hall senor fault, not detected by the owner. Although this can be responsible for a marked drop in top end power.

Vlocity

This is a great thread. I am using a Split Second A/F meter in my slightly modified 85.

My sense was that the car still wanted just a little more fuel although I was reluctant to increase the pressure any higher. Currently the car will pull just the first blue at light at WOT which acording the reference lights is 13.2. (Near lean best torque) I am at 54 pounds of fuel pressure with the vacum hose attached.

The next chance I have I will probably make about a 2 pound increase and see where I end up on my guage. I was not sure what the upper level rich was and did not want to wash the cylinder walls.

The fuel pressure guage I have is mounted in the end of the rail, so I can't observe it while driving.

Regards,

Ken `

Vlocity

One more observation.

The oxygen sensor keeps the car in the mid range of the A/F? guage and "hunts" as it should during light acceration on cruise. During throttle off situations the guage reads lean.

I think this is all as it should be.

Again....thanks

Ken