Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Could be a stretch, but isn't there an alcohol sensor of some sort under the vehicle on these? Could there be a problem there that could be throwing off the mixture? To be honest, I'm not really sure how they work or what they impacts. Just thinking/typing out loud.
Never really heard of that through doing everything else to this stupid truck. I know earlier in this post ScannerJohn mentioned T 5.3 motors are gas only and Z 5.3 motors are multi-fuel. I have the T motor. Is that what you're talking about?
Hey SJ... I didn't find the volts reading on my scanner. I'll recheck it today to see if it's on a different screen on my scanner. But this is what I found at Hot Idle, Loop is closed... MAF = 5.87 G/S and 2643 Hz
Yeah, I had a GM 5.3 in one time where I replaced some alcohol sensor or something that was under the car maybe half way back on the driver side. Actually, no. It was a broken wire to that part. I imaging it was a flex fuel vehicle though.
Yeah I will do that water test again SJ... I can't believe how impossible this is getting with this stupid truck. All the injectors were replaced with new O-rings but like I said I'll do the water test again.
Question... In one of the new fuel pumps I had put in came with a new electrical connector for the fuel pump. Could that old fuel pump connector be bad?
their is a complicated current test that can be done with the fuel pump to show that the pump motor is providing the proper RPM's to supply fuel, but with your pressure readings being what they are I'm going to say that's not the problem. It cannot hurt in anyway to check the connection to insure good contact.
At this point patience is the key... there is an air leak somewhere, finding it will take time and systematic testing. Keep a log of what vacuum lines and components you have checked. I was looking for a diagram of the vacuum lines and components for the 5.3 but I do not have anything to share. Positive 30 total trim is quite significant, we are all missing what it is.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
Thanks for your help because at this point I don't know where to even start now. I thought the miss on cylinder 6 would've went away with the intake gasket change. But, it still acts the same. I have other cylinders that miss but nothing like #6. I've changed the plug, coil and wire and it didn't make a difference. compression was 135 psi. I didn't check the compression on the other cylinders... figuring it's not broke so why screw with it.
I remember on an even older Chevy Silverado was throwing a code... can't remember the number... it was some kind of vent underneath the truck by the gas tank. It wouldn't be anything down around the gas tank would it?. I never thought to crawl under there to look for smoke around the lines down there.
I would check the compression on the other cylinders, so you have a reference point. If the others have 200psi, then that would be a low cylinder and certainly have a problem.
Hey SJ I did a smoke test again, a much better day today to do this, and this is all I found top and bottom of the truck. The only smoke I saw seeping out was the throttle body shaft. And a very small peep of smoke from the fuel regulator. Otherwise nothing else jumping up and down waving at me.
I'll check the compression next... Now this is going to sound stupid but don't you just hook the gauge up and turn the motor over several times. Then check the gauge again? I ask because the mechanic helping me over the internet had said to check the compression but don't let the motor keep turning it over and over. I would think that 3-4 revs of the motor or where the needle on the gauge doesn't get any higher is what I've always done... anyways.
No compression check yet. I decided to the water test again. Sprayed water here and there and the throttle shaft. Made no difference. Soaked the top of the motor... and nothing. Pinched off line to power brake and line to the pcv valve. I can not find this leak. There is a line going to the passenger side of the throttle body that if I pull the line of and hold my fingers over the openings... the STFT's would go even higher till I put the hose back in it's spot.
Baffled in the worse way on this. I even rechecked the fuel pressure and it was still good, 50 to 59 psi.
that line is part of the crankcase ventilation system. it connects to the valve cover on the passenger side of the engine (kind of like the old breather cap). it works in conjunction with the pcv which is connected on the other side of the engine. the ccv is a closed system. if you unplug it, you create an air/vacuum leak as you found out. make sure its connected at the throttle body and valve cover and has no leaks. a leak should have shown up when you doused the engine with water but maybe not.
does the truck have the stock air box system?
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
Thanks SJ it was weird because when I took the tube off I plugged the hole with my thumb and covered the nipple with my finger and it still trims went high. I didn't think it would still do it with me covering the holes. I don't know man... it's almost like it supposed to run at 25% on the long terms... lol. No, cause it runs like crap.
On the compression question, ideally you'd take all of the plugs out, hold the throttle to the floor, and crank until the needle bounces about five times. The reading will only go so high. You do each cylinder and compare the readings. You want them within about 15% of each other.
Here's those compression numbers. Bank 1# 1= 120psi, #3= 135psi, #5= 145psi, #7= 120psi. Bank 2 #2 120psi, #4= 120psi, #6= 130psi, #8= I couldn't get the hose to screw on
Interesting that #5 has the highest number, which is more than 15% of the 120 on the others. I'll let someone else interpret that, since my experience has always been having one or a few lower than the group. I'm not sure if it makes a difference or not.
I think I asked that poorly... does the truck use the standard air filter box and snorkel to the throttle body or does it have an aftermarket K&N setup.
Did you notice that ScannerDanner was posting on other problems? I was hoping that he might see your problem and offer some advice.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
