Truck started misfiring all of a sudden, need ideas

[Tooky]

I need some basic help. It's been a while since my truck had an ignition problem and never anything this bad.

Short Version: My truck seems to be misfiring and I don't know what's causing it.


Long Version: I was testing out my tune in Open Loop (normally I run Closed Loop) and I found it drove just the same in Open Loop, except at 50mph cruise it would be about 13.2 AFR instead of 14.7. I hammered it a few times and everything was great. I slow down to enter a freeway onramp and all of a sudden I felt a vibration in the truck. Thought maybe I was imagining things but by the time I got up to 60 mph it was enough to vibrate the rearview mirrors and I thought maybe a wheel was about to come loose so I pulled onto the shoulder. DM was recording at the time but didn't show anything. Couldn't find anything amiss so I carefully drove home and I can't find what's wrong.

It's got no power and I think it's just an ignition misfire. Idles rougher than usual. I pulled #2 and #4:

Way sooty compared to normal. Usually they are practically brand new in appearance. If 2 plugs look like this wouldn't you think its a more general ignition problem? I tried replacing the ign. coil and no change. I've got to be missing something basic. Distributor hasn't come loose, everything looks normal in DM, plug wires on cap all seated properly..

It's weird because this happened so suddenly. What are your ideas? Ign. module? Pickup coil? What can go bad in the middle of a drive like this? Would 15 minutes of 13.0 AFR cruise cause this much soot?

 

[supersports10]

Re: Truck started misfiring all of a sudden, need ideas

i say ignition module tooky,.....how long has it been since you swapped it out???

coils almost never go bad.

how does the fuel pressure look??

 

[Tooky]

Re: Truck started misfiring all of a sudden, need ideas

The ignition module was replaced about 2-3 yrs ago (I was chasing a different problem, and the new module didnt fix it, so I guess I still have an old one that's "good" I could try..) Maybe tomorrow I will dig it up and give it a try.

Fuel pressure, I didn't check, since the wideband read normal under all conditions. (My FP gauge is under the hood).

 

[TYTILIDIE]

Re: Truck started misfiring all of a sudden, need ideas

Is there even any tach flutter? I have seen plug wires do this, especially when they start to get too close to the exhaust manifolds.

 

[berzerker]

Re: Truck started misfiring all of a sudden, need ideas

to help narrow down the missfiring cylinder. start engine and after one minute of running shut off engine. then spray water onto the exhaust manifolds closests to the outlets at the heads . if the water dosen't sizzle or burn off a certian cylinder . you've found your problem . then it comes down to finding the problem with the ignition components or valvetrain - i.e. bent valve , broken rocker stud .

 

[Tooky]

Re: Truck started misfiring all of a sudden, need ideas

Update - Replaced the ignition module and no change. Then I remembered I have a new infrared surface thermometer gun. I found all cylinders to be 450-500*F (including the 2 plugs I showed in the photo above). However, #1 and #3 were only 250*F. I pulled the plugs from those and #3 looked as sooty as the photo above, but #1 was practically SOLID BLACK like a chimney.

Any more ideas? I can try replacing the fouled plugs but I'd rather find the root cause of the problem fouling them in the first place.

When I took it around the block, when it went into 4th at 50 MPH and low RPM and I gave it light throttle, is when it really bucks bad and the wideband reads 12.0-13.0 rich.

 

[turbodig]

Re: Truck started misfiring all of a sudden, need ideas

Update - Replaced the ignition module and no change. Then I remembered I have a new infrared surface thermometer gun. I found all cylinders to be 450-500*F (including the 2 plugs I showed in the photo above). However, #1 and #3 were only 250*F. I pulled the plugs from those and #3 looked as sooty as the photo above, but #1 was practically SOLID BLACK like a chimney.

Compression check. Those are the same 2 holes that I ended up killing.

Hope it isn't that.

Could just be a couple marginal wires, too.

 

[gkrcr882]

Re: Truck started misfiring all of a sudden, need ideas

Just for kicks, check out the cap and rotor, the terminals. Corrosion maybe?

 

[Tooky]

Re: Truck started misfiring all of a sudden, need ideas

I just got done spending the afternoon chasing my ass and still haven't figured it out. Cap and Rotor look like normal. Did 3 fresh plugs on the driver's bank (where the 2 cold cyls are), and swapped another set of wires on those cylinders, plus the coil wire. Same damn thing!! And the WB seems to be rich, in fact the Datamaster log shows the STerms in the 80s which is a lot richer than normal.

Now I'm thinking maybe the AFPR is leaking fuel, or what else could cause em all to run rich and misfire like this? I tried doing a compression test but I guess my tester doesnt work with the Vortec heads (maybe due to the long reach spark plug threads).

EDIT: Just checked the timing (yup still dead on at 0* with tan wire disconnected) and the FP gauge - about a 15 PSI difference between "key on engine off" and actually idling. Pulled the AFPR vac hose and it didn't appear wet inside or smell either. Frustrating!

 

[4C FED]

Re: Truck started misfiring all of a sudden, need ideas

When I was trying to find my miss, I used my timing light on all wires, revving the motor slightly and watching the strobe of the timing light to see if it missed a beat. I located one cylinder that was dropping. When I removed the cap I found a terminal that was loose in the plastic. I could grab the top post and wiggle it.

Check the center contact in the cap. Make sure that it moves up & down freely & it doesn't stick anywhere in its travel.

 

[berzerker]

Re: Truck started misfiring all of a sudden, need ideas

pull the valve cover off the drivers side and check for something wrong with the valve train .

 

[Merk]

Re: Truck started misfiring all of a sudden, need ideas

What kind of injectors are you using?

 

[turboj91]

Re: Truck started misfiring all of a sudden, need ideas

I do not think it is an ignition related problem. With that many plugs being that "dirty", if it was an ignition problem, the thing would be missing very badly. Follow the rich condition. Can you find a way to monitor fuel pressure while you drive? Watch dwell time of the injectors? Just seems like way too much fuel for some reason. One of your plugs is showing a very poor flame burn pattern in the cylinder which can be related to a rich condition.

 

[mmvic]

Re: Truck started misfiring all of a sudden, need ideas

Hope you find your problem and its nothing major. Wish I could help, but I can barely figure out my own,lol.

 

[Don W.]

Re: Truck started misfiring all of a sudden, need ideas

Hmmm. I'd have to go back and look but those plugs look familiar. Ya know what I think? You've blown an intake gasket when you hammered it. Do the inner tube thing and listen. If it's the lower, meaning valley, portion you won't find it with a squirt bottle but prolly just hear it. Another thought, this is a stretch, check inj o-rings at the manifold side. Maybe one blew out.

 

[canadian]

Re: Truck started misfiring all of a sudden, need ideas

Have you changed the plug wires at all?

 

[Syclone#2960]

Re: Truck started misfiring all of a sudden, need ideas

Josh I would replace all the plugs first & go from there. I remember cracking the #4 plug when installing them. It was enough to cause a small misfire...I could see a little spark coming from it in the dark.

 

[Tooky]

Re: Truck started misfiring all of a sudden, need ideas

The injectors are Delphi 50# installed new last fall with the vortec heads & cam.

I tried replacing the driver's side wires and plugs with no change. The #1 and #3 cylinders are still cold by 200*F compared to the rest. I hurt my neck really bad on Sunday (too much SyTy contortionism?) so I haven't had a chance to work on it since but I will try a new cap & rotor, swapping ECM/chips, and if that fails I will hit up the plugs & wires I didn't touch yet.

In the meantime I made two high quality (640x480, CD quality 44kHz sound) videos of the truck idling.

Video #1. (8 MB): Idling in the garage in Park, then Drive, then Park, and a walkaround near the driver's valvecover (seems a little noisy? but it's always been more noisy since the heads/cam upgrade) and finally the tailpipe (where you can really hear how off it sounds).

Video #2. (6 MB): It was wanting to idle at 500 RPM causing alot of bucking/vibrating (which you can hear in the video as the interior vibrates) but suddenly it smoothed out on it's own and brought the RPM up?? And I noticed the wideband was rich and leaned itself out when the idle RPM got better? This only happened once so I'm lucky I caught it on tape.

That 2nd one is what makes me think maybe the ECM/chip need to be swapped as a test. I will report back.

 

[fivetodrive]

Re: Truck started misfiring all of a sudden, need ideas

The ignition module was replaced about 2-3 yrs ago (I was chasing a different problem, and the new module didnt fix it, so I guess I still have an old one that's "good" I could try..) Maybe tomorrow I will dig it up and give it a try.

Did you try this yet?

Maybe try a spare ecm?

 

[turboj91]

Re: Truck started misfiring all of a sudden, need ideas

After listening multiple times, you might want to look under the valve cover and make sure things for 1 & 3 are ok (push rods & rockers). Almost sounds mechanical and those 2 cylinders being so cold is not cool (no pun intended). A compression test would not hurt either then depending on the results, a leak down test.