1982 928 no injector pulse.

[mk1mike]

Resolved. I am a european car mechanic and i have done extensive troubleshooting already. of which i will outline below

after hours of searching and reading on this forum and others, trying and fixing many things, i am here. it appears no other threads about this have a solution and are quite old

this car (1/82) was purchased a few weeks ago with another 928. I drove this car on to the truck with no issues when I picked it up.

I also have an 82 parts car that i am robbing stuff from, but the car is not a known quantity, i have never heard it run.

Now it does the typical start and stall. will run as long as you spray ether in the intake.

first thing i did was check fuses (twisting them all) and jump relays. the fuel pump and the fuel injector relays. I have battery voltage here. the pump runs, power is getting to both #87 terminals on the injector relay socket. no change

next i evaluated grounds, and relocated a few in the engine compartment, i also added supplemental grounds

next, the dreaded 14 pin connector. the entire starter/alternator harness was trashed. i built a new harness and installed it. i also replaced the "green wire" with one from the parts car . no bueno

next i pulled the ecu, disassembled it, found nothing amiss after close examination of the boards. i then also tried another ecu from the parts car. nope

I then pulled up the carpet in the p/s footwell and split the harness and inspected it as well as the rest of the wiring going to the fuse board, all in very good shape with no signs of moisture

i may be forgetting other things i have done, as i am at my wits end and ready to give it a "2 and 1" solution.

for the number of threads i have found outlining this exact issue, i am surprised no one has found a solution, or at least had the courtesy to post it after finding it. I have a few friends that are long time porsche mechanics, and i have also been following their advice along the way, but for them as it is for me, it is not a happy day when one of these comes into the shop. out of all of the air and watercooled porsches i work on, i dread these electrical nightmare 928s the most

[stepson]

1. If there is a short in the injector wiring harness, it will kill all the injectors. Check for a short there.

2. The green wire that you installed is an unknown commodity, ie., you really don't know if it's good or not.

3. Check the part number on the fuel injector relay. I know you've probably already done that, but check again. I had an '83 that SHOULD'VE been running a month before it was, and realized in the shower one morning that I hadn't check the relay. Sure enough, wrong relay no start. Changed relays, ran like a top.

[Danglerb]

Originally Posted by mk1mike

out of all of the air and watercooled porsches i work on, i dread these electrical nightmare 928s the most

That pretty much is the only reason many of us can afford to buy them.

I've seen many 928 offered for sale that "run on ether", so the fix according to the seller who hasn't gotten it to run correctly after months of trying things has to be something simple.

Very often it isn't fixing one or two things, its bringing all the PM up date. Cleaning all the electrical grounds and contacts, replacing bad wiring, chasing down all shorts and opens, replacing relays and switches etc.

Put a NOID light on one of the injectors, check the voltages at the injectors.

[928gene928]

Mike,
I have chased a similar situation with my 1980, checking all the things you mentioned, and replacing the green wire etc.,and ultimately discovered the problem was a relay.

[mk1mike]

i jumped the relay. i also tried another relay from the parts car p/n 92861511900

[mk1mike]

I found a bit of trouble shooting advice on rennlist

If you're having starting problems, this information could help.
This is how the system works. AFC [Air Fuel Control] relay XVI pin 30 always has 12 Volts regardless of ignition switch position. The AFC relay switches between pins 30 and 87, and the 12V at pin 87 then goes to the fuel injectors.

a. Measure voltage at pin 30?
-- If 12V present, next (for all test cases below, have the ignition turned on) is there 12V at pin 87? If yes go to (b)
-- If no, check the connection at the battery. A direct cable connects the battery to the AFC relay pin 30. Is there 12V at AFC relay pin 85? If there is no voltage, the ignition switch could be bad or the path between the ignition switch and AFC relay has an open or short circuit.

b) is there 12V at the fuel injectors (pick any one to check)?
-- If yes, this says that your problem could be with the fuel injection "ground" path. Go to (c)
-- if no, there is a wiring problem between the AFC relay and fuel injectors.

note: it may be confusing to see 12 V at both sides of the fuel injectors. The reason is when the engine isn't running, the circuit is open from the L-Jet module pins to ground. So with very little current flowing there is no voltage drop across the fuel injectors.

c) is there 12V at L-Jet connector pin 10 and 29?
-- if no, there is a wiring problem between AFC relay pin 87 and L-Jet connector pin 10 and 29.
-- If yes, check grounds for the L-jet controller. L-Jet connector pins 5, 16, 17 and 35 should have a very low resistance (via ohm check) to ground. For this check, set your VOM to Ohm mode and measure the resistance between the L-Jet connectors and a ground point on the car. If the Ohm reading is high to infinite, there is a wiring or connector problem with the ground points.

If all tests show OK, the L-Jet could be bad.

L-Jets are pretty reliable systems. As with any other system, the majority of problems in no-start or hard start situations are bad or non-existant signals from sensors or no voltage due to relays.

[mk1mike]

I do indeed have 11.xx volts at the injectors. so according to this i may still have a ground issue

[mk1mike]

so. i followed the "flow chart", I was pretty excited actually, as it felt i may be homing in on the problem....was






so everything checked out as it it should. i have battery voltage at pin 10 and 29

and i have zero Ohm resistance at pin 5, 16, 17, and 35. it only leaves the relay right?? hard to believe both the relays i have are bad, and that would then lead me to believe it is not possible to jump 30 and the two 87 pins and have any results

I ordered a new 92861511900 relay. i am not optimistic

its almost time

[JK McDonald]

Hey Mike, I think you are following a logical L-Jet troubleshooting sequence and from your description of testing the wiring, grounds and jumpering past the power relay socket, it sounds like you have verified all the major potential problem areas.

At this point you might verify that the "Engine Speed Signal" from the Distributor/Electronic Ignition is reaching the computer on Pin #1. This signal is used to alternately rotate/apply the pairs of injector grounds. Like Danglerb mentioned - a quick test is to unplug a couple of the fuel injectors and attach a NOID TEST LIGHT to each of their electrical connectors. While the starter turns over the motor, if the computer is correctly receiving the "Engine Speed Signal" you will see the NOID LIGHT flash at each connector.

Good Luck, Michael

[Landseer]

Please say more about relocation of engine compartment grounds, specifically which grounds and where are they now connected. Search for a pelican 928 thread " Ground cleaning, 16 v euro" for pictures. The ground points on the cam cover itself described in this thread are the important ones. On your car, one is buried under the valve leading from the air pump. One ground is near the O in Porsche cast onto the passenger cam cover, the second is near the H. Crucial as engine electronics ground to these on mid year 16 v cars, both for Ljet an LHjet (Euro) versions


Ljet needs pretty full battery charge and ability to deliver it to the car. Ground straps themselves have become notorious for hidden failure. They ohm-out with no resistance, but no longer have enough current flow capacity to pass enough power. Replace, you can use an Advance Auto round ground strap, at least to remove it from equation. Believe it, it is real. Can sometimes be seen as 13V or so on the battery, and 11 or less volts from if you remove the ground strap and use a DVM to measure current from neg terminal to a convenient ground such as top of shock tower at nut/bolt.

Long shot issue --- There appear to be a pair of final amplifiers within the Ljet brain box, each responsible for 4 injectors ( I forget which four go with each amp). With a noid light, it is possible to see 4 fire, and 4 not, as I did., or none fire. I found it during last-resort exploratory surgery on the brain. One of the amps had a screwed-on wire connector leading from the circuit board of the brain to the amplifier. It was corroded. similar to 944/951, brain is mounted in a location subject to moisture ingress. About the only thing a layman can service inside Ljet brain is these wire connections, by simply removing the outer metal cover. ( Rest is not really visible / the brain has two circuit boards facing each other such that you cannot easily do a common solder reflow job on other parts of the brain without electrical disassembly.)

On my ljet 84 cleaning those connectors solved my pulse problem.

You realize that jumpering the ign relay requires a three ended wire, right? Ive done this many times.

Can you post some detailed pics of your 82 CE panel?

Just some thoughts.

See also the last few posts of this thread--major troubleshooting ended in discovery that injectors gummed up, an obvious issue frankly.http://rennlist.com/forums/928-forum/858623-chasing-a-no-start-1988-s4-manual-updated-3.html

[mk1mike]

thanks for the replies. the one thing i indeed did not out line is where i relocated grounds, everything else asked about, i did, such as my inspection of the ecu, and jumping the injection relay. the grounds that attach at the front of the cam cover i relocated to an open hole nearby, since the thread insert at the original location had broken free. as for the other grounds, i cleaned them, and also added aligator clip leads to supplement

i have already verified that i have no injector pulse, w a noid light

I received my new genuine porsche (made in china...) injection relay, it did not change anything the p/n on the new relay is 92861511901. the original relay is 900. i dont know if this makes a difference, i have already complained to the seller, since he advertised it as a 92861511900 relay

[mk1mike]

injection relay jumper

[mk1mike]

ground relocation to water neck

[mk1mike]

Originally Posted by JK McDonald

Hey Mike, I think you are following a logical L-Jet troubleshooting sequence and from your description of testing the wiring, grounds and jumpering past the power relay socket, it sounds like you have verified all the major potential problem areas.

At this point you might verify that the "Engine Speed Signal" from the Distributor/Electronic Ignition is reaching the computer on Pin #1. This signal is used to alternately rotate/apply the pairs of injector grounds. Like Danglerb mentioned - a quick test is to unplug a couple of the fuel injectors and attach a NOID TEST LIGHT to each of their electrical connectors. While the starter turns over the motor, if the computer is correctly receiving the "Engine Speed Signal" you will see the NOID LIGHT flash at each connector.

Good Luck, Michael

i have not checked pin one, would this then verify the condition of the "green wire"? this is the sole source for rpm signal correct?

[Danglerb]

I don't like the use of the water bridge as a ground point, but it might be ok.

[JK McDonald]

Hey Mike, You are right in assuming that the Green Wire between the Distributor and the Transistorized Ignition Unit is also used by the Fuel Control Computer to Fire the Injectors. The Shielded Green Wire initially carries the Hall Sensor Pulsed Signal from the Distributor to the Ignition Unit representing the firing point for each spark plug. Aside from the Green Wire Signal - to Ignition Unit - driving the High Voltage Coil, the Ignition Unit also sends out a secondary pulsed signal to tell the Fuel Control Computer and the Tachometer that the engine is turning over.

If for some reason the Fuel Computer does not know the engine is turning, it will naturally not send out the timed ground signals to the injectors. It sounds like you are getting close to locating your fueling problem. Like many owners of an assortment of orphaned Porsche we all must remember the appropriate "Theory of Old Porsche Maintenance - With Enough Time, Money, Grief and Heart Burn, you too can maintain a 928"

Good Luck, Michael

[mk1mike]

Originally Posted by Danglerb

I don't like the use of the water bridge as a ground point, but it might be ok.

why wouldnt it be?? explain please... its certainly a far better location than where they were...
all of these ground paths have been verified by testing their resistance

[Mrmerlin]

water bridge is isolated from ground with corrosion and O ring seals,
use the cam towers for grounding

[mk1mike]

Originally Posted by Mrmerlin

water bridge is isolated from ground with corrosion and O ring seals,
use the cam towers for grounding

hmm, thats interesting, since i have checked the grounds, (the relocated ones specifically) with my multimeter, and they all check out as of now. but i will find another spot for them... truly an awful car i hope i never have to work on another!

[Landseer]

Multimeter for grounds is tough because they can read zero resistance at that minor test current but be unable to pass actual working level of current. Relocate them back to both locations on cam cover.