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Registered
Join Date: Mar 2003
Location: Toronto
Posts: 142
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Backfiring when cold....
My '75 911 backfires in the morning when it's cold.... What could
this be... It runs rough for about 25 Seconds until gas runs through the system.. I usually have to give the car gas for it to clear up... Could this be because of a faulty fuel pump... I also have a problem re-starting when hot... I changed my fuel accumulator and it seems to be starting better... Last edited by DMX; 05-27-2003 at 08:53 AM.. |
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05-27-2003, 08:50 AM
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Somewhere in the Midwest
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
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Could be your cold start circuit needs to be looked at.
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05-27-2003, 09:00 AM
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Unregistered
Join Date: Aug 2000
Location: a wretched hive of scum and villainy
Posts: 55,652
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Backfiring when cold usually means it is running too lean.
This could be caused by a faulty WUR, a vacuum leak, having the system set too lean, or a few other things. How does it run when fully warmed up, at full throttle at at idle? |
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05-27-2003, 09:03 AM
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Registered
Join Date: Mar 2003
Location: Toronto
Posts: 142
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When it's fully warmed up it runs great.. I shut it off and turn it on and
the it fires up right away.. But if I wait for a little bit I have a rough time starting.... I think I have my car running a bit too lean but I do not think that is the problem... |
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05-27-2003, 09:08 AM
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Registered
Join Date: Mar 2003
Location: Toronto
Posts: 142
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My thermo switch and cold start wires are disconnected...
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05-27-2003, 09:09 AM
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Somewhere in the Midwest
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
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Well, you might start there...the cold start circuit ( parts includes: thermo-switch and CS injector) work with your AAV and AAR as a choke curcuit pretty much so you will run really lean, until the AAR is closed and with the AAV closed. That's why you are backfireing when cold!
Why did you disconnect the CS injector a t-switch??? |
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05-27-2003, 09:13 AM
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Registered
Join Date: Mar 2003
Location: Toronto
Posts: 142
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Thats how the injection was put on... It was never connected..... Time
to get it connected... |
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05-27-2003, 09:18 AM
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Somewhere in the Midwest
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
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Yep, start there. Be aware if your parts were disconnected, they may be problematic. Good luck.
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05-27-2003, 09:37 AM
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Unregistered
Join Date: Aug 2000
Location: a wretched hive of scum and villainy
Posts: 55,652
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As far as the warm start problem, that is usually caused when the fuel in the injector lines boils from the engine heat. the system is designed to hold pressure on the lines to prevent this from happening.
The things that can cause the system pressure to drop too fast (and allow vapor lock) are the fuel pressure accumulator (you already replaced that) the fuel pump check valve, a fuel leak somewhere, or leaky injectors. The fuel pump check valve is cheap and relatively easy to change out. The injectors are easy to check, just pull them and stick them in containers and watch for leaking (when the system is pressured up). Just be extra careful when working with the flammable stuff (no kidding). |
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05-27-2003, 10:19 AM
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Registered
Join Date: Mar 2003
Location: Toronto
Posts: 142
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My fuel pump has an internal check valve.... Can I buy an external
check valve and attatch it or do I need to replace the whole thing.... |
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05-27-2003, 11:18 AM
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Somewhere in the Midwest
Join Date: Oct 2001
Location: In the barn!
Posts: 12,499
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Lets not get ahead of ourselves...
FIrst connect your CSV and tt-switch. And in the meantime, get a CIS fuel pressure tester from JC Whitney. IF you have a problem withg fuel delivery, it's best to test..not guess. If your check valve is not working, it is probably best to get a new pump. Or you can go homey style like I would and pop the ball out and check the spring in the pump..then when it's all messed up good, buy a 77+ fuel pump for a slight upgrade (and they are cheaper than the pre-77 pumps). |
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05-27-2003, 11:56 AM
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