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Registered User
Join Date: Feb 2014
Posts: 37
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Almost there!
After a lengthy amount of work before and after my day job I am almost done... Kinda. I bought a rebuilt MAF from Roger, complete intake rebuild. New seals, gaskets, injectors, vaccum lines, flywheel sensor, fuel lines, ignition control modules x 2, idle control valve, throttle position sensor, new fuel pump and filter. It starts runs great revs fine and smooth. 20 seconds later it dies. Any ideas
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03-12-2014, 06:56 PM
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Might I also add that it would not start at all for a week and the culprit was the factory alarm which I bypassed by bridging yellow to black with red stripe
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03-12-2014, 07:00 PM
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Network Native
Join Date: Jan 2007
Location: SoCal
Posts: 10,349
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What model year?
How does it die, struggle or poof? Twenty seconds sounds about the length of startup high idle period for some cars, when idle control valve sticks the drop can be larger than it should be and the car stumbles and dies. Whats the idle RPM during that 20 seconds? Have you verified throttle position sensor is working? |
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03-12-2014, 08:40 PM
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88 928 s4 automatic trans. It cuts off very suddenly and the fuel pump continues for approximately 1.5 sec after it stalls. FYI the fuel pressure regs were not replaced, all relays are new
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03-13-2014, 06:35 AM
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I will check the rpm at idle, how do I check to see if the tps is working? It's a new Bosch and it clicks at close like it should
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03-13-2014, 06:38 AM
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Location: Texas
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Dino,
Try jumpering the fuel pump to remove that relay from the list of possible causes. If that doesn't do it, either jumper (3 way jumper) the fuel injection relay or replace the fuel injection relay with a brand new 53 relay.
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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03-13-2014, 10:54 AM
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I will try both and let you know, and thank you so much
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03-13-2014, 06:54 PM
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Exactly how much play should there be in the throttle cable? Should the TPS click when the throttle is at dead rest?
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03-13-2014, 07:10 PM
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Quote:
__________________
John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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03-13-2014, 09:36 PM
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Sorry. I didn't see the add-on verbage in post #4 about the relays being all replaced. I think it would still be worthwhile to jumper the fuel pump and then the injection system to remove those relays from the list of possible causes.
Additionally, pull the vacuum line from both of the fuel pressure dampeners one at a time to see if they smell of fuel. (they should not) If one or both smell of fuel, the internal diaphram(s) are ruptured and fuel (maybe too much excess fuel) is being vacuum sucked into the engine. It could be enough to kill the engine in , say 20 seconds.  Replace whichever or both fuel dampeners that prove to be defective. You can also Mityvac each dampener at the vacuum fitting to see if it holds vacuum in lieu of smelling them. If they don't hold vacuum, replace them.
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) Last edited by stepson; 03-13-2014 at 09:49 PM.. |
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03-13-2014, 09:46 PM
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Is there a number not exceed when testing the regs with the mightyvac? I don't want to rupture them
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03-14-2014, 12:33 PM
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It would probably be okay, but I try not to exceed 15 lbs with the Mityvac.
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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03-14-2014, 03:02 PM
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Quote:
 The higher the vacuum the easier it is to see if it leaks, but anything more than 25 inHg should be fine. If I recall correctly the mity vac has a shut off valve between the pump part and the gauge, shut that off so you don't get any leak from the pump seal. |
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03-15-2014, 03:45 PM
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Quote:
I was having a brain lapse and couldn't remember inHg. LOL 
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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03-15-2014, 09:35 PM
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Quote:
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03-16-2014, 07:58 AM
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Join Date: Feb 2014
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Ok so the fuel pressure reg are good all three. I don't know whether to be happy or sad that I didn't find the problem
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03-16-2014, 09:52 AM
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For poops and giggles I am gonna replace the fuel filter
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03-16-2014, 09:53 AM
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Fuel filter I am thinking unlikely, fuel screen in the tank clogged, "maybe", but that kind of dropping pressure fuel starvation usually has a stumble to it, rapid stop seems like something electrical to me.
Measuring the fuel rail pressure would be a quick yes/no. Can you keep it running by pressing the accelerator pedal? |
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03-16-2014, 05:41 PM
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Yes I used to be able to keep it running by feathering the pedal but as of a few hours ago it immediately dies after start up. It never ran this bad, could the rebuilt MAF from Roger be faulty? Are the electronics freshened up upon rebuild?
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03-16-2014, 07:07 PM
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I think it should start and idle with the MAF unplugged, easy test.
Have you checked the Temp II sensor, as I recall you measure something between each pin and ground. Both coils failing sounds unlikely, but maybe check the ballast resistors and voltage at the coils. Ballast resistors are bypassed during cranking to give max spark energy, in series with key on after cranking. |
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03-17-2014, 08:39 AM
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