i bought a 99 sebring conv with seized engine ,bought a brand new short
block , reassembled and reinstalled , turn out great, no leaks, After it warms up, Its starts to missfire,buck,shake , idle bad , no accelaration,
there is no check engine light, no codes log, replaced iac , replaced distributor
check wire and all grounds, check connection at ecm, crank sensor,also
check intake manifold, with carb spray, seems to start missfiring sooner
when its hot outside, now that it has cooled off some im able to drive for about a half an hour before it starts doing again , i live in florida ,also
when a,c is on it really starts to run bad , runs great when its cold
soon as it hits operatng temp, its start to run like crap
my background is diesel for the last 25 years,
dave

thank you for your time any help is so appreicated !!!!!!!!!!!!!!!!!!!!!!!

 

Could be a bad computer. Sometimes, circuit boards have cracked solder joints that work well when cold, but as the thing warms up, the board expands, the joints separate, and it doesn't work. There used to be a "tap" test people did with computers, giving it a little "love tap" to see if that induces the problem.
Maybe you could put an ice bag on your computer to see if that will delay the onset on the problem. If so, then you may have found it.

 

Dear dcotter

thank you for the info, i have really thought of replacing the ecm, after
what i have already spent,i dont like replace parts if im not sure, sure
thought it was the dist, coil braking down after it got warm,not!!!!!

i will try an ice pack today,will let you know

p.s. had a 91 jeep lost fuel pump signal from ecm after it got hot

pull jeep over let cool off, it would start right up and run

remove ecm found soft jel coating cracked, replace ecm a year ago

still running, that also had no codes

thank you
dave

 

up date it was a cracked crankshaft sensor , it was a hair out of range , not enough to log a code , runs very good

thanks for all your help
dave

 

How did you find it?

 

i was going to get a new ecm after what i found out about a replacement

unit ,I started triple checking everything, i remove the crank sensor

and found the housing cracked right at the mounting bolt hole , i must of

nicked it when i installed the new engine , installed new sensor car runs great!!!!

thanks to all