Evolving electrical problem - slow crank, no start
02-17-2014, 01:57 AM
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Evolving electrical problem - slow crank, no start
Before beginning my saga, let me say first thanks for any help and yes, I've searched the forum.....This is on my '87 924s
Situmication: Car goes from running smoothly to won't crank. Jump start works, so battery is charged and all is well for 2 weeks. Repeat of initial problem w/wife at work. I bring new battery to work and replace - when cranking I notice an arc going from the back of the engine in the center to the firewall that coincides w/cranking, but the car starts fine and we drive home - arc only happened when cranking, not running. SCARY
Next day, car cranks VERY slowly and won't start. I look to see if there are any arc spots where I saw the arcing but none visible. I charge NEW battery and try again, same thing. So, I take out the starter and thoroughly go through it finding the brush springs were NOT pressing hard enough to create good contact. I fix this and the starter spins very nicely so I put it back in. Test it and same thing, slow crank, no start. I bypass the internal wire from battery to starter w/jumper and retest... Still cranking slow, so I order new starter.
New starter arrives, put in, and same thing - slow crank, no start. Now I'm worried. Out come the plugs, cranking is STILL SLOW. Check compression and w/slow crank 1st 3 cylinders show 150psi. On checking the 4th cylinder - miracle - FAST cranking begins again and I get 180 psi compression. I recheck first 3 and now, compression runs 172-180 w/fast cranking. I replace the plugs and get FAST CRANKING. BUT no start.
I check ignition coil output and there is now no spark from the coil. This is the current situmacation and my mechanical engineer neighbor and I are stumped.
My theory - something in the ignition circuit that was starting to fail is now completely shot. But what? That could have been the cause of the arc on cranking (which flickered inferring itnition connection)vbut I have NOT seen it since rescuing my wife at work....... Maybe its the 12v. supply wire to the coil that was arcing and has now failed?
My neighbor's thoery - gasoline collected in the top of the cylinder and cleared after removing the plugs and that caused the slow crank.
The lack of ignition spark is a separate problem.
ANY IDEAS YOU HAVE TO SHARE WILL BE GREETED WITH SINCERE APPRECIATION..... i'M STUMPED but leaning towards buying a horse.
Joe
Situmication: Car goes from running smoothly to won't crank. Jump start works, so battery is charged and all is well for 2 weeks. Repeat of initial problem w/wife at work. I bring new battery to work and replace - when cranking I notice an arc going from the back of the engine in the center to the firewall that coincides w/cranking, but the car starts fine and we drive home - arc only happened when cranking, not running. SCARY
Next day, car cranks VERY slowly and won't start. I look to see if there are any arc spots where I saw the arcing but none visible. I charge NEW battery and try again, same thing. So, I take out the starter and thoroughly go through it finding the brush springs were NOT pressing hard enough to create good contact. I fix this and the starter spins very nicely so I put it back in. Test it and same thing, slow crank, no start. I bypass the internal wire from battery to starter w/jumper and retest... Still cranking slow, so I order new starter.
New starter arrives, put in, and same thing - slow crank, no start. Now I'm worried. Out come the plugs, cranking is STILL SLOW. Check compression and w/slow crank 1st 3 cylinders show 150psi. On checking the 4th cylinder - miracle - FAST cranking begins again and I get 180 psi compression. I recheck first 3 and now, compression runs 172-180 w/fast cranking. I replace the plugs and get FAST CRANKING. BUT no start.
I check ignition coil output and there is now no spark from the coil. This is the current situmacation and my mechanical engineer neighbor and I are stumped.
My theory - something in the ignition circuit that was starting to fail is now completely shot. But what? That could have been the cause of the arc on cranking (which flickered inferring itnition connection)vbut I have NOT seen it since rescuing my wife at work....... Maybe its the 12v. supply wire to the coil that was arcing and has now failed?
My neighbor's thoery - gasoline collected in the top of the cylinder and cleared after removing the plugs and that caused the slow crank.
The lack of ignition spark is a separate problem.
ANY IDEAS YOU HAVE TO SHARE WILL BE GREETED WITH SINCERE APPRECIATION..... i'M STUMPED but leaning towards buying a horse.
Joe
Last edited by JosephK; 02-17-2014 at 02:14 AM.
02-18-2014, 02:54 PM
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I pulled and cleaned the rear 2 grounding bolts w/3 wires. One from the battery w/ another wire underneath and a second bolt with a single wire. The motor cranks well and this was likely the cause of my arcing because there was much corrosion (See pix 1) and the battery wire was loose. THANKS for the tip!!
Buit, there is still no spark.
There is a connector (see pix 2) at the top rear of the engine (right above the grounds) in a bracket w/2 wires going left and right each w/connectors one above the other in the bracket. The connector appears to have been juryrigged with cable ties to keep it engaged and it may not be providing a good connection. Somebody, PLEASE TELL me about these connectors. Where do the wires go? What is the connector called (so I can replace it!). Could it be causing the no spark condition?
Thanks again to all for any help!
Buit, there is still no spark.
There is a connector (see pix 2) at the top rear of the engine (right above the grounds) in a bracket w/2 wires going left and right each w/connectors one above the other in the bracket. The connector appears to have been juryrigged with cable ties to keep it engaged and it may not be providing a good connection. Somebody, PLEASE TELL me about these connectors. Where do the wires go? What is the connector called (so I can replace it!). Could it be causing the no spark condition?
Thanks again to all for any help!
02-19-2014, 06:45 PM
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HELP PLEASE - part name/number ??
Can anyone please identify the connector part name/numberin the photo so I can order a proper replacement.
I've also been checking this link for ideas - Nothing works yet.
https://rennlist.com/forums/924-931-...-no-start.html
Thanks,
Joe
I've also been checking this link for ideas - Nothing works yet.
https://rennlist.com/forums/924-931-...-no-start.html
Thanks,
Joe
02-24-2014, 03:56 PM
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Connectors are - Speed sensor and reference mark transmitter connectors
Just to close off this thread, they're the speed and reference mark transmitter connectors that are im my pix for anyone in the future who may be as baffled as I was. It only took bit of noodling to find a .pdf of the 944 service manual which thankfully has pictures.
I hope this helps someone in the future.
JoesephK
I hope this helps someone in the future.
JoesephK
