82 z28 cfi. car was running great just rebuilt the motor put a bigger cam and 1.6 rockers. all of a sudden its struggling to start and the idle is up and down. so i connect the computer to it and its in and out of connection. when the connection disappears from the computer to ecm is when the idle starts going up and down. not sure if the prom is bad or maybe the ecm or both. i went under the hood and checked the main wire harness on driver side fire wall and it was tight pulled it out just to check prongs. cleaned some of the tar off of it wiped the prongs clean and replugged it in. still same problem. checked vacuum and it seems to be right. the only diagram i have to look at is the little one on the fan shroud. but every vacuum line i pulled out i marked a number on each end with a number and tape so i made sure it went to the right place. I've been screwing around with this thing for that past 7 hours and can't figure it out. at first it was throwing a code 33 map sensor or circuits something can't remember exactly. i checked the troubleshooting on that and it said vacuum leak. i looked at the throttle bodies and noticed the vacuum line that went to the air pump was open so i plugged it because it is no longer existent. but now its not throwing any codes at all. this is my first non carb rebuild and its not easy so if any of you know anything i may have overlooked, please help.

 

also the computer stays connected until i start the car then 30 seconds into it it disconnects and it also says e cell expired

 

I'm sure someone has to know something. any help would be amazing

 

from what i understand,the E-cell (a simple plug in
circuit board inside the little tan plastic box with 3
wires)is just a 1-shot timer module to indicate when
the o2 sensor needs changed or something like that-
does not effect engine operation at all.
The idle going up and down can be caused by wrong
"minimum air"setting or too-low fuel pressure.

 

well the idle shifting only happens when the ecm losses connection with the computer

 

a computer hooked to the ALDL plug under the dash?

 

yea just losses connection. it reads everything just fine until you turn it over then its about 15 to 30 seconds then loses everything

 

wouldn't have anything to do with the timing would it.. i have yet to set the timing.

 

the timing being off could have an effect...(did you
find the EST bypass plug yet?) I don't know what may
be causing the ALDL/computer link problem-never used
on of those...

 

is the est bypass a single orange plug. on my crossfire its in the wire harness that runs by the egg valve down behind the distributor. if its that wire. the only thing that weirds me out is the connection problem. the motor just starts messing up without giving me enough time to even try to time the engine. unless unplugging the est will stop that problem

 

checked my factory manual,doesn't give plug color but
the EST bypass plug is in the position you describe-next
to the EGR valve.

 

ok good. thanks is that the only thing i have to unplug? I'm going to try that and hope my problems solve themselves.

 

Unpluggine the EST connector will take the ECU out of the equation and provide a steadier idle. Effect is the timing is locked at whatever you set it to.

I believe your vehicle does not use a resister in ALDL cable.

 

i cant even keep the car running long enough to even atempt to set the timing. this time i started it and it held to the ecm but then back fired out of a throttle body and died. the rest of the times it loses connection to the ecm and the rpms just start rising.

 

I going to take a shot at this.

Did you reconnect all of the grounds at the back of the engine? Also if there was any welding etc around the engine, then most likely the ECM is blown.

Back in 2003 when my 82 bird was be rebuild, I told the body shop manager to make shure that the ECM was disconnected during welding. Well, he didn't and the ECM end up being bad. They also missed up the MAF etc on my TunePort 350.

 

Raise your fuel pressure.

 

all grounds are good. i checked them all with a meter and they all read out 0. and i didnt do any body work all i did was pull the engine and rebuilt it.

 

fuel pressure between the throttle bodies is about 12-13 psi. do i really need to raise it. would that actually make the tb back fire

 

i pulled the est connection apart and set up the timing light. started up the car and by the time i got to the light it died. then next i started it up and sat in it giving it about 2000 rpms a little bit to warm it up let off and it back fired and died. not sure what to do

 

Did you connect all of the spark plug wires correctly. Did you pinch a wire that goes to the injectors on the TBI, turning on the fual all of the time.

 

I am experiencing the same issue with my Camaro. The car idles fantastic in open loop. Once the engine gets to temperature and the closed loop flag comes on, the connection to the ECM goes haywire, ON and OFF, and idle is all over the map.

I have a replacement ECM in transit. In the meantime I verified all ground connections, and I am making my way slowly through the wiring harness looking for any faults before I try another ECM.

 

The replacement ECM was the fix for me.

 

BF through the TBs usually means a lean condition ....... how's you fuel pump and filter .... could have a pump going south .....
from you posts one assumes it was running good ... and this condition just started ...without anything else being done ...????

just a thought ........