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I don't see mention of the braided cable ground from chassis to rear of engine, passenger side accessed from underneath. This is a major ground, is bare, not encased in rubber insulation.
For starters (pun): Why are you using optimum batt? I would return battery and connections back there to stock including a new battery ground.
its what the idiot clown had and to replace to original power line is a PITA, but I might have to. I need to check the strap. It’s on my short list tomorrow.
Originally Posted by dr bob
I'd also look hard at the original battery ground strap shown in your picture. It's a known weak point, although it usually shows up with charging and voltage maintenance symptoms. In your case, a weak battery strap means the whole primary system is floating above chassis ground while the starter is cranking. Watch jump-start voltage to chassis while cranking to help some with the diagnosis. I upgraded to a new 2ga tinned-braid strap and a lot of low voltage symptoms wandered away. Our favorite vendors carry them I think.
might just put a new one to eliminate the issue. I think I have another one that is good as well. Will look.
The original ground strap is bare copper braid, covered/masked by the plastic. Meanwhile, the spec Group 48/H6 battery has a dedicated vapor vent hose connection, intended to route fumes out of the battery well. Very few are actually plumbed correctly after the first battery change, so fumes from charging including some acid vapor carryover will attack the exposed copper braid. Strip off the plastic and get a good look at the brown and green remains of the copper braid before you decide to put another similarly-afflicted used part there.
The go-to replacement is a marine piece, heavier braid and with tin plating on the copper strands that make up the braid. The plastic sleeve is there to maintain isolation from the chassis when the chassis end of the cable is lifted, else serves no real purpose beyond maybe some mechanical protection where it passes under the edge of the lid.
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The minor positive terminal connections include dedicated feeders for the cooling fans, plus the injectors, fuel pump, injection and more. Clean (to shiny) and snug each of those wire connections by the battery positive terminal, and protect them with a bit of Vaseline after the clean-and-snug.
928 Sage Jim Bailey preaches "relay-relay-relay" as an early step in diagnosing odd staring and running conditions. The fuel pump, LH injection and EZK ignition relays top the list, with the X-bus relay close behind. Get four top-quality Bosch 53b-type relays for this duty, and you can forget about them for another dozen years.
Clean the battery post connections to shiny, and snug them up. Protect with a little Vaseline.
Go ahead and plumb the battery vent hose to the outside, as originally intended. Some 1/4" plastic drip irrigation tubing from the gardening bench works perfectly for me. This won't solve a non-start issue, but will slow the deterioration typical in non-vented battery wells.
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Clean the critical ground points for injection and ignition. Do all the grounds, really. Focus will be on the grounds at the rear of the block, accessible after removing the air cleaner housing. Also the grounds above the CE panel in the passenger's footwell. Your workshop manual has a handy 3-axis reference to ground point locations in the car. Cleaning ground points is part of the annual electrical maintenance protocol necessary to keep the electrons flowing properly. Avoid a lot of mysterious symptoms by performing this service religiously. Look on the 928 Specialists (www.928gt.com) website for the full documentation of this critical procedure.
The original ground strap is bare copper braid, covered/masked by the plastic. Meanwhile, the spec Group 48/H6 battery has a dedicated vapor vent hose connection, intended to route fumes out of the battery well. Very few are actually plumbed correctly after the first battery change, so fumes from charging including some acid vapor carryover will attack the exposed copper braid. Strip off the plastic and get a good look at the brown and green remains of the copper braid before you decide to put another similarly-afflicted used part there.
The go-to replacement is a marine piece, heavier braid and with tin plating on the copper strands that make up the braid. The plastic sleeve is there to maintain isolation from the chassis when the chassis end of the cable is lifted, else serves no real purpose beyond maybe some mechanical protection where it passes under the edge of the lid.
Yup. Decided just to go with new for the battery strap and the chassis to the engine. Tired of chasing this ghost, so off to new parts I go.
Originally Posted by dr bob
The minor positive terminal connections include dedicated feeders for the cooling fans, plus the injectors, fuel pump, injection and more. Clean (to shiny) and snug each of those wire connections by the battery positive terminal, and protect them with a bit of Vaseline after the clean-and-snug.
That is the plan, I have already yanked the old PO crap out and I am planning to go get a new battery. The nice thing about the optima is that last 6-8 years in AZ where stock batteries give me at most 2.5 regardless of the maker. I run them in my 79 toyota pickups and have for years. It is why I did not bother changing it in my Gray 928, but at this point I am going full stock at every turn.
Originally Posted by dr bob
928 Sage Jim Bailey preaches "relay-relay-relay" as an early step in diagnosing odd staring and running conditions. The fuel pump, LH injection and EZK ignition relays top the list, with the X-bus relay close behind. Get four top-quality Bosch 53b-type relays for this duty, and you can forget about them for another dozen years.
Its the first thing I check every time. I have put in new and swapped for known good used. Not change on this side. Since I know this could be multiple contributors. I am just going to go by 4 new Bosch 53bs.
Originally Posted by dr bob
Clean the battery post connections to shiny, and snug them up. Protect with a little Vaseline.
Will do once I have the new battery and ground strap
Originally Posted by dr bob
Clean the critical ground points for injection and ignition. - Done
Do all the grounds, really - Yup, Done, finished this AM. The two on the towers were covered in crap.
Focus will be on the grounds at the rear of the block, accessible after removing the air cleaner housing. - These were good where Dan did the engine a couple years ago.
Also the grounds above the CE panel in the passenger's footwell - Yup. I had done the smaller group of the wires, the bigger group needed attention.
Originally Posted by dr bob
Cleaning ground points is part of the annual electrical maintenance protocol necessary to keep the electrons flowing properly. Avoid a lot of mysterious symptoms by performing this service religiously. Look on the 928 Specialists (www.928gt.com) website for the full documentation of this critical procedure.
Did not find the link on 928 specialist, but I know the drill. Not new the 928 by any means, but still struggling to chaise this ghost. Gladly retracing all steps I have taken to just double/triple check. I have put less than 5K on the clock in 3 years because it has not been worth fighting this until now before it warms up again and the symptom mostly goes away. Cold this AM and she would not fire up. I should have all the new parts in next week (ground straps and Bosch made 53b).
Thank you for the help and keep the ideas coming. I have swapped LHs and EZKs in the past chasing this as well, but not against doing it again to try to nail this down if you think it would help.
Cold being what seems... and I mean seems only, to be a driver so all the relay and ground tasks seem to be the right place to play.
Parts in, installed and all ground points clean. 3 days of cranking up, no issue but it has not been significantly cold. I will keep hoping this is solved.... but I have seen this movie before.
This is what I follow when I chase this type of problem courtesy of Rich9928p:
928 Model year 1987 – 1988 System No Start Diagnostics (later model diagnosis is similar, consult the wiring diagrams for specifics):
Diagnostics should be only be performed by a trained technician. Always check for proper relay functionality and power/ground connections before undertaking further diagnostic testing.
a. Testing the engine RPM sensor. The EZK spark control is the system master, if engine rotation signals are not provided to the EZK, spark will not be generated and EZK will not provide a turn-on signal to the LH Jetronic fuel injection system. The RPM sensor input to the EZK is from an inductive RPM sensor. Inductive RPM sensors generate voltage so a VOM can be used for testing the sensor. EZK pins 23 and 6 are connected to the RPM sensor; pin 6 is ground and is connected to master-ground pin 18. EZK pin 24 is the shielding of the sensor cable and is connected internally to pin 18.
b. The Hall Effect engine position sensor can be tested with an LED tester. The EZK provides the power supply for the Hall Sensor at pin number 5 (12V). The EZK provides a 5V level at pin number 22, which the Hall sensor can pull down to ground. Pin EZK pin 22 is the "hot" signal cable and therefore is shielded. The cable shielding is connected to EZK pin 4, and pin 4 is connected internally to master-ground EZK pin 18.
c. The EZK spark module provides the signal to turn on the LH fuel injection module; it is the circuit from EZK pin 13 to LH control Pin 1. Check for continuity, if the wire is broken or the connection isn't clean, the car will not start.
d. The circuit from LH Pin 20 goes to the Fuel Pump Relay XX pin 85, check for continuity between these two points.
e. From the Fuel Pump Relay XX pin 87 the circuit passes through fuse 42 then to the fuel pump motor. Pull the fuse, check the fuse, and clean the connectors. Check the continuity of this path. Bridge Fuel Pump Relay XX socket points 30 and 87, the fuel pump should run.
f. There should be 12V (nominal battery voltage) at the fuel pump and LH relay pins 30 at all times. This same circuit connects to LH connector Pin 4, check for 12V there too.
g. The LH relay XXV pin 85 connects to LH connector pin 21, check for continuity between these two points.
h. The LH connector pin 18 connects to all the fuel injectors. The LH functions as the switch from the fuel injector to ground. With the LH relay jumpered between pins 30 and 87, there should be 12 V at pin 18. [Model Year 1989 and newer 928s have a spark monitoring system, consult the wiring schematics and workshop manuals.]
i. Power and Ground connections are key points to inspect and clean. The LH is grounded via Pin 17 to chassis ground point VIII. Use an Ohm meter to measure the resistance between LH connector Pin 17 and a chassis ground point. It should read as close to zero as possible. If it reads a high resistance, a corroded ground connection at MP VII or cut in the wire could be the problem.
j. If all of these items check out OK, and the fuel pump is functioning, then potential problems could be:
- The system fuel pressure is too low; fuel filter or pipes are restricted, fuel injectors are not functioning correctly
- The LH Jetronic fuel injection module is not functioning correctly and requires a rebuild.
Have you ruled out the ignition monitoring relay? Is it still there or have you or PO bypassed it?
Thank you sir. Something else to add. I waited until the car was in the sun (the engine area) for a while and then tried again. Fired right up.
There is a significant thermal component to this issue that is making it harder than normal to chase. Maybe try to replace the temp sensor next? Or other signals that can be impacted by the car being cold?
Your list is good. I a going to try that as well on a cold morning. Might have to test cold and warm to see if there are differences.
I'm following this thread with interest: Last weekend I sat down and replaced all the rubber rings/seals on my 86.5 engine. Car would have flat spots on acceleration and would sometimes stumble on acceleration but would always start on the first or second crank. Found that several plugs were loose (finger tight) and one of the seals had been folded under and improperly secured at one point so was probably leaking air.
Car now has no flat spots, plenty of power, *and* when cold will crank with nothing the first time, will crank, overspeed, and die second time, and will crank and start third time. When warm (even after sitting for 15 minutes) starts right up every time on the first crank. So fixing the leak seems to have made the car more grumpy in some ways. Weird.
I skimmed through all the suggestions...so I'm not sure if this was mentioned but....if there is a (randomly occurring) short on any of the electrical leads coming out of the fuel injectors plugs...the car will not start.
What condition are this leads in? Check the last couple of inches of wire before each of the eight injector plugs
K
I skimmed through all the suggestions...so I'm not sure if this was mentioned but....if there is a (randomly occurring) short on any of the electrical leads coming out of the fuel injectors plugs...the car will not start.
What condition are this leads in? Check the last couple of inches of wire before each of the eight injector plugs
K
Had not even considered that. Dan redid them with the new engine... but then again this issue started then. I wonder if there is something there. Will check in the AM
03-09-2019, 01:08 AM
