Cold Start Misfire

2000, ATK 4.0 reman < 3k, 161k, auto

Hello,
Had a thread on this already but due to finals at school and moving and yada yada had to abandon it for awhile. Now its back to it. Im able to bike to work so the ol heep's sitting comfy in a garage ready to be worked on.

Anyways, a lil back story, my old motor had a case of the piston slap so i got her a $$new one$$(kinda wish i had ol ticky back now ). worked out a few lil things with the new motor and now its running fine EXCEPT on a cold start. and when i say cold start i mean it, like even if its a hot day it wont do it.

I will go to start her up and it fires up fine, runs clean for about a second or two and then goes into a shuddering that sways the jeep side to side for about 10 seconds and then goes away. AND THATS IT. nothing else odd or strange will happen until the motor has FULLY cooled back down, usually from leaving it overnight or parking it at work for 8 hrs and getting off at 10pm, upon which it will produce the same effect

initially i suspected a leaking injector and have replaced two now with no change. doing this showed me that if i flash my comp the "misfire" will go away for a few days giving me the indication that ive fixed the issue and then crushing my joy later haha. i havent ruled out that it may be the cause.

i currently have a fuel pressure kit hooked to it and im at 9.5 with the key on ON and what appears to be 48ish and makes it way to 49 after awhile. as far as i can find my pressure should be at 5 on idle not 10? but as for the running idle its normal. could that initial high pressure be shoving to much gas in it on start up? ill be investigating and testing this further for now. possibly new a new reg or have a kink in the line

my next plan is replace the map and see if that does anything and also acquire a vac gauge and see whats going on with that.

thank you as always

Fuel pressure seems fine. Have you done a plug reading on all the plugs? Have you done a compression test?

plug reading? as in checking all the gaps with a gauge? i considered it may be plug related and replaced them(year old ngk's) with the spec champions and gauged every single one before installing.

i have not done a compression test but i have noted that i can rent the kit from Orielys

How cold is cold?

not hot is cold

example: we had a few days of 100+ weather. it didnt do it then, but when id turn the key to ON my temp gauge was almost to the first tick already.

not sure if its relivent but my a/c compressor bearing is about done for. makes a heck of a racket

I've been fighting a similar problem with my 99. It didn't want to start at all earlier. Going to swap crankshaft positioning sensors to see if that'll clear it up. Doesn't seem fuel related to me. Seems timing related.

Easy, and free, if you already have a compression tester, to see if you have a mechanical problem or an electronic problem.

my mileage is about an mpg lower than pre new motor and also i did bring it to a(3 now actually, none of which know whats up) shop and they said it had a lean misfire. shoulda put the in op. damn memory.

also i swear i hear it ping occasionally altho no one else does. these make me think its a fuel delvery issue

ill trade the fuel gauge for the compression tester on my next orielys vist

A plug reading is when you look at the plug, the ceramic and the electrode for color and buildup. You can tell a ton about how a engine is running without any computer. That coupled with compression can give you a pretty fair evaluation of an engine.
https://www.google.com/search?q=rea...spark-plugs-and-compression-tests%2F;1200;813

MrAnderson said:

plug reading? as in checking all the gaps with a gauge? i considered it may be plug related and replaced them(year old ngk's) with the spec champions and gauged every single one before installing.

i have not done a compression test but i have noted that i can rent the kit from Orielys

Click to expand...

i have the next two days off so ill pull the plugs and check them, thanks for including the link btw, and ill also pick up the compression test kit.

the whole, if i flash the comp it doesnt do it and the only hot thing really puts an odd twist to it imo

heres some of the plugs

ive hit a snag though. i got the compression tool all hooked up. spun the "plug" piece in and the snugged it with a wrench then fed the line onto it by hand(theres no other way) tightened it as tight as i can, even put some needle nose on it, but i cant get a reading. is there some trick to this that im unaware of? when i turn the motor, by hand yes, i hear the air escaping. ive tried two plugs now with same result

You've got to have all the plugs out, and the throttle wide open. Then crank with the starter.

haha yes sir, apparently my neighbor is a mechanic and informed me of this and also that my compression gauge is missing a scharader valve. he also seems to think a smoke test will do me good and offered it. oh and i tripped over my efan while talking to him and broke the shroud DAMNIT

the shroud may be repairable with crazy glue. use the cheapest you can find at Wal Mart. $1 for 2 tubes/$2 for 4 tubes or something like that in the auto parts or hardware section.

i just layed some duct tape across it for the time being ha

well Oriely's doesnt have another gauge or the missing part for that one.

Most compression gauges have an o-ring that seals the threaded piece to the head.

yea that was all there but the valve that would keep the pressure in the line was missing

a little update on this

So the shop hooked it up to their computer, fired it up and experianced the misfire... and the computer showed nothing:smsoap: showed that all cylinders were firing normal, no codes, no precodes no nothing!

he smoked it while i was there and no leaks as well.

stumped as he was he guessed that i had a bad injector, my original guess, and that i replace or clean them. well, i still have all the original ones so i switched them out, every damn one of them. this morning, still misfiring

guess i could give the compression test another go now that i know the correct way to do so. ill make sure i get all the pieces as well haha

at least im knocking possibles off the list:conceited

still scratching this itch haha

finally got around to pulling the valve cover. i should mention that after the motor is up to temp ive found that i can hear a metallic ?clacking? sound coming from the rear of the vc when i apply load by hand with my head in there. its faint and very hard to replicate but its there so ive been wanting to pull it to check springs and bolts.

pulled it off and checked the bolts for tightness and the springs and basically anything that would indicate foul play and found nothing BUT when i went to put her back together i noticed this

what appears to be two strike marks on the underside of the vc toward the back. i reinspected the lifter(? termology check) thats in that area and do not see any damage to it only the vc but something striking that cover enough to score the metal like that surely would cause the sound im hearing. and its in the right spot. really not sure if ive found a lead or not or what to do about it for that matter haha