DIY PROMDo It Yourself PROM chip burning help. No PROM begging. No PROMs for sale. No commercial exchange. Not a referral service.
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
Here it is again in case I didn't mention it earlier. Once the VE tables and spark timing tables are halfway decent, you need to adjust the Minimum air rate on the TBI unit. The IAC needs to be about 5 counts at a warmed up idle in park neutral. You also need to visit the Park to Drive IAC position change. Increase the number of steps that the PCM withdraws the IAC valve. Also make sure that the P/N switch is functioning properly.
To drop the counts down, adjust the throttle plate set screw (minimum air rate).
You want 5 (no more than 10) IAC steps with the engine fully warmed up, a/c and electrical accessories off, and the transmission in Park/Neutral.
Looking at the log, it looks like driveability is much better than it was to begin with. Then again, I haven't gone for a ride in it or driven it and am seeing this by looking at a log.
EDIT---
Your IAC counts on the log should look something like this.
Warm Idle = 5 counts
Warm Idle Drive = about 30 counts
A cammed engine is going to want about 15-25 counts to stay running at the same speed in Drive vs. Park neutral.
As soon as the shifter moves into gear, you should see an additional 20 counts or so added on. Make sure to look at this in the BIN and check the P/N switch operation, if this is not happening. Stock is like 1-5 counts for Park/Neutral to Drive
ok ill have to find the breakdown of that process cause its new to me
Setting the IAC
Jumper pins A&B on the ALDL (Assembly Line Data Link) connector under the dash. Pins A&B are on the upper-right-hand side. These are the same two pins to jumper to read codes from the ECM.
• Now turn the key on (the Check Engine light should be lit) and leave the key on for at least 30 seconds. The computer will extend the IAC plunger all the way out to allow adjustment of the idle speed.
• After the 30 second wait, unplug the IAC (square 4-pin connector on the throttle body) WHILE THE KEY IS STILL ON. This prevents the ECM from adjusting the idle speed while you make your adjustments.
• Block the drive wheels, set the emergency brake, and start the engine. Set the idle speed by adjusting the idle speed screw. The engine should be at operating temperature for this. The exact setting is on the emissions label on the radiator shroud, but in general, the idle speed should be about 500 RPM in Drive, 700 in Park / Neutral, or if you have a manual transmission, somewhere between 600-800 RPM. Remember that the truck is running during this adjustment, so stay clear of the fan, and make sure it can't roll or otherwise be put into gear while this is done.
• Once the minimum idle speed is set, turn the engine off, reconnect the IAC, and remove the jumper from the ALDL connector.
• The TPS minimum voltage must now be set. Turning the idle-speed screw may have moved the TPS idle voltage away from the specification, so it should be adjusted next. Connect a voltmeter between pins A (usually black) and B (usually blue, or green) of the TPS, and turn the key on. Don't start the engine. Loosen the two torx screws holding the TPS in place, but don't remove them. Rotate the TPS until the voltmeter reads between 0.45 and 0.55 volts, with 0.50 being ideal. Tighten the mounting screws (carefully, they thread into soft aluminum) and re-check the voltage to make sure it's still within range.
PS- Your TPS may or may not be adjustable. I know my old holley one was but my stock GM one was not.
ok well I cleaned my iac and adjusted my idle screw like you said but here are the results iac is still close to 100, but idle in gear seems better
I have not been ignoring you with this post. Just been very busy trying to prep for inventory on Sunday at work.
I am not real up to date on how the timing plays part in the idle speed control of the 8746 and quite honestly have not had time to look over the hack to see. If it is similar to the truck PCM I am running and my old 299 truck ECM, it can cause an erratic idle if it steps in too much when the engine is trying to idle. Non-stock cams make this action much more intrusive as the gains are calibrated for stock engines.
Also keep in mind that 100 IAC counts is alot of IAC opening.
If you are at 5-10 counts with a fully warmed up engine in Park/Neutral and it goes to 100 counts, investigate the timing where the engine is idling at. Try advancing it a couple of degrees at a time in an effort to bring up the idle vacuum and the drop the IAC counts.
Keep in mind that the 825-850 RPM that I am seeing in Drive is still too high for this mild of a cam. The stock converter stalls no more than 1,200-1,400 rpm. At 825-850 RPM the engine is fighting the stock converter like no other, this reduces idle vacuum. The reduced idle vacuum causes a domino effect which results in increased IAC counts and even further reduced idle vacuum. Once the IAC is open that far the air/fuel is no longer being properly drawn through the TBI unit. This causes a rough idle and occasional stalling. Bottem line is you may need to bump the idle speed higher than otherwise necessary in Park/Neutral in order to obtain reasonable IAC counts in drive.
I Hope I covered everything well enough, although in an abreviated form.
Bottem line is you may need to bump the idle speed higher than otherwise necessary in Park/Neutral in order to obtain reasonable IAC counts in drive.
I Hope I covered everything well enough, although in an abreviated form.
doesn't that contradict the statement that idle speed was too high as it is?
ok well then should i advance my timing then drop min. idle to try to correct this or could you explain a little better on what I need to look at to correct this
thanx
doesn't that contradict the statement that idle speed was too high as it is?
ok well then should i advance my timing then drop min. idle to try to correct this or could you explain a little better on what I need to look at to correct this
thanx
What I was talking about is if you want to keep the current idle speed IN Drive, you need to adjust the throttle plates open more. Allow more of the airflow in through the throttle body itself, not the IAC. The IAC is flow too much of the air coming into the engine. This causes un-even a/f mixtures at idle. The more the IAC opens the more un-even they become. Think of IAC as a vacuum leak. The smaller the leak, the better off you are. You have to keep a few counts to keep the idle speed controlled.
You have 66 counts out of gear and 97 counts in gear. Ideally, you want 5-10 counts out of gear and no more than 40 counts in gear. Adjust the throttle body to give you an idle of 650 RPM with the IAC closed and disconnected, via the procedure I posted. That should help your IAC counts.
As far as the timing, try advancing the timing in the IDLE MAP/RPM ranges just a little. Maybe 2*. If that shows positive results. Raise another 2*. Don't add to the distributer or to the whole timing map. Just the cells that you are idling in. Should be around 60 KPA/600-800 rpm, if I am reading the logs right.
The cam in my 305 was 224/224 @ .050. It idled with only 650 RPM in drive all day long. 70 KPA MAP.
EDIT-
Just to prove my point. It was still in the enrichment phase (54 seconds after startup), so the idle was a little high, but you get the idea. 700 RPM @ 65 KPA map. 13 IAC counts. 21* SA It is actually in DRIVE in this screen shot.
10 4 i got you and I will try to fiddle with it a little tomorrow afternoon and ofcourse let you know, BTW thanks a ton for all the help im still reading the stickies for the 8th time right now trying to get it all to stick thanks
ok now correct me if im wrong but if i jumped pins a and b together and the iac fully extends then i disconnect the iac i shouldnt be getting and iac counts when I turn her on right? cause with the valve ungluged im still getting 90-100 counts acording to winaldl
That's because the ECM reports what it TOLD the IAC to do in the ALDL data stream - not what it actually did! There is NO feedback from the IAC, so the ECM reports what he told the IAC to do. I got burned on this one for a while one time when the IAC quit working but the ECM didn't realize it....
ok well i get that now, and I did get my iac counts down but lol i think i went too far and iono how do just inch her up shes at 0 counts in p/n and about 38 counts in gear. she wants to idle now at about 800 out of gear and 675-700 in gear i think im getting closer what do yall think?
Close the throttle blades just a little bit. IAC counts in p/n should come up just a little bit when you do. Might have to rev it just a little a couple of times and let it settle back to see the change though....
ok well i get that now, and I did get my iac counts down but lol i think i went too far and iono how do just inch her up shes at 0 counts in p/n and about 38 counts in gear. she wants to idle now at about 800 out of gear and 675-700 in gear i think im getting closer what do yall think?
Sounds like you are getting closer. Is it holding idle in gear better now? Any stalling? I would shoot for about 5 counts out of gear. 35-40 counts in drive is not too bad. Not the greatest, but it sure beats 100.
it is holding idle alot better now and it stalled once all day but unfortunatly it was right after i closed win aldl so lol no info on what happened but i dont get a day off till saturday now and I really dont think my neighbors want me cranking her up at 11pm lol but ill try to grab a session or 2 in the next cpl days between classes at the university and wrk
well havent quite got it right but I did raise my idle to about 750 and well i feel my converter is giving out on me. I was also mistaken I went back and looked to see wich cam I went with and it was actually a xe268 while we were trying to tune given a smaller cam. so here in a week or so Im installing a new converter.
other reasons im replacing the converter is I'm leaking a little tranny fluid out of the front of the bell housing so I have to drop the tranny so I'll already be there plus she doesn't like going into 4th and dosn't wanna lockup so I can wrk that all out then.
The stalling problem now I believe is truly due to vacuum and since she actually wont stall and the iac valve will be the propper amount of steps when I bumped rpm up but she needs to be a little lower cause she wants to fight with the converter
thanx for reading, fast and everyone else here have been huge assets in helping me get this thing right
i know this is a blast from the past, but I wanted to do another update. lol nearly two years later so yall know the IAC and Idle propblems were all due to verry verry bad VE table i was then inclined to buy the EBL (Thanx Rbob) and did many VE learns. After doing these learn sessions I found that drivability was great and I have not once (knock on wood) have my car die at idle in gear. Just wanted to say Thanks to everyone here for the support.
