My 4.7 stroker is MISFIRING

Hey y'all, gotz a problem with meeee stroker!

Thing has been running great, tons of power. One day after a trail ride it developed what I believe to be a misfire on the way home.

It happens around 4000 rpm. It was really inconsistent at first, but now it's fairly consistent when it happens, and now it happens in all gears as well.

I'll floor it, accelerate hard and it misfires pretty bad. It idles fine. Power from 1000-4000 is still excellent.

-New plugs that Ryan at FRP told me to run BKR7E/4644 along with the DUI firepower ignition setup.
-New CPS from NAPA went in during stroker install
-New coolant temp sensor (just because I broke the old one, this is not all due to troubleshooting)
-New primary Oxygen sensor (had it on hand in case it shit the bed, so I went ahead and threw it in, didn't change anything)
-New Cam position sensor
-New fuel pump, old one made 46 psi, fuel level gauge was funky and bounced around. Installed new one (bosch from Napa) and confirmed I now have 49 psi.

I have had some issues with PCV and blowing my oil cap off. I turn over 6000 rpm and I don't do that every shift, but plenty hahaha. So I came up with a sorta/almost catch can setup to help keep motor oil out of the intake (I was getting quite a bit in there).

So could it be the new CPS? Some things point to that including Ryan who's tuning my Jeep. It just came in the typical NAPA box. It sure was expensive though

Sensors I have NOT replaced:
-Intake temp
-TPS
-MAP
-IAC

Any ideas? Posted over at Jeep strokers as well. Put this in OEM because I'm still using OEM sensors and it's an issue that plagues stock 4.0L's just the same

This isn't an OEM issue, this is a modified issue, are you running the comp cams 68-232-4 cam shaft by chance?

No it's a custom ground solid cam from Lunati. It's "bigger" than any of the off the shelf comp cams.

I'm roughly 100% sure it is not cam or valvetrain related. It has been running extremely well before this and I'm on my 6th tune revision from flyin' Ryan performance.

Are you sure you're not losing spring pressure on the valves? What does the AFRs look like when it starts misfiring?

Have you done a compression check?
What's your exhaust system past the header?

Exhaust is 3" and exits out the fender. No cats or muffler
https://vimeo.com/275532350

I can't imagine I'm losing spring pressure. The springs on the head from Russ I confirmed with the Tech guy at Lunati they would work well with this cam. I haven't had any issues up until now.

I have not done a compression check. Engine has about 500 miles on it. MAP readings on decel are indicative of a very well machined/assembled engine according to Ryan at FRP.

This thing acts normal up to 4000 rpm. When I say normal I mean feels like it wants to wheelie and pull you off the road.

Originally when it first started happening AFR appeared to go rich. Watching it yesterday it seemed to stay the same, around 15 ish.

15 under wot? That's pretty lean. Have you pulled plugs yet and visually checked them?

Crank sensor would also be high on the list of probabilities

I reinstalled the original CPS. I only replaced it as preventative maintenance and kept the original as a trail spare. It started and idled better than usual. Maybe the Echlin brand CPS from NAPA was junk

Going out wheeling, if it still misfires I'm still going wheeling.

First things first.
1) Like was said, pull the plugs and post up pix.
2) Check the compression. If low, do it wet as well.
3) Check the vacuum at idle, at 3000 rpms. Take it for a spin and measure at mild cruise 40 mph, 55 mph, 75 mph, and WOT

The misfire appeared to go away on the way to the trail. I was able to spin it to and sometimes over 6K while hauling the mail in the dirt.

Then it came back and the misfire was worse on the drive home. This is why I think it is sensor/electronic. If I had an issue with compression it wouldn't come and go. I don't think a vacuum leak would either.

I feel as though a high rpm intermittent misfire is ignition related. I'll pull the plugs today. I have a new set I can throw in as well.

Also, I don't have a compression tester or vacuum gauge. I live on an island in Alaska and would have to purchase those items. I'm not against acquiring them if I need them.

If it only happens at high rev, I would also check electrical power delivery to the coil(s)(Alternator, charge wire, etc,) and fuel pressure (regulator, pump, filter, fuel pickup in tank, etc).

Got it figured out. My manifold bolts had come loose and one even fell out. #6 spark plug was different than the rest and that's where they were the loosest, #5 and #6.

She runs like a raped ape again

Glad to hear, it's always the dumbest thing that gets you.

The_Punisher said:

Got it figured out. My manifold bolts had come loose and one even fell out. #6 spark plug was different than the rest and that's where they were the loosest, #5 and #6.

She runs like a raped ape again

Click to expand...

Hence the recommendation for a vacuum test. :anon: