Stumble when cold

[joeguyzxj93]

I got a 98 Xj with a 93 head and block has a 4.2 crank and bored over 30 I bought it becouse of the price and cylinder 2 exaust valve was stuck open . I put a new used head on it I got compression in all cylinders, fuel pressure checks out good and seems to be running better since head was replaced we found that the 99 intake was cracked from p/o around injector 1. I put 10 miles on it then changed the intake with a new 99 intake . Now when it starts up it seems rough and stumbles on acceleration then runs and idols fine after a few pops in intake and exuast . Today changed CPS , TPS , Distrubuter , cap and rotor . The engine lite did come on for CPS that's why I changed it . I also tried to set the distrubutor one setting forward and one back from the original position I took it out of and would not start unless my marks lined up . But either way it keeps sthmbleing . Also changed the temp sensor in thermostat housing . I don't know much about what was all done to motor execpt what I wrote above . I has a 99 intake . Seems to be stock throttke body 5.0 injectors they are orange. Also changed plugs and ran computer it says the 02 censors are running and working but p/o said it has somekind of bypass box plugged into them so they read normal it has stock cat on it and its not hollowed out . Also a k&n filter . Any help please thanks in advance

[joeguyzxj93]

It did idol rough with cracked intake but didnot have the hesitation untill I changed it . Thanks again

[SilverXJ]

Make sure your distributor is 100% synched http://www.angelfire.com/my/fan/dist_index.html

What cam is it running? Part number on the injectors?

[sly-jeeper]

starts okay...take off and it stumbles and pops...quarter mile later clears up and runs normal??? is this what your describing?

[joeguyzxj93]

FOTE D5A & 280150943 & 363 Besides the ford emblem that's all the numbers on the injectors .

[joeguyzxj93]

Yes sly jeeper that sums it up

[SilverXJ]

What you are experiencing is a lack of cold start enrichment. It is running too lean for a cold engine. The reason it clears up after 1/4 mile is that the O2 sensors heat up and begin adjusting the air fuel ratio. Also, your 98 came with 23.2 lb /hr injectors. The injectors you have installed are smaller than stock running 19.4 lb/hr on the 49 psi fuel system.

So, the problem could be caused by the cam or perhaps the injectors. I would verify the distributor indexing first. Then change those injectors out for your stock ones to begin with, reset the PCM, and see how the condition does. I would also check the fuel pressure while you are at it. Should be 49 psi +/- 5 psi.

[joeguyzxj93]

33007127 I have these injectors laying around from my 93 .Will they work or will I need something eles ? I wanna tty this before I jump into the timming . Thanks Again

[Cheromaniac]

Seems to be stock throttke body 5.0 injectors they are orange.

Those are stock Mustang 5.0L Gt injectors that flow 19lb/hr @ 39psi. Even with your 49psi fuel system they'll only flow 21.3lb/hr which is less than stock, so your engine could be running too lean during the open loop warm-up phase.
Your '93 injectors flow ~10% more so they'll be an improvement and might just work.

[Retlaw01XJ]

....02 censors are running and working but p/o said it has some kind of bypass box plugged into them so they read normal

Agree on the injectors being too small.... even my '01 runs rough for the first minute. It's on 'open loop' until the O2 sensors warm up and goes to closed loop, then it's fine. But again, it's only for about a minute. Sounds like yours lasts longer?
Chris, do you think his 'box' might be affecting his tune?

[sly-jeeper]

sometimes the upstream o2 sensor gets lazy and does this!! i had a stock 4.0 in a 97 zj that would start normal then when you would take off it would get lean, stumble, pop, and carry on for about a 1/4 mile or so i tried repalcing everything including the fuel pump and injectors sence i figured the 02 sensor was fine bc milage was 21 to 22 mpg then i read on a forum somewhere that the o2 gets lazy and does this and only to use an NTK 02 sensor so i did and it was fine till i sold it 40,000 miles later...but your injectors arnt doing you any favors either

[joeguyzxj93]

My upper 02 does not have this "box" on it I discovered last night . The one for the cat does , I am going to replace the injectorsbut may not be for 2 weeks due to work and vacation . I have a upstream 02 censor laying around and my engine seems to take longer to heat up than a normal one my thermost has 2 holes drilled in it and eletric fan kicks on as soon as key is on , I also used icey cool in it becouse of wheeling at slower speeds . Thanks. Again I will post when I change injectors and check the timming

[joeguyzxj93]

Sry for misspelling on a lot I am using a phone !

[SilverXJ]

Chris, do you think his 'box' might be affecting his tune?

Not if its on the downstream/after cat sensor. Its called an O2 sim. If it was on the upstream/precat, it would definitely be an issue.

My upper 02 does not have this "box" on it I discovered last night . The one for the cat does

Sounds fine. Out of curiosity, is there any writing on the box?

to take longer to heat up than a normal one my thermost has 2 holes drilled in it and eletric fan kicks on as soon as key is on

The holes are a normal procedure and could be part of the longer heat up issue, but I don't think its causing your cold start issue. However, the electric fan turning on as soon as the key is on is definitely not good. That will extend your heat up time considerably. Is this the stock e-fan or an aftermarket one we are talking about?

[joeguyzxj93]

I drilled 2 1/8 holes in flat spot of thermosat . The box has nothing onit and the fans are aftermarket one is on key and one is on toggle switch .