John Struthers

Guru's, racers, performance - mod guy's,
Pattycakes has run rich since the day I took possesion. I believe that the rich mix was the death of the Cat. .
For your consideration: I have always used (alledgedly) high octane, have used octane booster with every other tank, and a variety of high end injector cleaners every third tank.
The wires and plugs, rotor were close to, if not new. Timing WAS spot on. She starts at the turn of the key and has had excellent throttle response
- now even better. Idle was, initially,625rpm.
I had some alt/batt. problems dropping at idle to the 11 - 10volt range, which correctly or not, had me believing that the computer was dropping then booting to default (rich ?). So after dark idle was, for the most part, stumbling at best.
I raised the idle to 750 indicated - not really accurate, I know - which helped but did not cure the low voltage problem. replaced Batt. with a huge Interstate, and swapped alternators. Much better. Idle adjustments up or down did nothing to alleviate the rich mix.
Replaced Cat. with high flow unit, mufflers, with a Flowmaster and a primary can type unit. No O2 light warnings but still rich.
Advanced the timing back and forth settled on 5 degree advance . Idle and acceleration smooooth.
Milage increased, extremely strong bottom, and mid range. Third gear roll ons feel like I am in 2nd at 3000 rpm and she pulls like a locomotive.
BUT, still rich. <img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/crying.gif" border="0" alt="[crying]" />
Questions: 1.) With the change to a less restrictive exhaust have I inflicted an over rich condition on my sHARk?
2.) How much advance is to much? Ballpark would help.
3.) How do I adjust the fuel/air mix? I am desperate... I might have to hire a chimmney sweep soon.
John S. 82' Weissach, 4.5l, auto, 'Pattycakes"
<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

WallyP

The oxygen sensor warning light on a 928 is basically useless - it is nothing more than a mileage counter, and has nothing to do with the performance of the sensor.

First thing that I would check would be the WOT switch. You can check at the switch, or at terminal 3 of the control unit. Switch should be open at anything less than about 3/4 throttle.

You can check the air flow sensor per the procedure on page 24-20 of the Workshop Manual.

You can adjust the mixture to a small extent per the procedure on page 24-24 of the Workshop Manual, but this will have more effect at idle than at cruising speed.

A less-restrictive exhaust usually causes a slight leaning effect - rarely richening.

While best total advance varies greatly with combustion chamber design, most performance engines like about 34-36 deg BTDC total, all hoses connected, at 5000 rpm. I think that most 928 street engines will fall within this range.

Steve Cattaneo

John,

You need to fix your changing system problem first. All of the cars electrical components were designed to work with a voltage of 13.4 to 14.5 volts. Any deviation would cause a drivability problem.

High fuel pressure can cause a rich mixture. Buy and install a fuel pressure gauge, the one that goes in the fuel rail (928 specialist). It’s a great diagnostic tool. System pressure at idle is 29 PSI/2.0 BAR.

Lets isolate the O2 sensor from the LH controller. Disconnect the O2 sensor plug in the CB; attach a voltmeter, positive terminal to the shielded wire (signal) of the O2 sensor, negative to a good ground.

Induce a lean mixture by removing a vacuum hose in the engine. With a hot engine at 3000 RPM you should see a voltage of .2 volts or lower. If not the O2 sensor is bad.


This is where you need to start.

Low battery voltage or bad grounds, overcharging and undercharging alternator can cause an erratic computer control. Any input sensor, example, TPS, CTS (coolant temperature sensor), relay can malfunction or give a wrong reading under these conditions. With the ignition off turn on the headlights for one minute after one minute turn the headlights off; connect DVOM set to DC volts, negative lead to negative post, positive to positive. A fully charged battery should read 12.6 volts. Anything lower than 12.3 volts, you will need to charge the battery, with the main cables disconnected. With the meter connected to the battery positive-to-positive, negative-to-negative, start the engine; turn on the headlights, heater fan, and radio. This puts a load on the system. You should see 13.5 volts to 14.4 volts. Anything under 13.5 volts could be a bad alternator, bad diode, bad ground or high resistance in the positive cable. Anything over 14.5 volts is an overcharging alternator. With the car still running, lights and accessories still on, place the negative lead of the meter to the negative lead of the battery post, place positive lead of the meter to all of the ground wires. No more than 0.10 volts should read on the meter. A good ground is 0.00 or 0.01 volts. If you have 0.20 or more you have a bad ground wire. You can use a jumper wire for the negative lead of the meter to the negative lead of the battery post, so you can reach the engine compartment. Just be careful and use common sense when working in the engine compartment when the engine is running. You should check the alternator output directly at the alternator with the car running and all accessories on.
Make sure you have the decimal in the right place on your meter.

How is pattycakes doing dent wise?



Good Luck
Steve C.
The Great White


<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

John Struthers

Wally,
Danke Schon, Mein Herr.
The exhaust thread helped. I should have mentioned that the exhaust I was stuck with for awhile was the high flow cat. and Flowmaster -shorty, 15" -. I was having some popping upon letting off the throttle. I assumed it was under utilized fuel. When I stopped working 24/7 I had the long tube Canister installed between the Cat . and Flowmaster. Popping stopped immediately.
On the subject of advance: I was/am concerned about problems at the high end. Pattycakes - who impressed me from day one showed me even more after the advance diddling. Power, acceleration, smoothness, RESPONSE is immediate. Unfortunately,
my Catholic/Scotch/Irish upbringing has programmed me to expect woe in the best of situations.
I'll see if my Hot rod friends at the West Texas Old Timers Club have a degree wheel and dial gauge I can use.
Checked the WOT -LOOSE connection at switch. Fixed. Super on page ref's. ON it.
Steve,
Have a 02 ground cable from a dump truck as batt. alt. starter, hotwires, cleaned every ground I could find with exception of rear speakers. Added a bunch of FORD truck chassis grounds left and right, front and rear. Cleaned ALL lights in and out, sockets/blades. With the exception of a ammeter drop when I put the trans. in reverse all appears to be ok. I have almost 200 hrs of comp. time I have to use so I'll break out all of my homemade jumpers -thanks for the idea whoever you are- and multimeter and do a circuit by circiut test of everything befor sHARKANSAs. My old alt. is being rebuilt -will swap again -.
Dent wise, $3100.00 see the adjuster a.m. on Wednesday. I did not include the obvious - a (singular) new tire, and gee my speedometer quit, too, could my antenna, and rear wiper -should they suddenly come up sick - be replaced and my cat who sleeps in the car- not really - needs to see a feline neuro-surgeon, that's what the Pet's Mart orthopedic specialist says............
The adjustable regulator and gauge sound good .
Been putting it off. I hope the instructions help on where to tap into.
I always use common sense under the hood... it's just that there are 8 flats on the sides of my 3/4 chisel set and they roll fairly easy....thanks for the help.
Keep em' rolling.
J. Struthers & Pattycakes <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />