Hi guys,
First let me say i'm new to the forum and own a 1987 El Camino. Just by reading a lot of the posts here it's been a great help in getting this car figured out and working properly.
Secondly, like the title implies, i'm having some problems with my elky's qjet. She's an '87 with the stock 305 (not sure of the pro code, i think it's an lg4). She's got a 200R4 transmission and is 98% stock, other than dual exhaust and an edelbrock stock replacement intake. All emissions equipment is intact minus the cat and i believe most to be working properly except for the egr valve (vacuum soloid is dead). Anyway, i got a carb off and 87 caprice with a 350 (the original carb for mine is long since gone and i have none of the factory setting ie. idle air bleed setting, lean stop, rich stop, or even factory jet sizes) that i just rebuilt. It runs good, but i'm gaving a problem getting the dwell set right and she's giving me a slight stumble at idle. I replaced the jets in it (they were 29's) with some that i got out of an old core i had (i think they're 27's). Anyway i think i've got the lean stop set at the factory distance (it's about 2 1/2 turns from seated, i obtained the rich stop via the 1/8" plunger travel method, and the idle screws are set at about 3 1/4 turns from seated. The IAB is set at 4 turns from seated. Ignition timing is 8 BTD at about 600 rpm. What i'm asking is should the dwell vary with the air cleaner removed. Mine sits at 45 degrees on the 6 cylinder scale with the air cleaner off, but when you put it back on it starts to vary around 30 degrees. Is that normal?

 

Welcome aboard thirdgen.org.

Do you have all unused vacuum ports plugged while the air cleaner is off?

 

sorry it's taken so long to get back with you guys, been busy with the girl friend and her car, stinkin' fords anyway, lol jk. anyway, i have indeed plugged all the and the vac ports that aren't being used. when you bring her off idle she varies the dwell perfect, but at idle with the air cleaner removed she sits at full lean. and she is fully warmed up and in closed loop operation. the oxygen sensor is new, as is the map sensor, the baro sensor, the coolant temp sensor and the tps and m/c solenoid. i'm not sure what idle air bleed this car is supposed to have, the one that's on it now doesn't have a letter stamped on it. i've got a couple lying aroung, one of them has the letter "N" stamped on it. the one with the letter yields the best idle quality, but makes the mixutre very rich, almost like it's not bypassing enough air.

 

Are you verifying closed loop with a scanner? Off idle does the dwell respond to choking the airhorn by increasing?

If the ECM isn't seeing the readings it needs from the O2 it will default into its 'last known good' data or the factory default if the ECM has recently been powered down. The dwell will vary according to TPS and VAC sensor but it won't be re-writing the blocks based on O2 levels.

When it's running full rich and not varying dwell you'll get the smoothest idle although it will be pig rich. Once the ECM goes into closed loop and starts adjusting dwell based on O2 readings you'll see it begin to 'hunt' at idle as it seeks an ideal mixture. This is normal.

 

yeah, she's going into closed loop and varying the dwell off idle. if you open the throttle for a few seconds she'll start to vary the dwell then after you close the throttle she'll hunt for a lil bit (a few seconds) than if the air cleaner is off she'll just go full lean again (45 degrees on the dwell meter). if you open the throttle and choke the air horn with a rag it will make it go lean so it's working off idle, i just can't seem to get it to work right at idle.

 

If it's varying with the air cleaner off and idling you're probably fine.

Stuck dwell at idle with the air cleaner off (leaner) may indicate that the mixture screw settings are on the lean side though. Try opening them up 1/2 a turn or so and re-setting IAB to get 50% +/- dwell. See how it does.

The O2 sensor will stop sending info that the ECM can use if the mixture gets too far off (narrow band). Your mixture could be going just far enough out of O2 range when the air cleaner is removed.

The O2 sensor will also stop sending good info when it's temp gets too low. This is common to engines with headers, especially when the O2 is moved farther down in the exhaust stream or the exhaust just flows better. If you've got stock cast iron logs this shouldn't be a problem, although you've opened up the back end of the exhaust which 'could' be dropping the temps down. A fix for this would be a heated O2, I run one in my 87 where the O2 is in the Y.

 

i've been thinking about installing a heated O2 sensor, just to make tuning a little easier. the stock manifolds are still on it but i think the sensor does cool off after a few minutes of idling. oh, and i have another quick question reguarding the electronic timing advance on these things. technincally i shouldn't get any spark knock is the way i understand it. the inital timing is 8 degrees BTD, and it runs great right there, however it's giving me spark knock under some slight load conditions, it's my understanding that the computer should be retarding the timing when it does this. obviously because it's pinging a little it's not backing the timing off. it's got a new spark module and knock sensor. my question is, if the carb settings are out of range for the o2 sensor and the computer doesn't vary the dwell properly, will it affect the ignition advance/retard?

 

Closed/open loop shouldn't affect the operation of spark retard. A little pinging can sometimes sneak past the KS. If it's pinging at low load, light throttle it could indicate that the EGR needs attention, but 8 degrees is kinda high.

 

i do know that the egr vac solenoid is dead. i think i got it figured out finally. i took the air cleaner assembly off and plugged the vac line to the temp sensor. i mess with the idle mix screws until i got it to hunt at idle, it's not as close to 30 degrees as i would like it to be but at least it's progress. it'll cycle anywhere beween 15 degreese to 44 degreese at idle and it moves up and down the scale. ended up with around a little over three turns out on the mix screws with the air bleed at four turns.