Yetti53

Hey guys, so I just replaced the flex plate in my 2000 xj 4l 2wd auto. Got it all back together and when I tried to start it it was really rough backfiring through intake. After a bunch of tries and the right amount of throtttle I could get it to start and it then ran smooth, then shut it off and tried again and couldn’t get it to start still just rough with backfires in the air box. Initially I thought the worst that I had bought the wrong flex plate but I called the dealer gave them my vin and cross checked parts numbers and it was right. Naturally the next thing I tried was the cps, after changing that I thought I had fixed it until I drove it about ten miles and shut it off and then it began again on the next start up. It threw a flashing light for a slight second when I hit 80 when it was running good. I’m totally lost and about to push this thing into a lake please help

Griffyorcono

Make sure the map sensor vacuum line isn't disconnected or damaged during the installation of the trans.

Yetti53

is there a vac line to the trans?

Yetti53

Anybody?

Yetti53

I’ve also noticed that now once I can finally get it to fire which is not easy but runs fine once it does, the stereo hums in sync with rpms, did not do this before flex plate swap

lawsoncl

No vac line to the trans, but there is a vent line that comes forward to the engine bay for it.

doublechaz

Fire out of the intake would be a valve sealing problem or a spark at the wrong time problem. Either of those could also make for very hard starts.

Roler

Check the braided ground strap between engine and firewall (if the 00 still had those) for this.


Backfiring can be several things, usually timing/synchronise issues
After your CPS, check your CAM sensor. Mine gave the same symptoms with both sensors.

Yetti53

The braided line is there and looks fine, cps and cam both swapped out

97grand4.0

When you took the old flexplate off did it match the new one you bought?
Why did you replace it?

Roler

looking at grounds is not enough

Yetti53

ok well it looks, feels fine tight and snug on the connections with no corrosion or signs of being bad