dukenukemx

Been a year since I played with this car, but I'm at it again. Tried to start it and no fuel. The fuel pump relay engages and the fuel pump does make a noise when cranking the engine, but I don't hear the fuel injectors make noise. By fuel injector I mean the only one I can see, the very front left of the car. I was able to disconnect that one injector and test for Ohms and got 16.5Ohms. The harness that was connected to the injector was reading 3.5Ohms, with that one injector disconnected. A quick look at the wiring diagram for my 1985 928 shows that all the fuel injectors are connected in parallel. That doesn't make sense to me as that would mean all 8 injectors fire at once.

So a bit of quick math shows that if all 8 injectors minus one are suppose to be 15-16Ohms then one injector has really high resistance. But if the injectors are hooked in parallel in a 4 by 4 configuration then one injector must be shorting out and grounding all the injectors. I know I could figure this out by removing the injectors and testing them but I won't get to the car until sometime next week. I just wanna see if I need to order new injectors before I try again.

Jason89s4

Duke,
Per the posting of your wiring diagram, I assume that you have an '85. Please confirm.
Before worrying about resistance, pull the one fuel injector socket you have access to, turn the key to "run" and measure each of the female plugs...you should have 12v+ at each female plug ,with the other lead to a good ground. If not, the injector plug is not getting proper signal from the LH-Jet.
If you do have 12v at that test, do you have "noids" that you can plug into the same injector wiring plug and when you crank the engine does it light up?
I'm not sure where you are in this world, but a local Autozone can loan-a-tool you the noids.

Oh, and make sure you have plenty of good gas in the tank. You wouldn't be the first to forget that step after a car sat for a while!
Please report back.
-Jason

The Forgotten On

The fuel injectors are batch fired ie they fire at the same time. Once per revolution.

The computer switches ground in order to fire the injectors, they always have positive power as noted above.

Check to see if you have spark as well. The CPS can go bad and cause the car to not run.

Although with the fuel pump running when you crank I doubt that. Check all your relays though and replace the EZF, LH, and fuel pump relays. They commonly fail and can do this.

Also check and clean your battery terminals. The small ones on the positive side are what gives power to the fuel pump and computers IIRC.

Also check your ground strap for corrosion. They can fail in all kinds of weird ways.

dukenukemx

Yes 85 928.
I did measure the voltage as well with the engine cranking and got .5 volts. Yea, half a volt. Again with one injector disconnected.
I thought of that as well and threw in a few gallons of fresh gas.


I know there's spark because the engine runs when I spray starter fluid into the intake.
Already replaced them with new relays last year. They do click on when cranking.
Double checked all that and nearly welded my socket wrench apart by accident.

Kiln_Red

How long did the car previously sit? I assume you acquired it as a non-runner. How do you know the injectors aren't opening? Was the pump previously seized from varnished fuel? Have you checked the health of the MAF? You could try starting it with the MAF disconnected.

I found six frozen fuel injectors during a prior '85/'86 resuscitation. The fuel pump was also seized upon arrival.

dukenukemx

The car sat for 10-15 years. I've actually made a thread about this a year ago on this forum. Was a lot of bad wiring from some other mechanic on the fuse panel that I was able to correct. In the end it was an improper kick down relay that prevented it from starting and the Porsche mechanic ended up rewiring the fuse panel to the point where the kick down was essentially disconnected. The guy didn't know if you just simply remove the incorrect kick down relay then it would start. But in the process I did replace the CPS, MAF, relays, and had the EZF rebuilt. The man that helped me with all that was Rich.

The only way I know the injectors aren't opening is because I can't hear them click. I put a screw driver on one with my ear on it and nothing. I hooked up a multimeter and while the engine is cranking I get .5v. If I spray starter fluid when cranking, the engine will run, which suggests no fuel. I'm not 100% certain the fuel pump works, but I do hear it click on when the engine is cranking. Next time I'll check for fuel pressure.

I'm starting to think I need to change all the injectors as well. Hopefully the LH module isn't screwed but the injectors look like rusty hell. I may just order a set of injectors and replace them for the hell of it.

Kiln_Red

The pump is probably seized. You can open up the fuel rail where the pressure gauge mounts to see if fuel weeps. I will place a clear paint mix cup over the end of the rail and crank the engine over to see if fuel is dispensed. The fuel pump should buzz pretty audibly if it is working. If the pump is seized then replace it, the fuel filter, and injectors. The sending unit is probably salvageable. They seize, but I have had good luck getting them freed up.

Before I would do any of that, I would drop the tank to do a rigorous cleanup. Replace all of the fuel lines and inspect the evap system, too.

What is your location? There could be a helping hand close by.

dukenukemx

That makes sense since the fuel pump relay also grounds the fuel injectors, and if the pump is seized then that might ground away the 12v going to the injectors. I felt the pump jolt on but not buzz when cranking. I'm going to check that out next week.
I'm in NJ but the car is in NY. The plan is to get it running and put it on a trailer and drive it to Jersey where I plan to vigorously restore it. This was the same plan I had last year but a lot of stuff came up. Same color as the one in your avatar but imagine it being burnt by sunlight for 10-15 years.

dr bob

The fuel pump relay supplies !!unfused!! battery voltage to the red-with-green-tracer side the injectors loop. Power supply to the fuel pump relay is a dedicated feeder that runs directly from the battery positive terminal clamp.

The injector grounding duty falls to the LH controller. When inspecting the injectors wiring with a DMM, it will appear that there is battery voltage on both sides of the injector loop until the LH pulls the brown-with-red-tracer side towards ground.

The easiest way to test for LH injection pulses is with a "noid light", a simple tool that fits between the injector wiring plug and the injector. The little LED is lit when voltage is available to the injector. Noid Lights are available at most good local parts stores, or arrive in a brown truck on $demand$.

Testing for correct voltages in the fuel pump relay socket is best done with a set of jumpers that extend the connections to where you can access them to test with a meter. Terminal 30 in the socket is connected by the dedicated feed mentioned above. Terminal 87 connects to the fuel pump via fuse 42, and to the parallel fuel injectors with no fuse. Remove the fuel pump fuse 42 to get accurate ohm meter readings in the injectors loop.

Bill Ball

I would examine the fuel injector electrical plugs. The wiring often gets twisted and kinked near the plug ends and the old, brittle insulation cracks, shorting the harness. The result of this at any of the injectors is that NONE fire, due to the batch fire configuration. Also, the same thing can happen to the wires inside the plug boot. With age, the boots and the gel inside them harden as well as the wire insulation. If the boots are hardened, the only way to remove them for inspection is to destroy them. I've found shorted wires inside these boots often when none of the injectors fire. It's probably time to replace all the plugs. Plugs and boots are readily available. And you can upgrade to quick release plugs that have wire clips that are easier to deal with and won't fall off like the stock wire clips.

dr bob

Note to your first post -- Testing low resistance values (like 7 or 8 parallel injector coils) means that the resistance in your test leads risks being a substantial portion of your total resistance measurement. Try touching the meter leads together to determine the contribution that test-leads and plugs play in your measurements. Let's say you have 1.5 Ohms in your test-leads loop. That would take your one-injector reading to 13.5 to 14.5 Ohms. The wiring diagram shows the injectors loops in a 4x2 parallel-parallel configuration, but the effect is the same. Your measured loop resistance at 3.5 Ohms, minus the 1.5 Ohms in your test leads, is perfect for the seven remaining connected injectors.

jpitman2

Op says the pump jerks when powered - to me that signals its jammed internally - BTDT myself. Try connecting revered voltage to spin pump backwards - worked for me - spat out something.
jp 83 Euro S AT 57k