mysterious oxyen sensor - Page 3 - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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post #31 of 37 (permalink) Old 06-22-2019, 03:38 PM Thread Starter
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Results: no smoke into the crankcase after a solid 20 minutes on the machine. Still some smoke coming out from the arm with the spring of the throttle body.
Will a 94 Throttle body be the same as my 97? I found a brand new one on ebay. it looks the same but I figured you would be the guy to ask.

https://www.ebay.com/itm/LT1-5-7-Thr...w/254264800566

Before I buy it I will do a compression and let down test but my thoughts are if 1psi of smoke can get through it its probably not helping the problem.
Furthermore, If I do buy I feel like I should just do the intake gaskets to be safe.

One last thing. I noticed with I blocked both the PCV valve and the vac line of the left side the fuel trims actually got higher. Why is this?

This may be normal but both o2 sensors stay pretty close to the .6/.7 mark at cold start but drop low after 30 seconds.
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post #32 of 37 (permalink) Old 06-23-2019, 06:38 AM
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94-97 use same throttle body. Yes, new intake gaskets would be good. Be sure to follow directions in 96 service manual. Use a good grade of silicon sealant on front & rear of intake. Let it skin before screwing in bolts. Then just snug it up. Let silicon cure for 24 hours before tightening down & torquing. bolts.

Only guess I can make as to why fuel trims increase when pvc system is plugged is; pvc system sends out oil vapor which has O2 mixed in. When system is hooked up, this extra O2 is being sucked out of engine. When plugged, the O2 is somehow getting into the combustion chamber causing leaner O2 readings and causing pcm to increase fuel.

This has been a long thread. Did you ever put a fuel pressure gauge on fuel rail to see if fuel pressure was within proper limits during idling & different driving conditions?

When you do leak down test, you will be listening for air flowing from combustion chamber to oil pan, intake system, & exhaust. If you get air in pan, you have piston, ring, or cylinder problem. If you get air in intake, intake valve problem, or mis adjusted intake valve. If air in exhaust, exhaust valve or adjustment off.

One last place to look will be air coming out of valve guide. And test must be performed with that cylinder at top dead center, on firing stroke. That is with both valves closed. If test is done with piston in any other position than tdc on firing stroke, you'll get air going out either intake or exhaust valve or both.

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post #33 of 37 (permalink) Old 06-25-2019, 09:46 AM Thread Starter
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It certainly has been. Ive made more progress on this issue in a few weeks then in the years ive owned it and that is thanks to you.

Fuel pressure test: within normal limits of the of the service manuel. (42psi when primed and about 39 during idle. once turned off fuel pressure holds loosing only 10 psi over night.)

Compression test: Still trying to get my hands on a let down tester might just buy the harbor freight one.

Throttle body: ordered with delco TB gasket.

Beers: running dangerously low

Unfortuanly due to my upcoming board exam further tests will be postponed until next weekend
Ill let you know the results of the next few test. Thank you again

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post #34 of 37 (permalink) Old 07-05-2019, 03:49 PM Thread Starter
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Compression test on Bank 1 was #1 155lbs #3 155lbs #5 150lbs #7 155lbs.
PCV valve, Throttle body, and an evap line replaced with no change.
I will check compression on the other side tomorrow.
I still dont understand why even the long term on bank 1 will sit at 25 at idle and jump to 3, then 10, then back to 25 while driving.
What are normal values for MAP, MAF, on a stock motor at idle?

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post #35 of 37 (permalink) Old 07-07-2019, 11:22 AM
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Danomax, pic attached is very old log from my 1994 LT1 back in the days when it was stock and prior to any tuning. Ignore the DTC 77 as I was doing some home brew messing with the fan switching, prior to tuning the fans it. The log is at idle on a warmed up engine, in closed loop (BLM Enabled). Remember there are 19 BLM cells, idle uses cell 16, an will show any vac leaks as much higher due to the TB being closed and higher vacuum being pulled. Also when you plugged the PVC vac side of the system there is also a PVC input to the engine that feeds MAF measured fresh air to equal whats being sucked into the intake (keeps trims balanced). It's a hose on the right valve cover to the TB on the '94, not sure where it is on the '97. If you plug PVC vac to crankcase then any blow back will go thru that open hose to TB and could be why trims changed.
What are your readings at idle in BLM cell 16 ? . MAP , ST trims, BPW (injector Pulse widths), INJ DC (injector duty cycles), AFGS (air flow gms/sec), TPS%, TPS voltage, IAC position, RPM, IAT (input air temp) , spark advance and retard. I know your scan tool may not have all these diaplays but the more the better.
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I'm Bob 1994 Z28, A4, cam, 1.6 RR's CAI, LT's, stall, cat back. Custom tuned. 2007 GMC Envoy, tuned. 2015 Kia Sorento, bone stock.
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post #36 of 37 (permalink) Old Today, 12:31 PM Thread Starter
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Thank you for the reply! unfortunately I do not have scanner capabilities to know the different tuning cells. HOWEVER! after disconnecting the fuel pressure regulator Vac my bank 2 to dropped to 0 long and short term fuel trim and Bank one dropped to 0 and +10! The line to it doesn't appear to be crack bc I can plug the end going into the fuel pressure regulator and the trims stay low. The weird thing is that the regulator seemed to be working correctly when pluged in but maybe there is a leak in it somewhere?
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post #37 of 37 (permalink) Old Today, 01:12 PM
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Pulling that vac line increases fuel pressure, so injectors are going to pump in a little bit more fuel but not a lot since your PSI numbers are pretty close. Your FP test in post #33 only showed 3 psi difference between high and low ranges, did you test with vac line off (acceleration/ low-no vac/higher fuel pressure) and then with it connected (idle/ high vac/ low fuel pressure ) Is there any raw fuel entering the the intake from the regulator vacuum line ?



Coco.. I've been using the old OBD1 scan programs (Tunerpro, CAT's, TTS Datamaster,Scan9495) for years, has there been any LT1 OBD2 free software that developed since I've been away from the LT1 mainstream the past 5 years. Sure could use it here, I'm so used to fixing problems with data logs that I'm running out of ideas.

I'm Bob 1994 Z28, A4, cam, 1.6 RR's CAI, LT's, stall, cat back. Custom tuned. 2007 GMC Envoy, tuned. 2015 Kia Sorento, bone stock.
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