Running poorly
 

Hello,

I've been pouring over this forum for a while now; trying to solve my issue. But, I think I'm at the point I could use some help. I have a 2000 GMC Jimmy with the 4.3 vortec, 4wd, and AC.

A month or so ago, I was having really hard starting (multiple misfire code). Crank for a few seconds, let it sit, crank again. Eventually it'd start, but run real bad. I did some research and decided to replace my fuel pressure regulator. It was indeed bad, with the washed clean intake. After putting it together, it fired right up and ran good. The next day, on my way to work, all of a sudden, it started bogging down and died on a hill. I messed with some stuff. Threw some electrical tape on some vacuum lines (they're in pretty bad shape), and was able to get to work. Figuring my issue was an vacuum leak (both banks lean code), I went around and plugged stuff off. Unplugged the vacuum line that goes to the auto-4wd and blocked it off. Same with the PCB. Unplugged the evap solenoid.

Then I went around with a squirter of water while it was running, and it didn't bog down at all. Went back to work, and I died in the same spot (it's not the first hill climb). Was able to limp it in after a while. Did a bit more research and suspected it could be a fuel pump issue. Replaced that (with the e-bay one, which was the prior pump that was in it for years). Issue persisted. At least now, it's not making such a loud high-pitch whine.

Eventually through tinkering, I found I could get it to run if I unplugged both the MAF and IAT sensors. Figuring that was the issue, I replaced both, but it didn't fix it. So I started digging deeper, learned a bit more about how to use my scanner, and what all the read-outs meant. I noticed that my bank 2 upstream sensor, was hanging at .2-.3. So, I replaced that (what a pain), and now it barely runs at all. I was able to just barely get to work (back roads) with the o2 sensor unplugged. Just to double check, bank 2 is passenger side?

Throughout this saga, I've also been throwing a few parts at it, trying to score a luck shot. Replaced the idle air control valve, which fixed an issue with my idle bumping up 400 is RPM every 5-6 seconds. Replaced the throttle position sensor. Don't think it was necessary, but at the time I didn't know I could view it on my scanner. Replaced the MAP sensor. The rubber on it was pretty shot. Replaced the evap solenoid, doubt it was necessary.

I have the PCV boot repaired and hooked back up, but the vacuum line that takes off next to it, is blocked off. Am I correct in my understanding that this only controls the automatic 4wd? I can leave it disconnected until I figure out these issues?

Now for some driving symptoms:
When I start in the morning, it starts up real easy, then will slowly chug down after a few seconds, and usually die, rarely it'll recover. Usually when I start it again, it'll rev up pretty high before settling down again, sometimes chugging down to die. When starting to move it in the morning, any amount of throttle will bog it down. It seems totally fine if I just let it do the idle slow creep. Seems to really dislike any throttle while driving except for ultra-slow increases.

I took a fuel pressure reading, and with the key on, not running, I had 48-49 psi. Maintained the value when started at idle. Replaced the fuel filter, no change. It looks like this value is lower than it should be. Are there any other things I can try besides a new fuel pump? What is the square thing in the very back driver side? It has fuel lines running to it.

I took a vacuum reading. At idle I was showing 15 in/hg. When I gave it a blip of throttle, it dropped down then bounced back, finally settling back at 15. From what I've seen, this value is a bit low? I ran it for a while at idle, then opened the throttle a bit for 45 seconds or so. It didn't drop below 15.

Before I tried replacing the o2 sensor, I took some readings. It was recommended that I disconnect the battery for the replacement, so now a bunch of monitors are INC. Just for thoroughness sake, these are older numbers:

shortfueltrim1 : 21-25%
"" 2: 13.3-16%

long trim 1 : 25%
long trim 2: 25%

Fuel trim checked @ 2500rpm in park
short1 - 45%
short2 - 30%

spark advance 18-20 (usually 19 or 20)

MAP kpa 32
RPM at idle 840-860
MAF : 6.4-6.9 at idle
16.5 at 1700rpm in park

As you can see, I've been trying a bit of everything. I'm mostly dealing with this for the satisfaction and education. If I need some new tools to diagnose this, I'm happy to get them. If I need to do any more tests, or provide more specific info, I'm happy to do it.

I'm going to try cleaning the EGR today, and probably put the old o2 sensor back in bank 2. At least it was driveable then. I'm pretty sure I screwed myself by trying to get the cheap ones on amazon. Is there ones that you guys recommend (that I can delivered to a PO box)? It's a 24 mile round trip to the nearest parts store, and as of time of writing I'm boot bound. Is there a decent multi-meter you guys like? I found a link to the Tekpower TP8268, but they sent me a bunk one. Try again, or go for a different one?

Sorry for the giant wall of text, but this has been a saga, and I'm not sure which information is going to be helpful, so I'm throwing as much as I can remember out there.

One last thing before I head out to tinker: Is there an updated link to the GMC drive cycle? The one that is linked in a bunch of threads doesn't work for me. I found a couple that listed it out, but they were pretty low quality copy-paste "articles". Is there something that explains it a bit better? I'm specifically looking for how to complete my fuel trim and o2 monitors, but also pretty curious about the concept. Never heard about monitors before this adventure. Seems like kinda a jank way to operate, but I'm betting that's because of my poor understanding of the system.

Quick update before I'm off to work: Threw the old bank 2 upstream sensor back in and it's now "driveable". At least hopefully for my backroad commute.

My Friend you have a lot going on there. But let's hit them in the most logical steps. So to keep it simple, your fuel pressure is very low. Below my signature block you will see a link to a "How To" article on the steps to take to check your fuel pressure and leak down. Start there. You only want either AC Delco or Delphi fuel pumps for these trucks. But do a step by step pressure/leakdown as described by Captain Hook in the article. Let's see if the pump is the problem or the regulator you put in, etc. Let us know the results.

Your MAF reading is too high, fuel trims are all out whack, just so much going on.

I like the Fluke 115 meter as a very good reliable meter.

Saving money on parts, often ends up not saving you money.

Okay, thank you for taking the time.

Is there a good place to get battery power from, near the fuel pump prime terminal? Am I correct in understanding that I can move past this step, as I know the fuel pump turns on when the key is on?

It'll take me a bit to get to step 2 (busted multimeter). Is it worth doing the other tests in the mean time?

I've ordered the parts for the DIY fuel filter adapter. Am I correct in understanding that this goes on the engine side of the fuel filter?

Okay, I think I'm on the right track now. Thank you so much.

So, the 48psi fuel reading that I got could be: the pump not sending sufficient pressure, the pressure being released by the regulator because the spring it too light, or some other fuel line obstruction?

P.S: Symptoms update #2: When I threw in the old o2 sensor, it ran really bad, but I was able to really slowly accelerate up to 25mph (over 3 blocks). Once it shifted into 3rd(?), it picked right up and ran "serviceably". Now it runs okay in first and second. Dunno if that's helpful, but I'm going to forget, so I'm throwing it out there.

As noted in the article, you want to check for pressure to be 60-66psi WHILE the fuel pump is running. So just knowing your fuel pump turns on is not enough. Don't skip the step. If you are able to watch the pressure gauge reach that pressure as someone turns the key to RUN for you and as the pump is running (not the truck (KOEO (Key On Engine Off))) for that initial two seconds, then you don't need to prime at the prime terminal. It is always best to use source voltage so IF you need to prime the pump so a fused jumper wire from B+ to the prime terminal is best.

Don't sweat step #2 yet (measuring power/ground at the pump) because it is very difficult if not impossible to reach the connector while the fuel tank is still in place. Right now the pressure gauge is your main friend.

Note: If the pressure is still climbing when the two second prime from turning the key stops it (for instance, let's say it stops at 43psi only because the pump turned off), you cycle key OFF then back to RUN and pressure resumes climbing from that 43psi to 60psi, then you MIGHT be looking at a power/ground issue.

You are correct that you will measure pressure at the engine side of the filter if the initial pressure test at the test port fails. I know you stated you tested pressure at the test port in your OP, but do it again. Insure you are watching the gauge as the fuel pump is running (KOEO or using the prime terminal). Let us know what the gauge does. (i.e. Does pressure go to 60psi while pump is running and then fall to 49psi when pump turns off? Does it only get to 49psi? If you cycle the key to run the pump twice does it reach 60psi? What is the pressure reading after 10 minutes? etc)

Yes the 48psi could be bad pump, bad regulator, obstruction, leak in a fuel line, leaky injector(s), high circuit resistance, etc.

Besides fuel delivery issue, you may also have a restricted exhaust. That can cause the truck to bog down. You can do a back pressure test with a gauge designed for testing back pressure that many auto parts stores have as loaners. A regular pressure gauge won't work as well. You want an Exhaust Backpressure Gauge kit. It comes with adapters that you would put in place of the O2 sensor closest to the engine. At idle it should read no higher than 1psi. At 2500 rpm it should read no higher than 3 psi. Another way to test is to just remove the O2 sensor and take the truck for a very SHORT drive down thhe block (you have to consider that hot exhaust gas will be coming through the bung and could melt any wires, etc near it). It will be loud, but if exhaust is restricted, truck will perform better. Using the Backpressure Gauge kit is better.

Reading thru your OP am I correct that you blocked off the PCV system ports? Do not block off the PCV ports. You could end up blowing a rear main seal or other seals.

You need a baseline to start with, so insuring you have a correctly operating fuel delivery system is key first step. Without that you could be chasing a problem that isn't there (ex. all the parts you have bought already).

Thank you again for your time.

I'll run the tests that I can Saturday morning.

B+ is access to the main battery connection to the fuse box, before it branches to each specific fuse? This connection is un-fused so I need a fuse on my jumper wire? A bit of searching and it looks like I want a 20A?

The PCV is hooked back up. It was just disconnected as a road-side repair attempt. Thanks for looking out. Does it need vacuum to function properly, or can it be disconnected from the port to dump into the engine compartment (not gonna do it, just curious)? The other little one is fine to be blocked off though, right? It looks to me like all it does is control the auto-4wd?

Was taught a long time ago: "More than two things can be wrong at the same time." I'm pretty sure in my case it's probably closer to 20.

P.S. This was a $500 vehicle that I'm trying to keep running as an exercise in stubbornness. I know about getting burned by cheap parts, but it's almost against the ethos of the project to spend too much money on it. A less dumb person would then tell me I spent a bunch more money by being a dumb-ass...:rolleyes:

Personally I like to use 10amp jumper wires. But you'd be fine with 20amp. When I state B+ I'm referring to the positive battery post so you are getting source voltage. Use an alligator clamp or such to attach. You want a good contact when you prime so your test isn't skewed. A helper turning the key instead of priming works fine.

Vacuum is part of the PCV system. You can functional test it by removing PCV from the rocker arm cover, run engine at idle and putting your thumb over end of valve to check for vacuum. Wouldn't be a bad idea to replace the PCV valve if you never have. Sludgy oil can be an indication of a poorly functioning PCV system.

Yes the rubber hose is for locking the front axle and also HVAC controls.

While your working thru things you might want to do a compression test on all your cylinders to insure your not pumping money into a truck that has a couple bad cylinders. Doesn't cost anything, may help with some later diagnosis and can give some peace of mind that you are working with a good base.

Ok, I just got finished with the "fuel system leak-down test" (is that correct terminology?).

When I put battery power to the prime terminal, the gauge shot up to 52psi. Sounded like I could hear flow in the plenum. As soon as I removed power, it dropped to 48psi (basically instantly).

It was @ 47 when I first recorded the time.
T + 3m 46psi
T + 7m 45psi
T + 10m 44psi
T + 20m 44psi minus the thinnest hair

Ran it a second time. 52psi when power was applied to the terminal. Dropped to 44psi instantly. After 10 minutes, it had dropped to 42psi.

From my current understanding of the system, this would seem to indicate a fuel pressure regulator that has too weak of a spring? The pump is supplying 52 (maybe more depending on how much is getting by the regulator), but the regulator is letting it into...I don't know where. The return line?

I guess it's also possible it's leaking back down the fuel pump? Thus the test at the fuel filter? But...in that case, wouldn't pressure drop to zero?

Anyway, I'll know more when I get the parts to do the test at the filter. Looks like Wednesday.

As far as exhaust restrictions go, is a vacuum test insufficient to diagnose the problem? Couple of YT vids I watched told me to hook up a vac gauge, and watch what happens when I gave throttle. If I had an exhaust restriction, vacuum pressure would slowly fall when the engine was at steady throttle for a while. Mine stayed steady at 15 in hg.

Fuel pressure leak-down is what I call it.

The pump needs to be able to hold pressure, so yes, that's why you're testing at the filter. It's dead-ending the fuel at the gauge. I've personally never heard of a a bad fuel pump on these trucks immediately dropping pressure to 0psi. I'm sure it's happened, I just haven't run across it.

Once you have tested at the filter, you'll know if the problem is at the tank or at the plenum. If you've never changed it, you might want to consider replacing the fuel filter while you're messing with it anyway. Be very wary though, those lines and the filter ends can get rusted (not always but they can be). Take your time disconnecting the lines. Replacing the fuel lines can be a real pain.

Out of curiosity, what brand fuel pump did you install?

Based off of your fuel delivery pressures, I don't think at this time exhaust restriction is an issue. Yes a vacuum test can also test for exhaust restrictions. I did do this several years ago on this truck, but found the back pressure gauge to be more accurate. But again, it looks like a significant fuel delivery issue is going on for you.

I put in this fuel pump:
A-Premium aka no-name. It looked the closest to the one that was already in it. Been running okay for the 6 or 7 years I'd had it, so I figured I'd go for it.

I replaced the fuel filter recently. It was rusted, and it was a mega-pain.

Will report back when I get my filter-adapter-gizmo built and run the test.

Thanks again.

Have my gizmo assembled, but I have an issue.

How does this Dorman #800-121 disconnect? I didn't really get how it would work, so I plugged it on to my old fuel filter. It snapped right on, but now I can't get it off.

Do I need a special tool to take it off?