nealpellecchia
Active Member
anybody find any?? my boat mechanic says that on fords a leak in the return line can bleed down the pressure and mimic a suction leak. I can still barely start it but I'm gonna miss the 49er game unless...
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suction leaks in fuel system
- Thread starter nealpellecchia
- Start date
- Staff
- #2
I'm assuming you have a 6.5 TD, since the question was posted in the 6.5 tech library. Please fill out your signature so we can 'see' your ride!
There really aren't any suction leaks in the 6.5 system... it's all push pressure. Pressure from the LP to the IP, Pressure from the IP to the injectors, then low pressure from the injectors to the tank (return line).
The return line might develop a leak, all that should do is make a mess, shouldn't be able to affect the rest of the circuit at all.
NVW
Well-Known Member
There is suction from the tank to LP.
nealpellecchia
Active Member
nealpellecchia
Active Member
They want you to plug the return at the tank and put pressure on the supply hose to try and force it to leak. So does that make the return line leaks a possible source of bleeding down the siphon and producing hard starts? My big hope is that someone who has found some will respond with their findings.
NVW
Well-Known Member
I can't see a leaky return causing hard starts, it would also make a visible mess. Put a clear section of hose where the return begins at the IP and check for air bubbles.
Does the LP work?
Does the LP work?
bison
Well-Known Member
Verefy first by opening the T-valve located on the water crossover if the LP is pumping(engine running),a runnnig pump doesn't always pump.
secondly losen the tank cap and check for exessive vacuum.
A plugged filter or a plugged tank sock will create a suction effect between the IP and filter or between LP and tank.
You can replace the IP return hose with clear plastic tubing and check for air bubbles passing trough,there should be none ,save for one tiny bubble after shut down,even sitting overnight.
The fuel system is closed loop and in the absence of a leak will allways remain full of fuel.
secondly losen the tank cap and check for exessive vacuum.
A plugged filter or a plugged tank sock will create a suction effect between the IP and filter or between LP and tank.
You can replace the IP return hose with clear plastic tubing and check for air bubbles passing trough,there should be none ,save for one tiny bubble after shut down,even sitting overnight.
The fuel system is closed loop and in the absence of a leak will allways remain full of fuel.
bison
Well-Known Member
closing off and putting pressure on the return line will most likely pop or pop off a injector return line,..don't do it.
nealpellecchia
Active Member
lp replaced 2 yrs. ago passed volume test and pressure test pretty good...leaky connector on drain fitting. Guy says that on fords a leaky return will bleed off pressure and make for hard starts...like you say it's a closed loop...if it becomes open the siphon is broken and the fuel is replaced by air and goes back to the tank. Making for hard cranking starts with frequent air bleeds from top of filter.
ak diesel driver
6.5 driver
if your OBD1 that's especially true. OBD2's have a pre prime during wait to start, OBD1's do not
nealpellecchia
Active Member
db2's are you referring to the injector pump? please elaborate.
dangerousdave
1994 6.5 Suburban
Welcome, Neal. What he said.:iagree:
Please fill out the signature with the info on your 6.5 vehicle so we can help you better.
The guy you know that keeps talking about fords doesn't seem to know anything about our trucks, at all.
let's start at the beginning with you telling us all about your truck, the circumstances of the problem, and anything else you can think of.
It's free.
ak diesel driver
6.5 driver
obd1 vs obd2 is the electronics ie ECM/PCM obd1= pre 94 obd2= 95+
- Staff
- #14
What I said to start with... yes, there is suction between the tank and LP, but minimal. If there is suction between LP and IP, you have issues; if the IP is trying to suck fuel, your LP isn't working or your fuel Filter is plugged. After that, there is no suction.
Repeat; a leak in the return line will not mimic a suction leak.
However, a leak in the supply lines will cause the system to bleed down pressure and potentially cause starting issues. However, a leak in the supply lines is almost always accompanied by fuel because they are under pressure.
If they don't leak, your LP isn't doing its job.
Repeat; a leak in the return line will not mimic a suction leak.
However, a leak in the supply lines will cause the system to bleed down pressure and potentially cause starting issues. However, a leak in the supply lines is almost always accompanied by fuel because they are under pressure.
If they don't leak, your LP isn't doing its job.
JMJNet
Recruit
Actually, a bad LP can cause a small siphon in the supply line.
If you have siphon effect in the fuel filter, chances are the 2 o-rings or the 3 hoses in the fuel filter bowl are bad or all of them.
Rubber parts tends to deteriorate overtime.
If you have siphon effect in the fuel filter, chances are the 2 o-rings or the 3 hoses in the fuel filter bowl are bad or all of them.
Rubber parts tends to deteriorate overtime.
nealpellecchia
Active Member
now that's the kind of info I wanted! alright I'll check for that. I rechecked the fuel pressure because it's hard to get a good seal from the attachment on the hose of my old tester and still I'm getting a little leakage but I think it is the lift pump that's weak more than a little fuel dribbling loosing pressure during the test. But also I'm doing the test off the drain hose and not the fuel line going into the filter. When I get it right and the test still fails I'll disconnect the the line in to the lift pump at the pump and see if it's easy to suck fuel out of it and blow into it to clean the mess off of the sock before I change the pump.
nealpellecchia
Active Member
pressure very good with tight connection at line into the filter housing. narrow connection id into the guage hose...does that raise pressure??
bison
Well-Known Member
No.
But best place to take pressure is to T in just before the IP inlet
But best place to take pressure is to T in just before the IP inlet
dangerousdave
1994 6.5 Suburban
Ditto.
I have my fuel pressure gauge T'd in to the line going into the IP
so I get an accurate read on the filters and lift pump, as well as the tank intake "sock".
That's how I knew to replace the return spring in the Walbro, and now the sock is starting to clog, so I'll drop the tank and remove it.
Knowlege is power; accurate knowlege prevents mistakes.
nealpellecchia
Active Member
yeah it's the only thing that I can do while I still can't find the leak is to T in a gauge... I think I can get it in front of the filter...then I can keep track that it is actually happening. I was told to look for a leak like you do on a gas engine by spraying substances around fittings and hope it will suck in and raise the idle or stall the engine. Not as immediate or as sensitive as a gas engine because it's much less immediate the effect on the engine.