Mongo

I noticed today after 2 WOT runs that there is what feels like and sounds like pinging at 4,500-5,500 RPM in first gear.

Since my O2 sensor is disconnected (deadski) I assume that this may be normal since there is no timing advancement on a default map the LH has preprogrammed?

jcorenman

Andy,

It's not an O2 sensor issue-- with the WOT switch closed the LH runs opens open-loop and ignores whatever the O2 sensor says, and just goes off its maps (RPM vs. load-according-to-MAF). The job of the O2-sensor and closed-loop operation is to keep the AFR hovering around stich (14.7) to keep the cats happy, and for good economy and minimum emissions.

If you are detonating then generally either the engine is running too lean at WOT or the timing is too far advanced. Both are unlikely-- the S4's with stock maps run quite rich at WOT AFR around 12) so even if the MAF is aging the AFR should still be OK. And the timing is fixed by the computer, and again for the S4 is pretty conservative.

It could be a MAF that is way out of calibration-- under-estimating the air flow which would cause the LH to inject less fuel, and run lean.

In any event the EZK will listen for knocks and dial the timing back before you can likely hear them. And if there is a bad sensor then the EZK takes out a flat 6 degrees which should certainly be safe.

What is needed is a Sharktuner, you are mostly working blind without it.

So did one of those Berkeley gas stations slip you some 87-octane?

What else changed recently?

Mongo

Well the knock sensors are definitely catching it before the pinging continues. I can totally tell that because of the power dropping off in that high of a rev range. With that being said, since the O2 is disconnected, the only sensors the LH has to manage the fuel mixture is the MAF and the Temp II. Both checked out when tested with the multimeter. MAF is still new by JDS.

I am pretty sure that when the O2 is included in the loop, the issue should be solved and the engine can advance accordingly instead of defaulting to the original map preloaded in the LH.

AO

Just because the MAF is new, does not mean that it's out of spec...

dr bob

Andy-

The lh sees the WOT switch, and from that point (~75% throttle) it ignores the oxy sensor even if it does read perfectly. Open loop map inborn ezk and lh. Then retards timing if it hears pinging. It does the retarding before you can hear it, especially at higher RPMs. If you have knocking you can hear, there's more to the issue. Could be MAF although if new it's unlikely. Could be a partially obstructed injector, a plug with a glowing electrode, excess carbon in the chambers or under the valves either increasing compression or glowing. Could be oil ingestion too. Or bad gas, although 6 degrees retard is usually enough to mask a 'regular' mistake.

mark kibort

on the dyno, o2 sensor or no 02 sensor was the exact same hp and fuel mixture. It does nothing but keep things nice an lean at cruise settings. your full throttle switch might be bad, then the 02 sensor might be looked for , and its not there and the fuel mixture could be bad. the boys here should be able to answer that question or possiblity.

Mongo

ah I see. At WOT the O2 Sensor is completely ignored. I checked both the idle and WOT switches with the multimeter and they both had the correct ohms that I was looking for per the workshop manual. How would I know if this new MAF is out of calibration? The only other way I can describe what happened at WOT in first gear was shuddering. And I don't think that was my tires spinning...

Canuck928

I have an 88 S4 and like jcorenman says they do run rich at WOT.In the 5 years i've owned my car anytime there was high RPM pinging it was due to fuel issues.I now only run Sunoco 94 and have had no problems since.BTW my 02 sensor is also unplugged

Mongo

hmmm... Maybe bad gas then.... Another thing I am thinking about is when the car is running in open loop, the hall sensor is ignored. This can also lead to no ignition advance, maybe even 6 degrees retard. That would cause a drop in power at high RPM if there is no advance.



EDIT: If I am wrong about the hall sensor and knock sensors being disabled in open loop mode please tell me. I will start to search elsewhere then. This car even with a bad O2 sensor had tons of power in the RPMs because it was running rich on closed loop. Disconnecting it was the only change I have done. Thanks!

soontobered84

You could be lean at WOT due to a bad internal fuel pump if your model has one. I replaced the internal on my '89 and it was a heck of a difference in performance. I think ROG100 had a similar experience when we replaced his in Ed Hughes drive one Saturday morning. (Back when Ed had something besides a lawnmower to drive)

Mongo

'87s didn't have one. I'm pretty sure in '89 Porsche did this idea.

Mongo

Looking through the search I found something indicating a possibility of running lean in open loop posted by John Speake. Theoretically, my symptoms could be exhibiting this condition. There is not much I can do right now except wait and install the new oxygen sensor when it comes in. If I had sufficient fueling when the faulty one was plugged in and this problem arises when discconnecting it, the solution may be in my spiffy new one

dprantl

A new O2 sensor will not do anything when you are at WOT. If you are running lean when at WOT, you *need* to figure out why. This condition is not good for your engine. Possibilities for leaning out at WOT on a stock car would be partially clogged injectors, MAF out of spec, temp II sensor giving wrong reading, vacuum leaks, bad gas, or LH strangeness.

Dan
'91 928GT S/C 475hp/460lb.ft

Mongo

Again, it never happened up until disconnecting the O2. It'd be great to hook a fuel pressure gauge up to see what I'm pulling on closed loop though. With new injectors, clogging is ruled out, although I haven't done a fuel filter in about 35,000 miles. Vacuum leaks are nil right now. I spent my birthday on Sunday trying to figure out what caused the retarding of timing at upper RPMs.

Would there be another way the Idle or WOT switch would be bad even if it passed the ohm tests I did? Lack of timing advance is the only thing I'm pondering as there may be none when in open loop. I can't confirm that for sure though since I can't locate it in the WSM.

I've got my fingers crossed that's for sure. I also found out from John that the knock sensors still work in open loop mode. Is there another way to tell I have bad gas though???

mark kibort

get a simple air fuel ratio meter and connect it to the 02 sensor. it uses a tap on the one sensor wire, so when you are WOT and the sensor is being ignored by the LH box, it still is registering mixture. This absolutley is good enough to see if you are going lean up top. you can also just do this with a good fluke meter. go WOT and see what the voltage does. Its in the 1volt range, so you need a pretty accurate gauge for reading the variances. It should be hunting at idle and part throttle , but when you are WOT or near WOT, it will stay at one voltage unless the mixture is changing.

Next would be fuel pressure at WOT. you can mount one on a fuel rail and have someone watch it. all you need to do is have a decent e-brake, and some jack stands. jack up the back of the car, put it on jack stands, and start the engine. Put it in gear and get it into 5th. at about 3000rpm start fetheriing the gas toware WOT, as you keep the rpm down with the hand brake and/or foot brake as this acts on the rear wheels. you can get a momentary reading on if fuel pressure at WOT is a problem.