88porsche928

I orginally had a question to dr bob about testing the connector to the LH Ecu here is what he said

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Test from pin 18 --in the LH controller connector--, not from a pin in the brain itself. Test with the battery disconnected. You are trying to determine if there's a short to ground in the wiring harness to the injectors.

The test method goes on to look at each bank of injectors for shorted wiring between the wires to the injectors. Each injector coil is about 16 ohms, so having four of them in parallel should give a reading of about 4 ohms. Less than that means there are wires touching each other between the protection relay socket and that particular group of injectors. It narrows down (a) what you are searching for, and (b) where you should look for the fault you found.

A few more questions have arised.
You said test from pin 18? Are the pins numbered? Also how do i test from pin 18? Do i put the positive on the pin and where does the negative go? Alright so which pins are for the fuel injector connectors? so doing this will narrow the possibilites down to 4 instead of eight? I understand your mehtod I need to unplug the lh ecu then the only thing i get is i need to test from pin 18, im not sure which one pin 18 is and im not really sure how to test it or what to look for. I think after working on this car for a couple years im going to write a book called "Fixing 928s for Dummies".

Gtaebr

"LH feeds power to the injectors via pin 18 in the connector. With the connector removed, you should test from 18 in the connector to ground and see an open circuit. If anything less, there's a fault to ground someplace in the injector wiring or in the ignition protection relay itself.

The other side of the injectors is split between 1-4-6-7, and 2-3-5-8 at the monitoring relay. Pull that relay, and test from pin 5 on the relay socket to pin 18 on the LH connector. The resistance may be somewhere north of a few ohms, but not a dead short. Test from pin 2 in the relay socket to pin 18 at the LH connector, and the resistance should be the same as you measured from pin 5 previously. If one of these is less (closer to zero or actually zero ohms) you have at least isolated the problem to one set. If pin 5 is low, look at injector connectors 1-4-6-7; If pin 2 is way low, look at 2-3-5-8 connectors for shorted wiring."

Landseer

Respecting of Tampa's advice and significant knowledge of course, but do be absolutely certain that you have an injector wire short, testing above, BEFORE carving on the harness.

There seem to be an awful lot of other things that can force a no-start or intermittent stall/no start.
Like unclean ground near the top of the bellhousing; bad ignition switch and so-on. (am fighting one myself and just pretty much ruled-out the injector wires.)

WallyP

OK - The problem is that either there is no power to the injectors, or the power is shorted in the injector harness.

Back to basics:
First thing to do is to go to the battery and carefully clean all of the connections, especially the medium-sized red wires on the positive terminal. Then check to make sure that Plug W in the Central Electric Panel is fully seated.

If that doesn't fix the problem, pull Relay XXV, the LH relay. Find Terminal 30, and check for battery power there. If there is no power, check the red wires again. If there is power, install a TEMPORARY jumper between Terminals 30 and 87.

If that doesn't fix the problem, go to the Ignition Monitoring Relay on the right kick panel, and with the jumper in the LH Relay socket in place, check for battery power on the red and red/yellow wires in Terminal 87. If there is battery power on 87, check for battery power on the red/green wire in Terminal A1 and the red/yellow wire in Terminal A2. If you have power here, you should have a glowing noid light on any injector.

Be sure to remove the temporary jumper in the LH Relay socket.

the flyin' scotsman

Hopefully this helps:

88porsche928

i decided to skip the multimeter part and cut on suspected bad boot open and the inner insulation of the two wires where cracked off I am assuming the wires where touching each other. im going to replace all 8 of them. I am would like to use ford ones becuase from what I read they are almost exact replacements for a low cost.

Mrmerlin

Ahh Wallys advice should be followed first ,as you might be correcting a problem that you dont have.
Simply replacing all of the injector connectors might NOT be the problem, go back to the start and follow Wallys instructions, He didnt take the time to type them so they could be ignored

88porsche928

ok thanks for the advice, but will the two wires that touch each other cause some strange results while further troubleshooting

Tampa 928s

We spoke on the phone and he said motor had been replaced!
Every problem with the inj circuit on the last three rebuilds has been a short. The lamp not lighting either means 12v is missing or it's shorted. If he unloaded the items I suggested and used a meter that should tell him if there is a short in the harness. I assumed he would do this first before the cutting He should be able to read the 12v on one of the connectors if the voltage is present.
Wally has a lot more knowledge and experience on this but his harness should be loose by now and can be tested.

88porsche928

i had a strong feeling one of the injector connectors where messed up, the fire was slightly burned so when i removed the insulation i found the bare wires could have been touching, i will continue to do more testing

88porsche928

i honestly believe theirs more then one problem with this harness, i usually have the worst of luck with cars. the passat i sold to my brother in law has the turbo blow out on him on the interstate and oil went every where along with black smoke.

Mrmerlin

on your car there are also 2 injector grounds at the back of the engine these both must be bolted to the block they are under the crank position connection

dr bob

The meter tests I shared are extremely definitive when diagnosing harness problems on '89+ cars. Did you find a short in the harness, an open circuit, or a short to ground? If not, it's possible to create new problems while 'fixing' the old harness, where no problems existed before.



Test procedure simplified:

-- With the ignition protection relay out:

A1) Ohms between LH connector 18 and relay socket terminal 1A should be about 4 ohms. Much more means an open in a connector, injector coil, or a broken conductor in the harness.

A2) Ohms between LH connector 18 and relay socket terminal 1A (same test...) should be about 4 ohms. Less than 2 ohm means you have an internal short between conductors in the harness. This is the damage you reported when cutting open that first connector boot.

B1) Ohms between LH connector 18 and relay socket terminal 1B should be about 4 ohms. Much more means an open in a connector, injector coil, or a broken conductor in the harness.

B2) Ohms between LH connector 18 and relay socket terminal 1B (same test...) should be about 4 ohms. Less than 2 ohm means you have an internal short between conductors in the harness. This is the damage you reported when cutting open that first connector boot.

C) Ohms between LH connector 18 and ground should be infinite. If they are less than 1 ohm, you have a short to ground on the LH side of the harness, and it could be at any injector.

D) Ohms between LH connector 18 and ground should be infinite. If they are around 4 ohms, you have a short to ground on the power side of the harness, and it could be at any injector. Proceed to E1 and E2 to narrow down where it might be.

-- E1) Ohms between protection relay socket at 1A and ground should be infinite. If they are less than 1 ohm, you have a short to ground on the power side of the harness, and it could be at injector 2, 3, 5, or 8.

-- E2) Ohms between protection relay socket at 1B and ground should be infinite. If they are less than 1 ohm, you have a short to ground on the power side of the harness, and it could be at injector 1, 4, 6, or 7.



*** Do these tests BEFORE you remove any of the injector connectors. The resistance values presume that you still have all the injectors plugged in. Each injector coil is real close to 16 ohms. Two coils connected is about 8 ohms, 3 connected is a little over 5 ohms, four connected is 4 ohms. On the '89, the harness is separated on the power side and is fed through those two contacts on the protection relay; with the relay removed they are connected only on the ground (LH brain) side, and to the brain through LH terminal 18. With that protection relay installed, the power sides are connected to each other through the relay contacts, and also to the heating coil on the oxygen sensor, even when the LH power relay is not energized.


PLEASE POST WHAT YOU FIND WITH YOUR METER.


--

88porsche928

thanks for all the information, its strangly raining like it does in florida in san diego right now.

dr bob

I generally don't work on cars for others. There are liability reasons and there are time commitment issues. My car is sitting next to a couple $thousand in parts, waiting for my time to do an intake and cam cover refresh, with chains and tensioners, shocks and springs, brkesm plus all the normal cleaninig stuff. I did take a rainy-day break and start the exterior clean and wax, on the painted parts. You get the idea. Your car is a potential black hole that might never be able to leave. Plus, even at half of my normal billing rate, you wife won't be able to cook fast enough...

There really is a logical scientific method to troubleshooting. I used to teach a course in troubleshooting. Anyway, there are a few critical things needed for the engine to run: Spark, Fuel, and Compression. 928 fuel problems, except for failed pressure regulators, failed connecting hoses, and plugged fuel filters, ALWAYS fall into the electrical category. Going back to that scientific method thing, if you are searching for no fuel, start at the fuel pump to see if it's running. If it isn't, find out why. If it is, put a pressure gauge on the front of the right side (Passenger side on US cars) fuel rail and make sure you can see >50PSI when cranking with the starter. Use logic and good sense to test for and eliminate possibilities.

Be as minimally invasive as you can be when testing and troubleshooting. It's too easy to do damage on systems you are testing if you aren't careful.

Using logic in our problrm-solving mission, we should really be looking at things that get damaged when an engine is replaced, and more importantly what might have worked OK then failed. You diagnosed with the Noid light, and it didn't light at all while cranking the engine on the starter. Wally gave you instruction on testing for power at the protective relay, and some hints on how the power for that feeds through a dedicated red wire attached to the battery positive terminal. WHAT WERE THE RESULTS OF THAT TEST? Is there power there when the key is in the run position?

I gave you some very specific testing instructions for the injection harness, using an ohm meter, testing from the passenger's side footwell. The LH brain is the box closest to the door, on that bracket normally hidden by a carpet cover on the right-side kick panel. Connector is retained by a locking latch. Disconnect the battery ground BEFORE you open the connector latch. All of this harness testing is done with the battery disconnected. The Protection Relay plugs into a socket mounted on the bottom of the frame that holds the two engine controllers. It's undr the EZK ignition brain, socket points towards the driver's feet. Do the meter tests I described and POST THE RESULTS!


Some other thoughts:

You had a local mechanic or shop do the engine replacement, right? Do they warranty their work? If so, you need to let them take a shot at fixing the problem before you do any more work on it and do any damage.

If you get to the point where you can't seem to get anywhere even with the coaching from the list, you can either host a troubleshooting party with some SD locals, or take it to a good repair place for a look. Bill Swift is down there, and is good at this stuff from his racing years with AAR. I can't speak to his availability these days though. Offer beer and pizza and get a gathering of locals. Repair places: Problem with any repair place is that you do have a potential black hole as far as they are concerned, so you'll be handing them a blank check and saying "fix it!". There are probably some 928-saavy shops. get a recommendation from one of the locals, maybe Randy V.

Greg Brown is the best 928 wrench I know, at Precision Motorwerks in Anaheim. He isn't cheap, but is the best value around when it comes to stuff like this. It's a 40-mile shorter tow than coming up to Glendale, and his driveway isn't steep at all. He's right by the 5, 57 and 91 freeway, close to 928 International. Plus he keeps business hours and his wife actually makes him work on the cars.