LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

New Opti installed - need to test

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Old Oct 3, 2019 | 11:25 AM
  #61  
Injuneer's Avatar
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Re: New Opti installed - need to test

Things that stand out:
  • takes an excessive amount of time (352-seconds vs 206 normal) to enter closed loop, due to a very slow coolant warmup. CLT had to reach 140-degF. Should warm up faster than that.
  • Fans-low relay turns on at 184-degF. OK w/ a 160-deg t'stat, but a bit low with a 180
  • at idle, the RPM is very stable, but is always above the target idle RPM because the idle air counts are "0". May indicate a vacuum leak - see next comment
  • TPS volts at idle is 0.73. See if dropping the TPS volts into the 0.60-0.65 range opens the counts up into the range of 15-20, - see next comment
  • MAP is a bit high at idle, at close to 40 kPA. Normal s more like 32-35 kPa. May indicate a vacuum leak - see next comment
  • MAF grams/second at idle is maybe on the low side, at less than 6.0 G/S.... may indicate a vacuum leak
  • Idle cell 16 long term fuel corrections are 135 (+5.5%) - bank 1 / 137 (+7.0%) - bank 2. Again, where is the extra air coming from?
None of the departures - IAC, MAP, LTFT - is grossly out of whack ,but they may all be pointing to a small vacuum leak, affecting both sides of the engine.
  • All of the cells except the closed throttle coast-down cells are adding fuel with the LTFT's. Again, not a huge departure from the normally acceptable +/-5%, but a definite pattern with all the non-coast-down cells adding fuel. And in almost every case, the extra fuel seems to be added, raising the LTFT's when the EVAP system purge solenoid is commanded open. That may indicate a leaking hose between the canister and the purge solenoid, or there might also be a leak in the line from the purge solenoid to the throttle body.
  • when you open the throttle enough to put it into "power enrichment" (PE) mode, the Bank 2 O2 sensor goes upward to ~0.90 volts, which is fairly normal due to the higher A/F ratio used on PE mode, but the Bank 1 O2 sensor only goes up to ~0.75 volts, which is on the lean side. Any number of things can cause that. And keep in mind that the narrow band O2 sensors are not very accurate at the rich A/F ratios use in PE mode. But normally, the results are similar on both banks.
Old Oct 7, 2019 | 08:25 PM
  #62  
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From: Duvall, WA
Re: New Opti installed - need to test

Originally Posted by Injuneer
Things that stand out:
  • TPS volts at idle is 0.73. See if dropping the TPS volts into the 0.60-0.65 range opens the counts up into the range of 15-20, - see next comment
I think someone before i got the car mess with this screw (see pic)


if so how do i fix it!
Also when i was putting the opti back in i notice one of the throttle body bolts is missing as you can see in the picture, would that cause any of the added air problems your saying?

Thanks!
Old Oct 7, 2019 | 11:04 PM
  #63  
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From: Hell was full so they sent me to NJ
Re: New Opti installed - need to test

What is wrong with the screw, other than possibly being extended slightly? Will it not retract into the throttle body when you use a screwdriver from the back side? The TPS voltage is not a problem by itself. The acceptable range is about 0.25-0.90 volts (varies by year). The problem is you MAY need to back the voltage down to get the IAC counts above 0. Or, just finding the small vacuum leak may raise the IAC counts.

A missing TB bolt might allow a vacuum leak between the TB and the manifold, particularly if the gasket is damaged as well.
Old Oct 8, 2019 | 03:26 PM
  #64  
chevykid's Avatar
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From: Duvall, WA
Re: New Opti installed - need to test

Originally Posted by Injuneer
What is wrong with the screw, other than possibly being extended slightly? Will it not retract into the throttle body when you use a screwdriver from the back side? The TPS voltage is not a problem by itself. The acceptable range is about 0.25-0.90 volts (varies by year). The problem is you MAY need to back the voltage down to get the IAC counts above 0. Or, just finding the small vacuum leak may raise the IAC counts.

A missing TB bolt might allow a vacuum leak between the TB and the manifold, particularly if the gasket is damaged as well.
is there instructions as to set the screw to proper setting? Thanks
Old Oct 8, 2019 | 07:02 PM
  #65  
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From: Hell was full so they sent me to NJ
Re: New Opti installed - need to test

First, check the TB gasket, and replace the missing bolt. That might fix the IAC counts, requiring no further changes.

If IAC counts at idle are still less than 10, while monitoring the TPS volts and the IAC counts, start retracting the stop screw (counter-clockwise). Keep retracting it very slowly, until the counts reach 15. Let it idle for a while (couple minutes) to insure it’s stabilized. Check the TPS volts. They will have dropped, but as long as it doesn’t drop below ~0.35, you are OK. I doubt it will drop that low.

This doesn’t require extreme or precision. You already have an engine that appears to be running very well. Just need to get the IAC counts up to the level that gives them headroom to control the idle RPM at all times. And, while keeping the TPS voltage within the very wide range that allows the PCM to baseline closed throttle volts as 0% throttle precision.
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