JSJJ388

Ok guys, I put this here because its a XJ motor in my ZJ. I put a 92 4.0 in my ZJ and Im having some issues with it. When start it, it tries to run but it makes a loud sucking sound through the TB and when I give it gas it backfires bad. To the point of blowing my hose off of the TB. But heres the kicker, half the time it runs like a top..... took the TB off my 94 ZJ motor with good sensors on it (ran fine before motor blew) and it made no difference. CPS is new (casualty of the engine swap). Any idea?

JSJJ388

Here it is when it's acting up

freegdr

Was distributor removed during swap ? Also check map sensor vacuum line.

JSJJ388

It was not initially, but we did check the timing on the distributor as well as replaced it and the wires. I have checked map sensor hose but will again just to be sure. Im honestly stumped. Ive done a few swaps and worked on plenty of motors, but this is a first.

XJeepCheep

check your fuel pressure! The same thing happened to me and I put a gage on it and sure enough the fuel psi would drop right when the backfire would start. If you don't have a Gauge you can borrow one from auto zone. I too changed just about every sensor before I went and got the gauge. Let me know if this helps.

JSJJ388

I have read this as well and I am gonna go rent on tonight. Im hoping that is it. What did you replace? Fuel pump?

XJeepCheep

So I replaced the whole fuel pump assembly with a bosh one. Then I had a hard to start problem it would crank for 10-15 sec before starting, but no more backfire. So I returned it and got another bosh pump that had no power at high rpm's and I put the gauge back on and it was loosing pressure. I returned this pump and got the cheaper airtex pump and all problems solved. The guy at the napa was shocked and later told me that every bosh pump he sold for the next 6 months were returned. They must have had a bad run at the factory? I am now a pro at dropping the tank by myself on the ground!

investinwaffles

It sounds like a tuning/ignition/fuel delivery issue - TPS/IAC/MAP sensor perhaps? Or a reaaaally bad vacuum leak

Definately check fuel pressure at the rail to be 100% sure. Check it while its primed (engine off), and while the engine is running too, it should be holding 40-ish PSI

GreaseMonkey17

Bosch can't seem to do much right . They can't even make a decent spark plug .

freegdr

Dist does not point at No 1 on cap......

http://www.angelfire.com/my/fan/dist_index.html

cruiser54

Oh bull****.

Contribute or keep quiet.

JSJJ388

Well, how do I miss the good stuff, and on my own thread lol. Anywho.

I went and rented a pressure gauge ( damb those are expensive) and it was broke. Went to get another one, and it's broke as well. Thanks oreilys. It's running fine today, drove it for an hour around town and cracked back fine. I'm still getting a slight skip at 2500 rpms under load bit it runs good besides that.

JSJJ388

I THINK this is how we set it. I was wiring my push button start (long story) and my dad checked and set the timing and put on another distributor.

freegdr

Will never run correctly if its not . Computer controls timing big difference from older cars.

XJeepCheep

You can buy a cheap one from Harbor freight if you can't find a good one to rent. I think like 30$.
I hooked it up and tucked the hose under the wiper so I could drive with it and watch The pressure.