Looking at replacing my fuel pump in a 95 Tahoe. Any reason to think that a bad or cracked fuel pressure regulator in the throttle body would cause fuel pressure in the line from the tank before the throttle body to be low - as in computer controlling pump getting a bad signal an lowering output? Just making sure covering all bases before I drop fuel tank. Thanks.
Fuel pump going bad? 95 tahoe
- Thread starter Texast224
- Start date
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SunlitComet
OBS Jedi-Do Good
The VCM just turns it on briefly for priming after the engine is running ignition pulse references seen by the VCM tell it to keep the relay actively closed so it will run continuously. You should see about 9-13 psi with the key on but engine off. The pump control is either on or off there is no variable output on the system. A bad regulator can certainly be an issue.
Okay so testing pressure in fuel line right before fuel filter, has pressure when on, but pressure goes to zero when turned off. Thinking pump should retain pressure in the line line when cut off instead if frail fuel back into tank. Replacing fuel pump assembly.
I'm guessing better to replace the entire assembly than just the pump? Don't you have to crack open the assembly and soder wires and such?
I'm guessing better to replace the entire assembly than just the pump? Don't you have to crack open the assembly and soder wires and such?
SunlitComet
OBS Jedi-Do Good
Don't recall if the tbi pumps had a check valve but if it is maintaining 9-13 when running you should be fine for the most part with the pump and regulator. The unit primes when the key is turned on. If it is not and takes a while to start then yes there may be a weak point some where in the pump if after starting it still maintains the proper pressure. There are some improvements over the old design so if never replaced before the module would be a better choice. Still under $185 for a delphi unit at Jegs or Amazon. With the new design there is a new connector pigtail to install but it will include the butt connectors. No soldering involved. It is a complete module on a 4dr version I believe. The 2dr is pretty much exposed so no covers to remove once you get it out.
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retorq
Full Access Member
No the TBI's don't retain pressure once the pump is off. The pump is easy, the unit comes out of the plastic bucket its in, there are two of those lame ass socks on there so it might be worth it to grab another one. My after market pump didn't fit in the bucket and I hacked it till it fit and wound up using only the sock on the pump. No soldering, mine had clips on the ends of the wires. Do you really think the factory would sell you a fuel pump that needed soldering done to it?? LOL
Got that nugget from a "high end" mechanic. Of course he also said the unit would be 700 if he did it, when I found Delco at XL parts for 225.
So is my basic assumption accurate - that the pump should maintain pressure in the line when the system is off? Not talking about at the fuel line intake at the TBI unit, this is at the tank.
Where can I get detailed description of this if that is the case, if there is no pressure retained in the line? Everything I read online says pumps retain pressure, if you don't have pressure at the tank you have a weak pump. Alldata I'm finding is next to useless....
---------- Post added at 04:00 PM ---------- Previous post was at 03:42 PM ----------
Okay, so how often is a hard start when cold, resulting in about 3 cranking attempts with it dying out after try #2, then starting on try number 3, a function of a fuel pressure relay and how often a fuel pump?
Reading that the fuel pressure relay is responsible for priming the pump for 2 seconds once key turns system on, creating pressure in the line.
Read further that fuel pressure regulator will bleed fuel back to the return line once system is off.
So could the lack of pressure in the line next to tank be a function of a faulty seal from fuel pump in tank or something like that, rather than fuel pump?
Bottom line, read that 98 / 100 times the pump is bad when you have problems. That is why I'm focused on changing this first.
But I also thought that either the pump works or it doesn't, and you would know when it finally went out because you just can't get it started in the morning. Never really heard of a "weak" pump at ignition and when accelerating.
SunlitComet
OBS Jedi-Do Good
Don't think you mentioned what the pressure actually was yet. You have to read between the lines of the service manual you are reading and sometimes little glimmers of info from other sources to make an accurate assessment of what should happen when. If you were to power the pump directly with 12 volts and it does not output 9-13 psi "before" the filter then just replace the entire unit. It is more cost effective. Not sure what fuel this vehicle has been drinking but there is a TSB about a possible ruptured pulsation damper on the pump to because it was vulnerable to high amounts of ethanol. They redesigned it with a different material. Bad connections can also weaken power out and effect a pumps output. Get under there with a voltmeter and have someone cycle the key a few times and measure the volts at the pump connector as well. Bench test your relay as well. Never mind for now about pressure in other lines next to tank. Test your pump output with a enough voltage and do the same with your relay if all is good including the filter and it holds pressure then look else where on the ECM side of things.
What was the pressure you saw during your testing and do you have a 2dr or 4dr?
What was the pressure you saw during your testing and do you have a 2dr or 4dr?
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11 psi 4 door
SunlitComet
OBS Jedi-Do Good
11 psi all the time when pump actually is spinning? If so then look for problems with the Ignition control module or something else. Once started the oil pressure switch puts power to the pump as a backup in case the relay goes haywire. Have you actually tried to look for DTC codes yet?
11 psi until system turned off, then goes to 0. Did not check as I did not throw a light.
I actually had someone do it for me as I didn't have the time and didn't want to get stranded.
Performance is much better, on the crank and accelerating. Only thing is they also replaced fuel pump relay, after I said I only wanted the pump done so that I could narrow down symptoms/cause for next time.
Well now that brings up a new question. Could a poor crank and pulsating performance been caused by the relay only, in which case I got screwed because the pump didn't need to be changed.
That still would not answer the original question tho - will the pump hold pressure in the line when the key is turned off, or is zero line pressure out if the tank when system off normal. If true, then I screwed myself by not replacing the relay first myself.
BTW - took three pumps to find one that worked out of the box, first two were Delphi, third was Delco, even after I insisted on Delco before the job was ever started. Me being the unschooled customer I guess I wasn't supposed to know what I was talking about.....
Guess the Delphi are now manufactured in China and are garbage. Delco out o Mexico I guess?
I actually had someone do it for me as I didn't have the time and didn't want to get stranded.
Performance is much better, on the crank and accelerating. Only thing is they also replaced fuel pump relay, after I said I only wanted the pump done so that I could narrow down symptoms/cause for next time.
Well now that brings up a new question. Could a poor crank and pulsating performance been caused by the relay only, in which case I got screwed because the pump didn't need to be changed.
That still would not answer the original question tho - will the pump hold pressure in the line when the key is turned off, or is zero line pressure out if the tank when system off normal. If true, then I screwed myself by not replacing the relay first myself.
BTW - took three pumps to find one that worked out of the box, first two were Delphi, third was Delco, even after I insisted on Delco before the job was ever started. Me being the unschooled customer I guess I wasn't supposed to know what I was talking about.....
Guess the Delphi are now manufactured in China and are garbage. Delco out o Mexico I guess?
