For the record here is what is installed:
1. 1989 Chevy 350 engine with complete TBI setup minus factory wiring harness, EGR,oil pressure sensor.
2. Painless wire harness for TBI setup (been on for 4 years now same system differant motor).
3. Fram inline fuel filter (the good one with the oil looking filter) and Carter external fuel pump 15 to 18 psi.
4 Fuel pressure gauge by the TBI.
5 1227747 computer.
Here is what is happening:
Start the motor cold and I have 11.5 psi at the guage. All seems fine...let the thing get to operating temp and still runs fine for a while but the fuel pressure will steadily drop. still have good throttle response and engine runs fine in all RPM ranges. Engine will drop to 7 psi and still run good. Here is where it gets wierd. All of the sudden the fuel pressure will go from like 6 psi to 0 psi up and down and then will eventually stall. Also there is hardly any fuel being returned to the tank. It spits or none is going back at all.It is hard to start after this but will start but shortly afterwards it will start doing the same thing. Till eventually there is 0 pSI but it will start and run for while. You can slowly accelerate and get it going but it will eventually die on you. NO CHECK ENGINE LIGHT! Now if you let it sit say for 2 or three hours it will start up again with 10 to 12 psi but it will eventually do the same thing. It may be with in the hour or it may be 8 to ten hours later.THE FUEL PRESSURE ALWAYS WILL STEADILY DECREASE! BRAND NEW FUEL PUMP AND FILTER INSTALLED!
Example: was out wheelin Memorial day this year and was pulling another Jeep when all of the sudden the Jeep died on me and the problem above was there. I disconnected from him and limped it back to camp. Let it sit for about 4 hours and all was fine. Went on a night run and no problems. The next day were headed out and roughly 6 hours into the day it was doing it again.
Get it home and can duplicate the problem after letting it run for like 3 or 4 hours...but no check engine lights.
Engine stays at around 190 degrees to 210 degrees. This only happens when the engine is completely warm.
Here is what has been replaced:
1. ECM with good spare
2. TBI base.
3. New pressure regulater( today)
4. CTS sensor (today)
5. Map Sensor ( today)
6. O2 sensor (today)
7 Fuel pump brand new
8 fuel filter brand new
9. Fuel relay
10. Ingnition control module
11 TPS with known good one from other throttle body (spare)
12 IAC valve
14. Check entire harness for melted wires and such no problems
Basically the only thing I have not replaced is coil, Distibuter and associated parts and Knock Sensor. Could any of these be causing the PSI to drop and causing my problems?
Further more what in the world would cause the pressure to drop in the first place. The NEW pressure regulator and spring I installed should keep it a constant 10 to 12 psi, shouldn't it?
ARRRGGGGG I am losing my mind here please HELP! You can call me if you like or give me a number and I can call you if you would like to talk rather than posting responses.

 

Is fuel sloshing away from the pick-up. Back when I had my stock 38 gallon carb tank on my G20 it would do something similar when the fuel level got low.

I am thinking that you are getting heat onto some part of the fuel system and are getting vapor lock.

You might try putting a small pre-filter in front of the pump, install your cartridge filter between the pump and TBI, then put the inlet/return into a 5 gallon gas can. See if the problem goes away.

 

Well I have a sump in the bottom of a custom aluminum tank and the tank is half full. Plus the test I did today was stationary. So fuel pickup is not the problem. All the fuel lines are away from any exhaust and the fuel pump is not hot at all. Same with the filter. Plus I never see the injectors stop spraying at anytime. till it stops running naturally.

 

Are you running an oil pressure switch in parallel with the fuel pump relay to drive the fuel pump like stock. If not, have you tried directly wiring the pump to the battery and just letting the fuel system pump? You are getting a lack of fuel volume from some place. My guess is that the rise/fall of the pressure is vapor/air bubbles in the system. The lack of fuel returning from the regulator further reinforces this. Find out the bottleneck and you will find your problem. Does the pump sound normal when this occurs?

I don't know of any ECM related problems that would cause this.

One other thing that might help troubleshooting is a cheap see-through plastic $2.00 fuel filter, mount it right before the pump to see what is getting to the pump. You might suprise yourself. A loose fitting that is pulling air will cause all kinds of grief.

 

In the wiring harness there is a seperate wire for the Oil pressure and seperate for the fuel also. So no they are not tied together.

The pump sounds fine. IT does qeit down after about 15 minutes or so. I never hear the puimp turn off and I have checked the voltage going top the pump when the problem occurs. 12.8 volts or so.

I will get some clear line tomorrow and runn that to the inlet where my guages is and into the TBI. Good sugestion!

My lines are new and 3/8 in size. Steel from front to the pump itself. I have no leaks and there is only one union. Rubber going from steel line in engine compartment to guage then rubber to inlet on TBI. Rubber from tank to filter and rubber from filter to inlet on pump. All 3/8 lines.

 

In stock trim, both the fuel pump and oil pressure sensor are tied together through the fuel pump relay on the stock wiring harness. Double check you're connector plugging into the fuel pump relay, and you'll see both (fuel pump, and oil pressure sensor) wiring being prevalent.

You mentioned that you have adequate voltage to the fuel pump, even when the problem is at hand. Just out of pure curiousity, is you're fuel cap on? Also, are you trying to pull fuel with that external fuel pump, with the stock internal fuel pump still being inside the tank?

With the fuel pressure gauge, start the engine up and get a good reading. Shut the engine off after a few seconds, and wait to see just how long the pressure still holds...

 

Wanted to clarify... the wiring found inside of the fuel pump relay's connector leads to both the battery, oil pressure sensor, 12 volt source and ECM. It isn't directly wired to the fuel pump, it's linked to it through the ECM.

 

I am using a stock fuel pump relay. and ONLY the external fuel pump. All my tank is hunk of aluminum that hold 23 gallons of fuel. There is no pressure in the tank at all and the problem is with the cap on or off. Does not matter. Pressure will hold for about a second. The pump shuts of and the pressure is gone.

 

That's good, as I just wanted to make sure that the stock internal pump has been eliminated. Using a fuel pump relay, is of course, optional, with an aftermarket fuel pump. But it's always good to have though...

For pressure to drop off immediately would indicate a very bad fuel leak. Draw a better picture here, this aluminum fuel tank.... did you fabricate it? Is it meant to be a fuel cell, or is it just some convereted aluminum box. Does it even have a filler neck, and if it does, check to see if it's leaking when pressure is present.

I would also re-inspect you're fuel lines again, and as mentioned, all of the fittings that were used to tie everything together. You mentioned that the pump is noisy upon the first few minutes, but then quiets down soon afterward. This has me interested, as when I ran my Holley external on my 86', it made the same noise constantly...

You said you checked pressure, and it immediately went to 0-psi once the pump was turned off. Did you check this in both conditions? Meaning, did you check with the engine cold (before the problem starts), or did you check afterward... when the engine is warm, and acting up?

 

So, pressure is fine during Open Loop... but once Closed Loop is completely realized, pressure will slowly, but surely, make it's way down. Lets eliminate the possibilty of a fuel leak for a second. Between you're new fuel pump "sounding" okay in the beginning stages, but then eventually quiets down after a few minutes, would lead me to suspect that there is a fault in the wiring somewhere. Something, when Closed Loop is realized, is causing the pump to gradually lose power, either that or you have a defective pump....

If memory serves me correctly, I believe the distributor (ESC sensor) has much to do with "triggering" the fuel pump (through the ECM)....

 

Ok this is a newer fuel cell, filler neck and all. Even a tipover valve. There is absolutley NO fuel leak anywhere. It is a brand new fuel pump and the pressure is fine when I test it off the system.

Could heat be causing all my problems. The fuel pump is roughly 1" to 1.5" form the exhaust....

 

Yes, but it could be the system itself in which is causing it to seize pumping. You stated that you're running it with the stock fuel pump relay, which obviously means voltage is being regulated by the ECM. It could be a bad reading.

Possible, as this is why the factory electric pump is located in the gas tank... the fuel helps to keep it cool. Excessive heat causes metals to expand, and with the Carter pump that close to the exhaust, it might be seizing on you. The only way to know for sure is to re-locate it elsewhere.

Re-locate the pump, and if that doesn't solve your issues, hook up the fuel pump directly to the battery, bypassing the ECM entirely....

 

did that hooked it up directly to the battery. also relocated the pump and still no change. Starts out at 10 to 12 and will steadily decrease psi.

 

I am beginning to think the pump is bad. I got a heat gun checker today and the problem is constant with the change in the temperature. The higher the heat the less fuel pressure is there. Does this sound right? Or could the distributer be causing the injectors to release more fuel?

Furthermore if the injectors were for some reason releasing more fuel just sitting at idle would the pressure drop? If this is true then would the pressure drop when you accelerate or would it remain constant? I thought it woshould stay at a constant 10 to 12 psi????

Also now that I have clear lines installed when the fuel pressure gets to 7 pounds and below I can see no air bubbles on the inlet side however on the return line it has a ton of air in it. Almost looks like the return is boiling but I don't think it is. The pump was at 112 degrees on the housing when it dropped below 5 psi. This is with the NEW pump installed on the outside of the frame rail no where near the exhaust now. Which brings me to another question...could a NEW pump go bad in say 10 hours of running to create this problem? As the pump heats up the fuel pressure drops...

 

You say it is a Carter style pump, but is it an EFI style pump? Alot of carb applications only run 3-7 PSI. If you have a carb style pump, it could be overheating the pump and causing it to shut down. You might get a frame mounted pump for a late 80s FI Ford truck and see where that gets you.

 

It is a pump that flows 15 to 18 psi and was recomended buy JEGS. Why a ford and what PSI does it put out?

 

Despite what the people at Jegs are recommending, tell us what the part number of that external pump is...

 

HP 4601 hp

here is a link

Carter Universal Rotary Vane Electric Fuel Pumps: CRT-P4601HP - summitracing.com

 

With only 18-psi, that electric fuel pump is more intended for carbureted applications. It simply can't keep up with the demands of a throttle body injected system. The pump is definitely overheating, causing fuel pressure to slowly drop. I wouldstrongly recommend getting yourself an "intank" pump from a Tuned Port Injected application, along with the proper sending unit, and you'll be back on the road in no time....

 

Given the nature of his tank, that is why I recomeended the ford frame mounted EFI pump. It flows 190 LPH at the factory ford MPFI pressure, like 38 PSI! That is more than enough to feed my TBI engines. It will push 100+ PSI, but is limited by the regulator to 10-12 PSI in your application.

 

I definitely agree with you're recommendation Fast, but it all "boils" (pun intended lol) down to personal preference. Having the pump submerged in fuel will keep it cool, as well as completely away from the naked eye...

 

Yeah, but he has a FUEL CELL, it has a sump in the bottem. I doubt that you could even put a TBI sending unit in it, atleast the ones I have seen.

I agree though, I am no longer using the ford frame mounted pump, mine is a TPI pump in a TBI Van Tank. It runs quieter than the ford frame mounted one did. In fact, unless you have your ear down next to the tank, you don't even hear it unless you are below 1/8 tank, which I don't go below often.

 

I'm aware that he's running a fuel cell, as this is why I touched on it being personal preference. As for sending units not fitting his fuel cell application, I would imagine that he could have one fabricated (the sending unit doesn't have to be from an F-Body). It's not as expensive as one would honestly think. Either that, or simply obtain a different fuel cell entirely. In the end though, any external pump designed for fuel injected applications will have him back on the road...

Good luck Jeff!

-Lethal

 

I just ordered a proper fuel sending unit from Holley. You guys are right on track with the other pump. I did not know it was for a carburator. Guess the sales guys are just that...salesmen.

Wish I would have known all this 4 years ago. I have replaced the same fuel pump 5 times now. Seems like one a year. I just thought they were going bad. All were under warranty and no one has ever said it was not for a TBI system. Stupid me...and just when I thought I knew it all...hahahaha!

 

WAIT!!!

Is Your gas cap a Vented type? If not, get a vented cap or just remove the thing and see if it runs better/longer.... that oughta solve the problem...

 

The system does the same with or without the cap on. There is no pressure in the tank...