Misfire on Cylinder 7

[Inferno333]

I figured that I would make a new thread since the last one had a title that made it confusing.

History:

The plugs and wires were changed in October 2014. I found the #7 & 8 plugs basically hand tight. That was four hours of hell changing them.

The big shitstorm happened in October/November 2015. I had a broken lifter that resulted in a terrible misfire on #1. I replaced the lifters with non-DOD parts and the PCM reflashed by PCM. All the associated parts were replaced at that time also. My mechanic said the heads and piston tops looked good.

Fast forward to a week ago. I was pulling a lightly loaded 6x12 uhaul trailer from Waterloo, IA back to Omaha, NE. Everything was all good until a little ways out from home. Light pops up and the pending code is a cylinder 8 misfire. I got it home, parked it, and let it sit overnight. I checked it again and the same code was on cylinder 7 only this time.

The #8 code has never returned. The #7 code is still present as pending and current. It's obvious by how the truck is running. I switched the coil with #5 and the misfire stayed on #7.

It was mentioned that it could be the injector. I checked my Chiltons manual and it talks about pulling the fuel fuse and cranking the engine. Is that the best way to test the injector?
Are they hard to replace in a basic garage?

I just want this thing reliable again. It's paid off in two weeks, but the wife is already pushing to get a new suv. I'd rather replace the 2003 Saturn that I'm forced to drive first.
(None of our new vehicles will be a GM product after the last few I've owned.)

 

[Inferno333]

No ideas this time around?

 

[dfc739]

I would troubleshoot by swapping coils and swapping spark plugs. If the misfire doesn't change to a different cylinder then it has to be a bad fuel injector, burned valve, or something more sinister like broken valve spring/cam follower or electrical (such as the coil or injector not being energized). Do a compression test to rule out bad valves, valve seats, and piston rings. You can borrow the compression tester from any auto parts store. You can also borrow an electrical test kit which you plug into the injector wiring and will light when the injector gets a pulse.

Do you smell unburned gasoline in the exhaust? Does the check engine light blink when driving?

 

[Inferno333]

I've done the coil swap. Nothing changed.

I highly doubt it's an issue in the head since they were just off for the lifter replacement.

I'll swing into an auto part store and grab an injector tester. I'll grab a sniff of the exhaust too. I'll have to ask my wife if the light is constantly on now. It was when I checked a couple days ago.

 

[Mooseman]

A compression test will also confirm it's not a mechanical issue like a valve or lifter.

 

[Inferno333]

It better not be a lifter! Damn things are brand new.

I called O'Reillys and they don't have any test kits for injectors. I'll call around and see if I can find one.

Would a basic voltage probe work? Obviously it would just blink with the pulses.

 

[Mooseman]

I think they're called noid lights, basically LED's that flash with the injector activation.

 

[Inferno333]

I might be able to grab an led from RadioShack and probe the connector myself.

 

[Mooseman]

Has to be 12V or add a resistor so it doesn't blow out.

 

[Inferno333]

I might have just got this figured out!

The injector reads within the 11-14 ohm range. Good!

The biggest thing I did notice was the lack of green lock and the gray press lock on the injector connector. That would make sense why it would go from pending to current for the code. It just works itself loose with vibration.

I'll just order a new connector and boom it'll work after I pull the plug and clean it.

 

[C-ya]

Hope that is all it is!

 

[Inferno333]

Hope that is all it is!

After $3000 of work and replacing the lifters it better be!

Ordered the connector, timkin wheel hub, and a new oil pressure sensor last night.

 

[NJTB]

After $3000 of work and replacing the lifters it better be!

Ordered the connector, timkin wheel hub, and a new oil pressure sensor last night.

Just throwing this out there. Years ago I worked on a Chevy that had a broken inner valve spring. If you looked at it you couldn't see it unless you took it apart. It idled fine, compression was good, plug good, everything seemed ok. but when driven there was a miss at speed.
The way I found it was a running compression test. Screwed a compression tester into the plug hole, started it, and at about 1300 rpm the compression just went lower and lower.
Was working piece work at the time, price of the compression gauge at the time was cheap compared to the money I lost. (destroyed it)

 

[Inferno333]

Just throwing this out there. Years ago I worked on a Chevy that had a broken inner valve spring. If you looked at it you couldn't see it unless you took it apart. It idled fine, compression was good, plug good, everything seemed ok. but when driven there was a miss at speed.
The way I found it was a running compression test. Screwed a compression tester into the plug hole, started it, and at about 1300 rpm the compression just went lower and lower.
Was working piece work at the time, price of the compression gauge at the time was cheap compared to the money I lost. (destroyed it)

Thanks for the tip! I'll have my mechanic run a compression test when he has the truck changing the wheel bearing.

 

[Inferno333]

Little update:

I changed the connector so that's good now. The plug didn't look bad, although it did have what looked like gas/oil mix on it. I couldn't tell exactly what it was.

I took it for a drive after clearing the codes. The pending misfire code came back. My wife took the truck to work and the light on the DIC came back on so it must be a current code now.

I'm at a loss on what it could be. The wheel bearing and ECT sensor will be getting replaced on the 15th. What else should I have my mechanic check other than the compression?

 

[Sparky]

Pull the plug if you can. The coloration of the spark plug can possibly help hint towards whats going on. Really white/blistered would indicate running lean, so a fueling issue, or carboned up could be way rich indicating possibly the injector sticking open.

 

[AWD V8]

Shortly after I bought my truck I would have a misfire come and go on #8

It would drive fine and I wouldn't feel anything. I checked and swapped the usual compression, plugs, coil, wires. Still the light would come and go. It finally got to the point where I was feeling it at WOT.

Finally after checking the fuel pressure which I had a difficult time pinning down exactly WHAT the pressure should be, I finally went by O2 readings, I replaced the fuel pump.

When you have borderline fuel pressure usually one cylinder will misfire first, weakest link in the chain thing. I never got a lean code, just the misfire.

Worth checking the fuel delivery at WOT to see if the pump can keep up with demand. I monitor the O2 voltage, MUST stay maxed out at WOT, or you are not getting enough fuel to the engine.

 

[Inferno333]

Pull the plug if you can. The coloration of the spark plug can possibly help hint towards whats going on. Really white/blistered would indicate running lean, so a fueling issue, or carboned up could be way rich indicating possibly the injector sticking open.

I did pull the plug. It was neither white nor had carbon build-up. It was wet with fuel/oil. It mostly smelled like fuel. Made sense to me since it was misfiring.

 

[Inferno333]

Shortly after I bought my truck I would have a misfire come and go on #8

It would drive fine and I wouldn't feel anything. I checked and swapped the usual compression, plugs, coil, wires. Still the light would come and go. It finally got to the point where I was feeling it at WOT.

Finally after checking the fuel pressure which I had a difficult time pinning down exactly WHAT the pressure should be, I finally went by O2 readings, I replaced the fuel pump.

When you have borderline fuel pressure usually one cylinder will misfire first, weakest link in the chain thing. I never got a lean code, just the misfire.

Worth checking the fuel delivery at WOT to see if the pump can keep up with demand. I monitor the O2 voltage, MUST stay maxed out at WOT, or you are not getting enough fuel to the engine.

Just noticed that I said the misfire was on 8. It's actually on 7.

The idle smoothed out some, but it's still not where it should be. It didn't hesitate from a stop when I drove it.

I added a screen to my EngineLink App. Fuel pressure, Fuel rail pressure, and throttle position. I didn't see any O2 voltage ones I could add.

Is a fuel pump a normal thing to go bad on a 2006?

 

[Inferno333]

I'll be dropping the truck off tomorrow. What should I make sure he checks?

Compression on all cylinders
Fuel pressure
Injectors
Possible clogged catalytic converter

Anything else you guys can think of to troubleshoot this misfire?

 

[Mooseman]

Maybe not the misfire itself but a check or replacement of the O2 sensor(s) wouldn't be a bad idea, especially since one got soaked on fuel.

 

[Sparky]

Soaked in fuel tells me it isn't running lean which also tells me it has nothing to do with the fuel pump. You have fuel, it just ain't burning it all.

If you clean off the plug does it fire OK at first then start acting up again? Or does it miss regardless? I wonder if you're getting spark on that cylinder.

An injector that is sticking open could also cause that.

 

[Inferno333]

Good call on the O2 sensors. How many are there?

Pretty much. I cleaned the plug and drove it a few miles without it throwing a code. It started running worse and throwing a current code a little while later when my wife took it to work.

I switched the 5 & 7 coils a while ago and the misfire stayed on 7.

Will the injector still give the proper ohm reading at rest if it's sticking open while under load? Is it possible the injector got damaged when engine was tore apart a few months ago?

 

[Sparky]

Yes it can read correctly while stuck. All you're reading with an ohmmeter is the resistance of the coil of the solenoid in the injector. There is a mechanical aspect to the injector as well that actually controls the fuel. That functionality can be seen electronically via an oscilloscope (the coil current changes) but that gets a lot more technical and it is cheaper to replace the injector than buy all that stuff, or heck probably than even setting up for testing and diagnostics.

 

[Inferno333]

Thanks for all the help! The truck is getting dropped off on the way to the airport.

I just want this thing running well again. I got the title in the mail a couple days ago and the wife is itching to get something different... I'm enjoying the lack of vehicle loans right now.

 

[Sparky]

It is a nice thing to not have payments. I was payment free from 2011 until last year and it was great, but I couldn't afford to buy my truck straight cash so now I'm stuck with payments again. It is far more likely to cost less to fix this than to replace the whole thing!

 

[Inferno333]

It is a nice thing to not have payments. I was payment free from 2011 until last year and it was great, but I couldn't afford to buy my truck straight cash so now I'm stuck with payments again. It is far more likely to cost less to fix this than to replace the whole thing!

Try getting my wife to understand that!

 

[Inferno333]

I got the truck back today. My mechanic tried all the same stuff that I did. He did a compression test and it came back ~135psi. He pulled the valve cover and didn't find anything wrong along with swapping injectors and blowing out the fuel rail.

After all that he found that it would misfire would only occur below 1000 rpm and would go away while driving. He let it sit overnight and this morning it didn't throw any code and ran smooth. I drove it home and it felt good and no codes came up.

And damn it's nice to have that wheel bearing changed! So quiet!!!

We shall see how it goes since I'm driving to Dallas, TX in less than 12 hours.

 

[Inferno333]

All is well! "Crosses fingers"

The truck is running pretty good. The idle is a bit rough. I'm not sure why.

Could it be some difference with the non-DOD 5.3L cam?

 

[Mooseman]

Shouldn't idle rough but hey, could be something else going on.

 

[Inferno333]

Pardon my language.

FUCK!!!

I'm at a loss here guys. It drove fine all 600+ miles to Texas, in and around while we were there, and about 450 miles on the return trip to Nebraska. We stopped for gas in Holton, KS and right after jumping back on Hwy 75 it started having a current misfire on #7 again.

I'm pissed beyond what my face is showing. The idle is still pretty rough after its at operating temperature. The code is back while driving too. The fuel consumption has been pretty decent for the whole trip.

Any clue what my next step is?

 

[Inferno333]

And what does the Torque app look like? I've been using EngineLink, but I'm curious if the other one will give me more information.

 

[Mooseman]

I don't know Enginelink but Torque is pretty good. Can show just about any live data, including misfire counts.

Did your mechanic swap the #7 injector at all? I'm thinking it's pooched. You didn't mention if he checked the fuel pressure.

 

[Inferno333]

EngineLink doesn't keep count from what I can see. Seems like it shows most everything else. It doesn't show fuel pressure or O2 sensors though.

I'm pretty sure he swapped the injector and checked the fuel pressure. I'll check the invoice. I need to call him today anyway to let him know it's back.

I'm going to clean the TB, replace the air filter, and do the reset today. Maybe that will magically help.

 

[Inferno333]

The TB was wicked dirty. Tons of gunk in there plus a little fine sand around the gasket where it seals to the intake manifold.

I cleaned it up, slapped in a new Wix air filter, and did the ECU/PCM reset. I topped off the coolant and checked all the intake manifold bolts for tightness. And checked torque on the wheels.

The idle is smoother and slightly higher in rpm. There hasn't been any codes popping up either.

Is there a video tutorial for the CPS/CPAS cleaning? Thinking about that too although I'd hope my mechanic did it while the top half was taken off.

Next comes brakes... They make noise all the time now.

 

[Mooseman]

How To: Clean The Camshaft Position Actuator Solenoid (CPAS) Picture Heavy

Not a video but will do.

Just thought of another possibility, loose intake manifold bolts or leaking gasket.

 

[Inferno333]

Thank you. It wasn't coming up in my search for some reason.

I did check the intake manifold bolts. All are tight. I still have some TB cleaner so I can check for leaks.

 

[Inferno333]

Is the CPAS on the V8? I noticed that thread was about the 4.2.

 

[Sparky]

Nah, CPAS is for the variable valve timing on the exhaust camshaft on the 4.2. The 5.3 doesn't have VVT.

 

[Inferno333]

Nah, CPAS is for the variable valve timing on the exhaust camshaft on the 4.2. The 5.3 doesn't have VVT.

That's what I thought since I couldn't find it in my Chiltons manual.

Let's see if I can clean the CPS without tearing a bunch of stuff apart.