Only sparks once...
08-19-2011, 12:25 AM
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Racer
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Only sparks once...
85 928 automatic US model. When I bought the car it ran and drove. We have driven it less than 10 miles. When we looked at it before we bought it started right ran well. You could turn it off and it would start no problem. When time came to get it off the trailer it started but took quite a while to get it started. Since then it has gotten progressively harder to start. Once you get it started if you turn it off it won't restart for a couple of hours. Yesterday we drove it home from our storage building and it was extremly hard to start, put in the garage and now it wont start at all So tonight I put new plugs in it and still no start. I cleaned the ground strap in the back ( wing nut ) also I found that the ground on the back of the drivers side distributor was not connected, the connected was broken. I replaced the ground and still no spark. But I find that if you pull a plug to test for spark that each plug will spark 1 time only then no spark. Any ideas? I have worked on and owned 911's for years but have alway loved the look of a 928. A 928 was the first Porsche I had ever driven! Any pointers would be great. Thanks Paul 
08-19-2011, 12:55 AM
#2
Inventor
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Does the engine spin quickly with the starter?
Could be as simple as an old battery. If the voltmeter shows less than 10 while cranking the ignition/injection computers won't turn on.
Worst case is thrust bearing failure. Have you checked/released the flexplate clamp?
It may need a new crank position (reference) sensor. (Under the airbox.)
Could be as simple as an old battery. If the voltmeter shows less than 10 while cranking the ignition/injection computers won't turn on.
Worst case is thrust bearing failure. Have you checked/released the flexplate clamp?
It may need a new crank position (reference) sensor. (Under the airbox.)
08-19-2011, 01:44 AM
#3
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Thanks for the quick reply, I have installed a new battery, cranks over normal and I have not checked the flex plate. I will save that for this weekend. I was leaning towards the sensor, would that cause it to spark only once?
08-19-2011, 02:11 AM
#5
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Key switch will fire the ignition while in start mode, then not spark anymore. Pretty common. Roger has key assemblies for your car.
08-19-2011, 08:55 AM
#7
Drifting
Ever check the distributor cap points and all of the wires to insure they are in tight? Ignition coils clean and connected to the distributor. Is fuel getting to the cylinder?
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08-19-2011, 10:54 AM
#9
Rennlist Member
The 85 was the first year for the 32V engine to be stuffed into the engine compartment.
The wiring harness is also stuffed around and over the engine. With age and heat cycling, the outer harness embrittles. Some of the Bosch sensor ends degrade. Corrosion attacks ground points for the brains / sensors / accessories.
So many cars got parked for intermittent electrical problems. So many are sold-off (hopefully they run the day somebody comes to see it). Isolated troubleshooting is not generally easy, nor lasting even if you get it running. Because at this age, in my experience rescuing downed cars, there are layers of light maintenance that are due and that interact to foil troubleshooting.
Its a great thing. Kills their value. Puts them in our hands.
Usually, all a person needs to do to revive one of these cars is cycle-through the inspection, cleaning and replacement of the basic electrical stuff.
So, everybody has given you a quick-check item above --- the " if it ran yesterday, tweak something small to make it run today" approach.
Now its probably time to engage at the next level and punch-list the electrical system. And its the perfect time to change the fuel lines, which is numero uno refresh item on any one of these cars.
So, bed the car down for week or two.
Disconnect battery.
Remove and polish clean the CE panel electrodes, replace all fuses with new, replace 10 #53 relays with new, and polish the other accessory relay contacts (too expensive to replace all, not usually needed).
Pull air cleaner and box off. Look at the very back base of the valley, there is a bracket that spans across the back of the V of the engine. One each side is a ring terminal with mission-critical computer and sensor grounds. Polish with Dremel wire brush.
I'd replace the mission-critical CPS and inspect the MAF plug under the boot for twisted exposed wire shorting.....
The coil ground wires are simply for radio noise supression, but you were on the right track there.
Fully disassemble and carefully clean / maybe replace the 14 pin connector on the inner pasenger fender. Unscrew the jump post 11mm thing and clean the positive wires under it.
Under / behind that stuff, on the inner fender, is another ground wire / ring terminal. Its for the final stage ignition amps. Clean.
Now hit the coil ends (they corrode up inside). In fact, remove the coils (very painstaking/tight) and clean inside the ends. Order a $350 OEM wire set to replace the coil and spark plug wires --- two bad coil wires will take the car down. Known issue.
Clean the engine strap ground from block to frame, under car, passenger side.
There are other things, but get your car to a baseline first with this stuff. Don't forget the fuel lines, the car can burn so fast you wouldn't believe it.
Once running you will be amazed by it.
The wiring harness is also stuffed around and over the engine. With age and heat cycling, the outer harness embrittles. Some of the Bosch sensor ends degrade. Corrosion attacks ground points for the brains / sensors / accessories.
So many cars got parked for intermittent electrical problems. So many are sold-off (hopefully they run the day somebody comes to see it). Isolated troubleshooting is not generally easy, nor lasting even if you get it running. Because at this age, in my experience rescuing downed cars, there are layers of light maintenance that are due and that interact to foil troubleshooting.
Its a great thing. Kills their value. Puts them in our hands.
Usually, all a person needs to do to revive one of these cars is cycle-through the inspection, cleaning and replacement of the basic electrical stuff.
So, everybody has given you a quick-check item above --- the " if it ran yesterday, tweak something small to make it run today" approach.
Now its probably time to engage at the next level and punch-list the electrical system. And its the perfect time to change the fuel lines, which is numero uno refresh item on any one of these cars.
So, bed the car down for week or two.
Disconnect battery.
Remove and polish clean the CE panel electrodes, replace all fuses with new, replace 10 #53 relays with new, and polish the other accessory relay contacts (too expensive to replace all, not usually needed).
Pull air cleaner and box off. Look at the very back base of the valley, there is a bracket that spans across the back of the V of the engine. One each side is a ring terminal with mission-critical computer and sensor grounds. Polish with Dremel wire brush.
I'd replace the mission-critical CPS and inspect the MAF plug under the boot for twisted exposed wire shorting.....
The coil ground wires are simply for radio noise supression, but you were on the right track there.
Fully disassemble and carefully clean / maybe replace the 14 pin connector on the inner pasenger fender. Unscrew the jump post 11mm thing and clean the positive wires under it.
Under / behind that stuff, on the inner fender, is another ground wire / ring terminal. Its for the final stage ignition amps. Clean.
Now hit the coil ends (they corrode up inside). In fact, remove the coils (very painstaking/tight) and clean inside the ends. Order a $350 OEM wire set to replace the coil and spark plug wires --- two bad coil wires will take the car down. Known issue.
Clean the engine strap ground from block to frame, under car, passenger side.
There are other things, but get your car to a baseline first with this stuff. Don't forget the fuel lines, the car can burn so fast you wouldn't believe it.
Once running you will be amazed by it.
08-19-2011, 03:29 PM
#10
Racer
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Join Date: Aug 2011
Location: Fayetteville AR
Posts: 324
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The 85 was the first year for the 32V engine to be stuffed into the engine compartment.
The wiring harness is also stuffed around and over the engine. With age and heat cycling, the outer harness embrittles. Some of the Bosch sensor ends degrade. Corrosion attacks ground points for the brains / sensors / accessories.
So many cars got parked for intermittent electrical problems. So many are sold-off (hopefully they run the day somebody comes to see it). Isolated troubleshooting is not generally easy, nor lasting even if you get it running. Because at this age, in my experience rescuing downed cars, there are layers of light maintenance that are due and that interact to foil troubleshooting.
Its a great thing. Kills their value. Puts them in our hands.
Usually, all a person needs to do to revive one of these cars is cycle-through the inspection, cleaning and replacement of the basic electrical stuff.
So, everybody has given you a quick-check item above --- the " if it ran yesterday, tweak something small to make it run today" approach.
Now its probably time to engage at the next level and punch-list the electrical system. And its the perfect time to change the fuel lines, which is numero uno refresh item on any one of these cars.
So, bed the car down for week or two.
Disconnect battery.
Remove and polish clean the CE panel electrodes, replace all fuses with new, replace 10 #53 relays with new, and polish the other accessory relay contacts (too expensive to replace all, not usually needed).
Pull air cleaner and box off. Look at the very back base of the valley, there is a bracket that spans across the back of the V of the engine. One each side is a ring terminal with mission-critical computer and sensor grounds. Polish with Dremel wire brush.
I'd replace the mission-critical CPS and inspect the MAF plug under the boot for twisted exposed wire shorting.....
The coil ground wires are simply for radio noise supression, but you were on the right track there.
Fully disassemble and carefully clean / maybe replace the 14 pin connector on the inner pasenger fender. Unscrew the jump post 11mm thing and clean the positive wires under it.
Under / behind that stuff, on the inner fender, is another ground wire / ring terminal. Its for the final stage ignition amps. Clean.
Now hit the coil ends (they corrode up inside). In fact, remove the coils (very painstaking/tight) and clean inside the ends. Order a $350 OEM wire set to replace the coil and spark plug wires --- two bad coil wires will take the car down. Known issue.
Clean the engine strap ground from block to frame, under car, passenger side.
There are other things, but get your car to a baseline first with this stuff. Don't forget the fuel lines, the car can burn so fast you wouldn't believe it.
Once running you will be amazed by it.
The wiring harness is also stuffed around and over the engine. With age and heat cycling, the outer harness embrittles. Some of the Bosch sensor ends degrade. Corrosion attacks ground points for the brains / sensors / accessories.
So many cars got parked for intermittent electrical problems. So many are sold-off (hopefully they run the day somebody comes to see it). Isolated troubleshooting is not generally easy, nor lasting even if you get it running. Because at this age, in my experience rescuing downed cars, there are layers of light maintenance that are due and that interact to foil troubleshooting.
Its a great thing. Kills their value. Puts them in our hands.
Usually, all a person needs to do to revive one of these cars is cycle-through the inspection, cleaning and replacement of the basic electrical stuff.
So, everybody has given you a quick-check item above --- the " if it ran yesterday, tweak something small to make it run today" approach.
Now its probably time to engage at the next level and punch-list the electrical system. And its the perfect time to change the fuel lines, which is numero uno refresh item on any one of these cars.
So, bed the car down for week or two.
Disconnect battery.
Remove and polish clean the CE panel electrodes, replace all fuses with new, replace 10 #53 relays with new, and polish the other accessory relay contacts (too expensive to replace all, not usually needed).
Pull air cleaner and box off. Look at the very back base of the valley, there is a bracket that spans across the back of the V of the engine. One each side is a ring terminal with mission-critical computer and sensor grounds. Polish with Dremel wire brush.
I'd replace the mission-critical CPS and inspect the MAF plug under the boot for twisted exposed wire shorting.....
The coil ground wires are simply for radio noise supression, but you were on the right track there.
Fully disassemble and carefully clean / maybe replace the 14 pin connector on the inner pasenger fender. Unscrew the jump post 11mm thing and clean the positive wires under it.
Under / behind that stuff, on the inner fender, is another ground wire / ring terminal. Its for the final stage ignition amps. Clean.
Now hit the coil ends (they corrode up inside). In fact, remove the coils (very painstaking/tight) and clean inside the ends. Order a $350 OEM wire set to replace the coil and spark plug wires --- two bad coil wires will take the car down. Known issue.
Clean the engine strap ground from block to frame, under car, passenger side.
There are other things, but get your car to a baseline first with this stuff. Don't forget the fuel lines, the car can burn so fast you wouldn't believe it.
Once running you will be amazed by it.
08-19-2011, 03:41 PM
#11
Rennlist Member
Just show some pictures, both perspective and closeup, of the areas you are working in.
That helps a lot. There are dozens of guys here with 85 and close cousin 86 cars here that can see so much in the pictures. Helps the diagnosis. Some, like Mike Frye and Jason Howell have done extensive work. Others, a number of which already posted above, are pro-level, just trying to give you that first magic bullet before they suggest the deep dive.
My main point is take it slow, go thru it systematically. Even if, at the end of the work, it turns out being a bad computer or bad MAF, this work, and tracing the various wires back to the computer plugs, is basic and prerequisite for keeping the car reliable. I'm suspecting CPS connector degradation or maf plug short right now, but don't really know.
Get the CD from Roger at 928sRUS that has the WSM, wiring diagrams + extremely useful ancilliary information. It includes the 85 USA electrical "test plan" which is helpful.
Great news that it was running --- I owned mine for 7 months and invested many, many hours before knowing if it would even run.
That helps a lot. There are dozens of guys here with 85 and close cousin 86 cars here that can see so much in the pictures. Helps the diagnosis. Some, like Mike Frye and Jason Howell have done extensive work. Others, a number of which already posted above, are pro-level, just trying to give you that first magic bullet before they suggest the deep dive.
My main point is take it slow, go thru it systematically. Even if, at the end of the work, it turns out being a bad computer or bad MAF, this work, and tracing the various wires back to the computer plugs, is basic and prerequisite for keeping the car reliable. I'm suspecting CPS connector degradation or maf plug short right now, but don't really know.
Get the CD from Roger at 928sRUS that has the WSM, wiring diagrams + extremely useful ancilliary information. It includes the 85 USA electrical "test plan" which is helpful.
Great news that it was running --- I owned mine for 7 months and invested many, many hours before knowing if it would even run.
