Thad Brej

After having enjoyed my newly acquired 928S 5 speed manual for a few months, she recently lost power (reduced HP....forward motion inconsistent with throttle) and then wouldn't start after I stalled her at a stop sign.
She has a nearly full tank of 93 Octane gas.
I suspected fuel supply after researching here on Rennlist.
My son and I took the cover off of the fuel pump/fuel filter.
Upon turning the ignition to the 'ON' position, no sound or activity with the fuel pump.
Upon cranking the engine, no sound or activity with the fuel pump.
We pulled the fuel pump relay and jumped pins 30 and 87. Instantly the fuel pump ran, even without the key in the ignition.
We cranked the engine with the fuel pump running, and she wouldn't start. I thought for sure she would run.
I am out of ideas and need your collective knowledge.
Is it safe to assume the fuel pump relay is shot since the pump wouldn't come on at all without the jumper?
What is the next thing to look into regarding why the engine won't run despite strong cranking and fuel pump running with the jumper?
I still suspect a fuel blockage. I have a new Bosch fuel pump and fuel filter. Is it prudent to change them out as well as replacing the relay?
Is there something that I need to look into concerning the fuel injection relay?
Any help or direction you can give would be appreciated.

Kiln_Red

Sounds like a probable green wire failure!

Not a safe assumption, no.

Mrmerlin

Please follow Austin’s advice green wire

Jason89s4

^^^per Kiln and Stan, likely your green wire.
It is the ignition current and pulse supply, runs from your distributor, across the front of the engine bay to the RH side where it plugs into a socket near the jump post. You cannot miss seeing it if standing in front of your open engine bay. A very special wire: 928.602.907.00. Your gradual degredation of power, and then complete loss are particular indicators of a "dying" green wire.

To answer you questions for both your benefit (and others), by jumping 30 and 87 at the fuel pump relay, you have determined that the circuit from the relay socket to the fuel pump is good, and the fuel pump will run. However, this provides no conclusion as to whether your fuel-pump relay was working--you basically just bypassed the relay. But, if you have jumpered 30/87 and you can hear the fuel pump is running and you try to start, and it does not, then it was likely not the relay.

Test: put the fuel pump relay back in (XVII) or jumper it, and try to start the car. Does the tachometer move at all? (the green wire provides the signal for the tach.)
Also is your battery new and fully charged? Not asking for assumptions...what is your voltage measured at the jump post before starting?
Test and report back.
-Jason

-Jason

jpitman2

It would be helpful to tell us which version Injection you have, and maybe where you are. My 83 Euro has CIS/K-jet, which has a different pump relay from an L-jet system - it runs a couple of seconds at turn on, but an L-jet system needs air moving through the AFM to trigger the pump. LH-jet is different again.
jp 83 Euro S AT 57k

Thad Brej

I will be looking at and replacing the 'green wire' as soon as possible.
A few additional facts that I neglected to post that might be pertinent:

• The car only drove with 'reduced power' for about 500 yards before I stalled it at the next stop sign and then she wouldn't start
  • It all happened very quickly; does the 'green wire' degrade so suddenly?
• My tach has not operated during the 2-3 months that I've been driving her since purchase
  • I'm hopeful that the 'green wire' replacement may bring my tach back to life
• She is a US spec 928S with the L-Jetronic injection
• Isn't the fuel pump relay on an L-Jetronic 928S supposed to run the fuel pump for a few seconds when the ignition is first turned on?
  • J Pitman's post indicates that this is not the case and that it only initializes the pump after 'sensing air flow'

I have proactively already purchased a Bosch fuel pump and fuel filter. Would it be prudent to just go ahead and replace the components to be safe? How about the fuel pump relay?

j.kenzie@sbcglobal.net

Hi Thad,
I suspect the green wire will solve the problem. It's always a good idea to carry a spare fuel pump RELAY. I would not proactively replace the fuel pump if green wire solves problem. Fuel filter should be changed if of unknown longevity.
BTW the fuel pump does not run with only ignition on for a few seconds. It needs a RPM signal from starter motor action. Once again green wire probably will fix.
Good luck,
Dave

Kiln_Red

Not to add confusion, but it should be noted that there is a priming feature built into the pump relay. It's not uncommon for this part of the relay's function to be inoperable. The spark box must see revolutions via the green wire for the L-jet to start its duties, including energizing the fuel pump relay.

Fun tip: If your fuel pump doesn't momentarily run with key to 'ON', try cycling the H/L switch before start-up with the key to 'OFF'. You very well may notice your fuel pump priming after H/L switch cycling. It's not supposed to work like that obviously, but it's not uncommon.

To the question about the manner of the green wire failure.. Yes, they can and do fail all at once and symptoms can also be gradual. You will likely be surprised it ever worked any time within the past 15 years when you see its condition after disconnecting it. You'll likely need a pick tool to remove all of the remnants of the male connector from the female connector before being able to reinstall a new green wire.

Thad Brej

Many thanks to all who have responded.
I will let you know the results of replacing the green wire that should be delivered by Thursday.

76FJ55

The green wire has been mentioned numerous time, But it doesn't seem anyone mentioned aside from the fuel issue, a failed green wire will also cause loss of ignition spark. before replacing the green wire I would check to see if you have spark. you likely won't but on the off hand chance that you do have good spark that would rule out the green wire.

Wisconsin Joe

^This. Big time.

Basic diagnostics of a "No Start" condition should include checking for spark & fuel injector pulse.

An inductive timing light can be used to check spark, a noid light can be used for FI pulse.

Throwing parts at a problem without knowing what the actual problem is can get expensive.

If the fuel pump runs when you jumper the relay socket, a new pump is probably not needed.

Relays, OTOH, are both 'wear items' and the normal 53 relays are a few bucks each from Roger. Most owners carry a spare or two in the car as a matter of course.

Mrmerlin

Since the pump is still working swapping it now is not needed nor is replacing the fuel filter.

NOTE there is not a service limit placed on fuel filter replacement,
that said any time a fuel issue arises swapping in a new filter couldnt hurt.

Please note that the 1983 928 uses a specific 5 pin fuel pump relay,
NOT the more common 53 relay thats found on the later cars.

NOTE Its still good advice to carry a spare fuel pump relay in the car,
as well as an assortment of the best fuses

The Green wire can work till it stops, sometimes suddenly.
Usually the whole wire and connector ends degrade.
NOTE the engine will usually stop running /starting after it has been subject to a car wash event.
water corrupts the computer signal.

NOTE its also a good idea to remove the computer connector and inspect it and add deoxit 100 to the pins
Computer is buried under the hot post about 10 inches down.

If you will post pictures of the green wire connection to the car side of the harness at the hot post area,
it will be easier to assist with further diagnosis.

NOTE the green wire can also fail from cracked insulation then moisture corroding the shielding wire

Kiln_Red

Replacing the green wire isn't a matter of "throwing parts" at something. All 16V cars (except for Euro S2) utilize the green wire. '84 US is the last model, so unless you're the original owner or you know when it had been replaced by a PO, I would work under the assumption that the green wire is 35+ years old.

Good idea to get a new one on the way..

Wisconsin Joe

True to a large degree, but if there's spark, then the green wire is still good.

It may be a good idea to put a new one in proactively, but if it's not the problem, it won't fix it.

I'm currently dealing with an intermittent 'no start' situation on a different vehicle.

A friend who I share it with wants to 'throw parts at it', yet none of the parts he's replaced has fixed it. So, back to basic diagnostics.

Mrmerlin

Joe what are you working on and what has been done