dr bob

Hi Chuck, and welcome to the group!

The "green wire" is the conduit for the signal from the Hall sensor in the distributor to the ignition module. Since the ignition works now, I'd be tempted to leave that exactly as you found it until you solve the fuel problem. After the car runs, go back and get that deferred stuff done. Fiddling with the wires there now risks consequential damage that you won't know about. Remember the HippoCritical Oath when it comes to cars like the 928: Do No Harm. It also helps that you'll be chasing one problem at a time.

The symptom you describe sounds like it could still be the fuel pump, even though it sounds like it's running. The relays get "weak" as the contacts get damaged over time and cycling. You can get right to the end of that process with a fuel pressure gauge, one that connects to that cap at the front of the fuel rail. I made an adapter for a GM-style gauge by drilling and tapping 1/4-20 threads in a spare fuel rail cap, and replacing the ball temporarily with a 1/4" brass tubing compression ferrule. The hose for the gauge then threads directly into the cap with a little thread sealing paste and an o-ring. Be aware that the cap just needs to be snugged up, and a little of that thread sealing paste on the ball will help it seal again easily when restored to normal. --Over-tightening that nut will stretch the threads on the end of the fuel rail, making it forever hard to get the cap on and off again-. Add a little of the same teflon thread sealing paste to the threads and start with about 75% of the WSM-recommended torque on the nut. The paste on the threads is a lubricant not a sealant; that duty is left to the ball. Do Not Drop The Sealing Ball when you first take the nut loose. A shop towel draped strategically under the end of the rail will catch any dribbles and maybe the ball, but you can't really rely on it falling perfectly. Selective Diagonal Gravity syndrome applies in this particular area.

You will want to add a few specialty tools to your collection if you don't already have them. One will be a three-legged jumper for relays, with a switch between one of the legs and the other two. On the ends of the ~30" legs, fit 1/4" male spade terminals. Use at least 16ga and preferably 14ga wire for this. With the jumper, you can unplug the fuel pump relay and plug the spade connectors into the socket, using the switch to replace the relay contacts and run the pump manually for testing. This jumper will go into your travelling toolkit bag.

The fuel pump relay includes a tap into the tach circuit to tell when the engine is running. Operation includes closing for a couple seconds when you first turn the key on. Then the relay opens until it sees tach pulses. If you get in an accident that causes the engine to stop but the dazed driver doesn't turn the key off, the fuel pump will stop and hopefully limit any extra fuel to a fire in the engine bay.

The injectors are "batch fired", same as "they all fire at the same time from the same circuit". The injectors are all wired in parallel, so a short in any injector feed means a short in all of them and no fuel injection. As others mention, a "noid light" is a good weapon for diagnosing this problem. There are singles available at your local parts place, and kits of more are available from some online sources. You really just need one though if you are searching for a short in a batch-fired system. If you have fuel pressure but no flashing light on the noid light while cranking, you get to work back through the injection wiring.

The injection system presents full-time battery voltage to one side every injector, and pulls the other side -almost- (within one Volt or so) to ground to get the injectors to fire. The injection relay supplies the power. The ground is to the block at the right rear (right side is passenger side on US cars) of the valley under the air box. Grounds are a known weak point with both age and environment working to corrode the exposed connections. So maybe a first step in your process might be a careful cleaning of ALL the chassis ground points and the connections there. The wiring diagrams for your car in the workshop manuals show the location of all the ground points in both plan (overhead) view and side elevation view. A little careful work with a brass detailer's toothbrush will let you cross this off your list. The car is only 35 years young, yet its electrical arteries and connections already need a little care.

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Again, welcome to the group! Consider spending the $few for a Rennlist membership. It adds some handy features to your presence, like being able to put a signature line in with car details. It also opens some other features anf forums to you, and reduces the advertising pops as you read. Worth the investment for sure, and the advice and support you'll receive here will more than pay you back.

Chucks928

Dr Bob..thanks for the note! the 928 is definitely a different beast than the older Mopars I,m used to working on. very well engineered and built! I did replace the forementioned relays just in case and am waiting for the new pressure kit to arrive. The pump had good flow but could still be short on pressure. I think it could be the pump and a lot of TLC,cleaning,de-oxing and replacing vac lines,and hopefully no major issues! Chuck

Chucks928

Just thought I would add these pics. the first pic is of fresh 89 octane from my gas can. There is not a lot in the bottle but you can see its pretty clear.
The second pic is what I pumped out of the 928 when I was checking my fuel pump...think its any good?!

Majestic Moose

I would drain out this old stuff (probably smells bad too) and try starting it with a couple gallons of fresh fuel. This might be the root of your problem. Gasoline does not last much beyond six months anymore.

Chucks928

Just an update..I pumped out the tank full of old fuel and replaced with fresh 91 octane and some fuel injector cleaner. turned it over but wouldnt fire.A little fuel down the TB and it fired right up. I was able to get about 10-20 seconds of decent running before it started missing and stumbling. If I held a little pressure on the pedal and kept the rpms around 1300 or so,it would run steady,but with a misfire coming and going. I think if I had held the pedal there the car would have run all day,but as soon as you let off or gave it the gas it would stumble and die..somewhat similar to a stuck choke on a carbed car. as time permits I,ll finish hunting down grounding spots and any loose wires and vac lines.Then I may have to pull and clean the injectors. Slowly getting there and appreciating all the advice and help! Chuck

Chucks928

The weather is slowly bringing things to a halt,but I,m knocking off a few of the checks as I can. Finally got my fuel pump pressure kit today and looks like the pump is in decent shape..held at 2,6 bar ( approx 37lb). In spec as per WSM. Also found a ball to install in check port so thats sealed up. Car fired with fuel added to TB and still runs but not terribly well...rough and needs the throttle feathered to keep running. As soon as weather and time permits,it goes inside to check all grounds. Slowly but surely...

dr bob

Chuck--

Sometimes Stoopid Stuff beats you up. Your description of it sort of running at a particular RPM suggests that the airflow sensor may be sticking. You have a "barn door" air volume flow sensor, with mass correction provided via the temperature senor in the bottom of the air cleaner housing. Is the 'barn door' sticking? Good time to clean the connections for the flow and temperature sensors, and to verify that the door actually moves. IIRC there's a fairly simple diagnostic for the airflow sensor in your workshop manuals. You can do the flow unit testing indoors, safe from the cold and snow.

Chucks928

Dr Bob, you did remember correctly,checking the manual there is a nice procedure for checking. I will give it a look as soon as I can. If it was running a carb instead of Fi I would say it was acting like it had a stuck float or even a vac leak somewhere. Starts with a little help and for the first 20 seconds or so runs half way decent,then gets rougher and needs the throttle continuesly pumped,just slightly,to keep running like its being starved. Carbs I know somewhat but EFI is all new to me,but I am learning! Chuck

hinchcliffe

Hey Chuck, which side of Rochester? I'm in Fairport/Victor. Though admittedly a S4+ guy I can help if needed.

What shop is near you? CDI in Victor has done 928's but electrical fun is expensive to have anyone chase down. I end up doing everything myself with help from rennlist here. Let me know how I can help a local Rochester guy. then.

Chucks928

Just thought I should post a brief update.Due to the holidays and winter weather,nothing major has gone on with the 928. I did get some time to clean as many groundspots as I could get to,the only one I need to do is the one near the air intake which I believe is connected to the L-Jet system. I,ve cleaned and de-oxed the fuse connections,relay connections and flushed the old fuel out of the system and cleaned and de-oxed as many of the sensor connections as the weather and time has permitted.Thanks to all,and thanks to Wayne Strutt for the massive amount of info and maintainence files he has sent! The car still will only kick a little when starting and needs a shot of fuel into the TB to get it to fire. It will run somewhat steady for 4-5 seconds,then I have to start working the throttle to keep it running.
The next few days i will be checking injectors with a noid light,checking the Airflow sensor,the temp 2 sensor and that groundspot in the back. Hopefully the weather will cooperate!
Its a slow process but I am learning a lot! Chuck

Chucks928

Slowly walking my way through diagnosis....Finally had a chance to check signal with the noid light. All injectors lit when cranking the motor,not exceptionally bright but I,m not sure how much that would matter? Either way it appears the injectors are getting a signal to fire.
Took off the air filter and air flow sensor. The barn door seems to be moving without a problem,smoothly and freely. Checked resistance as per the WSM.
pins 6-9 560
6-8 361
8-9 200
6-7 100
7-8 310
and 27-6 4.25 k
these measurements were in spec for a sensor dated 042 and beyond. I,ve posted a pic below showing the stampings on the body,I,m not sure which is considered the date stamp?

Checked temp sensor 2... 2.5k ohms . WSM shows it should be 7-12 ohms?

Checked the temp time switch.. terminal W-ground.. .6 ohms ( spec 0 )
G-ground 37.3 ohms ( spec 0)
G-W 37.3 ohms ( spec 25-40)
The specs were taken from the WSM and were for approx 10c temps...its was approx 45f out and the engine was cold when I was taking my readings,I,m not sure if a cold engine would affect these readings.

I wasnt expecting any change in the problem by just checking resistances and its still the same,runs with a little fuel down the TB,but after a minute or so wants to die and finally does after keeping it going by working the throttle. I,m hopefully getting it narrowed down a bit though!

Next, a fellow member who has been walking me through this has suggested replacing the injector screens and hoses. Then maybe rechecking those temp sensor 2 readings and temp time switch readings. They may be the issue and finding used, good sensors would help verify! Chuck

Chucks928

Not sure which are considered the date stamps

Chucks928

And this is the other end of my green wire..injectors are getting a signal and the noid lite lights up...but it is looking rough.

mskar

Its a total hack but... I used that two-part formable plastic putty to recreate a crumbled connector. I cleaned everything, especially the terminals, then greased the inside of the mating connector with a q-tip, put the terminals in then pushed the putty in, making sure the terminals stayed separated. Stuff smells awful while curing btw.

This connector was to one of the knock sensors on an S4 that would have otherwise required a complete manifold removal to replace. It's held up well over the past year and will definitely be replaced one day when I do an intake refresh but in case it helps!

Chucks928

MS..thanks for the advice! Sometimes thats what you have to do to keep things running until you get around to shelling out the bucks for some of these parts. I was looking at a new engine harness on-line.... almost choked on the glass of Jack I was sipping,and decided mine is good until a later date!