LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums - Reply to Topic
Thread: mysterious oxyen sensor Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


  Additional Options
Miscellaneous Options

  Topic Review (Newest First)
07-28-2019 01:31 PM
TealHornet I would take off throttle body off seal it with sillicone and plastic plate or glass un plug all vac lines exept one on manafold
and put vac guage on it and crank engine like you would on compression test starting or not it should be like 17 to 20 hg
if needle bounces a valve is not seating if the manafold is leaking youl know that too.
You should be able to tell without doing that just hooking up a vac gauge and running it.
On my 97 it shows 16 on vac guage with evap solenoid stuck open.
Its old school But its how I work being cpu tune Illiterate.
And being a second hand car guy I dont think Ive seen a throttle body or carb that didnt leak a little through linkage etc.
and any bouncing of guage will tell you valve.
Just trying to think outside your box a second.
and it should 0-2 when you hit throttle
I used the vac line going to opti worked well to test rest of system
just remember behind the two one way valves
Sorry for interupting
07-19-2019 03:25 PM
Danomax6.6 once I unplugged the vac line the pressure stayed at a constant 45ish at all speeds and for awhile all my fuel trims went to zero! then today when I drove it under the same conditions the fuel trims on bank 1 started increasing again.
I did notice however that in between fuel primes it jumped to 45 then slowly dropped to 39 (with the car off) some times. a few times it held at a constant 45. I notice that the short term fuel trims on both sides jump whenever I pin and when I back off they lower sometimes in the negative. Those symptoms make me think its not getting correct fuel pressure but when I test it they are within normal limits. to be sure it wasn't a leaky injector I switched the injector sides and put new o rings on them with no change.

I will run logs on it later and get back with the data
07-16-2019 12:57 PM
Danomax6.6 awesome I have ordered the adapter and downloaded the software.
07-15-2019 03:39 PM
cocobolo95 Bob, you will find a free obd2 scan program at the same site you got scan9495 at. It's called "gdscan" It should do 96 &97 lt1 cars, plus many other GM obd2 cars.

Data cable will need an elm327 interface chip to work. Same as other obd2 scan cables. The obd 1 16 pin cable that works with scan9495 on 95 lt1 cars,won't work with gdscan.

If you don't remember site that has scan9495, let me know and I'll post a link. Our member GaryDoug wrote gdscan as well as scan9495. If you need help with gdscan, contact him. However, he's more active at the firebird nation forum.
07-15-2019 02:51 PM
Danomax6.6 I see what you mean. That was tested with the line on with the engine off, and on at idle. I have not noticed any fuel in the line. I will retest the fuel pressure next. thank you.
07-15-2019 01:12 PM
bobdec01 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.
07-15-2019 12:31 PM
Danomax6.6 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?
07-07-2019 11:22 AM
bobdec01 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.
07-05-2019 03:49 PM
Danomax6.6 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?
06-25-2019 09:46 AM
Danomax6.6 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
06-23-2019 06:38 AM
cocobolo95 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.
06-22-2019 03:38 PM
Danomax6.6 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.

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.
06-21-2019 07:20 AM
cocobolo95 Sounds like a plan. Let me know results.
06-20-2019 08:52 PM
Danomax6.6 now that I think about it I bet if I ran the smoker with the pcv valve off and crank case line on the right side blocked I could tell if the leak was from going under the manifold.
06-20-2019 02:22 PM
Danomax6.6 high performance engine mods? this day might turn around after all. LOL That's a good point too. I assumed it already had at least some tranny work done bc it churps 2nd gear religiously.
I do not have the obd2 tuning program.

the only way I have checked for intake manifold leak was through the smoker into one of the vacuum lines and I saw no smoke from the intake manifold. If it was leaking out and not from the top would it travel into the space drained by the PCV? Now that you say that I do remember a slight bit of smoke coming out of the PCV when the smoker was hooked up. I thought the smoke may have traveled through the right vac line into the right valve cover and through.

Either way I think I should be telling people it has internal engine mods now
This thread has more than 15 replies. Click here to review the whole thread.

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

For the best viewing experience please update your browser to Google Chrome