Symptoms of a return line being blocked?
03-29-2006, 06:23 PM
#2
Member
Join Date: Mar 2006
Posts: 329
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1987 IROC 1991 RS
Engine: 5.7 TPI 5.0 TBI
Transmission: T-5 , 700R4
Axle/Gears: 2.73 twice
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.
03-29-2006, 09:15 PM
#3
Supreme Member
iTrader: (1)
Join Date: May 2004
Location: houston
Posts: 2,262
Likes: 0
Received 0 Likes
on
0 Posts
Car: 83 POS monte carlo 2015 chevy P/U
Engine: 92 5.7 tpi 5.3
Transmission: 700r4 6L60E
Axle/Gears: 2.42 too high
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.
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.
03-29-2006, 11:16 PM
#4
Member
Join Date: Mar 2006
Posts: 329
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1987 IROC 1991 RS
Engine: 5.7 TPI 5.0 TBI
Transmission: T-5 , 700R4
Axle/Gears: 2.73 twice
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.
03-29-2006, 11:36 PM
#5
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: https://www.thirdgen.org/forums/ltx-lsx/345610-lt1-knock-sensor-picking.html
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: https://www.thirdgen.org/forums/ltx-lsx/345610-lt1-knock-sensor-picking.html
03-30-2006, 11:36 AM
#6
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.
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.
03-30-2006, 12:33 PM
#7
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.
Thread
Thread Starter
Forum
Replies
Last Post
gixxer92
Engine/Drivetrain/Suspension Parts for Sale
5
09-01-2015 04:32 PM
