Any GM heads in here? 4.3 Vortec V-6

Sierra3

Sierra3

Registered
Got a problem that has been plauging me for the last three months or so. Seems funny , come to think of it now that it started happening after i got my truck back from the dealership for the newest PSD update flash on my stock computer.
Anyways, heres the problem. It's a 1998 4.3 Vortec V-6 5 Speed CK1500. Idle is hanging at 1500RPM to 2100. Throttle is very sluggish now and slow to return to 0 RPM. It used to rev instantly and go back down same speed. Now it's slow both ways. You can leave it in gear and take foot off gas and cruise with no cruise. idle shold return to close to 500-800RPM with foot off gas or brake pedal switch is hit, or clutch is pushed in like it used to. When on highway and you throw it down into 4th or 3rd sometimes it bogs with no throttle response at all....then slowly creeps up into the pull RPM band like normal.
Sometimes it hangs at 2500 with foot on clutch and at a stop at redlight. People look at me weird at stop lights thinking im trying to race them and about to dump the clutch. lol It's got dual magnaflows so it sounds like a V-8 but is all bark and no bite actually. Does it hot and cold, morning and night. truck is all factory stock with only AC Delco replacement parts. Only mod is a dual exhaust split after the Y pipe for the front manifolds.

Here's things i replaced. Took off entire throttlebody and hand cleaned all the carbon deposits and soot off underside and inside throttlebody and intake. Blade seals good with no cracks when blade is in shut position. Bushings good. Linkage is good and oiled,return spring is still tight, blade returns fully against idle stop correctly ect.Replaced TBI gasket,IAC,TPS, Air Intake Temp sensor in air intake pipe, Removed entire Aircleaner assembly and MAF/tubes and cleaned with contact cleaner. My realtime scanner says its 115-120 degrees incomming air, when its only about 80 degress ambient temp outside. IAT and one of the 02 sensors is 220 and the other one is jumping up and down between 115. Not sure if this is way off or not as they always move up and down. Only trouble code i got was a P0507 Mod$10 1/1 is what scanner showed for "High Idle" noooo..really?. Cleaned out trouble code and reset ECM dissconect battery way for 2 minutes.
Truck has new plugs wires and coil.
Truck idled fine afterwards but on road test problem came back, but with no engine light. Does it with AC on or off position.Took it to GM dealership and they put it on diagnostic and said it already had the new PSD flashed on it. I said i know, thats why i have the problem now. Truck used to smoke the tires in 1st through 3rd. Now its a gutless terd. lol I can't stand the slow idle return to lowside and sluggish throttle response either.
Something is tripping off the computer to do the high idle thing. The dealership couldnt find it and said "its normal" for the 5 speeds. Never did it before and ran like a raped ape. i looked at him and laughed, its normal to rev at 2000 RPM at stoplight? Well, at least they didnt charge me for the diagnostic. Won't be going back there..
I have been reading alot on LS1 tuner and the S-10 pages alot in the tuner sections. Things were said about the new bulletin with toned down settings due to blown headgaskets and such for warrenty work. Not sure it applies to my truck. But im convinced its the new flash they gave me for an update. I bought a JET DST flasher/burner for the GM. Got it today, but had to get a stupid USB to Serial port connection. Who really has a comuter with serial port capability nowadays anyways? I loaded the software onto my laptop but was unable to get a "read PCM" because of the adapter cord i believe. Going to get different brand tommorow. I'll kill the 98MPH limiter,lower the fans on temp, and look at where the throttle cracker and TPS fade off tables are set now, and take out the delay on revup and dropdown. My guess it it's in there that the sluggishness came from. You can also raise the shift light schedule,to your talioring also or turn it off by pegging it. I always hated that thing.RPM limiter can be raised a squeek or two also. GM has a power enhancement table that i think they detuned to combat knocking and or engine abuse. This thing used to be a little terror for a V-6. If they cant do or find it. I'll do it myself. Any thing i should look for?
 
RE: Any GM heads in here? 4.3 Vortec V-6

Is it under warranty? If not, take it back and have them reflash it back to where it was. ::uh::
 
RE: Any GM heads in here? 4.3 Vortec V-6

If GM is anything like Ford, they will NOT or can NOT reflash back to an older flash. Local dealers say manufacturer won't let them. We have same problems with the Ford Power Stroke Diesels. Dealer just won't (or can't) reflash to a previous program.

Bud Pytko
'97 LSC Silver Frost
'05 F250 SD CC PSD 4 X 4 AZ Beige
'94 Prowler 5th Wheel
http://squarebirds.org/images/BudPytko97LSC.jpg
 
RE: Any GM heads in here? 4.3 Vortec V-6

Well one thing that would help narrow it down is to warm up the engine, then unplug the IAC. It will probably idle low (and possibly stall), but if it's acting like its normal self then you'll know for sure that the problem is caused by the computer mucking with the IAC.

The 5-spd Ford Contour was notorious for problems w/ its idle hanging at 2500 rpm and taking forever to fall back down. Apparently it was to reduce emissions caused by the engine spitting out unburned gas when you suddenly let off the throttle. The IAC on those cars gets its air through a separate tube, so the fix in that case is to jam a washer in it so the IAC can't get enough air to rev the engine past ~1500 rpm.

Hopefully you can just get it reflashed so you won't have to resort to any creative fixes like that!
 
RE: Any GM heads in here? 4.3 Vortec V-6

Wow, thanks all for your responses. Its actually a good thing that this happened. Forced me to buy the equipment and start learning it myself. Spent all day yesterday with the burner. 6 hours of looking up what acronym was what, and what its function was in the setup. And reading what all the acronyms are and actually do for GM fuel injection. Found alot of things that were changed for the worse to hold back and tone down the engine. Had to much fun on my secret test road for the Lincoln after i did some common changes.
It was definately the toned down tune cause truck is 30 percent better now. I will definately be visiting the Astro site and introduce myself there to learn more. The S-10 site that i saw was kind of limited to tuning. From what i've read there more of a buy a chip crowd.
I need to learn more about volumetric efficency table as thats what all the other GM sensors are based on like in the fuel table and ignition. I only changed what i knew would work, and the standard threshold/governor deletes, but there is so much more that can be better once the VE and ignition advance, spark tables are set properly. Truck is fun to drive again! Thanks all for your responses. :)
 
RE: Any GM heads in here? 4.3 Vortec V-6

[div class="dcquote"][strong]Quote[/strong]
Well one thing that would help narrow it down is to warm up the engine, then unplug the IAC. It will probably idle low (and possibly stall), but if it's acting like its normal self then you'll know for sure that the problem is caused by the computer mucking with the IAC. The 5-spd Ford Contour was notorious for problems w/ its idle hanging at 2500 rpm and taking forever to fall back down. Apparently it was to reduce emissions caused by the engine spitting out unburned gas when you suddenly let off the throttle. The IAC on those cars gets its air through a separate tube, so the fix in that case is to jam a washer in it so the IAC can't get enough air to rev the engine past ~1500 rpm. Hopefully you can just get it reflashed so you won't have to resort to any creative fixes like that!
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Thanks Adam. I'll go out and try that now. I want to make sure this problem is fixed first and all is well before i put on my 75MM throttle body i got from CFM technologies and tune the VE for that and the Edelbrock intake and Comp cams V-6 cam. haha jeeese...why can't we just leave our vehicles alone? I have a bad disease called modding. :) If its stock, its too slow to me. Unless you can afford a Buick GNX Grand National or above in the Vette tier/Viper crowd. And those guys still mod em for more performance.

1995 DK Blue Lincoln Mark VIII
1998 DK Blue Chevrolet 1500 P/U
 
RE: Any GM heads in here? 4.3 Vortec V-6

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I have a '99 Checy Astro van with the 4.3L Vortec.While it's mainly a van site, check out www.astrosafari.com - there's a bunch of gearheads over there, (very active), that know these engines inside-out.John[link:www.goldengatemark8.com|Golden Gate Mark VIII Website]http://mark8.org/users/johnaec/Mark_VIII_s.jpg'97 Mark VIII LSC (Sold to SCcouper)'96 T-Bird 4.6L
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Wow....Im going to be busy for a while reading. Thanks for the Link John! I even found more links in their archives to better s-10 sites that i didnt even know about. Seems there knowledge is alot more than the other s-10 site. I am a sponge looking for water and more intel..lol :)

1995 DK Blue Lincoln Mark VIII
1998 DK Blue Chevrolet 1500 P/U
 
RE: Any GM heads in here? 4.3 Vortec V-6

Just an update to close this thread. Prob solved. Most of the headache was found in the updated idle contoll tables and they changed all the Throttle Follower tables and the decay times. Mine didnt have the throttle cracker setup, only the older TBI's had them. Mine controlls all that dance with IAC percentage opened and time and throttle follower tables that ride along with the TPS settings. Fixed them to be where i want them. RPMS come down fast again like normal to my chosen 900 RPM idle. Most of the abuse mode settings were way tuned down. Put them back. Upped my RPM ceilings and killed the MPH governors. Made my power enrichment table come in a little sooner than they had it set at around 97% TPS. Did mine around 77% TPS so it comes in sooner and im not wasting RPMs to hit the sweet spot.
Just bought MXscan so now I can datalog while driving since the Jet module can't datalog. This should be alot better than my handheld realtime scanner sliding all over the seat. Only thing now im missing is a nice wideband for it so i can get the new VE tables tuned in for my exhaust and new 75MM throttle body i put on today. It breathes ALOT better now, but its still running on the old STFTs and LTFTs and pathetic VE tables from the factory setup for the single exhaust and little throttle body. I didnt mess with them till i can use the datalogger after i get my unlock code. But at least now ill KNOW where its running too rich and too lean and compensate the tables so they flow smooth into the next cells. Then i can do the timing advance tables once all that is set. I left them alone too untill i get the datalogger hooked up.
Only took me about 15-20 reburns to figure it all out, haha but truck is a lil screamer once again. And im happy with its top speed now. lol No more lurching forward when it cuts fuel off at 98MPH anymore. Just keeps on trucking even though the speedometer stays burried at 100. Pulls hard and idles smooth now. I knew it was that funky tune they gave me...(mumbles & cracks a cold beer). :)

Also, ty for the invite to Chevy Astro website. Never knew it was there...Those videos of the vans doing burnouts and tearing up the track were awesome. I pulled and saved some of their info for the 4.3 vortec too and learned some more about the lil brother 350 i didn't know.
Looking for a nice duel electric fan setup now so i can loose the clutch fan. Settings are there in PCM for threshold upper and lower triggers for the bigger trucks that had them, but just are not turned on yet. :9
 
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