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94 TBI fuel problems

Kenny78

Kenny78

1/2 ton status
Joined
Nov 7, 2007
Posts
496
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Location
Around Tulsa, Oklahoma
1994 5.7 TBI
My truck barely runs and is getting worse. If it were carbed, I would say that the float bowl is running out. It was running alright at idle b ut right after you take off it sputters and dies. Now it will barely start, if at all. In an effort to save money and correctly diagnose the problem.

I got a fuel pressure tester and adapter(what a pain to install) and here comes the question: When the fuel pump primes, should it go to 12-13psi?
While cranking and after prime the fuel pressure never moves. If I press the bleed off valve some fuel will come out eventually, but nothing like I expected

Does this tell me that my pump is not building any pressure and needs replacing?

P.S. I checked to make triple sure that the pump was priming, and i found something else.
When I turn the key on and listen for the prime, it runs continuously
 
TBI should be 12-13psi period. If your not getting proper pressure its probably the regulator in the TB. For the most part a bad fuel pump is black or white.
 
In my opinion the most useful tool you can get if you've got TBI is a cable and WinALDL software. You can really end up chasing you tail and throwing parts at those things otherwise.

Anywhooo, did you change you fuel filter?
 
how many miles are on that fuel pump, personally anything over around 125k on them and they are usually on borrowed time.

0 psi in the fuel line, obviously, no fuel pressure, no fire.

and i have had them before to where they are pumping, just not enough pressure under throttle, it idles and "almost" sound fine, but once on the throttle, it sputters, spits and just acts like it's out of fuel,,,
when i had this happen though, i was getting a lean condition code from the O2 sensor.
 
Yeah little bit of pumping, but little volume and no pressure. It probably has actual vehicle miles of 234,xxx. 5/8 of a tank of gas too. No codes and the bulb lights up like its supposed too Guess the tank is coming down for inspection.:(
 
If you get no fuel pressure it is either a bad regulator diaphram or a bad pump. I would buy a new regulator diaphram first since that's the cheapest. I have a good workiong stock TBI pump you can have for cost of shipping if you want it. I removed it to install a high pressure pump for my new HOT engine last year. The pump i have was replaced and doesn't have many miles on it since doing so.
 
Thanks Scott, I might take ya up on the offer.(crosses fingers) I am not running around like a headless chicken for once since my 85 is running great and I also have the 73 rustbucket if I'm desperate. (Driving the vert with the top on is kinda like a haunted house ride; squeaky, groaning, and the top bolts will loosen themselves and hit you in the head!)

I will take your advice and replace the regulator diapragm tomorrow.
 
Let me know, i just pulled the pump out the other day as was going to throw it away. I initially figured i would keep it in case i needed to go back to a stock TBI but that isn't going to happen so i don't need to keep it around any longer.
 
Truly doubt if it is your regulator. If the diaphram goes bad it will leak. Plan on replacing the fuel pump.
 
O well if you have 0 psi it can only be a few things.

Fuel pump cutoff fuse. Believe its labeled ECM1 on the panel. Bad ign module will cut fuel pressure. Or a bad fuel pump.
 
If you can hear the pump running continuously then it is most likely a problem in your tank - Either the pump motor is spinning but the pump itself is bad or the pump dislocated from the fuel lines. Can you hear fuel sloshing around in the tank while the pump is running?
 
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