Backfiring through intake

[freid_guy]

So I recently purchased a 2000 XJ with a 4.6 stroker.

Long story short, it had problems and I repaired a lot of things.

Now, after all my efforts, it's popping out the intake as soon as I give it gas in drive and has no power. It doesn't backfire in park and idles pretty good.

Aside from the typical lean condition problems from O2 sensors (will be replacing tonight), stuck valves (none), vacuum leaks (all repaired) and cam timing (will replace and index tonight if necessary) is there anything that needs to be done to the 4.6 to make it run right?

Thanks

[Cheromaniac]

I suggest you use a borescope to inspect all cylinders and perform a compression test.
Backfiring into the intake suggests that an intake valve is partially open on the compression stroke when it should be closed. Possible causes are a bent valve, damaged valve head or valve seat, or a broken valve spring.

[freid_guy]

Compression tested at 150psi per cylinder.

I replaced the rocker arm bridges and the valvetrain looked great (though this was some time ago).

I replaced the RMS and thoroughly examined the engine and the camshaft and cylinder bores looked great.

I checked the indexing on the cam position sensor and it all seems great.

I replaced both upstream O2 sensors with OEM mopar sensors.

I'm ordering a host of OEM mopar sensors in case that's my problem.

I'll have a look at the valvetrain tonight to see if something changed (bent rod, broken spring, etc).

Thanks

[75SV!]

New Member. Lurker for a few years. I had this problem recently. I did a mini-stroker. Finally, completed the head etc,. Anyways, since the 2000-2001 are waste spark, mine would run with the 'distributor 180 degrees out. Yes, I could run it on the road. Lots of back firing, blowing vacuum hoses off. So, make sure you are on the compression stroke, when you index the 'distributor. I took all the sparkplugs out. Put some 30 wt oil on the threads of #1 sparkplug. Threaded it back in, put backed it out 1/2 turn or so. Rotated crank till I heard air pushing out. Then brought the timing mark to Zero.

[freid_guy]

Good suggestion (and good to know). I checked my cam timing and verified it's indexed properly on the compression stroke, and it is.

I ordered a whole set of OEM mopar sensors that I'm waiting for and will replace them one at a time and test. I've got all the parts for the viper coil mod just in case it's my coil pack (and I rather dislike that coil pack anyway).

I'm going to check the valvetrain in the next hour or so here.

[freid_guy]

It's been a bit difficult to work on my jeep, but I've had some time over the last few days and here's where it stands:

I've changed out all the sensors, one at a time, to genuine mopar sensors-- except for the O2 sensors.

I changed out the fuel pump/regulator assembly.

I installed new fuel lines.

I checked my valvetrain again-- perfect.

I checked the manifold bolts-- all were tight.

I smoked the engine-- no leaks.

I threw in bosch 04669938 fuel injectors.

I changed to a dodge viper coil and spark plug wires-- when I did this I found that the connector to the coil was flakey-- it was causing stumbling/stalling when moved, so I soldered in a new one.

After all this-- still spitting/backfiring/stumbling/stalling.


Out of desperation, I changed out my spark plugs to colder ones... RC9YC... no more spitting/backfiring/stumbling/stalling. Headers stopped glowing.


I drove it around for 20 minutes after letting it idle for 20 minutes... engine seemed weak, but no "problems" with it.


Then I idled it in the driveway for 20 minutes more or so and during that time I got a CEL P0175 (bank 2 too rich). I'm assuming that's what's making it run like a dog.

What could be causing that error?
Leaky injectors?
Injectors too large? (my fuel pressure is 54psi)
O2 sensors?

TIA

[SilverXJ]

Those injectors are what I am currently running, so I don't think the injector selection is an issue. Perhaps you have a failed injector on the rear bank, cylinder 4, 5, 6. Probably stuck open. Also, in the past years there have been crappy Chinese counterfeit injectors popping up all over. They have problems.

[Russ Pottenger]

Those injectors are what I am currently running, so I don't think the injector selection is an issue. Perhaps you have a failed injector on the rear bank, cylinder 4, 5, 6. Probably stuck open. Also, in the past years there have been crappy Chinese counterfeit injectors popping up all over. They have problems.

Good to see your post SilverXJ. Haven’t seen you post up in a while.
Hope to see more of your post contributions. The Jeep community could certainly benefit from it.

[dwg86]

Those injectors are what I am currently running, so I don't think the injector selection is an issue. Perhaps you have a failed injector on the rear bank, cylinder 4, 5, 6. Probably stuck open. Also, in the past years there have been crappy Chinese counterfeit injectors popping up all over. They have problems.

Good to see your post SilverXJ. Haven’t seen you post up in a while.
Hope to see more of your post contributions. The Jeep community could certainly benefit from it.

Yes good to see you back Silverxj. How’s your engine running? Give us an update in a another post.
(Sorry to hijack your thread)

[amcinstaller]

Silver AND dwg?! How have you guys been

[dwg86]

Silver AND dwg?! How have you guys been

Good. I waiting on my 4.0 to die before I build another striker. At 315,000 miles right now and shows no signs of stopping.
I put a 5.9 magnum in my Jeep truck.

IMG_4338.jpeg

[dwg86]

stroker not striker