Athenian.

Hello

I have a novice question for the folks who have 1987-88 S4s....I have a fuel problem with a S4 car I'm working on...More specifically there is TOO MUCH fuel when engine is running (at idle)...I know it's not the fuel pump or the relay (I have checked both). I think the ignition brain box might be at fault but I'm not sure....Any ideas???

Also I was wondering if the ignition brain for 1987-88 S4 are the same...Can they be interchanged??...I know someone who can sell me a 1988 brain....I just like to know if the ignition maps are the same for those years, before I go spending money for nothing.

Thanks for your help

Mike Schmidt

There are a few different possibilities. It could be a bad fuel injector or injectors. It could be a bad fuel pressure regulator or fuel pressure damper. It could be the fuel injection computer.

Check the fuel pressure to see if it is within specs. Pull the connector off each fuel injector one at a time to see if one causes a different reaction than the others. If the fuel pressure drops faster than it should when the car is shut off, it could be a bad fuel pressure regulator, damper or leaking injector. Pull the vaccum line off each fuel pressure damper and the fuel pressure regulator one at a time. If any of the diaphrams in any of those is bad, you'll get fuel out of the vacuum hose fitting on it.

The ignition computer shouldn't affect the amount of fuel being delivered. The only real possibility of too rich of a mixture being caused by the ignition computer would be if the fuel injection was working properly, and the cylinders weren't all firing to ignite the fuel that's being delivered.

It's practicly unheard of for one of the ignition computers to go bad. The fuel injection computer is the one that's known to cause problems.

The ignition computers for the '87 and '88 have different part numbers, but either one should work fine in the other model year car.

Athenian.

Thanks for the resposne Mike....I'm a bit confused now...Is the fuel injection computer different from the ignition computer??? Where is the fuel injection computer???
I thought there was only one computer in the S4. The one located on the passanger side right footwall.

I have a Porsche part number :
928 618 124 12....is this number for the injection computer or the ignition computer for a 1987 S4???

Thanks.

Steve Cattaneo

Number 928- 618-124-12 is the EZK control unit (ignition control). The LH control unit (fuel Injector) is right next to the EZK unit. They should be back to back to one another. The LH number is 928-618-123-11.

Don’t waste your time and money changing the LH control unit it’s probably not your rich running drivability problem. Buy and install a fuel pressure gauge, the one that goes in the fuel rail (928 specialist). It’s a great diagnostic tool.

Other components that would contribute to a rich mixture are the temperature sensor 11. This is duel input sensor, pin # one sends a signal to the EZK unit for ignition timing. Pin # 2 sends a signal to the LH unit for fuel mixture. If the sensor malfunctions you will have an excessively rich mixture. Its easier and cheaper to just replace the sensor.

The other component would be the O2 sensor

The 02 sensor is one of the most important input of any car. It controls the air/fuel ratio by means of the fuel injector pulse time.

Less 02 in exhaust = voltage increase = computer reduces fuel = lean mixture.
More 02 in exhaust =voltage decrease=computer increases fuel=rich mixture. Closed loop control.

A bad O2 sensor could give you a rich fuel mixture.

A caution about the LH fuel Injector unit for 928 S4 models. There is only one controller used worldwide. But they are coded (mapped, programmed) differently for each car application. A 928 with an automatic transmission and a Cat is coded differently than a 928 with a manual transmission without a Cat.

Installing the wrong LH controller can create a different drivability problem.

Steve C
The great white

Jay Wellwood

If you are going to install the fuel rail pressure gauge - I'd also recommend installing a Fuel Air Ratio meter (like the ARM1). This along with the gauge is a very handy dynamic duo for trobleshooting.

Athenian.

Thanks so much Steve, Jay and Mike for your expert advise on the subject....I will follow your advise and look at the fuel pressure sensor first...I was thinking about installing an air/fuel mixture also...Any idea where to get a good one???

Happy Holidays

Mike Schmidt

Any S4 or GT LH computer will work. The coding that's done is with a plug. That plug is on the bracket that the EZK and LH computers are attached to, but is not part of the computers. The LH computers can have several different part numbers, depending on what year that they were initially used in. The mapping was changed slightly, but any of the different part numbers will work just fine. Even if you try to get one with the older part number from Porsche they will tell you that the part has been superceded with a newer one.

John Struthers

Mike and Steve,
Some questions specific and general.
Would the installation of the fuel rail pressure gauge and ARM-1 help isolate what I think is my 'NEW' O2 sensor problem?
Long term I need to isolate my battery drain problem. Before trickle charging under low charge conditions Pattycakes still starts up at the turn of the key but starter sounds weak, idle is rough/hunting, and O2 light will come on once or twice - Mapping?-. Self curing as I drive and Batt. builds up a charge.
If this is a, strictly, JUICE problem will the fuel rail/arm-1 actually benefit me?
There are no other mods other than a free'er breathing exhaust. Basically, if I fiddle with fuel air mix/pressure that is more related to an electrical problem than anything else won't the brain have to remap after Batt. recharge/disconnect and adjust to whatever fuel/airmix/pressures 'I' changed instead of the original factory map values? I'm trying to force myself to go find the drain if you haven't guessed already. And I think the system as designed with a stock 4.5L with only minor exhaust mods can handle the fuel/air mix without further tweaking unless you guys can convince me that somewhere in that wide powerband of ours I need to manually adjust the fuel pressure/air fuel ratio. Is there something about the fuel rail gage I don't know in the way of diagnostics? The way I see it - but, I do wear glasses - the gage would let me know there was a fuel pressure problem but I would still need to check the pump(s), regulator, or dampners, right?
Unless there was some kind of visual needle spike how could I identify any kind of injector problem let alone which one? I'd be back to pulling connectors of each injector and the Vac. lines from various dampners and regulators, or can it somehow narrowly isolate a specific problem? If it can't, all I'd be looking at are some pretty lights on the console and a spiffy looking gage under the Hood.
Enlighten me, I know I'm missing something here!
John S. and Pattycakes

dr bob

Shark Chums:

Some thoughts on the multiple subjects in the thread so far:

-- Too rich at idle: I'd like to know how you are diagnosing the "too much fuel" condition. Often, a 'too rich' problem is misdiagnosed by using tailpipe sensor (or your nose) to detect high HC. This is a problem related to "not burning the fuel" rather than "too much fuel." Too rich or too lean is most easily diagnosed with a gas sniffer that's attached ahead of the cats, looking specifically at CO values.

-- Look at all the plugs to get a color pattern. Various shades of brown show mixture. Black soot is usually misfire. Plug wet with fuel has no fire.

-- Installing a new but 'incorrect' O2 sensor will cause uneven running at idle and low load as the sensor response may not be what the LH box is expecting. Go with the correct sensor rather than a generic fitz-all if you can.

-- The oxygen sensor reads the CO (carbon monoxide) in the exhaust rather than any free O2. CO is related to fuel combusted. Voltage rises on higher CO, indicating a richer mixture. CO, and therefore the sensor output, is not a function of misfire conditions that might cause raw fuel (HC) to pass through to the exhaust.

-- Do the basic tune-up steps before you get seriously into any controller-level diagnostics. Too many folks go for the controllers when they have common ignition-related maladies associated with old age and wear. Plugs are easy, then caps and rotors, then wires. Still a lot cheaper than a new brain. Gas sniffer will isolate the problem to ignition or injection. Pay for this diagnosis and save in the long run.

-- If all the other tests, including the gas sniffer test, indicate a rich condition, I'd be looking at MAF sensor and the throttle position switches. A full-open switch that's true at less than WOT will cause you to see a real too-rich condition. A MAF failure will show decreased performance, and a too-rich "limp-home" condition. Last but not least, do the diagnostics on the LH brain. The brains are expensive, known-failure points.


Good luck!

Mike Schmidt

A fuel pressure gauge and an air/fuel gauge like the ARM-1 can give you some good information if there's a problem. They won't necessarily give you the exact cause of the problem, but can narrow it down a lot faster. The cars are pretty sensitive to lower than normal voltage when starting. The rough idle and other conditions you mentioned that are self curing sound like the computer's going through it's learning process, as if the battery had been disconnected. If you're having a voltage problem somewhere, the ARM-1 will not specifically indicate it. If you adjust the mixture for idle or part throttle, the computer will adjust to compensate for this during it's learning process. It goes to a fixed map at full throttle, so any changes you make will cause an effect there that the computer doesn't correct for. The only thing that you should really need to change the air/fuel mixture for would be for full throttle. The computer should handle the rest by itself. With the fuel pressure gauge on, you'd still need to check the pump, regulator, or dampners, injectors, but it would help to narrow down the possibilities to those items. You might want to check your ground connections, particularly the engine to chasis one. A bad connection there can cause some strange problems with the computer and hard starting. Disconect the battery to reset the computer's memory if you do find a bad connection and clean it.

Steve Cattaneo

John,

You need to fix the electrical system first. Start with the battery drain problem. Do a parasitic load test. You’ll need a DVOM, set it to read amps. Disconnect the battery’s negative cable. Then connect the positive lead of the DVOM to the negative battery cable. Connect the negative lead of the DVOM to the negative battery terminal. Parasitic drain should not exceed 100MA. If there is excessive drain remove the fuses and relays one at a time until the drain is found. Check that circuit for shorts or corroded connectors.

Run extra ground cables from the engine block to the cars body.
Remember electricity flows from negative to positive, so grounds are very important.

What year is your car? Do you have pulsed injection? Or CIS?

Below is one of my previous posts I hope this helps.

Low battery voltage or bad grounds, overcharging and undercharging alternator can cause erratic computer control. Any input sensor, example, TPS, CTS (coolant temperature sensor), relay can malfunction 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 need to charge the battery, with the main cables disconnected, of course. With the meter connected to the battery positive to positive, negative to negative, start the engine, turn on the headlights, heater fan, 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 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 a negative ground strap in the engine compartment. The ground wire should join the engine block to the body. 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. I hope you used soldered or crimped cable end connectors not those cheap bolt on connectors on your battery. 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.

Good luck,

Steve C

John Struthers

Steve,
Thanks for the concise post.
To date I have:
1. Pulled ALL Known fuses and relays for contact/terminal cleaning. Console, dash, under hood, under dash, and the fuse cabinet.
2. Blew everything out in #1 with canned dry
air.
3. Removed both ground straps, shined with new green pad including mount points.
4. Cleaned starter & alt. leads/mount points.
traced what I sincerely hope was the majority of small wire body grounds. Removed grounding screws/bolts cleaned contact points and terminal ends.
5.Trickle charged for up to 3 straight days.
Leads disconnected.
6. Put all rocker lights in OFF mode after cleaning contacts, bulbs and clips. Pulled the door frame plunger switches cleaned and dry lubed. Reinstalled switches and checked lights for operation.
7.Christ, I even checked the handbrake switch.
NO JOY!
Pattycakes idles, accelerates and performs beautifully - as designed by the boy's and girls in Deutschland - as long as she has a good charge. Several days after a good trickle charge she either goes to as low as 10v discharge and over 14v while charging.
"Go figure", says I.
I have a replacement alt. on the way. Will load test the old one and the replacement in situ under load. If the replacement does not keep a charge on the Battery I'm heading back to Interstate for a replacement.
If that doesn't work I will hunker down and circuit test as you, drbob, and other have recommended. You guys are probably right but I'm a couch - ****, really! I am as lazy as
I can get while still maintaining a heartbeat/pulse and a smidgen of brain activity! Not blowing anyone off...way to many good ideas...and will post results ASAP.
John S. and Pattycakes