I've finally got my car back together after a rebuild and so far all seems to be in working order minus a few things, or at least one major thing. The car has a hard time idling in drive, with a/c on, or reverse. It will occasionally stall and die when there is any sort of load applied to the engine. Engine runs decently strong through acceleration and as long as the RPMs stay above 900. During the rebuild I went mostly stock minus a few things. Those being 1.6 RR, LT4 Hotcam, GMMG Springs, (the whole hotcam kit) 58MM TB and a higher stall, and ported heads, lapped valves, TCI Saturday Night Special) I believe it should be int he neighborhood of 2000-2500 stall. Part of the troubleshooting that I have done so far.

• pulled all 8 injector plugs to ensure one wasn't misfiring. After pulling each injector plug engine it makes a difference on the engine running. So i know I don't have a dead cylinder.
• Listened to each injector with stethoscope for good measure. All are ticking.
• Thought i had the preload set too tight, so i pulled the valve covers off and tightened while running and then a 1/4 turn past.
• Replaced Ignition coil. post rebuild. prior to rebuild (in last two years) it's had new ICM, Coil, Plugs, Wires, OptiSpark.
• I thought maybe i had fouled plugs, but after pulling one or two, they looked just as clean as when i put them in. (NGK Iridiums that I installed when i first got the car 4 years ago.)
• Replaced idle air control motor, replaced MAP sensor, replaced throttle position sensor, MAF sensor is only a couple of years old.
• More or less all of the sensors are new. within the last couple of years. I have been chasing a slow response on both of the rear o2s but turned out longtube headers will do that, and post hotcam install PCM4Less tuned that error code out.
• I have had the engine tuned post hotcam. Not dyno, mail order by pcm 4 less. To be honest, before and after tune, engine seems to run the same.
• When I watch on an OBDII data reader, i can see that my ignition advance is on average 25-30 degrees at idle, and at rpm it goes up to about 40.
• I don't have a fancy data logger to view IAC stuff.
• I can see where the engine keeps trying to load up with more fuel on the data logger and then it starts to bog down and then immediately leans out the fuel mixture so the engine goes back to idling normal
• I have tightened the screw down on the throttle body to force it to idle higher, however the IAC and what not fight it pretty damn hard to bring it back down to 675. whenever it's in the 800-850 range it holds pretty solid.
• Hooked up a vacuum hose and it stays relatively steady. about 12-14 inHG. Varies based on idle RPM.
• When reading the OBDII scanner the idle likes to change +-100 rpm
• Runs fine at 1000rpm -6000pm No misfires, only a slight hesitation as it pulls out of whatever gunk is going on in idle land.

I did pressure test the coolant system prior to topping and first starting, and a little bit of coolant leaked. However, I don't believe this got anwhere near the Opti. But at this point anything is possible. However i'm not ruling it out.

I'm sort of at the point of.... WTF. In closed loop on first startup, it'll run almost perfect for the most part. However once it gets up to temp it starts to flip me off and say eff you, i'm going to kill myself.

What are thoughts? Should I bite the bullet and pull the water pump and hub off and replace the Opti? Is this a tuning issue? Are the rear o2s actually bad this time?

 

It starts cold in open loop. Does your scanner confirm it's going into closed loop after about 3 minutes, and coolant at least 140-degF?

If the programmed target idle, fully warmed up, is ~675 RPM, the IAC counts will drop until it reaches 675. But if you opened the throttle blades, and the counts are bottomed out ar 0, the idle speed should start to come up as you continue to open the blades. Visibility of IAC counts would be helpful.

If you don't have a “fancy” scanner to view IAC or produce a data log, there is free OBD-2 scanning software available, written by a member here. A log helps to see the inter-relationships of the various sensors and parameters. I would look carefully at the sequence where you indicate the engine loads up with fuel, then leans out and starts the process all over again. I can help you with the log.

https://www.firebirdnation.com/forum...nner-software/

And, seems like the tunes coming out of pcmforless in the past couple years aren’t what they used to be, based on feedback on multiple sites like this. Vacuum seems a bit on the low side. You can watch vacuum in a data log by looking at the difference between MAP and BAR (barometer).

 

Sounds good. I'll download the scan tool and give it a whirl. I have a ROSS TECH VCDS scan tool. (I've owned Audi's and VWs for years) there isn't a paramter you can't read with this tool on those. Hopefully the software will be able to use the scanner and view it. Or the Ross Tech software can actually pull more OBDII info. Once I get some logs I'll post them up.

 

Turns out the VCDS doesn't work on non VAG cars. I've ordered the recommended OBDII cable from amazon to use the tool mentioned above. Tested a few more things this morning just to verify, the actron scanner I have does show closed/open and pretty much as soon as it went to closed which was within a minute of starting... it started to do the nonsense stuff. Couple of snap shots of data from the basic scanner.

• Eng Speed: 728
• Calc Load %: 4.3
• MAF Glow g/sec: 11.54
• MAP KPA: 60
• Coolant: 105 degrees
• IAT 86
• IGN Advance: 35.0

The other snap shot was as such:

• Eng Speed: 832
• Cal Load: 4.3
• MAF Flow g/sec: 11.92
• MAP KPA: 54
• Coolant: 100 degrees
• IAT: 86
• IGN Advance: 31.0

Based on other things i've read seems my vacuum is a tad low, but not unheard of. Once i get a different reader and can actually see the IAC readings, i'll be able to actually gauge the idle and such.

Right now i'm still leaning towards bad tune and possibly a small vacuum leak. (Maybe may brake booster is leaking? I'm going to disconnect everything and see what happens to my vacuum specifically. Maybe even go as far as swapping back to the old throttle body. I hear a massive amount of suction coming from the cold air intake post rebuild.

I've also read a lot of people saying that have had issues with timing chain being off one tooth one way or the other, but wouldn't my ign advance read crazy one way or the other if that were the case? I'm about 90% certain i put the timing chain on right and double/tripled checked as it was going together.

 

larger TB's need either the IAC hole drilled or blades opened some which then requires the holes of the TPS to be slotted so you can clock it to "trick" your tranny into seeing correct throttle position. Without the ability to read IAC counts while you do any of these adjustments you are pissing in the wind. Put the stock TB back on, your build does not need a 58, period

PCM4Less.....run Forest run. Contact moehorsepower. A blind monkey tunes better than pcm4less

your vacuum is low for a hot cam. to low. find out where your vac leak is

 

A more common mistake than the timing chain being 1 tooth off is the cam dowel pin not being indexed correctly into the correct hole in the Opti. It can end up in one of the 3 "clover leaf" holes, and if it's still close to the correct hole, it will still seem to run OK. But obviously that would affect timing and vacuum.

http://shbox.com/1/opti_back.jpg

The timing value you see on the scanner is the advance the PCM has calculated from the timing tables and some offsets. That's where it wants the advance, but there is no feedback as to the actual engine timing, and whether it is "off". In the OBD-2 engines, with the added crank sensor for misfire detection, the Opti being indexed incorrectly can cause the PCM to set a code for the CKP sensor "out of range".

 

Update: after pulling the 58mm throttle body and putting the factory one back on, the car runs damn near perfect now. I stumbled on quite a few threads (Thanks Chimera 96) for pointing out the throttle body drilling fix and such. I do have the data logger tool now, however i was having some trouble getting the GDScan to work entirely. I was able to log the GM Enhanced list, but i couldn't get all the other things to work like MAP pressure and such, so I plugged my old scanner in and at 800rpm idle it's still pulling 55-60kpa. Maybe I still have a slight vacuum leak somewhere. I suspect the PCV valve.....

Anyway. the log i got showed 0 misfires across the board which seemed odd to me. I figured there may have been at least 1 or 2. I couldn't find the knock portion of the log, but one of the tools that came with the usb cable was saying #1 TDC to spark was in the neigborhood of 22-26 degrees advance. I'm guessing i'm getting a little knock probably (poly motor mounts and a cam.)

So on to getting this thing fine tuned.

• At WOT, my TPS is reading 3.92 volts. (Me flooring it not tapping on the throttle itself.) At that time the IAC counts sit around 130
• At idle, my TPS is reading .784 volts and IAC count avgs at 106. High 130 Low 77

I'm guessing based on that i still have some tweaking to do for the bolt that adjusts the amount the blades are open.

I'm going to drill out the 58MM throttle body to match what the factory has as well, the 58mm throttle body is easier to adjust while on the car so I can get it set right at .67 volts.

I'm guessing there is someway to adjust the gas pedal cable? Because when I floor it, it goes into the floor literally. I don't believe i'm bottoming out on the ASR. But perhaps that's by design to prevent breaking the throttle cable?

Glad I asked here. Been a lurker for a long time, but first time poster. (I used to post over at ls1tech but it's not what it used to be, every response is, buy an LS1, etc.)

 

I've asked GaryDoug if he could help you with the GDScan issues.

The TPS WOT voltage is not important, as long as the PCM is interpreting that voltage as 99% or 100% throttle position, AND the throttle blades are actually in a true horizontal (90-deg) position - not under or over. Any chance the carpet mat is under the accel pedal? Buddy of mine was running a 9.0-second 30th SS convertible, made a weak pass, and looking at the data log we realized the TPS was less than 100% and the floor mat had slipped under the pedal.

The PCM checks the closed throttle voltage at key on, and baselines that voltage as 0% throttle position. As long as the voltage is in the range of 0.25 - 0.90 volts (varies slightly by model year) it is OK. If the voltage is outside those limits, it sets a code. Typical closed throttle volts for an unmolested factory TB, are in the range of 0.65 - 0.67 volts, but there is nothing sacred about those values.

Your IAC counts at idle are not consistent with the throttle blades being opened up excessively. Also not consistent with a vacuum leak. What makes you feel the PCV valve may be the vacuum leak?

 

GDscan issue: Are you saying you cannot get any data on the Live Data tab? If not, have you followed the instructions in the GDscan guide pdf file, to press Connect the then press Scan?

 

Injuneer & Gary have way more expertise on data files than I do. My understanding is TPS DCV stock are .65 DCV closed and 4.5 DCV wide open. But if I understand Fred he advises as long as the TPS data is reading 100% at WOT you should be good.

IMHO you don't need the 58mm TB for the build you have but if you are intent on using it (assume you had the intake manifold machined for it) you absolutely want to have the ability to read wtf your IAC counts are. Do not blindly drill a hole and see how that works as it gets difficult to "undo" a drilled hole. The stock hole is 1/8". If you do drill it (after initially drilling the 1/8" hole) increase in 1/64" increments and check IAC count as 1/64" makes a big difference. Take baby steps. Every motor build is diffrent

IMHO getting a stock TB bored to 52mm is the way to go vs aftermarket TB's

IAC counts at idle with engine at operating temps wants to be 32 (30-35). With yours varying from 77 to 130 at idle that is not right. You turn on AC or turn wheel so power steering is adding load to motor and you will peg it and have trouble keeping the car idling

If you have messed with the stop screw on the stock TB, adjust it so your TPS is close to .67 with blades closed and your IAC count is 30-35. That stop screw should really never be messed with from its stock setting

A note on 58mm TB with a automatic trans...you need to program the PCM to adjust for the command line pressure as otherwise the tranny will sooner or later fail. There is the "slot the holes of the TPS" mod to clock the TPS to trick the PCM into seeing correct throttle blade position

 

What brand is the 58mm throttle body? I did not have an idle problem with my Holley 58mm.

Why is it easier to adjust the (slotted?) TPS sensor on the 58mm TB, compared to the stock TB?

And, as mentioned above, you do not need it. My 381ci, 7,000 RPM engine makes 496 HP at the flywheel (not that outstanding, but the relatively mild cam allows it to pass dyno emissions) and with the engine on an engine dyno, the shop was able to show me the engine made max HP with the throttle blades at 77% open. Opening them further didn’t increase HP. If you back calculate based on blade area, a 52mm TB would have been adequate. They still laugh at my 58mm TB.....

 

Yes, I read the instructions a couple times. I'm using a newer version of one of the recommended USB to OBD port devices. ScanTool OBDLink SX. The program it came with shows the live data just fine. I click connect, and it goes green, however the "start scan" button never becomes clickable. When I first launched the app, clicking connect, the program kind of spun and hung.

I do have the two csv files and the three varients of the app on a folder in the root of C:/ that I run it from. The enhanced scans for IAC counts, TPS volts and misfires all seem to work correctly. Just not sure why on the other stuff. I'm running it from a laptop.with Windows 10 1903.

 

I have the BBK 58mm. I read a pretty thorough article on superchevy where they tested bolt on mods and the 52mm made a difference. And the 58mm made the slightest more with a cam and rockers arms, and considering it was a whole whopping $10 dollars more, I went with the 58, because why not at that point? It does look good too.

I feel like I have a vacuum leak specifically because of the 60kpa vacuum at idle. Which isn't far fetched by any means. Vacuum leak out of the pcv.... Purely suspicion because I've checked everything else. Since it connects under the throttle body I couldn't reach it easily to plug when screwing around with it.

Now that I can somewhat log data, I'm kind off addicted to the info it provides and I'm reading all the info I can find about IAC counts and such. I find it strange that when cold my car has IAC counts in the 70s, but once warmed up it stays in the 100s. I thought it was supposed to go the other way.

However idle is steady at 825 +/- 50. I'm assuming pcm4less upped my idle with the most recent tune and the engine was just struggling to maintain 625 with the throttle body not allowing enough air in.

I'm tempted to get the jet dynamic tuner program now and start my journey of endless tweaking.....

 

Oh and it's easier to adjust the 58mm bbk because the screw to adjust the blade position is easier to get to. I can't get the Allen key around on the stock one. The casting is a little different on the bbk and allows me to get an Allen key on there. The tps itself isn't slotted.

Sorry for the multiple long replies. Just trying to fill in as much info as possible so if someone has the same or similar issues they aren't left hanging without details or an answer. There is nothing worse than a thread of problems without an answer on what the fix was!!!!

 

Generally, adjusting to the correct IAC counts vs. idle RPM is done using the throttle stop screw. You can't adjust the TPS sensor voltage (if it does not correspond to your desired IAC/RPM target set with the stop screw) unless you slot the screw holes on the sensor, allowing it to rotate. With an aftermarket TB, those two steps often have to be done independently.

If you get Gary's program functioning, one of the columns shows the target idle RPM corresponding to the indicated coolant temp, as entered into the program by pcmforless (if different than stock programming).

I understand you think the idle vacuum indicates a vacuum leak, I mentioned the low vacuum earlier. I was not suggesting that was “far fetched”. I was simply asking what observation or test led you to the PCV valve.

On the other hand, you don't seem to give my info much credence, so I'll drop out and let others help you without my interference.