SOLVED! Higher LTFT at idle and higher at rpms

[gmcman]

@2001ZR2 those are still some hight trim numbers.....I think the next course of action is to get a fuel pressure reading. One possible scenario is low fuel pressure with poor atomization and the PCM is adding a little bit of fuel to compensate.

Two things need to be checked before moving forward.

1) All intake manifold bolts need to be torqued to 89 INCH- pounds. All 10 of them.

2) Fuel pressure needs to be checked.

The intake is notorious for having loose bolts.

I've never really monitored intake temp. I might have to clean my green filter although I did about 3 months ago or I could be pulling to much warm air from the engine bay some how

122 deg isn't uncommon on hot days, I wouldn't sweat it. There's a lot of heat under the hood.

 

[mrrsm]

There is "...another Player on the Field..." that can often get overlooked if it does NOT throw a Code...and that is the CPAS. Because of the way this Solenoid can actuate the Camshaft Phaser motions INFINITELY over a range of 25% Retard-Advance via the shuttling of the Engine Oil into and out of the Camshaft Phaser, which does NOT get sensed by the PCM.

And because it replaces the Old Style Exhaust Gas Re-circulation Valve, if those Screens have gotten clogged up even just a little... it could affect the CPAS<->to<->Camshaft Phaser Performance enough to substantially alter the Exhaust Stream and likewise... whatever the O2 Sensor winds up sniffing of the Exhaust Stream over a Power Band that can run all the way from a Low Idle up into the Higher RPM and Torque regions.

Around the time of your next Mobil1 5W-30 Motor Oil and Mobil1 Oil Filter Change... It would not hurt to pull the (3) Bolts holding on the Power Steering Unit. Then Unplug the CPAS and Undo the 10 mm Bolt from the CPAS Tang. Gently pull out the CPAS without damaging the "O" Ring and then ...Clean up the Fine Mesh Screens with a Spray Solvent; just on the outside chance that it has become a bit sluggish over time. If you see any Oil Contamination in the CPAS Electrical Connector or leaking down the Passenger Side of the Engine Block...replacing the CPAS would be in order.

It would be interesting to see if this action would have any affect whatsoever upon your Fuel Trims.

 

[mrrsm]

@xavierny25 ... Regarding Post #40 ...If you perform the "Green Filter Clean" Procedure as a separate "How To" write up that will show how to do this without damaging it... along with posting the Before and After Images demonstrating the results... I will NOT be the only Member-Lurker who will say, "Thank You!" in Advance for memorializing your efforts. :>)

 

[xavierny25]

@gmcman here a shoot while on the highway at speed posted.
LTFT never got below 6. AC was running since my wife was in the car and couldn't deal with the heat and humidity.
STFT did get into the negatives -6 is what I can remember seeing.

 

[2001ZR2]

well I am just short of the halfway point on replacing the intake gaskets but I need to separate or move the fuel line to the fuel rail. I can't get the manifold out without doing this.

Maybe I can open the loom and move the line that way but I am tired and it's dark so I will regroup for tomorrow.

As I drove around yesterday and today the vacuum cap came off the throttle body. Not sure why or how.

I will keep the group informed.

 

[gmcman]

I don't know what the fuel plumbing looks like on the 2005, but on my 2002, I need to remove the FPR and move the line out of the way to get the intake manifold off.

As far as the cap you put on the TB, I don't know if that will throw a code with the evap disconnected. I was curious if the idle dropped down.

If the cap was tight, and it came off......does the engine ever pop or backfire through the intake?

With the intake manifold off, be sure to check the vacuum line from the TB to the solenoid and with the intake removed, it would be an ideal time to replace that solenoid.

 

[Maverick6587]

On my 2006, I think all I had to do was unscrew the A/C tube that goes over the engine and the screw holding the fuel line to the engine. I think there's another bolt holding that A/C line on the passenger's side of the engine. You might want to remove that one as well to be able to move that tube out of the way even further.

You can still get the intake manifold off without unscrewing the fuel line attachment but, You'll damage the upper firewall padding on the bottom of the cowl.

 

[2001ZR2]

I have pictures but the intake manifold and intake runners were oily and carboned up. I got to practice putting the intake twice as I forgot to install the new gaskets. Doh!!!

Time to slow down and do things right.

 

[Maverick6587]

You just noticed that and you're going to fix that or you already installed the new gaskets??

 

[2001ZR2]

I was so excited to begin reassembly that I forgot to put them in. Also I was trying to get it done before my special needs son's helper left.

The intake is in and torqued down. Now to connect things to bracket that holds up everything.

 

[gmcman]

Were you able to check the vacuum hose from the TB to the purge solenoid for any leaks, and/or replace the purge solenoid?

 

[2001ZR2]

The connection at the TB was broken so I replaced the hose from the TB to the Solenoid.

Wouldn't a faulty solenoid throw it's own code?

I got a chance to eat dinner so now i can finish up and see if the truck will run tonight.

 

[2001ZR2]

I got the truck running and while not an epic fail it isn't fixed.

It went thru the throttle body relearn sequence and idled at 650 rpm.

I was able to drive for about 1.5 miles before the idle crept up to 900 rpm where it stayed.

The LTFT would get to mid to upper 20's at 1750-2000 rpm.

It hasn't set a code yet but my iPad died before I check the pending ones.

What is the part number for the evap solenoid? I have one for my wife's 5.3 Envoy which is 1297567 ACDelco part number.

It does seem to run better and the pinging at 1500-2000 wasn't there on a short test drive.

The shutdown is still harsh with it bumping about 3 times before it completely stops.

I will drive it to work tomorrow and see it runs better. I will have my iPad charged and see what we get.

 

[gmcman]

As far as the purge solenoid is concerned, yes, if the solenoid is faulty or there is an excess vacuum leak in that system it will generally throw a P0440 code.

I was suggesting to replace it if original due to being hard to access with the intake installed. Slim chance it would be damaged causing a leak but it's kinda cheap and just something you don't have to worry about.

Have you checked the fuel pressure yet?

Checking the fuel pressure will also tell you how fast it bleeds down when shut down.

The screenshots I showed with the torque app and the throttle position with the evap line connected and disconnected.....3.9% with the line connected and .8% with it disconnected tells a lot. Tells me my TB is cutting off the air to maintain idle speed and air/fuel ratio.

If you can find out what these values are would help, as well as fuel pressure.

Sorry, I didn't know you were removing the intake, I would have suggested to change the injectors if feasible.

Like stated earlier by @whodwho & @MRRSM regarding the injectors, the engine is getting a fuel source from somewhere, either hot carbon or a leaky injector so by verifying fuel pressure we can try to pin down if the injectors are dribbling a little or spraying a nice high pressure mist.

If the throttle body doesn't close down then that could be the air source and the engine needs to add fuel, but this is your high idle situation, not your high LTFT at cruise.

It's tough to pin down a lean issue, but I would have done the same thing by replacing my intake gasket if original to cover that base.

I'm curious as to how it behaves from a cold start with the codes cleared/PCM reset.

With a cold engine, pull fuses 10&28 for about 15 min, then replace fuses, with the AC off, turn key to ON, don't start the engine, , let the TB run through its series of checks and don't touch the gas pedal.

After about 2 min, start the engine and let it idle for about 10-15 min..observe the idle during warm up and see if drops to 600 and if so, how long until it raises to 900.

Just don't touch the gas pedal during the warmup and report your findings.

 

[2001ZR2]

gmcman thanks for all the no worries on fuel injectors. They are fine and putting another $250 in it is not in budget. Especially when we have other known issues.

Here's what I have done in the last to days:

1. Replaced EVAP hose from TB to soleniod. ACDelco part
2. Replaced intake gaskets with FelPro
3. Clean the intake runners in the head and throughly cleaned gasket surface. #1 clyinder was the worst and was the non firing cylinder when I got it.
4. Cleaned the intake with degreaser and water to flush out oily residue. Used paper towels with solvent to clean ends. Again throughly cleaned gasket surface.
5. Replaced PCV hose with ACDelco part.
6. Replaced plug on intake manifold with GM part. I was at the dealership anyways.
7. Cleaned throttle body thin edge again and removed nothing.
8. Triple checked torque on intake bolts. Meaning I went around the manifold twice after reaching 89 in/lbs.
9. The battery was disconnected as part of the intake replacement from 5:30 pm Tuesday till 10:15 pm Wednesday evening. Then did Throttle relearn procedure with 2 min key on/engine off then started vehicle and let idle for 10 minutes.

Here is what I found. See attached pictures

The 1st picture shows the manifold ends and gasket.

The second picture shows the head but not the oil residue on the bottom of the port. If oil can leak out then air can get in.

This morning I found 2 pending codes...the P0171 and P0410 which is new. I cleared them and drove to work. The idle stayed low until I had drive 22 miles to work. The LTFT was going up 23 but then would fall when I let off the gas. After a while it would go above 25 to 27-28%.

I have a data log of the trip. I have seen throttle position and it was about 15% at idle. I will dig into Dash Command to find later today or tonight.

If the rain starts late afternoon I will take a day off but if it holds off then I will pull the EVAP hose at the TB to see what happens. If it resolves the problem then I will look what it would take to swap out the solenoid. Also if I am really energetic then I will get fuel checked.

 

[gmcman]

What does the top of the piston look like on Cyl #1? You can shine a flashlight in there and see if you see silver or black.

I think the fuel pressure test is a high priority.

The P0410 is the secondary air injection and I'm not well-versed in that option and not sure if that would inject excess air or just have a faulty check valve. Others can chime in on that.

I would also strongly suggest a can of BG44K. The Techron is good but if it's not the "Super Concentrate" or "Concentrate Plus" can't remember off hand.. then you're likely not getting any fast cleaning. The 44K works very fast and is one of, if not the highest concentrations of PEA.

Edited to correct Techron name.

 

[Mooseman]

The P0410 could be what's the cause of all this. It might be introducing air into the exhaust and making the PCM think it's lean. It is a failure prone troublesome system. You could remove the valve and block off the port in the head by sandwiching a piece of sheetmetal. If that proves to fix your problem, then you could work at getting rid of it permanently by blocking it off and getting the codes deleted with a tune.

 

[2001ZR2]

The P0410 code is interesting but has only occurred once. The scanner program I have indicated the system is not active during normal operation.

The drive home was interesting with the P0171 code set easily with it being 20 degrees warmer. The truck indicates that it gets better gas mileage on the way to work.. Some is no A/C going to work but running it some on the way home.

I did get a fuel pressure tester from O'Reilly Auto it showed 38 psig at idle with little if any bleed down. It also showed 0 psig at idle and yes the engine was running, I will have the fuel test confirmed maybe I'm an idiot who can't properly test the pressure or maybe the test kit is garage.

Pulled the hose off from the EVAP system with little if any change in LTFT or throttle position.

The throttle position with vary from 13-15% at idle with no code pending or set but will be 18-19% with the code set. I am now wondering is the throttle body worn or boogered just enough to create the issue?

it could be the EVAP purge solenoid sticking open

It could be a dying but not yet dead fuel pump with a bad ass regulator.

Vacuum at the TB at 650 rpm idle is 18.5 in Hg with a swing of about 0.5. At 2500 rpm it jumps to 23-24 in Hg then settles in at 19 in Hg with less than 1 in Hg swing.

I will see about getting the fuel system diagnosed with a professional scanner tomorrow.

But Saturday I have an appointment to get the truck brought up to current specs on the computer system.

I was hoping to diagnose the problem but this appears to be an onion with many layers. I will update the group as I find out more.

 

[mrrsm]

In combination... The P0410 AND the P0171 point towards a Failed or Stuck Open SAIS (Secondary Air Injection System) Solenoid Valve located on the Passenger-Exhaust Side of the Engine Head. I found the Linked Video to be very comprehensive in the Diagnosis-Solution. Your excellent images display the 'Oily-Carboned Up' Intake Ports on the Head as being 'Par for The Course' for the copious amount of Oily Vapors and Blow-By Gas that rise up to strike the Metal Cooling plate along the upper inside length of the Cover... and get vacuumed into to that vertical pipe through the Short RubberTube guiding the fumes into the Intake Plenum.

From there...all of that Crap gets pulled in and re-circulated through the Throttle Body where it collects inside of the IM Runners and all of the "Figure 8" IM Ports. Unfortunately...this is a common occurrence for ALL of these engines but a relief for you to know it is not something unique to your motor.

Getting back to the SAIS Solenoid... The Video should prove helpful and guide you to an R&R of that Solenoid. Other Members may suggest just Blocking off that SAIS Solenoid Port with a Plate/Gasket Kit and having the Dealership or someone with a Tech 2 Delete the Feature that so the irritating Dash Warning Light stays permanently OFF. The attached Illustration shows the layout of all the SAIS Components::



You know and understand this for certain... but for the sake of others following along on Your Thread who may be unfamiliar with the SAIS System... It's only purpose is to Inject Additional Atmospheric Air into the Exhaust Stream to provide additional Oxygen to the CAT during the first few minutes after Start Up and allow the CAT to Heat Up sooner than later... so it is one of those "Nice" Functions ...but NOT entirely a necessity. If that Valve stays locked open... the added O2 only serves to confuse the Upstream O2 Sensor and elevate the RPM after prompting the PCM to command the EFIs to Dump in More Fuel to Achieve "STOICH". I'll chime right in with ALL of us who really hope that with an R&R of that Solenoid...or a Block Off of that SAIS Port... it will end this Damned Problem for you... For Good.

 

[Mooseman]

The SAIS has been known to cause weird issues such as lean conditions and misfires, even without a code and not operating. I removed mine before it failed. You can pick up a block off plate for it at the dealer for a 2002 with a new gasket and just remove that valve. Later, after you get it running right, you can get the PCM tuned to get rid of the codes but you will get a CEL for it but you'll know what it is for.

 

[gmcman]

The P0410 code is interesting but has only occurred once

The code has come up once, but with the fuel trims not being over what the PCM seems as a problem....I think we discussed 25%? Then until the SAIS really has a problem like a bad check valve you probably won't see the code. I don't know the inner workings of the SAIS, can it crack or have a broken tube and still not throw a code?

Also the fuel pressure test and injector leakdown will tell a lot.

 

[2001ZR2]

After sleeping on it I am leaning towards the SAIS system. For a couple reasons first the LTFT increases with RPM which is the opposite of vacuum leak and pulling the EVAP line at the TB makes no change. Second I believe the fuel pressure is not accurate because of the 0 psig pressure with engine idling.

Also the mileage is better in the morning commute and the code sets quicker when the air and truck is warmer. I am thinking the extra O2 is expected with cold start which would delay code set and dampen the LTFT increase.

I should have new check valve tonight and it's supposed to be a 20 minute install

Edit O2 sensors don't measure O3 appearently.

 

[2001ZR2]

Well I had the fuel pressure double checked and it's 38 psig. I forgot the 1st of troubleshooting you know nothing until you test it.

I honestly still can't believe the truck starts and runs as well as it does. The computer must be compensating for the bad fuel pump. I include the regulator, filter, etc as they are all in the fuel pump package in the tank

Gonna order the fuel pump tonight and drive the truck tomorrow to reduce the amount of fuel in the tank. Drop the tank on Sunday and hopefully have the fuel pump from Amazon then. .

 

[gmcman]

Don't know off hand what the min pressure per service manual is off hand, I'm speculating that 38 PSI is below the minimum. I would suggest fixing the P0410 issue before the fuel pump. That way you can document the change from the SAIS repair.

 

[NJTB]

If I remember correctly, in the trouble shooting tree for those codes, one of the checks is fuel pressure. Should be 52 to 58?

 

[2001ZR2]

NJRB I was admitting to skipping that step because I knew the pressure was good. I was basing that assumption on the fact the truck drives just fine. No reall starting issues, no lack of power and no WOT throttle surging. In troubleshooting if someone knows something your next question is can you prove it? A test of the fuel pressure would led me to the fuel pump sooner.

I did get the truck software updated at the dealership today. Found out the truck was there in 2014 for plugs and plug wires and had just under 135k miles.

The biggest victory was the "Blanking" spare tire hoist was defeated. The secondary latch was hung up and with enough penetrating oil and big enough pry bar and hammer The latch moved enough to lower it. The county called and wants their gravel road back as there was tons of it above the tire.

The dealership mechanic said is rare for him to not have any recommendations on a vehicle but since I knew about the fuel issue he didn't mention it.

Tomorrow I will get the truck in the garage and drop the fuel tank, The idea will be to be ready for a Monday reassembly when Amazon will delver the fuel pump.

Oh the numbers I get is 50-57 psig fuel pressure at the rail

 

[gmcman]

Well I had the fuel pressure double checked and it's 38 psig

Oh the numbers I get is 50-57 psig fuel pressure at the rail

Correct me if I'm wrong, but the 38 PSI is what you tested and 50-57 PSI at the rail is the specs or what you have recently tested?

the truck drives just fine. No real starting issues, no lack of power and no WOT throttle surging.

This can still be the case if the injector pulse width has lengthened. I'm assuming if you have 38 PSI that it should be drivable, but obviously much under the minimum spec.

Could be a combination of the fuel pressure and you SAIS...but looks like it's getting closer to being pinned down.

In the end, more comforting knowing you have these items taken care of when you send you kid down the road with it.

 

[2001ZR2]

Both tests gave 38 psi and the spec is 50-57 psi

 

[NJTB]

When you drop the tank, there's a pressure sensor at the rear of the tank. You can reach through the spring to disconnect it. As careful as I was when I did mine, it was the one wire I missed. $80 at the dealer.
You did replace the fuel filter?

 

[2001ZR2]

The filter is inside the tank on this one.

 

[2001ZR2]

The dealer reflash didn't change things too much just slowed the time before the code sets slightly.

The SAIS check valve didn't change a thing.

The DIC still lies about fuel usage should have had 2 gallons in the tank but filled a 5 gallon container. My fuel gauge swings a bit in the last 1/4 tank.

 

[gmcman]

Is there any damage to the SAIS pipe, or tube? Any way air can infiltrate the exhaust?

 

[2001ZR2]

no damage noted

 

[2001ZR2]

Also if check valve is closed then they could be open and no added air would get in

 

[2001ZR2]

OK this one is solved. It was the fuel pump. I got the new one in and ran the truck thru it's paces.

Idle never changed from 650 rpm, the LTFT was negative for the most part but never above 1% and STFT swings were much lower about +/- 8%.

I think the intake gaskets were leaking a little bit and the EVAP hose wasn't sealing.

Driving the truck will clean up the carbon especially after I add the BG44k tomorrow.

I will drive it to work and back to confirm everything is good before I fill up the tank completely

Thanks about for all the help. Still can't believe the truck ran with 38 psig at the fuel rail. I will get an updated fuel pressure tomorrow.

 

[gmcman]

Awesome

Once everything smooths out, negative LTFT will likely be the norm... anywhere between 0 to -10....occasional peaks beyond that.

Should bounce all over the place generally a little bit more negative on deceleration.

 

[mrrsm]

Nicely Finished with LOTS of Due Diligence @2001ZR2 ...and Some Serious Props for @gmcman for...Nailing This One...

Another Problem... Sorted Out.and...