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Join Date: Nov 2002
Location: Cincinnati, OH
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1983 928S Not Starting

trying to troubleshoot a no start condition. Engine cranks but nothing. Just some background. This car has set for at least a year in my garage. ran fine before. parked it due to brake issues. brakes are all back together now and ready to get it back on the road.

I went through some of the basic troubleshooting. pulled a couple spark plugs and they look dry. So I figure fuel delivery problem. I took apart the connector on the fuel rail and as soon as i loosened the connector fuel was coming out so I assume fuel is making it to the rail so pump and filter is good. I am thinking maybe an electrical issue with the injectors. How can I test to see if the injectors are running and delivering fuel? anyway to test their electrical connection to see if they are getting triggered? Manual says relays are a common failure. Anyway to check that? just looking any ideas of what I should look for to narrow down the search for the point of failure.

thanks.
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Old 10-06-2018, 12:25 PM
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just an update...

i have tested voltage at pin 30 on the relay, i get a solid 12V. I tested pin 10 and 29 on the L-Jet connector, they show 12V. I tested both pins on the injector connector, 12V there too. The grounds on the L-Jet connector, pins 5,16,17,35 and they all show 6 ohms. not sure if that is typical. But i don't think that is high enough to cause a problem and the grounds are good. Probably should clean them at some point. I went and bought a NOID light set and put it on the injector connector, I get nothing. No pulse, no solid light, nothing. I assume this means the L-Jet isn't signalling the injector. So my best guess is some sensor is out and cutting off the L-Jet. now i just need to figure out how to test each sensor to make sure it is working.
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Old 10-06-2018, 04:06 PM
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short Cuts -

Hey 9er - I've found the trick to breathing life back into a previously known runner is to :

1 Fresh Fuel Helps
2 Check Air Filter Housing for Mouse Nest
3 Fully Charge Battery + 2nd Battery to Jumper Post (Assures sufficient Power to FI Computer and Ign Coil During Hard Start)
4 Pull FI Computer Relay (# 16) and Fuel Pump Relay (# 17) Fuse/Relay Panel
5 Jumper Both Relay socket pins 30 and 87
6 Clean Ground Wire On Side of Passenger Cam Cover (Grounds for injectors - Noid Lite)
6 Key to "ON" Listen for Fuel Pump to run- Allow Fuel Rails to Pressurize
7 Start her UP

If these short cuts don't have her running - naturally there are many more things to check. Do a search on "928 Porsche No Start".

Porsche 928 cranks but wont start

https://rennlist.com/forums/928-forum/600089-82-928-won-t-start-fixed.html

Good Luck, Michael.
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1986 930 - "Well Hung"

Last edited by JK McDonald; 10-06-2018 at 05:44 PM..
Old 10-06-2018, 04:53 PM
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Progress -

Hey 9er - How are things going in getting your car started ? Did you try using two batteries while jumpering power directly to the FI computer and Fuel Pump with their control relays pulled ? Did you get your injectors (NOID Light) firing ? The +12 power supplied to the computer also connects directly to the pos (B+) side of all the injectors. The computer supplies the ground pulse to the injectors in pairs triggered by the Tachometer signal. This is usually a reliable input but you might check to see that the Tach pulse is on the FI Computer connector at pin 1.

Sometimes there are just enough voltage drops along the wiring from the single battery in the rear to the key switch, ignition unit, injectors and the computer that she just wont run. Using two hot batteries will often initially get you over this "Voltage Loss" hump to get you started.

Ever so often my Miss Purdy gets cantankerous after a long spell of hibernation or bad weather and I have to go through the wiring - cleaning the battery terminals, electrical wiring connections and all the major and minor grounds.

If you continue to have starting problems don't hesitate to ask for help. There are lots of long term ownership and many years of accumulative experience on this site.

Good Luck, Michael
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1984 928S - "Miss Purdy"
1987 911SC - "Frau Helga"
1986 930 - "Well Hung"

Last edited by JK McDonald; 10-09-2018 at 04:10 PM..
Old 10-09-2018, 03:44 PM
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To jumper the fuel injection relay requires a three pronged jumper. The power from terminal 30 must go to each of the 2 terminal 87's. The diagram on the side of the relay shows which terminals are which.

The FI relay jumper will not work without that third leg.

Make sure to either remove the fuel pump jumper or place an on-off switch inline to turn the power to the fuel pump off when you are not testing. Leaving power to the fuel pump is to invite a leakiy injector to fill up the cylinder with fuel and chance hydrolocking the engine.

Best idea is remove all the jumpers when not directly testing the systems.
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Old 10-11-2018, 09:45 PM
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FI Power Jumper -

Thanks Stepson - A while back I started soldering in a permanent jumper on the under (wiring) side of the socket for Relay XVI between the two 87 output terminals. After finding a couple of flaky/intermittent new (OEM) internal relay contacts - the added soldered in jumper assures long term reliable power distribution to both the Computer and all the Fuel Injectors. I've worked on so many different model FI cars I should have relied on my 928 notes and modified schematic instead of my memory when offering troubleshooting suggestions.

Thanks again - Michael
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1984 928S - "Miss Purdy"
1987 911SC - "Frau Helga"
1986 930 - "Well Hung"
Old 10-12-2018, 09:50 AM
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Michael,

I prefer to think of assistance in a forum as a "team" of people offering help. You had already posted a lot of great hints and things to check. My post just expanded on a tiny part of what you previously posted.

If the OP was not aware previously that a three legged jumper was needed to make the FI work, the correct diagnosis of his problem might be delayed.

In addition, I think it's an important safety note to either switch off the jumpers or remove any jumpers from the CE panel to prevent additional damage above and beyond what the OP may be experiencing currently.

Keep up the good work Michael, you make the "team" better.
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John Curry (Drift King) 928OC member
Grand Prix White 1994 GTS AT (The GTS)
Cobalt Blue 1989 S4 AT (The Blue Car)
Indishrot 1984 Euro S AT (The Stepson)
Black Metallic 1984 Euro S 5 speed (The Schwartz)
Old 10-12-2018, 08:58 PM
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