Rebuilt Engine, Multiple Misfire Codes

[hurtconveyor303]

please help! i have a 97 dodge avenger with the 420a engine. i recieved the car but it wouldn't run. had the motor redone by a professional engine shop, kammer racing out of huber heights ohio. they honed the cylinder walls, milled the head to take out the warp, hot tanked the block, and put in new pistions and rings.

heres the problem. car ran fine for 127 miles. now when i try to run the engine cold i get multiple misfire codes and misfire on cylinders 3 and 4. but if i let the car run for about 15 minutes to warm up it will run fine and smooth. i'm running short on cash and cant go chasing after problems unless i know for sure what they are.

and note. used oem plugs, wires, and coil. i was just trying to get a nice running car i could work with and add to eventually but i gotta take care of this first. so if any of you 420a guys know anything that could be useful to me please help. i don't know of a bad sensor or anything but those are my only codes and the problem totally goes away after warm up. new engine now has 1,600 miles on it and should be broke in.

 

[RoninEclipse2G]

I'd start with the simple things first. Test the resistance on the coil, plugs and wires. Another thing to check is the coolant level at the filler cap on the block, because if you've got an air bubble in the system it will freak out the CTS and cause things to run like crap until the T-stat opens and allows that bubble to move.

Double check your vacuum lines and such as well, sometimes when you drop an engine back in a car things that you thought were secure come loose again after a few miles.

Always remember to check the simple stuff first, 90% of the time that will lead you to your issue instead of throwing money at the problem and still not having it fixed

 

[bullettdsm]

Agreed with Ronin.

For funzies, try switching plug wires to see if the misfire will follow. Might also want to look at what's going on with the plugs.

MB

 

[artindsm]

check your crank shaft sensor, i recently had the same thing happen. and check it beofre your on the side of the road

 

[hurtconveyor303]

i replaced the crank shaft sensor already. thats how i was able to get it running enough to get it home to pull the engine. i read that the best plugs are ngk bkr6 for the non turbo, do you recommend those for my engine? the only work ive had done so far is the cylinders honed and head milled .007" with brand new pistons. i've got direct oem factory replacement plugs gapped at .050" and oem wires along with the coil

 

[RoninEclipse2G]

REREAD THIS and give it a try. Your cold misfire is most likely what I've marked in bold. Also pull the plugs like Bullet said and check if one is obviously different than the others

I'd start with the simple things first. Test the resistance on the coil, plugs and wires. Another thing to check is the coolant level at the filler cap on the block, because if you've got an air bubble in the system it will freak out the CTS and cause things to run like crap until the T-stat opens and allows that bubble to move.

Double check your vacuum lines and such as well, sometimes when you drop an engine back in a car things that you thought were secure come loose again after a few miles.

Always remember to check the simple stuff first, 90% of the time that will lead you to your issue instead of throwing money at the problem and still not having it fixed

 

[hurtconveyor303]

ok. so i had an air gap in the cooling system. had a bad radiator cap. replaced, now it keeps pressure in the system but my misfire is still the same. very dissapointed in the wires and plugs from ADVANCED AUTO PARTS! wires already showing wear and i just purchased them when i rebuilt my motor! i have a new cam angle sensor coming as its the only thing that has to do with timing i haven't replaced yet. and am looking at new plugs champion double platnums or ngk iridiums. let me know if you guys can help anymore

 

[RoninEclipse2G]

Do NOT use platinum or Irridium plugs. Waste of money for our cars. Just get the standard NGK copper plugs. Spend a little money for decent plug wires if they're already looking worn.

 

[hurtconveyor303]

JUST READ!!!! i just read i might need a colder plug since i increased displacement and compression. what about that?

 

[southrneclipser]

i believe the correct plug gap for us is .044. put your plugs at this and see if it helps

 

[hurtconveyor303]

my plugs are at .044. but they're autolites. i just went to advanced and got oem parts when the rebuild was complete. oem coil, oem plugs, and oem wires

 

[Kyle97-clipse]

When does the car miss when its cold warmed up or all the time?

 

[hurtconveyor303]

only when it's cold. i have to let it warm up in the mornings before i leave for work even when i'ts 90 degrees out

 

[RoninEclipse2G]

When does the car miss when its cold warmed up or all the time?

Very good question! That could mean several different things.

OP - I'd still get rid of the autocrap plugs. Don't use irridium or platinum, even with a change in displacement and compression they won't help.

You mentioned higher compression andlarger displacement? I saw in your first post that the clock had been bored and the head decked. Was there anything else that was done? high compression pistons? stroker kit?

If it was just overbored to fix the cylinder walls along with decking the head then I wouldn't worry about colder plugs.

Edit: Just saw the cold miss reply. The air bubble was probably causing it to run rich as hell and fouled the plugs. There might even be a small bubble in there still. Pop your rad cap when it's cold and check. You might need to burp it. If that's ok then check the plugs. Pull them and see if the look like crap, and maybe try replacing them with a set of stock temp NGK coppers.

 

[brassc2007]

have you checked the tps or the iac, sensors send different readings when they are cold and when they are warm.

 

[hurtconveyor303]

what are those sensors you mentioned and where are they located? i had .007 taken off the head and .010 from each cylinder to just clean it up and take the warp out of the head. the shop said it shouldn't be enough to cause any problems. i JUST checked the plugs, they look really dirty and are still gapped fine. i will replace with ngk soon.

 

[brassc2007]

the (tps) is the throttle position sensor it tells the ecu how far opened or closed your throttle is and the (iac) is the idle air control valve. They are both located on the throttle body. And im not 100% percent sure but have you tested the coil to make sure that it is good. Our 420a coils are actually two coils molded together im not sure what coils fire what but i do know that 3 and 4 are on the same side.

 

[brassc2007]

what have you all tested and done so far?

 

[hurtconveyor303]

i've only tested a few things. i've mostly just concentrated on spark and timing. i had both of those sensors off and on. i unplugged them and just checked if they LOOKED bad. they looked ok, i dunno how to really test them. the car sat for about 2 years before i got it runing again so i don't know if it sitting for a long time could've messed sumthing up but it ran perfect before my coworker ran it outa oil and trashed it. any help at all would be great. all i know really is muscle cars and trucks. this is new to me

 

[brassc2007]

just curious but have you checked the fuel pressure regulator? just pull the vacuum line off it and if you see gas its bad i do know on carberated vehicles if the choke is not working right they will flood and spit and sputter it kinda sounds like when its cold it may be chokeing itself out or something.

 

[hurtconveyor303]

wheres that fuel regulator located ad what does it look like?

 

[Kyle97-clipse]

i had both of those sensors off and on. i unplugged them and just checked if they LOOKED bad. they looked ok, i dunno how to really test them

You have to take the throttle body off, which is very simple to do. Then you will see the tps is the sensor located on the top of the throttle body and the iac is the one on the bottom. Use a multimeter to check their resistance in ohms. The iac should be 38 to 52 I think and the tps should vary when you move the butterfly on the throttle body, I'm not sure on this but I think that is 3.1 to 6.1 ohms???

 

[Fotowntalon]

OP - I'd still get rid of the autocrap plugs. Don't use irridium or platinum, even with a change in displacement and compression they won't help.

I can't belive you said that ronin! I use to work at honeywell, the branch that made autolittes!!!! Then they laid me off so they could produce in mexico... oh yeah, thats why i run NGK's in my car now...

Sorry for thread jack, but on a more serious note, do the misfires happen in a certain RPM range? During idle? Acceleration?

 

[hurtconveyor303]

NEW NEWS! took the throttle body off and took the iac sensor off. DIRTY! must've missed that one when we put her back together. didn't have a torx to take off the tps but now my error code coming up is the throttle position sensor and no longer multiple misfire and misfire on cylinders 3 and 4. gonna borrow my buddies torx bits tomorrow to remove the tps and check it over. i'll cross my fingers this does it. oh by the way, it's been really chilly out the past couple mornings and it idles like total crap and acts like its gona die but after the usual 15 min, it's fine. i will post after i get the tps off and go over it

if i let it warm up for about 5-10 min, the miss is around 3500 rpm. i can't go any faster until its completly warm or the AT shifts

 

[brassc2007]

sounds like the tps is not reading the right amount of air coming in or the iac is not opening correctly replace those two sensors, the iac is a little spendy but the tps shouldn't be luckily i work at a parts warehouse and get about 25% off all my parts