I want to check the fuel pump pressure on my SS so I called the dealer and was told 55 P.S.I. while engine is cranking. I don’t know how to prevent the engine from starting while cranking. I do have 45 P.S.I. while running with vacuum line at regulator hooked up and 55 P.S.I. with it disconnected. What is the proper pressure and procedure? I can’t seem to find that info anywhere. Thanks for your replies in advance.
for what reason are you checking fuel pressure?
Mechanic said pressure was on low side at 45 P.S.I. which it still is now after replacing fuel pump. I installed an aftermarket fuel pressure regulator and the fuel pressure dropped 5 P.S.I. and the performance dropped with it. I put the original one back in and performance went back up. I actually suspect a faulty injector but need to rule out the fuel pressure regulator first. I actually found moisture in one injector connector. After I cleaned and dried it my light throttle stumble went away but I can still hear a light misfire sound in the exhaust at light steady throttle and overall performance is down. I thought maybe if the aftermarket fuel pressure regulator reduced performance by dropping fuel pressure 5 P.S.I. then maybe raising it 5 P.S.I. would put me back on track. So I need to verify or rule out this theory by properly testing fuel pressure. I hope this clears things up a little. Thanks
A dirty fuel filter will drop fuel pressure. Try a can of Techron Fuel Injector Cleaner in a tank of gasoline. A 5 psi lower fuel pressure doesn’t seem enough to be causing your problem. I would expect to see such a problem, possibly, under hard acceleration, not at idle.
Haynes or Chilton’s Repair Manuals are sources of instructions on how to check for fuel pressure, with vacuum connected to the fuel pressure regulator, or not connected. It will, also, have the specified fuel pressure values. You can acquire such a manual?
Thanks for the responses on my SS issue. The fuel filter is a year old, and yes it does’nt have the pick-up it always had. On an upgrade you rarely had to push more on the accelerator to climb the hill. Now you have to push down a decent amount and it kicks down one gear and sounds real throaty through the air intake. It kind of feels like the difference between a car full of people and luggage (and maybe a small trailer) and just one person in the car (no trailer or luggage)! I have not had good luck with generic manuals. I usually break down and get the factory shop manuals but, I don’t want to spend the money right now. My Daughter is getting married this summer so I have to pinch pennies!
Your public library has FREE automotive repair information, in book form and on line. Some libraries have free access to www.allata.com, for free. Ask a liberrian.
Test the fuel pressure with the engine under load. You can load the engine by putting the A/T into DRIVE and raise the engine speed to 2,000 rpm. Or, you can drive the car (with the fuel pressure gauge on a long hose and laid on the windshield), and load the engine by keeping pressure on the brake, and observe fuel pressure.
The performance problem may be in the ignition system, or the fuel injectors. A repair manual (of any type) could help you troubleshoot.
Your fuel pressure is regulated by, as you’ve seen, a fuel pressure regulator. To check the pressure, you’d want to know the pressure with the regulator regulating, and with it not regulating. Not regulating might be considered the raw pressure the fuel pump is capable of supplying, as compared to the pressure the regulator regulates to.
The “pressure while cranking” might be more appropriately called “unregulated pressure”. You can measure it by simply removing that which operates the regulator, which is engine vacuum. If you remove the vacuum hose, the regulator is rendered inoperative. It’s much simpler though, to just measure the fuel pressure with the ignition switch on but with the engine not running or cranking. Just turn the key on, don’t try to start the engine, and read the pressure. The pump will only run for two seconds or so, so read the pressure quickly. If you miss it, turn the key off and try it again.
As for regulated pressure, as you’ve seen, just read it with the engine running. If you have 45 psi with the engine running, I’d suspect you have no problem with fuel pressure. If you can’t find what the pressure should be, you haven’t tried very hard. Check a Haynes manual for what your running fuel pressure should be. I’d guess 45 psi is plenty.
I replaced the fuel filter to rule that out. I am going to my local Chevy Dealer next to ask them the proper procedure and if need be I’ll purchase a new fuel pressure regulator. Just to let you know, I’ve been putting STP injector cleaner or gas treatment in the gas regularly since the car was new. I will keep you folks posted. Thanks…
The Chevy Dealer said 55P.S.I. when key first turned on or at idle with vacuum line disconnected! I’m at 55P.S.I. so pressure to the injectors is good. Part throttle acceleration is ok since I cleaned the one injector connector. Overall performance way down. Intake very throaty. I noticed what looked like a cloud of blue smoke behind me when I first punch it, also I smell rotten egg smell also. The only time I ever smelled that was after I cleaned the throttle body. Could to much fuel be the issue? My daughters Saturn used to do that because of a faulty temp sensor telling the computer the engine was always cold(thought it was blueish but was mostly blackish). Gas mileage is down overall on the SS. I actually replaced the sensor on the SS because the temp guage in the dash was reading a little high. It reads ok now as far as the guage goes. I probably replaced it not long before the problems started and it is possible the cloud is blackish. I will check further. Lastly I have noticed a very slight lifter tick as it drops to idle?? I have been very religous on my oil changes, 3000miles or less. The car has 126,000miles on it and it never burned oil! I’ll keep plugging away at it so hopefully other people won’t have to!
There are usually two engine temperature sensors, one for the gauge and one for the computer. The Coolant Temperature Sensor is usually right in the same vicinity as the gauge temperature sensor.
Modern PCM computers do adapt to the conditions of the engine, i.e. they learn the best injector pulse width to arrive at the correct air/fuel ratio. If you change a part the computer has to relearn the correct values for fuel map. This may take some time.
I did’nt notice a second sensor in the area. I’m sure it would look kind of like the one I replaced. However, Here is the list of parts replaced: TPS, MAF, Plugs, plug wires, fuel pump, fuel filter, put original coil packs back on (nothing wrong with them, thats another story!), upper intake gasket, throttle body gasket, tested ICM, crank sensor, cam sensor, and just now the battery. My wife says that the car is ticked off at me for taking her to Belle Tire for tires, struts, strut tops, and an alignment! She had all these strange men violating her! Ha! Maybe I best keep my hands off for a couple of weeks, and drive her like my wife does! Thanks for the input!
Checking the injectors is usually a matter of doing a resistance check on each injector after carefully disconnecting the wiring from each injector. Chilton’s/Haynes will tell you how and what the resistance reading range should be. A V.O.M. (volt/ohm meter) is the tool required here.
Is the check engine light on? My WAG is a partially restricted catalytic converter.
No codes. What is WAG? I have two new things to toss around. My wife had mentioned several months ago that the engine seamed louder(throatier) I dismissed it because back then driveability seemed ok to me. I don’t drive the car all the time like her. However, I took it to the muffler shop twice after the driveability issues started and they said nothing was wrong with the converter and that it seemed to run ok to them. I kind of dismissed the converter because manifold vacuum is so good. The resonator has a very slight rattle in it when you bang it. My wife also noticed a sound from under the car kind or like a garden hose nozzle or air compressor seeping (very quiet hiss). That started a couple of weeks before driveability issues started. The second thing is someone on another discussion board has a son who is or was a chevy mechanic and he saw quite a few ICM’s go bad. They tested ok but they caused driveability issues such as misfire, overadvance, loss of power, and over a long period of time converter failure(on 3.4L’s anyway) I had it tested and it was ok, or is it? I noticed the driveability issues right after I gave the engine compartment its annual spring hose down with soapy water and compressed air drying! I’ve done this every year since it was new, by the way. Like I mentioned I found moisture in one injector connector and dried it out. For some reason that injector was missing the secondary retainer clip and I’ve never touched it. Anyway, that was the light throttle stumble. So back to the driveability! What do you think fellas…
What is WAG? It is a non-scientific SWAG. Which is a Scientific Wild A$$ Guess.
Ya know americar…I’ve suspected that all along. But two trips to the muffler shop and both times they said it was ok. Of course that was just by revving the engine and listening I think! After I resistence test the fuel injectors (as profhandy mentioned), I’m going to have to figure out how to rule the converter, resinator, and/or mufflers out! Maybe I can find a different muffler shop that will help me out. Maybe they make a universal converter that is more affordable. Anyway first things first. I’ll keep you posted…
Hey profhandy, I found the resistance specs for the injectors which is a minimum of 11.8 ohms. Mine were all 12.2 12.3 ohms. BUT, I sprung a major coolant leak and had to replace the lower intake manifold gasket! Actually, a coolant pipe at the front of the intake manifold broke but, you have to remove the manifold to replace it. Have not had a chance to really road test it since the new gaskets but, at least vacuum leaks at the gaskets will be ruled out! I’ll keep you informed…