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Old 03-29-2006, 01:44 PM   #1
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Symptoms of a return line being blocked?

What would they be? How much Increase/Decrease in fuel pressure, etc. And what if the line was slightly blocked?

Last edited by Firebat; 03-29-2006 at 02:12 PM.
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Old 03-29-2006, 06:23 PM   #2
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If the fuel return line would be blocked then the injectors would get the full fuel pressure and would not fire, keeping the engine from starting. Same with a slightly blocked line, its possible.
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Old 03-29-2006, 09:15 PM   #3
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how high the pressure would be if the return line was completely blocked depends on the pump, the better the pump the higher the pressure.
the same thing applies if it is partially blocked.
partially blocked with a weak pump may not cause any problem.
completely blocked will kill the pump sooner or later if it doesn't blow out the regulator or rubber hoses in the fuel system.
like ResurrectingZ said, completely blocked could cause the injectors to lockup & not fire.
i have seen some that would still fire at 125 PSI, others that were locked at 35 PSI, both of these were on a TBI.
if the pressure is too high & the motor starts & runs, it will run rich, which could damage the rings & cylinders by washing the oil off the walls, or possibly even hydraulically locking the motor causing bent rods or splitting a cylinder.
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Old 03-29-2006, 11:16 PM   #4
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It might not be a bad idea either to check the fuel pressure at the schrader valve on the fuel rail. Should tell you right there the pressure you are running, not quite sure the stock fuel pressure or if you have an afpr, would be worth posting the info though.
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Old 03-29-2006, 11:36 PM   #5
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Its actually an LT1 swap. But i swapped the entire carb fuel lines for tpi lines and put in a new pump during the swap. The ecm is trying to lean it out as much as possible but it still runs rich and my fuel pressure is just a little high but still within range. I'm supposed to be seeing 43.5 psi with the vac line off the regulator and i'm seeing about 47. 46 is the highest it should be.

I dont know whats causing it to run rich and i've checked about everything and this blocked return line idea popped into my head.

Here is where i posted my problem in the engine swap forum, i have more details there: http://www.thirdgen.org/techboard/sh...d.php?t=345610 (LT1 knock sensor is picking up knock, giving me bad spark retard and timing)
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Old 03-30-2006, 11:36 AM   #6
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The LT1 systems also run at 43.5 PSIG (3 BAR) so you really didn't need to change the whole system. If you're certain the gauge is calibrated correctly, try another regulator. With a good pump and blocked return line, the pressure would be much higher. It seems that the regulator is trying to maintain correct pressure, and may just be a hair off calibration. The ECM should be able to manage that little bit of pressure difference when in Closed Loop so long as the injector size is correctly set in the programming.

Have the injectors been changed? Has there been any reprogramming?

FWIW, the TPI system factory fuel pressure specification as I read it is 44 PSIG, 3 with no vacuum, and 37 PSIG 3 with full 17" Hg vacuum. Looks like you're right on spec, but on the upper end.
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Old 03-30-2006, 12:33 PM   #7
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It could be regulator but i've replaced it once already while trying to hunt down the problem. Injectors are the same and they don't appear to be leaky. It is programmed to be tuned better but even with the stock tune the engine still detonates. Detonation is the other problem which probably has something to do with running rich. I'm going to try swapping fuel rails, which have the injectors and reg on them, from a known good running LT1 this weekend and see if anything changes.
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Old 03-30-2006, 12:33 PM
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