350 Tbi- fuel pressure issue

[Tbbreck]

Finally looking for help after three weekends of "fun".

Swapped my carb for a tbi on my 350. Ran poor at first, but ran consistent. Always slow to prime system.

After several months of decent running, it began to have issues. Worst issue was it would start, run, but if I cut it off and started again within minutes to an hour, it would only run for a bit and sputter out. Sometimes it would not start at all, and if I waited 5-10 minutes after not starting, it would finally start. On inspection I found out the fuel pump was not pushing or pulling fuel from the tank. I had disconnected the hose from the fuel pump and engaged the pump by turning the key- no fuel coming out.

Here is what I have replaced to try and fix this issue
- new high pressure fuel line from pump to manifold
- new external fuel pump (second one) 15-17 psi
- new fuel check valve
- new fuel filter
- new high pressure fuel line from sending unit to fuel filter
- dropped and cleaned tank

After all this, is runs rough and still dies after I run it, kill it, then try to restart. It will eventually start if I wait for a bit. It will not start after sitting overnight for three days running, since I put in the new pump/valve/filter. I will start later in the day.

I have a new sending unit to put in, but hate dropping tanks. This is basically a brand new fuel system from tank to manifold. Jets are sloppy, but spray. Issue seems to be between the pump and tank, but not sure why.

 

[Sam5038]

I have a TBI on my 4.3ltr V-6 and it needs 35psi fuel pressure to run. I'm using the factory S-10 fuel pump that I mounted in my tank.

 

[csuengr]

Not enough fuel pressure from the pump. You need 25 to 30 psi.

 

[Torxhead]

I wonder if you are even getting enough fuel to the pump? If you have a properly vented fuel tank, the fuel should be able to siphon out on its own prior to getting the pump. A pump without enough fuel will be warm to the touch also. Not sure where you have the pump mounted, but the best location for it is as low as possible.

 

[Old Dog]

my chevy tbi runs on a 15 PSI. pump so I think your ok there.
I'd double check your not drawing air in somewhere.
or as torxhead said make sure the pump can pull the fuel from where you have it mounted.

 

[Torxhead]

my chevy tbi runs on a 15 PSI. pump so I think your ok there.
I'd double check your not drawing air in somewhere.
or as torxhead said make sure the pump can pull the fuel from where you have it mounted.

I would agree with that, the tbi has an internal regulator that can be adjusted from underneath. The place to check pressure is just outside the tbi.

 

[Tbbreck]

Thanks all,

It is getting NO fuel to the pump when the issue happens, usually after sitting overnight. I know this because I can pull the hose off the fuel pump outlet, and nothing. Eventually, after sitting for a while, the pump will catch some fuel, and all is fine.

I do believe air is getting in, which is why I put the check valve in. I took it out yesterday when I found out the pump would not pull the fuel past it. As soon as I plucked the check valve out, fuel started dumping out of the line (behind the pump.

Perhaps I should try and put the check valve in front of the pump.

Other option is an in tank pump with or without the inline.

The inline is installed on the passenger frame rail. Can't say it is lower than the tank, but as low as it can go without risking being ripped off.

 

[Tbbreck]

Just when I thought I had it narrowed down

So right after I typed the last response, I go outside and turn the key again, just to find it still will not start. I pull the hose of the rear of the pump to see if there is fuel getting to the pump, and fuel proceeds to just dump out of the line. I quickly stick it back in the pump, turn the key to let it prime for about 10 seconds, and it starts right up.

So, would there be a chance air gets trapped in the front of the line, between the pump and manifold? I have all new fuel line there.

Still wondering if a check valve closer to the manifold, or an in tank pump would help.

 

[Torxhead]

Running a add on fuel injection system to a CJ can be tricky, but can be done successfully with an external fuel pump. I really don't understand that check valve that you have, and it sounds like you got the air out o.k. A few tips: Don't run out of gas in the tank, going below 1/4 tank can cause problems with air entering the system. To check if the fuel tank vent system is working properly, remove the gas filler cap after a drive and listen for air rushing in-there should be none. The fuel line between the pump and the tank is actually just a siphon hose as electric pumps do not suck very well and needs all the help it can get. I have heard going to a 3/8" line can help here and is on my to do list. The in tank electric fuel pump is the best way to go if you want to set one up since they run cooler and operate right in the tank. My tbi runs at around 9 psi.

 

[GatorBate]

I have a TBI from an 89 Chevy on my 303. I had similar problem at first. I found that a 15 to 20 lb fuel pump would not move enough fuel at a high enough pressure to keep up. The TBI does have a built-in regulator that tries to keep the pressure at The injectors around 12-15 lbs. But I found that I needed a pump that put out about 50 lbs in order for it to work good. Also my fuel line was to close to the exhaust pipe and it would vapor lock on hot days when I was far from town.

 

[GatorBate]

I have a TBI from an 89 Chevy on my AMC 304 . I had similar problem at first. I found that a 15 to 20 lb fuel pump would not move enough fuel at a high enough pressure to keep up. The TBI does have a built-in regulator that tries to keep the pressure at The injectors around 12-15 lbs. But I found that I needed a pump that put out about 50 lbs in order for it to work good. Also my fuel line was to close to the exhaust pipe and it would vapor lock on hot days when I was far from town.

 

[Tbbreck]

Check valve just maintains pressure in a system, like putting your finger on a straw in a glass of liquid and pulling the straw out. The liquid stays in the straw, until you pull your finger off.

I keep hearing both sides of the psi argument. Half say 30-50, half say 15-20. Guess it depends on all the factors- lines, pump, tbi, settings and adjustments, tank, etc. only way to find out is put a higher psi pump in there and see for myself. The 17-20 just seems to not keep up with the demand, especially getting the fuel from the tank. I could certainly run an in tank with an inline rather than just one. Once the fuel gets in the inline, it runs. However, after sitting overnight, it seems to back drain into the tank, and has to prime for quite a while.

Can't see where 30-50 psi will hurt, if the jets/Tbi has a regulator.

 

[GatorBate]

Good luck with the TBI. You will love it once you get the bugs worked out. I ended up using a Airtex E2000 fuel pump. Don't let them sell you a substitute. They are not the same. I tried two or three that the local parts places said were a direct replacement. Finely had to go on line and order an one summit racing. Ford used them a lot in the 80s. They put out 30 to 40 gph at between 70 to 95 psi.

Anyway that's what worked for me.

 

[Tbbreck]

Do you have a regulator on that, or is it pumping full throttle?

I heard that was a good one to use in another forum. Also heard it was too much

 

[GatorBate]

No, it goes straight into the TBI. I have a screen in the tank and a filter on the outside of the tank, then the pump and straight to the TBI. My TBI's regulator has a return line that bleeds the extra fuel back into the tank.

 

[Torxhead]

Check valve just maintains pressure in a system, like putting your finger on a straw in a glass of liquid and pulling the straw out. The liquid stays in the straw, until you pull your finger off.

I keep hearing both sides of the psi argument. Half say 30-50, half say 15-20. Guess it depends on all the factors- lines, pump, tbi, settings and adjustments, tank, etc. only way to find out is put a higher psi pump in there and see for myself. The 17-20 just seems to not keep up with the demand, especially getting the fuel from the tank. I could certainly run an in tank with an inline rather than just one. Once the fuel gets in the inline, it runs. However, after sitting overnight, it seems to back drain into the tank, and has to prime for quite a while.

Can't see where 30-50 psi will hurt, if the jets/Tbi has a regulator.

I would suggest ditching the check valve, you need flow between the tank and pump, not pressure. Whatever the oem pressure is for the tbi equipped 350s are set to, start with that.

 

[jdarg]

Some TBI setups did require pumps > 30psi. 94-95 BBCs come to mind, where they ran a smaller injector, i think from a 4.3L, at about twice its normal
"rated" pressure. but most TBI application were about 15psi IIRC.

I run TBI on my YJ for the past couple of years.

The stock 92-95 MPFI YJ pump works great w/ either TBI or TPI and those pumps should also work just fine in a CJ tank.

 

[PistolDave]

One thing I have not seen mentioned in this thread is fuel return line pressure. On the TBI systems I have messed with, you want as close to zero pressure on the return line going back to the tank as possible. I usually like to run a larger return line than the supply line. Most of those internal regulators will not function properly if they see any 'backpressure' on the return line side. Maybe something to check. My 0.02$ worth, and that may be about what its actually worth.

Dave