SOLVED: Another misfire chasing threads (2008 express van)

[Tonyv__]

Intake is where to start for sure. Any vacuum hoses in the area.

There’s a vacuum hose on the valve cover directly above cylinder 7. Seems tight. But I’ll check it out. I’m gonna make a makeshift smoke tester tonight

 

[OR VietVet]

Yea, could be as simple as that hose.

 

[Tonyv__]

So nothing on the smoke test. And I used carb cleaner all around cylinder 7 and any hoses I could see. Nothing noticeable. I even pulled the hose off the valve cover and there was a noticeable difference when I did that. Put it back on and the engine went back to semi normal…. I’m gonna try a noid light for the fuel injector. If that doesn’t show me anything. I’m at a loss. Might have to cave into a mechanic

 

[Rocket Man]

So nothing on the smoke test. And I used carb cleaner all around cylinder 7 and any hoses I could see. Nothing noticeable. I even pulled the hose off the valve cover and there was a noticeable difference when I did that. Put it back on and the engine went back to semi normal…. I’m gonna try a noid light for the fuel injector. If that doesn’t show me anything. I’m at a loss. Might have to cave into a mechanic

Well that sucks. I don’t have any further suggestions other than it could still be an intake leak. I have done a smoke test on my 02 and can’t find anything but I know it’s leaking according to Blackbear and the fact it randomly throes P0300 random misfire. I can look at live data and see lots of misfires on #4 & #5 but can’t find the leak. I am running a Whipple blower but it shouldn’t matter, the smoke should show it but doesn’t. I guess it could be internal between those 2 plenums but wtf. I’ll be following your progress.

 

[Tonyv__]

Well that sucks. I don’t have any further suggestions other than it could still be an intake leak. I have done a smoke test on my 02 and can’t find anything but I know it’s leaking according to Blackbear and the fact it randomly throes P0300 random misfire. I can look at live data and see lots of misfires on #4 & #5 but can’t find the leak. I am running a Whipple blower but it shouldn’t matter, the smoke should show it but doesn’t. I guess it could be internal between those 2 plenums but wtf. I’ll be following your progress.

I just bought an autel handheld today but of course I didn’t check. I need a windows pc. So now I’m in the process of installing windows on my mac. Then I’ll get the handheld running then I wanna watch my live data and see if the mis is consistent or goes away at certain rpms. Don’t know what that’s gonna tell me but I’m not giving up just yet

 

[Tonyv__]

Tried a noid light on the fuel injectors. They checked out fine. Really hoping it’s nothing internal. “Fingers crossed”. But I imagine compression test should of shown that. The search continues

 

[exp500]

Do you have an accessible place to add a tee to get a good vacuum reading you could watch driving? Old school but very accurate on a chase. Look for a 1960's vacuum diagnostics chart. Hopin for an easy fix, Good Luck!

 

[Tonyv__]

Do you have an accessible place to add a tee to get a good vacuum reading you could watch driving? Old school but very accurate on a chase. Look for a 1960's vacuum diagnostics chart. Hopin for an easy fix, Good Luck!

I don’t see why not. Especially because you service the engine from inside the cab. I could put a T on the vacuum line going to the valve cover and mess with that while driving

On another note I dropped the van off today to a mechanic my dads been going to for years. They seem to think I have a “strong motor” and also can’t find any leads other than the PCM might be the culprit. They don’t have a tech 2 and suggested I take it to a Chevy dealer to have it diagnosed.. now I’m wondering if I should just gamble with a pcm company i found for $149 already programmed to vin and shipped before I take it to the dealership. Because if the dealer tells me it’s the PCM. I’ll be paying diagnostics fees and probably a grand for a GM PCM.

 

[Tonyrodz]

I don’t see why not. Especially because you service the engine from inside the cab. I could put a T on the vacuum line going to the valve cover and mess with that while driving

For me to get that center hump out I gotta pull the passenger seat--plus all of the other crap between the seats lol.

 

[Tonyv__]

For me to get that center hump out I gotta pull the passenger seat--plus all of the other crap between the seats lol.

My passenger seats been out for weeks now until I have this problem under wraps. I’m tired of it taking 15 minutes to get to my engine lol

 

[Rocket Man]

For me to get that center hump out I gotta pull the passenger seat--plus all of the other crap between the seats lol.

You mean old French fries and such?

 

[Tonyrodz]

You mean old French fries and such?

Nope. Just $hit that I drag around with me. I pretty much have anything in my van that I might need to do any interior repair, or tool to disassemble--something.

 

[Fless]

Nope. Just $hit that I drag around with me. I pretty much have anything in my van that I might need to do any interior repair, or tool to disassemble--something.

So, not old french fries, but NEW ones. Got it.

 

[Tonyv__]

Took a gamble on the PCM since the mechanic recommended that. No luck but I also did a trans flush over the weekend and either the fluid or the PCM solved the 1-2 hard shift. So that’s one thing off my list. Might just have to take it to the dealer and get the issue resolved..

Also some useful info for anyone that needs to program passlock 3. The instructions are very vague. It says insert master key turn it to on. Leave it for 10 mins. Turn off for 5 seconds then turn it back to on for 10 mins. Repeat this process 3 times…. Well I spent about 2 hours repeating this until I watched a video. They want you to turn the key all the way and attempt to start the truck then leave it on for 10 mins. 3 times in a row. Then it works

 

[Rocket Man]

Took a gamble on the PCM since the mechanic recommended that. No luck but I also did a trans flush over the weekend and either the fluid or the PCM solved the 1-2 hard shift. So that’s one thing off my list. Might just have to take it to the dealer and get the issue resolved..

Also some useful info for anyone that needs to program passlock 3. The instructions are very vague. It says insert master key turn it to on. Leave it for 10 mins. Turn off for 5 seconds then turn it back to on for 10 mins. Repeat this process 3 times…. Well I spent about 2 hours repeating this until I watched a video. They want you to turn the key all the way and attempt to start the truck then leave it on for 10 mins. 3 times in a row. Then it works

Did you use a Tech2 to program the PCM?

 

[Tonyv__]

Did you use a Tech2 to program the PCM?

Bought it pre programmed to my vin. I don’t have a tech 2 but I been tempted to get a knockoff one. I just really don’t understand how they work. I’m worried I’ll change or be reading stuff that I have no business messing with lol

 

[Tonyv__]

Do you have an accessible place to add a tee to get a good vacuum reading you could watch driving? Old school but very accurate on a chase. Look for a 1960's vacuum diagnostics chart. Hopin for an easy fix, Good Luck!

Vacuum test 08 express van

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Gave it a try. Not Sure what to make of it. It hovers in the low “normal engine” zone. Then drops when it’s misfiring Then comes back up. I’m not sure how to mess with timing. I thought that was all computer programmed now a days

 

[exp500]

There are a few more things I'd like to see on vacuum tests. Try a med RPM (3000 or so)steady state run, close throttle. What is max vac? Around 28-30 and steady? Like a freeway exit ramp decel. Next is steady state cruise, Vac steady above 15? Test drive results more reliable than driveway.
Here is a quick search diagnostic link There are better old school charts but didn't take time to search.

How To Diagnose Common Engine Problems with a Vacuum Gauge

One of the easiest, cheapest, and fastest ways to check an engine for serious issues is to perform a vacuum gauge test...

m.roadkillcustoms.com

Lastly, engine oil/carbon can cause that minor miss via intake valves(or lifters), so a can of cleaner in gas may help.Spark plugs also. NGK/AC only. Good luck.

 

[Tonyv__]

There are a few more things I'd like to see on vacuum tests. Try a med RPM (3000 or so)steady state run, close throttle. What is max vac? Around 28-30 and steady? Like a freeway exit ramp decel. Next is steady state cruise, Vac steady above 15? Test drive results more reliable than driveway.
Here is a quick search diagnostic link There are better old school charts but didn't take time to search.

How To Diagnose Common Engine Problems with a Vacuum Gauge

One of the easiest, cheapest, and fastest ways to check an engine for serious issues is to perform a vacuum gauge test...

m.roadkillcustoms.com

Lastly, engine oil/carbon can cause that minor miss via intake valves(or lifters), so a can of cleaner in gas may help.Spark plugs also. NGK/AC only. Good luck.

I was running couple bottles of cleaner earlier this year and premium gas.. I’ve been having trouble for months. Around Jan 2021 misfire in cylinder 8 and rough idle. Which is why I initially changed wires and plugs then ran cleaner in the fuel. The cylinder 8 code went away after that but the rough idle never really settled. About a month or 2 ago the frequent cylinder 7 misfire started showing on the scanner.

I’ll try to go for a ride with the vac pump hooked up

I also used ngk plugs

 

[Tonyv__]

There are a few more things I'd like to see on vacuum tests. Try a med RPM (3000 or so)steady state run, close throttle. What is max vac? Around 28-30 and steady? Like a freeway exit ramp decel. Next is steady state cruise, Vac steady above 15? Test drive results more reliable than driveway.
Here is a quick search diagnostic link There are better old school charts but didn't take time to search.

How To Diagnose Common Engine Problems with a Vacuum Gauge

One of the easiest, cheapest, and fastest ways to check an engine for serious issues is to perform a vacuum gauge test...

m.roadkillcustoms.com

Lastly, engine oil/carbon can cause that minor miss via intake valves(or lifters), so a can of cleaner in gas may help.Spark plugs also. NGK/AC only. Good luck.

Took a quick run down the road. Hope this is what you were looking for

a lot of the ruckus you hear banging around is equipment in the back.