rsam1013

Because I didn't have anything better to do, I decided to replace the fuel injectors on my running 1985 928S3 32V Auto as the performance seemed off, and gas mileage was horrifying, even by 928 standards.

If you're not familiar with my car, it's a $4,000 Barn Find I'm documenting the restoration of on my GuysWithRides YouTube Channel: @GuysWithRides1

Here's what I replaced (all parts sourced from 928SRUS:

• All eight fuel injectors with Bosh Design II units.
• All eight fuel injector connectors with new pins and shields, as seven of the originals cracked upon removal.
• The Crank Position Sensor ("CPS") (mine came out relatively easily without breaking), as the connector crumbled in my hand upon inspection.
• The Throttle Position Sensor ("TPS") - another connection that fell apart in my hand.
• All of the vacuum lines using the kit supplied by 928sRUs. I triple-checked the connections after two of the existing tees in the car broke in my hand.

Before I took on this project, the car started easily and was driveable before I messed with it. Now, with everything back together, it cranks but doesn't start.

Here's my troubleshooting thus far:

• I confirmed the fuel pump is running, and I have fuel pressure in the fuel rails.
• The attached video shows the spark plug from cylinder #8. I currently have no spark.
• The plugs, wires, distributor caps, and rotors are only two years old, with at most 2K miles.

So, I have two questions:

1. The wire colors for the fuel injectors on S3 32V cars are very confusing (it's maddening Porsche engineers didn't use better contrasting colors!), and it appears from the connectors I disconnected there is no pattern to which each pin resides. Will this affect the fuel injector's performance?
2. Will getting the polarity of the fuel injector wiring wrong on any of the injectors cause a no spark situation?
3. If the fuel injector wiring is pin-agnostic, what else would cause no spark after I just replaced the CPS and TPS?

Any help is very much appreciated!

Thanks,

Rudy

The Forgotten On

Because the car runs the fuel pump you are getting a crank signal so the sensor and its wiring is probably alright.

Fuel injectors are just a magnetic coil, a solenoid, so they are pole agnostic as far as I know. It shouldn't cause a no spark.

I would inspect the coil wiring and verify the ignition amps are still good. They fail randomly, but are easy to get to. They're under the plastic cover next to the hood latch.

Also, check that the small wires coming off of the battery positive terminal are clean and tight. Those wires directly power the fuel and ignition computers.

NewToPig

How about grounds you may have taken off the engine that could affect spark return?
On the LH all injectors are fired together so the wiring kind of doesn't matter as long as no power and ground are tied together.

Petza914

Do you have tach bounce when cranking? Is it only cylinder 8 that has no spark or do none of them or only half of them (one side of the engine) not have spark?

rsam1013

Other than swapping out the original fuel injector connectors with new ones that included carefully repinning the wires, I didn't knowingly remove any other ground wires.

rsam1013

Thanks. I posted a full video below that confirms I have tach bounce, and confirmed there is no spark to the plugs on either cylinder bank.

rsam1013

All, thank you for your comments thus far. Attached just now is a video showing the tach at startup and the spark plug from cylinders 4 (Passenger side) and 8 (Driver side), confirming there is no spark. Also noteworthy is the lack of fuel on either sparkplug, but I'll deal with that after I figure out the no spark problem. On Sunday, I'll start working my way back to the coils and amplifiers. What a disaster!

Mrmerlin

did you replace the CPS with a new Bosch part?
or just the connector?
Could you have swapped the ICV and CPS connectors?
this is easy to check go from the computer connector

Did you replace the TPS unit ?
AND the TPS short harness?
did you replace the ICV or remove its harness connector?

rsam1013

Hi Mr Merlin, I was hoping to see you weigh in, and I look forward to seeing you at an upcoming show in the Philly area if I can resolve this issue!

To answer your questions:

• I replaced the CPS with a new Bosch part.
• I didn't remove anything from the ICV; I made a point of not doing anything to it. I'm 99.9% confident I plugged the new CPS connector into the right connector; it's the one that joins in the punched-out slot on the fuel damper bracket.
• I did not replace the TPS unit, only the short harness as the original had a cracked connector.

Mrmerlin

please run a test on your TPS connector at the computer its a slight possibility that the wires could be reversed.
you want to verify that the TPS signal works for idle and then for WOT.

verify that the ground wires at the back of the V are clean and tight
The injectors can be wired anyway.

Go to the CE panel and put your finger on each of the running relays ,
turn on the key to run,
see if each of them click,
the FP relay may need to see engine revolution to turn on.
check the following relays.
X bus ,
Fuel Pump,
LH,
EZK

NOTE make sure you have the battery charged up use a 6 amp charger

soontobered84

Did you clean and test the new injectors just prior to installing them? Sometimes injectors are stuck closed and won't allow fuel to pass through unless they are re-cleaned and lubricated.

And sometimes relays die for no reason at all. Check the FI relay XXV. (top row of the CE panel, and next to the last relay on the right side)
In an 85, it's a standard 53 relay. Swap it out for a known good one.

rsam1013

April 22 Update - Good news, so-so-news:

Good news: After cleaning and tightening the two ground wires at the rear of the engine's "V" underneath the two rear fuel dampers, my car has spark and starts.

The So-So news is that now my car either has a vacuum leak or a fuel injector is not firing, as it's running rough.

I've attached a quick clip to demonstrate what my car is doing currently.

I will spend Tuesday morning going through each injector, it's harness, the vacuum lines to figure out the current cause of the rough running.

Attached is a video of my car's current behavior:

Thanks to everyone for your advice.

Mrmerlin

well thats great,
Now all you need is a 9 volt battery soldered to a 2 pin AMP connector to test each injector for a click.
If you find one not clicking then you should remove it,
spray PB blaster into the inlet then squarely tap the inlet onto a block of wood gently,
then retest it you want them to click.
NOTE as an alternative if you can put a long screwdriver onto any of the injectors you can see,
then you can listen for them to be clicking with the engine running,
OR ,
use a IR gun aimed at the cold EX manifolds and see what cylinder is not making the port hot.
Make sure you have verified the wires on each cap for correct orientation

Michael Benno

Have a look at this Porsche troubleshooting guide, it;s specific your model year. These diagnostic guides are a gold mine for troubleshooting and test procedures.

https://drive.google.com/file/d/1Nth...usp=drive_link

rsam1013

Wait, I'm confused. So you're saying that the two wires feeding into the injectors have to be on the correct side of each injector? In your earlier comment, you said, "The injectors can be wired anyway."

Using an IR thermometer to find the dead cylinder(s) is a brilliant idea! Hopefully, that will help me isolate the offending cylinder(s) quickly Tuesday morning.

Stay tuned!