I've been trying to track down fuel pressure issues on my 2000 S-10 Blazer 4.3 and now my 98 Sierra 5.7.
Reading all the helpful info on the site, all help has been appreciated.
I was reading a chat that told how to isolate and test the fuel pump for bleed-off once pump stops running. (Hook a fuel pressure gage on the supply line at the fuel filter). Sounds easy but how do you connect the pressure gage in???
My solution, the fuel feed and return lines that bolt to the top of the intake, the feed line(the one with the shratter valve) has the same line fitting as the fuel filter.
I had a spare left over from my engine swap, I cut the feed line loose from the return line, cut it just past the shratter valve, crimped it down and welded that end shut.
Now I have a connector that the fuel line bolts into with a shratter valve and isolates testing the fuel pump seperate from the FPR and injectors.
Now my question
On my Sierra the pressure rose to almost 100Lbs but when the pump cycled off it drops to zero in less than two minutes. Is the running pressure a bit high?, (you are checking the full pump output with no regulator), and how much pressure should the fuel pump hold and for how long? Also what pressure numbers and hold times should I look for on the Blazer. I didn't get to check it yet tonight.

 

The answer is in this post:
96+ Fuel System Diagnosis

 

Running pressure should be high the way you did it. As for hold, there are no specs for that pressure (that's high) but there is a check valve in the pump and holding the normal 60lbs it should lose no more than 5lbs in 10 minutes.

 

So considering that the pump is the only thing in the system being tested with this set-up. As far as the Sierra goes when I lost all pressure in less than two minutes, it's safe to say that the check vavle is shot. I lost the fuel gage about eight mounts ago, the test would explain the long crank times at start-up these past few weeks, it just figures I wouldn't be able to get by with replacing the sending module alone.
I read the 96+ fuel post a few nights ago but was more interested if the 100Lb+ pressure reading seemed high and wanted to share a way adapt a tool for those that either don't have, can't find, or don't want to spend $$ renting suck a tool.
Thanks for the quick replies after dinner I'll go open up the Blazer and start checking it out, just hope that the pumps not bad in it also. It's bad enough knowing what I'll be spending on one.

 

100psi dead-head pressure isn't out of the question with these pumps. If it still bled off after the pump shut off, then the check valve is the likely culprit.

 

Just ran test on the Blazer. The pressure only went up as far as 50Lbs held firm and only lost two pounds after five minutes time. I re-energized the pump and bleed the pressure gage a few times to see if any air in the line was giving me a low reading this time it went up to 54Lbs and after ten minutes I'm holding at 50Lbs.
This test was performed on a cold pump, my running issues start in usually at running temp.
I'm going to hook the Filter back up and run the motor till it starts acting up and run the test again.
Just wanted to see if the 54Lbs sounded to low. Of course each gage is different.
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After the cold test and seeing that the pump was maintaining pressure at just above 50Lbs for over ten minutes I started the Blazer to let it get to running temp. to see if it would act up and if the pressure would change. I never got the thing to act up while up on the jack stands idling in the driveway. So I let it down and cleaned everything up to take it for a spin. As I pulled out onto the street it choked and puked, backfired and cleared up a bit. Ran as usual up to the gas station, seeing I was about on E. Figuring that the pump wasn't bad I felt safe to fill it up. I added a bottle of concentrated injector cleaner and put in about three gallons of E85 to a full tank of gas.
Took it out on the highway and ran the s**t out of it. Needless to say my truck doesn't have that certain MPH shutdown that most trucks have and it's the first time I've ever gotten that much spunk out of it. I'm figuring I have something clogged in the fuel system somewhere. Figure I'll drive it till the additives have a chance to do there thing and hope it gets better.
Stopped over a buddies house and took him for a spin to see what he was thinking it could be. He thought the TPS was acting up. So we stopped and unplugged it. It seemed to have better throttle response, and we didn't get any lights even after running up and down the road a few times with it unplugged. After plugging the TPS back in I came back home and changed the TPS with the other one left over from the engine swap. It ran the same, only this time when I tried unplugging it, it threw a code just idling in the driveway.
Is it me or does it seem that the gremlin I'm chasing is in the computer not the motor or a sensor?
I also rechecked the fuel pressure and it was just under 60Lbs at idle and shot up just over 60Lbs if you dropped the throttle open. After shutting off the engine it held pressure at just under 60Lbs.
Either way the longer it ran tonight the better the throttle response got.
Just confused on the check engine light acting the way it did earlier compared to later?

 

You should be close to 60psi key-on/engine-off. But if you are not having starting trouble, I would chalk that up to gauge inaccuracy. Sounds like your engine-on pressure is good.

You can test the TPS sensor with a multimeter and some back-probe test leads. Back probe the ground and sensor return for the TPS sensor and test with the key-on/engine-off. The voltage should go from ~0.5V at closed throttle to ~4.5V at wide open throttle in a smooth progression.

 

Thanks Swartlkk for the TPS diagnosis procedure, I'll check it when I get a chance. I did the later check on the fuel pressure at the fuel rail shradder valve and that was the 60Lbs. at idle and 60+Lbs. if you throttled the motor. I'm thinking that I have an injector that is sticking or a clogged popet. The thing just runs to sporadic and the only other thing that would act that way may be an electrical problem which is why I mentioned possible gremlins in the computer. May need a reflash, but I'll run through some of the test you guys have posted to rule out the injectors and such.
I'm mainly relieved that I only have to buy one fuel pump (for the Sierra), but I already had planned on having to do that.

 

Have you check for codes usually when gremlins get to your PCM they set codes. LOL

 

I check for codes everytime a light comes on, the problem is I hardly get a light at all and if I do it's because I've unplugged or disconnected something to see if anything changes. I did speak to my machanic buddy and he said that I got a code for the TPS the second time only because I cycled the key all the way off and then back on. When we ran it unplugged the first time I never turned the ket to the off position, just restarted it and carried on my way. The computer didn't have a chance to cycle for codes or something like that.
I sure miss the old one wire HEI, machanical fuel pumps, and carburators.

Hay Swartlkk, I just came on a posting where you mentioned that the timing on your 2000 Brav. was some 12-19 degr advanced at idle via scanner. My 2000 4.3 Blazer was (I need to recheck it) coming in at 12-17 degr retarded, what's your thoughs. Keep in mind I've had the distributor out three times and am pretty versed at lining up the marks ect. ect. so I'm pretty sure everything is in right!!! If I do have computer gremlins, could that be the reason for the stumbling and lack of umph!!!
MY buddies scanner gave us the reading of 12-17 retarded at idle and stated that it should be reading 0 degr + or - 2 degr.
I'm still planning on replacing the timing chain, don't know if it's worn or if someones been in there and not got it lined up correctly!
I did pull the distr. with the entent on replacing the drive gear, but the one on it looked brand new. Absolutly no wear marks!!! However while I had it out I noticed that the distr. had a lot of up and down play so I drove the roll pin out of it and a extra one from the engine swap and added a shim to take up some of the end play. It had close to .100 of play and now only has .040 give or take a few. It didn't make any noticable change in runability but I have yet to rescan it to see where the timing is falling since adding the shim.