CPU's and Grounding
03-10-2014, 05:10 PM
#17
Track Day
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Join Date: Jul 2006
Location: Merritt Island, Florida
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Hi Jim,
Thanks for taking the time out to put together your post – that was a wonderful schooling on cause / result that will prove to be very useful.
Okay I will answer some of your questions first and then I will chronicle the history of my car which may help (sorry if the post is a little long winded)
The current status: Right now I can start the car and it will run but it does not run great. It feels like it is missing here and there but it would be drivable. It seems as I replace / diagnose more problems that things get better. For instance, the vacuum leak made a huge improvement – and I also feel that the FPR and Damper made some difference. I imagine that once I get through cleaning the caps / rotors / coils things will also improve.
The ongoing problem: The car will be running fine and then out of nowhere will start to rev up and then drop rpms (down to like 400)…. And yes it will almost always stall after a few of these ups & downs. Originally I thought it was just when the car was warm but the other day proved me wrong. I turned it on cold and within 1 minute it gasped choked and died. The problem is that this doesn’t always happen at a prescribed time. Sometimes I can have the car running for 20-30 minutes or even more without a hiccup. After this problem occurs the car will always restart: sometimes the problem will come back immediately (most of the time) and sometimes the car runs fine for a long time again.
When this happens I don’t think I would say the car is running rich or lean (although I am not a mechanic by any means). Note: I have been under the back of the car when it happens and listened to the fuel pump and I can hear it change tempo with the impending stall but it never stops humming until the car dies.
The fuel volume test is something I have never investigated. Once I finish the coil cleaning I can look into that.
As for the CPS wire repair – I feel pretty confident in my work. I cut back as far as necessary and soldered everything plus put shrink wrap over the wires for protection.
MAF’s & LH: I can’t say I know anyone locally that has these available as a loaner. In fact since I moved here I have only seen one 928 (late 70’s). It’s a small island I live on with only about 35K people.
The Chronicles of my Shark (1987 928S4)
2000 – PO broke timing belt and had it fixed. Did timing belt, water pump and normal required parts plus had to pull the heads to replace two bent valves – looks as if they did a basic intake refresh at same time.
2001 – PO car was running bad (would cut out at 2k rpms and blow black smoke). Porsche did service – replaced o2 sensor, coolant temp sensor, ignition wires plus fixed numerous bad connections
2001- I purchased car was running badly. Replaced MAF, Coolant Temp sensor, LH (rebuilt), Air filter.
2001-2009 – The best years of my life. Did nothing but normal service and driving. Began to think this was the best car I ever owned!
2009 – Car choked and stalled when I was out for a drive and had a hard time restarting. Finally got it running and headed home. Time for a visit to shop.
10/08/ 2009 – SHOP – said engine was misfiring. Replaced spark plugs w/ porsche recommended. Replaced CPS because of faulty wave form. Replaced air pump filter.
10/19/2009 – Picked up car dropped dead as I left parking lot. SHOP – Replace fuel filter, MAF plug cleaned and drivers side ignition rotor replaced.
10/20/2009 – Picked up car….. dropped dead as I left parking lot. Moving to Florida 4 days later so I left it there to be fixed. Had them do the Timing belt service as well as fix problem since I would have to drive it to my new home 1200 miles away.
03/27/10 – Car has been at shop since the last date. Things done: Timing Belt, Timing Belt Roller, Accessory drive belts (2), Multi Rib belt, Water Pump, Thermostat (plus O ring), Timing belt roller (2), Tensioner Bushing, Hood struts, Spark Plugs, MAF rebuilt – MAF plug replaced. They also recommended injector flush or replacement due to bad spray pattern (but they did not do that). Other notes on this: 2 timing belt roller assemblies were seized.
I picked up car and guess what….. it barely made it to my Fathers house. Stored car at Dad’s house until I could arrange to tow it to Florida.
04-2011 – Finally picked up car and brought to Florida. Car still running just awful. Time for a new Mechanic…. Me (I really haven’t used a wrench in quite a few years). Replaced Knock sensor with cable that is on side of motor because connector was totally gone. No improvement.
11-2011 – Felt MAF could be contributing to problem. Was still under warranty from 928 Int so sent it in. They confirmed it was not working and fixed under warranty (excellent service!)
2011 – 2014 – Porsche put on hold since I had all to do to keep my other cars running. Time fly’s by when you are not paying attention.
01/13/14 – Tried to start car – no deal. Put it in the air and got to work. Fuel pump not working, replaced. New fuel filter & some muffler hangers. Tranny leaking probably from sitting so long so I had to top off (that is a project for another day). Many of wires under car lost there sheathing so I replaced them when accesible. New Battery installed (duralast). Car now starts but welcome back to the rev / drop rpm problem.
Great suggestions on Rennlist….. found a huge vacuum leak on Y pipe probably from when Timing belt service was done. Somehow managed to get the Y pipe connected to the manifold again (will handle that properly when I do intake refresh after car is running somewhat properly – but it is on there quite well… just can’t tighten clamp).
Went through all ground points on list cleaned properly. Cleaned up Battery positive and negative (note: I had replaced the negative strap a couple years ago – along with the negative strap under car).
Cleaned hot lug & all the connections in that area.
Replaced fuses (checked them first)
Did the WD 40 spray into ISV.
02-14 – Realized CPS connector on the harness side looked poorly. Ordered new and replaced. Car seemed to run slightly better overall (I know – that doesn’t make sense) but the wires were cracked and possible touching occasionally.
02-11-14 – Parts Order. Fuel pressure regulator, Rear Fuel pressure Damper (front had no smell of gas). Replaced other things like Headlight, Washer hood cap. Car starts – same problem.
Go back to electric.
02-25-14 – Replaced all 53 relays plus window winder (because it was hot). Replace rear light bulbs to stop annoying “stop lamp” dash warning (didn’t work – put that on the future list). – no improvement.
03-01-14 – parts order. Realized that in tank fuel screen was falling apart once removed. Replaced. Also did hose and new copper washers on fuel pump plus put in brand new gas. – no improvement.
Sorry for such a long post – I just thought if you had all the information it could be helpful. Today I will have a little time to go back to the Coil / rotors / caps. Then I will start it again to see if there is any improvement. I am sure that there are many other things that I have checked that have just skipped my mind but this is a pretty good list of items that have been done.
Thanks for all your help & time,
Regards,
Brett
Thanks for taking the time out to put together your post – that was a wonderful schooling on cause / result that will prove to be very useful.
Okay I will answer some of your questions first and then I will chronicle the history of my car which may help (sorry if the post is a little long winded)
The current status: Right now I can start the car and it will run but it does not run great. It feels like it is missing here and there but it would be drivable. It seems as I replace / diagnose more problems that things get better. For instance, the vacuum leak made a huge improvement – and I also feel that the FPR and Damper made some difference. I imagine that once I get through cleaning the caps / rotors / coils things will also improve.
The ongoing problem: The car will be running fine and then out of nowhere will start to rev up and then drop rpms (down to like 400)…. And yes it will almost always stall after a few of these ups & downs. Originally I thought it was just when the car was warm but the other day proved me wrong. I turned it on cold and within 1 minute it gasped choked and died. The problem is that this doesn’t always happen at a prescribed time. Sometimes I can have the car running for 20-30 minutes or even more without a hiccup. After this problem occurs the car will always restart: sometimes the problem will come back immediately (most of the time) and sometimes the car runs fine for a long time again.
When this happens I don’t think I would say the car is running rich or lean (although I am not a mechanic by any means). Note: I have been under the back of the car when it happens and listened to the fuel pump and I can hear it change tempo with the impending stall but it never stops humming until the car dies.
The fuel volume test is something I have never investigated. Once I finish the coil cleaning I can look into that.
As for the CPS wire repair – I feel pretty confident in my work. I cut back as far as necessary and soldered everything plus put shrink wrap over the wires for protection.
MAF’s & LH: I can’t say I know anyone locally that has these available as a loaner. In fact since I moved here I have only seen one 928 (late 70’s). It’s a small island I live on with only about 35K people.
The Chronicles of my Shark (1987 928S4)
2000 – PO broke timing belt and had it fixed. Did timing belt, water pump and normal required parts plus had to pull the heads to replace two bent valves – looks as if they did a basic intake refresh at same time.
2001 – PO car was running bad (would cut out at 2k rpms and blow black smoke). Porsche did service – replaced o2 sensor, coolant temp sensor, ignition wires plus fixed numerous bad connections
2001- I purchased car was running badly. Replaced MAF, Coolant Temp sensor, LH (rebuilt), Air filter.
2001-2009 – The best years of my life. Did nothing but normal service and driving. Began to think this was the best car I ever owned!
2009 – Car choked and stalled when I was out for a drive and had a hard time restarting. Finally got it running and headed home. Time for a visit to shop.
10/08/ 2009 – SHOP – said engine was misfiring. Replaced spark plugs w/ porsche recommended. Replaced CPS because of faulty wave form. Replaced air pump filter.
10/19/2009 – Picked up car dropped dead as I left parking lot. SHOP – Replace fuel filter, MAF plug cleaned and drivers side ignition rotor replaced.
10/20/2009 – Picked up car….. dropped dead as I left parking lot. Moving to Florida 4 days later so I left it there to be fixed. Had them do the Timing belt service as well as fix problem since I would have to drive it to my new home 1200 miles away.
03/27/10 – Car has been at shop since the last date. Things done: Timing Belt, Timing Belt Roller, Accessory drive belts (2), Multi Rib belt, Water Pump, Thermostat (plus O ring), Timing belt roller (2), Tensioner Bushing, Hood struts, Spark Plugs, MAF rebuilt – MAF plug replaced. They also recommended injector flush or replacement due to bad spray pattern (but they did not do that). Other notes on this: 2 timing belt roller assemblies were seized.
I picked up car and guess what….. it barely made it to my Fathers house. Stored car at Dad’s house until I could arrange to tow it to Florida.
04-2011 – Finally picked up car and brought to Florida. Car still running just awful. Time for a new Mechanic…. Me (I really haven’t used a wrench in quite a few years). Replaced Knock sensor with cable that is on side of motor because connector was totally gone. No improvement.
11-2011 – Felt MAF could be contributing to problem. Was still under warranty from 928 Int so sent it in. They confirmed it was not working and fixed under warranty (excellent service!)
2011 – 2014 – Porsche put on hold since I had all to do to keep my other cars running. Time fly’s by when you are not paying attention.
01/13/14 – Tried to start car – no deal. Put it in the air and got to work. Fuel pump not working, replaced. New fuel filter & some muffler hangers. Tranny leaking probably from sitting so long so I had to top off (that is a project for another day). Many of wires under car lost there sheathing so I replaced them when accesible. New Battery installed (duralast). Car now starts but welcome back to the rev / drop rpm problem.
Great suggestions on Rennlist….. found a huge vacuum leak on Y pipe probably from when Timing belt service was done. Somehow managed to get the Y pipe connected to the manifold again (will handle that properly when I do intake refresh after car is running somewhat properly – but it is on there quite well… just can’t tighten clamp).
Went through all ground points on list cleaned properly. Cleaned up Battery positive and negative (note: I had replaced the negative strap a couple years ago – along with the negative strap under car).
Cleaned hot lug & all the connections in that area.
Replaced fuses (checked them first)
Did the WD 40 spray into ISV.
02-14 – Realized CPS connector on the harness side looked poorly. Ordered new and replaced. Car seemed to run slightly better overall (I know – that doesn’t make sense) but the wires were cracked and possible touching occasionally.
02-11-14 – Parts Order. Fuel pressure regulator, Rear Fuel pressure Damper (front had no smell of gas). Replaced other things like Headlight, Washer hood cap. Car starts – same problem.
Go back to electric.
02-25-14 – Replaced all 53 relays plus window winder (because it was hot). Replace rear light bulbs to stop annoying “stop lamp” dash warning (didn’t work – put that on the future list). – no improvement.
03-01-14 – parts order. Realized that in tank fuel screen was falling apart once removed. Replaced. Also did hose and new copper washers on fuel pump plus put in brand new gas. – no improvement.
Sorry for such a long post – I just thought if you had all the information it could be helpful. Today I will have a little time to go back to the Coil / rotors / caps. Then I will start it again to see if there is any improvement. I am sure that there are many other things that I have checked that have just skipped my mind but this is a pretty good list of items that have been done.
Thanks for all your help & time,
Regards,
Brett