D-Jet Issues-getting close, Need a little more specific advice |
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D-Jet Issues-getting close, Need a little more specific advice |
OU8AVW |
Mar 16 2015, 09:17 AM
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#1
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Yacht Rigger Group: Members Posts: 1,803 Joined: 1-October 08 From: Granbury, TX Member No.: 9,601 Region Association: Southwest Region |
So I got my car back from the local Porsche shop and installed a rebuilt MPS from Bowlsby but the car is still not running right. Flat spots and intermittent dead fire misses. She starts right up, idles well and drives ok but when you get on it it has intermittent flat spots and when shes just cruising it misses once and a while. Seems like the advance is not ramping up like it should. Also, the mechanic left a vacuum line off the distributor. The line from the inboard connection on the pot is hooked up but the outside one is off. I understand that one of these is advance and one is retard.
Just need a list of crap to check (IMG:style_emoticons/default/biggrin.gif) |
OU8AVW |
Mar 16 2015, 10:29 AM
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#2
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Yacht Rigger Group: Members Posts: 1,803 Joined: 1-October 08 From: Granbury, TX Member No.: 9,601 Region Association: Southwest Region |
1974 2056. New injectors, rebuilt MPS.....
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worn |
Mar 16 2015, 11:08 AM
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#3
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can't remember Group: Members Posts: 3,283 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
1974 2056. New injectors, rebuilt MPS..... Timing light? Everyone correctly goes after vacuum but I would also check wiring. Two nights ago I had the lid open and saw arcing between a spark plug wire and a vacuum hose! I kept thinking I was making a mistake and it was another spark plug wire. Didn't really want to grab the offending item so I shut it down. Sure enough: hose for the vacuum advance. Black silicone rubber. I can only think that the black is carbon black, which I suspect might conduct high voltage. Misfire went away when I moved the hose. Maybe new HT wires soon?. At any rate I would check all the components including the wires that go to them such as the aux air, the throttle sensor, the temp sensor connections, and of course the MPS. One problem I had once was a leaking cold start valve that dribbled gas into the induction system at random. A flashlight peak through the throttle body would show wet gas in the plenum. So many piddly little things. Good luck BTW, how does Rich look for the leaks? Propane? |
DRPHIL914 |
Mar 16 2015, 12:07 PM
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#4
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Dr. Phil Group: Members Posts: 5,801 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
1974 2056. New injectors, rebuilt MPS..... Timing light? Everyone correctly goes after vacuum but I would also check wiring. Two nights ago I had the lid open and saw arcing between a spark plug wire and a vacuum hose! I kept thinking I was making a mistake and it was another spark plug wire. Didn't really want to grab the offending item so I shut it down. Sure enough: hose for the vacuum advance. Black silicone rubber. I can only think that the black is carbon black, which I suspect might conduct high voltage. Misfire went away when I moved the hose. Maybe new HT wires soon?. At any rate I would check all the components including the wires that go to them such as the aux air, the throttle sensor, the temp sensor connections, and of course the MPS. One problem I had once was a leaking cold start valve that dribbled gas into the induction system at random. A flashlight peak through the throttle body would show wet gas in the plenum. So many piddly little things. Good luck BTW, how does Rich look for the leaks? Propane? (IMG:style_emoticons/default/agree.gif) i believe i am suffering from this same issue(the leaky cold start valve) - WORN, can you tell me, did it have a hard time starting sometimes, like it was flooded out? if i leave the car for more than a day, it will be difficult to start, but anything from 15 minutes to half a day it fires right up... just wondering. |
r_towle |
Mar 16 2015, 12:13 PM
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#5
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Custom Member Group: Members Posts: 24,623 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
1974 2056. New injectors, rebuilt MPS..... Timing light? Everyone correctly goes after vacuum but I would also check wiring. Two nights ago I had the lid open and saw arcing between a spark plug wire and a vacuum hose! I kept thinking I was making a mistake and it was another spark plug wire. Didn't really want to grab the offending item so I shut it down. Sure enough: hose for the vacuum advance. Black silicone rubber. I can only think that the black is carbon black, which I suspect might conduct high voltage. Misfire went away when I moved the hose. Maybe new HT wires soon?. At any rate I would check all the components including the wires that go to them such as the aux air, the throttle sensor, the temp sensor connections, and of course the MPS. One problem I had once was a leaking cold start valve that dribbled gas into the induction system at random. A flashlight peak through the throttle body would show wet gas in the plenum. So many piddly little things. Good luck BTW, how does Rich look for the leaks? Propane? (IMG:style_emoticons/default/agree.gif) i believe i am suffering from this same issue(the leaky cold start valve) - WORN, can you tell me, did it have a hard time starting sometimes, like it was flooded out? if i leave the car for more than a day, it will be difficult to start, but anything from 15 minutes to half a day it fires right up... just wondering. Check your fuel pressure. That may be a leaky injector, and you need to check all five. Typical of a leaky cold start injector to relieve all the fuel pressure, drip raw ful into the plenum and make it hard to start. I always turn the key to run three or four times before I crank it when the car has sat for a long period of time. Rich |
worn |
Mar 16 2015, 02:38 PM
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#6
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can't remember Group: Members Posts: 3,283 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
[quote name='r_towle' date='Mar 16 2015, 10:13 AM' post='2160821'] right up... just wondering.
[/quote] Check your fuel pressure. That may be a leaky injector, and you need to check all five. Typical of a leaky cold start injector to relieve all the fuel pressure, drip raw ful into the plenum and make it hard to start. I always turn the key to run three or four times before I crank it when the car has sat for a long period of time. Rich [/quote] Yeah, i turn the key and listen to the fuel cycling through. Sometimes if it is quiet i will listen to the injectors click as i slowly press the pedal to the floor. Quick checks that tell you that so,e parts are alive. The sure sign of cold start leak is gas showing up in the plenum. My car will hold normal fuel pressure for more than half an hour with the engine turned off. If you have a leaking injector that pressure will slowly be dissipated as the fuel leaks wherever. |
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