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Crossfire Fuel Pressure problem/question

Old 09-18-2018, 09:48 AM
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Reddfalcon
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Default Crossfire Fuel Pressure problem/question

Hi folks, so I have an '84 crossfire 4+3. I recently did a few 'minor' upgrades. Crank pulley upgrade, camshaft kit, headers, ported intake, exhaust. I am having a huge problem that I can't seem to solve. It is DUMPING fuel in from the throttle bodies. It is getting way to much fuel. I have done some adjusting to the rear 'controlling' throttle body (where you can adjust the spring in the center), I've also adjusted the idle screw and TPS. Buddy has a car with identical upgrades and I am doing my best to match his settings for everything. Initially, when connected to OBD1 reader it was not seeing input from the O2 censor. I ohm'd the O2 wire to the computer and bench tested the O2 sensor itself and everything works. I have not had the chance to connect the OBD1 reader since then. I also think the issue could be the MAP sensor.

Does anyone have any experience with these crossfires that could help me out? I should also add that I removed the A.I.R and EGR. Currently, the car will start up and idle, but idles up to 2500+rpm when correcting itself. Obviously not driveable. It's also hard to get the timing correct since the fuel is not right. Pull the plugs and they are soaked. Not sure whats going on. I have tried many things already. If anyone has suggestions I would love to hear them.

Thanks folks!
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Old 09-18-2018, 01:20 PM
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corvettenorway
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bad ground to ecm ... temp sensor ... ??
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Old 09-18-2018, 01:49 PM
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Reddfalcon
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Originally Posted by corvettenorway View Post
bad ground to ecm ... temp sensor ... ??
I checked those before but I will double check again. I'm running out of ways to troubleshoot this. I thought maybe the MAP sensor had gone bad, but not sure how to test that.
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Old 09-18-2018, 01:55 PM
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and fuel pressure is ??
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Old 09-18-2018, 02:01 PM
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corvettenorway
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try to disconnect cruise control wire
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Old 09-18-2018, 02:05 PM
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Tom400CFI
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Originally Posted by Reddfalcon View Post
Initially, when connected to OBD1 reader
Originally Posted by Reddfalcon View Post
I thought maybe the MAP sensor had gone bad, but not sure how to test that.
Can you use your scan tool to datastream and see the MAP readings? Have you hooked up a simple vacuum gauge?

CTS could cause your symptom....MAP unhooked could too. What's the fuel pressure set to?

2500 RPM + "lots of fuel"....sounds like a big vacuum leak, to me.

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Old 09-18-2018, 02:07 PM
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Hot Rod Roy
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High idle and "dumping fuel" sounds like a vacuum leak. The ECM will try to balance the excessive air by adding fuel to get the correct air/fuel ratio, which results in a high idle.



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Old 09-18-2018, 02:08 PM
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I didn't check the fuel pressure itself, its just very apparent that its way to much. I did put in a fuel pump from a 3rd gen F-body, upping the pressure a bit. Maybe that's the issue. But like I said, my buddy did an identical setup on his ride and we didn't see any issues whatsoever. I didn't think to try the cruise disconnect, I'll add that to my list of things to try.
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Old 09-18-2018, 02:12 PM
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Thanks for the interest, lots of good suggestions. I don't know exactly what the fuel pressure is. fairly confident its not a vacuum leak. If it is I don't know where its coming from. Sprayed starting fluid around intake gasket to make sure there wasn't any leaks there. And I would think you'd be able to hear it too, but I dunno. I'm still learning. Tom400CFI you mentioned CTS issue. What is that? Also, yes I should be able to hook up my reader to see what the MAP sensor is doing, once I get the scan tool back.
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Old 09-18-2018, 02:49 PM
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Originally Posted by Reddfalcon View Post
I didn't check the fuel pressure itself, its just very apparent that its way to much. I did put in a fuel pump from a 3rd gen F-body, upping the pressure a bit. Maybe that's the issue.
Changing the pump won't change the pressure (unless your old pump was failing). The regulator is what sets the pressure. I put a walbro 255 LPH in my car and the pressure didn't change until I changed it w/the regulator.

Originally Posted by Reddfalcon View Post
fairly confident its not a vacuum leak. If it is I don't know where its coming from. Tom400CFI you mentioned CTS issue. What is that? Also, yes I should be able to hook up my reader to see what the MAP sensor is doing, once I get the scan tool back.
Most common place for a vacuum leak is the plenum lid gasket. Also, MAP hose, brake booster hose, booster diaphragm, and PCV valve/hose are places to look.

CTS is what Corvettenorway was talking about; Coolant temp sensor. If it's reading way cold, it'll make it way rich.

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Old 09-18-2018, 02:58 PM
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Ok cool, yah I know about the regulator, which is on the 1st (driver side) throttle body correct? with the spring that you can adjust? And I replaced or checked all the vacuum lines so I don't think that is the issue either. Could still be an option to look at thought. And I know about the Coolant temp sensor, I didn't put together that it was the CTS, my bad. I know I had an issue early where it just wouldn't start period because the CTS wasn't connected properly. They are probably cheap, maybe i'll just replace it and eliminate it being the issue.

Thanks again for all the suggestions guys. I'll try to get back in a few days and update you with any testing I've done.
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Old 09-18-2018, 04:09 PM
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corvettenorway
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get the right Coolant temp sensor for a 84
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Old 09-18-2018, 04:20 PM
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Originally Posted by corvettenorway View Post
get the right Coolant temp sensor for a 84
copy that!
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Old 09-18-2018, 07:18 PM
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ex-x-fire
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No, don't get a cts for an 84 vette, the design is junk. Get one (and the matching connector) from a 87 up GM truck Or any efi GM car after 1985.
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Old 09-18-2018, 07:21 PM
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This is the one you want.

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Old 09-19-2018, 11:33 AM
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Originally Posted by Reddfalcon View Post
Ok cool, yah I know about the regulator, which is on the 1st (driver side) throttle body correct? with the spring that you can adjust?
Yep. May have to grind off a weld blob to get adjustability out of it.
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