sncboom2k

For anyone wanting to see the gauges from today's testing - they are attached as well.

sncboom2k

I was finally able to find a tuner in my area that does LT1 engines using a dyno. Before I schedule with him, I'll wait for you experts to comment on my findings - see if there is anything I need to do / replace before I take it in. I'm tempted to change the optispark but it's so much work - if I don't need to, I don't want to! hehehe (Spoken like I've replaced it 4 times already in 16 years.)

I greatly appreciate everyone's time - thanks again.

sncboom2k

Just keeps getting better. So after the car being gone for months I decide to take it for a drive this morning. Now when I give it gas it completely stalls and then takes off. Sometimes 2 or 3 times before leveling out. So in some lame sounds - vroom dead vroom dead vroom.... Then goes. Not every time but most of the time. So I turned around and put it right back in the garage.

I had a brand new MAF on hand so I installed it real quick - no change. I have a new MAP and ICM showing up today. I'll install those as well. The coil was changed a week ago - I'm putting the old one back on today. Seems to have gotten worse with the new coil.

Injuneer

Scan for codes. The code for loss of low resolution pulse signal from the Opti (P1371) shuts down the fuel system while it is active. And, does NOT turn on the SES light.

Looking at your scan data... engine is hot (222-degF) but no signs of low RPM that would cause it to stall. RPM is excessively high at 840-860 RPM (should be 650) and the idle air control motor (IAC) has closed down to "0" counts, and is not able to pull the idle speed down where it is supposed to be. Couple possibilities - 1) IAC motor is defective, and is not moving (the scan shows what the PCM is telling the IAC motor to do, no feedback as to actual position, or even whether the IAC is actually functionaing); 2) engine is getting air from somewhere else.

MAF reading is at 10.7 gram/second, so it appears all the air is going through the MAF sensor. However, a torn rubber elbow (or one that i not fully over the throttle body on the bottom) between the MAF sensor and the throttle body may open up under sudden throttle opening, and allow air to bypass the MAF sensor.

When you rebuilt everything, did you clean the throttle body and in particular the IAC motor? Easy to damage if not cleaned correctly, or if you tried to move the pintle. Electrical check:

Courtesy of Shoebox

http://shbox.com/1/iac2.jpg

Does the engine ONLY stall immediately after you decelerate? That can be related to the IAC as well. As engine RPM and vehicle MPH increase, the PCM opens up the IAC to control the engine on decel and prevent stalling when the throttle blades suddenly close. That is a feature "terminal crazy" was alluding to in his post.

Again in your data post, you still have the big "split" between left (-10%) and right (+9%) banks, in Cell 16. But, the average LTFT's are not so bad. Average left LTFT is at 124 (against 128 "normal") or -3%. Average right LTFT os at 129 = < +1%. Whatever is causing the problem in the idle cell (16) would not appear to be affecting the other cells (0 to 15) that relate directly to various combinations of RPM and engine load (as represented by MAP).

sncboom2k

Thank you Injuneer - The idle was manually set by the last mechanic to be 850ish. He moved the TPS etc to accomodate the new higher idle speed. The engine stalls anytime it is warm, in gear, and at a complete stop. Just as a test last night. While the car was warm - and in park - I turned on the A/C - it started loping as if it was going to die - but did not. So it appears any kind of load just wants to stall the engine out unless you give it some throttle.

I'll check the IAC and the rubber neck - no elbow as it's a WS6 with the ram air. I'll get back to you shortly.

As for the engine being hot - it was in the garage and had been idling for over 45 minutes. When it reached 226 - the fans came on.

And yes - the manifold was taken with the engine to be tanked and cleaned - I do not think anyone cleaned the IAC.

sncboom2k

Ok - looking at the snap on solus - the IAC is at 0 when the car is at idle. It remains at 0 until I give the car some throttle. Road test shows it's position changing while driving. When I pull up to a stop - it goes back to 0 and does not change while the engine lopes and dies. The history count has not moved from 10.

I was not able to get my multimeter leads in the tight quarters to test the resistance between the pins - I will try again later.

No codes in the computer.

Injuneer

That's not the correct way to change the idle speed. It has to be set in the PCM. When he opened the blades up it took control of the idle from the PCM, defeating the purpose of the IAC system. He apparently then had to drill slots in the non-adjustable TPS, so he could get the closed throttle voltage back into the tolerance range of 0.20-0.90 volts.

You really need to eliminate the hacks and solve the idle problem before spending money on a dyno tune. A mail-order PCM tune could have got it into the ballpark better than trying to override the PCM.

Injuneer

OK.... the bellows on the WS6 can tear or not be fully on the throttle body as well, unless you have upgraded to the Fernco sewer pipe connector. The corrugations and offset don’t seem to promote smooth flow.

https://www.camaroz28.com/g/picture/8152310

Did he raise the RPM to 850 to try and solve the stall problem? The IAC is no longer functioning fully at idle, because of the idle speed/TPS hack. Who knows what else has been done to it. Should start to open open up when in gear, RPM drops below 550 RPM. It should react to the A/C being turned on by opening up, to prevent the stall.

sncboom2k

He did in fact change it to try and fix the stall issue. How would I go about returning it to normal? I have a new TPS here - but how do I adjust the blades?

I see a set screw on the side for the blades. Would I replace the TPS and then adjust the set screw until I'm back at about .73 volts?

Injuneer

There's a throttle stop screw on the driver’s side, at the top, accessible from the back. You can see the end of the screw protruding against the top “tab” of the cable quadrent. Screw is a Torx Head (T15 ??), set almost 1/2” deep inside the opening in the back of the TB.

Engine idling in neutral, fully warmed up, scanner showing IAC counts, slowly back the screw out (counter-clockwise), watching the IAC counts. When RPM reaches 650, IAC counts should move off of “0”. Keep backing the screw out slowly, until the IAC stabilizes somewhere in the range of 20-40 counts.

Then stop playing with the screw, and check the TPS volts. The PCM looks at the TPS volts at startup, and as long as the voltage is between ~0.3 to ~0.85 volts, is sets that voltage as the baseline 0% throttle position. It then measures the throttle position by adding about 4 volts to the baseline voltage and prorating between those two values. Most of the unmolested, stock TB closed throttle readings I have measured, or seen in data logs, are in the range of 0.63-0.67 volts. If the TPS is slotted (stock TPS is not slotted, because you shouldn't need to adjust it) loosen the two Torx screws and rotate to get a value in that range. Really not critical, as long as you don't go too low and set a low voltage code (~0.20 volts, but varies by years). Or high voltage code (over ~4.90 volts at WOT).

After you have 650 RPM, 20-40 counts and tightened down the screws, put it in gear and see if it holds 550 RPM. In general RPM variations +/- 25 RPM from the target idle speed are normal. If still OK, shut engine down, and key on, observe the TPS volts as you slowly rotate the throttle blades from fully closed to wide open. Voltage should increase smoothly with no dropouts or spikes.

Will be interesting to see if this helps the in-gear stall. The PCM should respond by opening up IAC to hold RPM at the programmed target. This is something else that becomes a problem as cam overlap is increased. But so far you haven’t mentioned if this happens when the engine RPM drops.

sncboom2k

Thanks Fred - I'll get on that tonight. My MAF took a crap today and the new cheapy I bought is not cutting the mustard so I've ordered a Delphi to replace them with. I'll post back once I have the throttle set back to 650 correctly.

sncboom2k

Ok Fred - I had to borrow some longer Torx (15) but idle is at 650 now
TPS voltage is .65
The IAC is now at: 27-32 depending on temp

Looking better?

Hack gone.

Now when the car lopes to die in drive at a dead stop - the IAC starts to increase - all the way up to 51.

TPS voltage is smooth through the entire range of motion.

Can you elaborate on this statement? "Will be interesting to see if this helps the in-gear stall. The PCM should respond by opening up IAC to hold RPM at the programmed target. This is something else that becomes a problem as cam overlap is increased. But so far you haven’t mentioned if this happens when the engine RPM drops."

I haven't mentioned if what happens? Sorry - confused on that one.

Thank you!

Injuneer

I was just pointing out that I hadn't seen a definitive answer on what the IAC did when it stalled. You indicated in post #21 that is didn't move, but somehow that shouldn't have been the case.

I agree the target idle speed should be raised to control the lope and the potential for stalling, and ignition timing can also be used control idle with a cam. Need a good tuner, accomplishing all that in the PCM.

If you want, after it's idled for a while, pull up the cell 16 LTFT's to see if setting the throttle blades correctly has had any impact on the "split" LTFT condition. As I noted earlier, larger aftermarket TP's sometimes suffer from split LTFT's. Maybe attempting to control the idle RPM by opening up the blades on the stock TB contributed to the problem.

sncboom2k

Yeah originally the IAC was not doing anything at idle and was at 0 due to the RPM hack.

Now it's working as it should but motor still eventually dies while at a stop in drive.
No aftermarket parts on my throttle body. The split you noticed in the PDF was before the hack. The split appeared to be worse after the hack. I noticed the blades are pretty dirty around the edges - I'll clean those up while I'm in all of this.

I don't think my solus can show me cell 16 specifics. Is there a better software I should be using with my PC? I have a bluetooth OBD-II adapter as well I can use.

Right now I've started stripping down the front of the engine to replace the optispark which should arrive today. I'm going to try and have it all put back together with the optispark, a new MAF, and IAC by this weekend. So I'll get back to this thread once I have completed that. Taking a coolant bath today

Thanks again Fred.

Injuneer

I wasn't suggesting your TB had any aftermarket parts. Only trying to convey the thought that opening up the blades, changing the path of the idle air away from the idle air passage, may be altering the distribution of idle air to the cylinders. Alteration of flow path is often suggested as the cause of aftermarket throttle bodies causing split LTFT's.

One of the .pdf sheets of data identified the data as being from Cell 16. If the throttle blades are closed, and the vehicle isn’t moving, the PCM should be operating in Cell 16 fueling.

The AutoTap OBD-2 software/data logging was very good. Unfortunately the company just stopped marketing it. I still have my AutoTap software/hardware. GaryDoug, best known for his excellent Scan9495 software, also has an OBD-2 version:

Free OBD2 scanner software - ECM/PCM - Firebird Nation