Help with misfire at IDLE

[oneluckypops]

Ok first let me say the truck I am dealing with is a 1996 Chevy K1500, 5.7L Vortec, Automatic Transmission.

It is kind of a long story but here it goes.

Considering my old motor was loosing oil pressure and was down on power, and I was moving from Missouri to Texas. I swapped in a used motor that I acquired that supposedly only had about 100,000 miles on a rebuild. After I made the swap, the truck never ran quite rite, I always had a slight misfire to it, I put the computer on it and determined that I had a #6 cylinder misfire. I then decided to swap spark plugs around on the engine and also switched the location of the plug wires. In doing that the Misfire still remained on #6 cylinder. (When I swapped the motor in I used the Distributor, Cap, & Rotor from my old motor as I had already changed it previously to a billet distributor.) I then determined that the ignition system was not at fault.

I ran out of time before I had to make the move, so loaded everything up and hauled ass to Texas. Figured I would get down here and mess with it some more. Well a few months after I got here I decided to go ahead and change the pop-it injectors to the MPFI conversion, After doing this the truck seemed to have a lot more response but still had a misfire on #6. Perturbed I gave up on it for a little while.

Well with it being a holiday weekend and the truck starting to get worse. I figured I would try to get to the bottom of the #6 misfire, Put the computer on it looked at the history misfire counts and had high counts on nearly all cylinders. Later that night I started the truck in the dark popped the hood and loaded the motor and noticed I was getting a little bit of a light show under the hood. The next day I pulled the wires, plugs, cap and rotor, and headed to get them warrantied. Well ended up not having the right wires at O'reillys so had to settle for the "Omni spark", put it all back together and it ran like ****. Took the wires back got my money back and went to Napa and got a set of Premium wires. Now its back to a misfire on #6 cylinder again. I did do a compression test on it before I put the plugs back in it and these are my numbers.
#1=180 #2=180
#3=160 #4=180
#5=175 #6=140
#7=180 #8=180
IMO it looks like my misfire is from a loss of compression.
My question is what would cause the misfire at idle, but off idle and cruising it doesn't seem to be misfiring?

I also had some codes in it, evidently my SES light is burned out.
Here's the codes I am getting.
P0122A TP sensor circuit low voltage
P0134A HO2S circuit Insufficient Bank 1 Sensor 1
P0141B Ho2S Bank 1 Sensor 2
P0300 Random Misfire detected
P0430A TWC system low efficiency
P1406A EGR Pintle Position sensor circuit

After clearing the codes the only ones that come back are the P0300 and the P1406

Any and all help would be appreciated thanks

 

[Boone83K10]

You said you determined that the ignition system was not at fault. What about the distributor? You said you moved the plugs/wires around and it stayed on the #6 cylinder. That tells me that it's the distributor. But your compression can also be an accessory to the problem as well...

Also you should address the P1406. You must disconnect the EGR sensor then disconnect the battery. Plug the EGR back up then reconnect the battery. The computer will throw the code again until it relearns when you drive it a while.

Oh and the P0430A TWC system low efficiency is probably directly related to the misfire. That is showing a bad catalytic converter. So it's probably clogged from the misfire sending raw fuel to the cat and now it is bad.

 

[89Suburban]

Subscribed

 

[oneluckypops]

You said you determined that the ignition system was not at fault. What about the distributor? You said you moved the plugs/wires around and it stayed on the #6 cylinder. That tells me that it's the distributor. But your compression can also be an accessory to the problem as well...

Also you should address the P1406. You must disconnect the EGR sensor then disconnect the battery. Plug the EGR back up then reconnect the battery. The computer will throw the code again until it relearns when you drive it a while.

Oh and the P0430A TWC system low efficiency is probably directly related to the misfire. That is showing a bad catalytic converter. So it's probably clogged from the misfire sending raw fuel to the cat and now it is bad.

Although these trucks do have a crappy plastic distributor in them, Mine has already been changed to a billet distributor. On these trucks when the distributor is bad the misfire's will usually spread around from cylinder to cylinder, the misfire on this truck is staying on #6.
I would agree that the 430 code is from the misfire, especially since it is on the same bank as the #6 cylinder. I will fix that after the misfire is corrected.

I am not sure what your saying on the 1406 though, The diagnostics I have done for the EGR is saying the EGR Valve is bad.

 

[MrMarty51]

Did You try to decarbon the engine ??? It could be a buildup of carbon under the no. 6 valve{s} and causing the low compression state.
Use water, just plain O~L clear tap water, pour it down the intake, or of it is a horizontal system, use a spritzer bottle that puts out a jet stream, rev the engine a bit whilst pouring/spraying the water into the intake, let the enjun stall and sit for about five/ten minutes, fire it up and give it a final shot, see how that does.
About ten to twelve ounces outer doit.
Besides, I`m wit 89 Suburban and subprescribeded to dis thread now tooo.

 

[oneluckypops]

Did You try to decarbon the engine ??? It could be a buildup of carbon under the no. 6 valve{s} and causing the low compression state.
Use water, just plain O~L clear tap water, pour it down the intake, or of it is a horizontal system, use a spritzer bottle that puts out a jet stream, rev the engine a bit whilst pouring/spraying the water into the intake, let the enjun stall and sit for about five/ten minutes, fire it up and give it a final shot, see how that does.
About ten to twelve ounces outer doit.
Besides, I`m wit 89 Suburban and subprescribeded to dis thread now tooo.

No I have not tried that. I am going to do a leak down test on it tomorrow after work. depending on what I find from the test I will try your suggestion and maybe even do the leak down test again afterwards if it turns out to be leaking thru the valves. Will definitely keep you all posted on this one.

 

[Jims86]

No I have not tried that. I am going to do a leak down test on it tomorrow after work. depending on what I find from the test I will try your suggestion and maybe even do the leak down test again afterwards if it turns out to be leaking thru the valves. Will definitely keep you all posted on this one.

Leakdown test may tell alot, what injector pack do you have? is it the OEM with the pintle valves at the intake end, or the injectors?
I dunno if you remember us talking to Dave about a year ago about this same thing. It was a huge recall by GM.
Only thing I can figure why its only happning at idle, is maybe the compression doesnt have a chance to go down to 140 before firing, and then there is the load that the engine is under.

 

[oneluckypops]

Leakdown test may tell alot, what injector pack do you have? is it the OEM with the pintle valves at the intake end, or the injectors?
I dunno if you remember us talking to Dave about a year ago about this same thing. It was a huge recall by GM.
Only thing I can figure why its only happning at idle, is maybe the compression doesnt have a chance to go down to 140 before firing, and then there is the load that the engine is under.

Yea I know all about the recall, I have replaced hundreds of the spider assembly's. I have already done the conversion not long after I got moved sown here.

I was able to get the leak down test done after work today. I cant say really how accurate the percentage of leak down is because my tester is an elcheapo from Harbor Freight. It was only putting 15psi into the cylinder, and the percentage gauge showed 30% leakage. I wasn't really able to say for sure if I could hear air hissing from any one spot for sure, when you figure the percentage of leak compared to the PSI feeding into the cylinder it was only 4.5 PSI worth of a leak. HOWEVER when I connected the air hose directly to the cylinder (1xx PSI) I was able to hear air coming from Both the Tailpipe and the throttle body. I also noticed that the coolant level would RISE with pressure in the cylinder Just ever so slightly, It never would bubble but just rise. ( maybe 1/2") higher with pressure versus with out, I have never had to add any coolant and the system is filled to the bottom of the filler neck on the Radiator.

It would appear to me that the Head is going to have to come off to resolve the Misfire. I did also have the valve cover off to confirm that both valves were closed, neither of the springs appeared to be broken, and the rocker arms weren't loaded to the point of not being able to move them, to the valve lash isn't set to tight.

I am seriously thinking about just trading the damn thing in for a Cummins.

Oh and I also tried to clean the carbon out dumping water down the throttle body, but no such luck didn't change anything.

Anybody else got any brain storms? I have never been 1 to believe in any of the "Miracle" engine cleaners or restorers but honestly at this point if anyone has any real experience with any of them I am all ears!!!!

 

[Jims86]

Yea I know all about the recall, I have replaced hundreds of the spider assembly's. I have already done the conversion not long after I got moved sown here.

I was able to get the leak down test done after work today. I cant say really how accurate the percentage of leak down is because my tester is an elcheapo from Harbor Freight. It was only putting 15psi into the cylinder, and the percentage gauge showed 30% leakage. I wasn't really able to say for sure if I could hear air hissing from any one spot for sure, when you figure the percentage of leak compared to the PSI feeding into the cylinder it was only 4.5 PSI worth of a leak. HOWEVER when I connected the air hose directly to the cylinder (1xx PSI) I was able to hear air coming from Both the Tailpipe and the throttle body. I also noticed that the coolant level would RISE with pressure in the cylinder Just ever so slightly, It never would bubble but just rise. ( maybe 1/2") higher with pressure versus with out, I have never had to add any coolant and the system is filled to the bottom of the filler neck on the Radiator.

It would appear to me that the Head is going to have to come off to resolve the Misfire. I did also have the valve cover off to confirm that both valves were closed, neither of the springs appeared to be broken, and the rocker arms weren't loaded to the point of not being able to move them, to the valve lash isn't set to tight.

I am seriously thinking about just trading the damn thing in for a Cummins.

Oh and I also tried to clean the carbon out dumping water down the throttle body, but no such luck didn't change anything.

Anybody else got any brain storms? I have never been 1 to believe in any of the "Miracle" engine cleaners or restorers but honestly at this point if anyone has any real experience with any of them I am all ears!!!!

tie a rubber glove to the t body, and another to the exhaust, make sure 6 is at tdc, and filler up again....but the gasket itself may be going,, or you have the dreaded Vortec crack betwix the valves.

 

[chengny]

I did also have the valve cover off to confirm that both valves were closed, neither of the springs appeared to be broken, and the rocker arms weren't loaded to the point of not being able to move them, to the valve lash isn't set to tight.


While inspecting the springs and checking that the valves were closed, did you have any opportunity to stroke/bounce the valves? Specifically, did you check for a sticky (exhaust) valve? Sometimes a valve with a gummed up stem will eventually close, but not fast enough to maintain a smooth idle.

2 common vacuum gauge diagnostics:

Idle (with random mild drop)

You must be registered for see images attach

When the hand drops occasionally from 3 to 5 points, from the normal reading, it generally indicates a sticking valve.



Idle (with occasional mild drop)

You must be registered for see images attach

Occasional drop as cylinder is firing may denote valve sticking open or plug not firing.


How about EGR valve function - should be closed at idle, stuck open is common cause of rough idle.

 

[89Suburban]

Throw some sea foam in it

 

[oneluckypops]

tie a rubber glove to the t body, and another to the exhaust, make sure 6 is at tdc, and filler up again....but the gasket itself may be going,, or you have the dreaded Vortec crack betwix the valves.

I am not sure I follow on the rubber gloves. Can you please explain the concept of what it is suppose to be doing? It seems like your wanting to plug the leak on the exhaust and the intake and force the leak out of the radiator?

I am afraid your correct, My money is on cracked head inbetween the intake and exhaust valves.

I did also have the valve cover off to confirm that both valves were closed, neither of the springs appeared to be broken, and the rocker arms weren't loaded to the point of not being able to move them, to the valve lash isn't set to tight.


While inspecting the springs and checking that the valves were closed, did you have any opportunity to stroke/bounce the valves? Specifically, did you check for a sticky (exhaust) valve? Sometimes a valve with a gummed up stem will eventually close, but not fast enough to maintain a smooth idle.

2 common vacuum gauge diagnostics:

Idle (with random mild drop)

You must be registered for see images attach

When the hand drops occasionally from 3 to 5 points, from the normal reading, it generally indicates a sticking valve.



Idle (with occasional mild drop)

You must be registered for see images attach

Occasional drop as cylinder is firing may denote valve sticking open or plug not firing.


How about EGR valve function - should be closed at idle, stuck open is common cause of rough idle.

I agree vacuum diagnostics could help a lot. My problem is there is not any ports to hook my gauge up to other then where the booster line is and I don't have anything to hook to that big of a line.

I know the EGR valve is Bad, and I am sure replacing the valve would improve the idle, but its not going to take the miss away, I am just trying to decide if it will be worth replacing the valve, and the heads on the truck. I cant bring myself to replace just the 1 head, either do them in pairs or don't do them at all.

The Truck has a little over 330,000 miles on it, I just had to throw 4 different used tires on it, they will probably be ok for another 6 months but Ive broken all the lug studs on the rear wheels, and it egg shaped the holes in the wheels, so I am going to have to get new wheels for it when I put NEW tires on it, converters are clogged, mufflers are blown out.

EGR Valve 120.00
Converters 375.00
Wheels 600.00
Tires 1200.00
Mufflers 150.00
Cylinder Heads 400.00
Head gasket set 100.00
Head bolts 50.00

Truck needs $2995.00 worth of work, kind or hard to take on a payment, but its kind of hard to cut loose of that much money on something this old.
Opinions?

 

[Jims86]

see if it inflates them...I used to tape a piece of paper on them, and watch for movement, but it does'nt wor too well on a windy day. it should also blow bubbles in te radiator if its cracked into the coolant passage.

 

[oneluckypops]

see if it inflates them...I used to tape a piece of paper on them, and watch for movement, but it does'nt wor too well on a windy day. it should also blow bubbles in te radiator if its cracked into the coolant passage.

That's what is so puzzling to me I can see the coolant level rise but it doe NOT bubble. I can feel the air coming out of both the tailpipe and the throttle body.

 

[Jims86]

That's what is so puzzling to me I can see the coolant level rise but it doe NOT bubble. I can feel the air coming out of both the tailpipe and the throttle body.

Maybe seal up the tailpipe and t body so the only exit is the coolant jacket.