Cylinder 2 and 4 misfire

[Upper tanker]

Hey all. So, I have 3xxx misfires on cylinder 2 and cylinder 4 in the history when I had the shop scan the obd2 for a small misfire that I can feel. I can only feel it when I'm in gear, at idle, with my foot on the brake. It's a very small stutter, and also when it's in neutral/park and you tap the throttle, the rpms stutter when they increase, and you can see it on the tach.

The block is the stock 97 vortec block that came with the truck. Full roller valvetrain, with comp hardened pushrods and full roller rockers. 020" pistons, longtube headers, MPFI conversion, full msd ignition. Blackbear tuned.

When I did the first start up on this engine, I was getting a terrible backfire out of cylinders 2 and 4 that was popping pretty loud, which ended up being the brand new MSD cap that we put on. Swapped it out for the stock one that we pulled off and it ran great. So, I got a replacement MSD cap and installed it and it was good (I thought.)

I pulled both plugs, and they looked great. Porcelain looked new still, no abnormal colors on the electrode. The gap was also correct.

My question is, does this seem like a valve adjust issue? The shop also checked all of the spark plug wires and all of them measured right around the same as one another (35000kv rings a bell? Not sure). Anyways, even though the wires measure all the same, does that definitely rule out a shorted cap? I'm thinking I'm going to swap out the msd with a delco unit, just because the MSD cap left a bad taste in my mouth. However, I'd hate to pull the valve cover just to find out that the valves are adjusted fine. I hate wasting time.


Anybody have any thoughts/input?

 

[swathdiver]

I'd do what you're gonna do, swap out the MSD for the ACDelco unit first.

 

[Upper tanker]

Could the cap be just bad enough to cause a very small misfire? I obviously know it can be bad enough to cause major misfires...I'd just think that if two of the leads in the cap shorted to each other, it would be a sort of "all or nothing" type of deal.

I already pulled the passenger side valve cover. The intake valve on cylinder 2 seems a LITTLE bit loose, but that's about all I've found. I'm going to adjust valves on 2 and 4 tomorrow, and still get the delco cap.

 

[east302]

A compression test wouldn't hurt since #2 and 4 are adjacent.

Have you noticed any coolant loss?


Sent from my iPhone using Tapatalk

 

[Upper tanker]

I don't have any coolant loss, luckily.

 

[willxfs]

Keep us posted. I'm fighting similar misfires on #2 and #4 after a rebuild/conversion to a 383 stroker. I have all new ac/delco ignition parts. I tried adjusting the valves but it didn't make a difference. Pretty sure they were ok from the engine builder. Good luck.

 

[Upper tanker]

Willxfs, thats sort of funny, but I do feel sorry for you! Last friday, I bought another O2 sensor to replace the already new (well, 2500 miles old) one on bank 2. I also bought the AC Delco cap and replaced my 2500 mile old MSD cap with that. I started it up, and had the same issue (I think). Then, just for S&G, I took a MAF sensor off of one of my dad's trucks and swapped it onto mine with no change. We did check the valves, and they were all perfect. I am sort of thinking it is the delco MPFI unit, but I wish there was a way to check it before going through all that just to have it be in perfect working order. I am at a loss here with this. Although I cannot officially say if the little stutter I am feeling (in drive, with my foot on the brake), is in fact a misfire(s) or if it's the cam and just me being paranoid. I'm wondering if the shop that pulled the codes pulled them from the history of when we first did the start up and it was REALLY bad (From the first MSD cap). It's wierd because it runs great, and when accelerating, it runs fine with no issues. I can only feel it when I'm stopped, in drive, with my foot on the brake.

 

[east302]

You can download a scanner app (DashCommand and CarGauge Pro are decent ones) and, using a Bluetooth OBD adapter, can see the misfire counts, clear codes, etc.

Is the check engine light on right now? Was it cleared originally?




Sent from my iPhone using Tapatalk

 

[Upper tanker]

I do have dash command already, where would I find the misfire parameters? Would I find them in the list of available PIDs and add them?

As far as the CEL, I initially thought everything was good, but as it turns out, the bulb is either burned out or it's disconnected. When I was checking the LTFT/STFTs on the little handheld scanner, I didn't see any current codes for it.

 

[east302]

I don't have it in front of me, but it should be in the list of PIDs. I think it gives a counter for each cylinder.

If the check engine light doesn't come on when the truck is started, it's either a bulb or some communication issue. Try swapping the bulb with another in the cluster.


Sent from my iPhone using Tapatalk