HELP! 94Z Lack of low end torque, hesitation, stumbling! - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #1 of 34 (permalink) Old 04-03-2017, 03:20 PM Thread Starter
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HELP! 94Z Lack of low end torque, hesitation, stumbling!

So I picked up a 94 Z28 LT1 Auto. Ran pretty good, some classic signs of Opti starting to go with a little hesitation here and there. Added a 100 shot wet kit which worked great. Car was a burnout monster and a riot to drive...


Well, then I left my nitrous switch on and punched it from a stop. Massive burnout I was not expecting and immediately let off and there was a huge backfire that blew up the MAF and sent the air filter flying! Very embarrassing lol.


Replaced the MAF and it ran but definitely never the same. Stumbles badly under 3K. It is better when cold but gets worse when it warms up but the earlier signs of Opti going were the same way. Will not do a burnout even with a brake torque. Runs good up top though. I replaced the following:


MAF - Stock unit
Opti - Brand New Delco full unit
Waterpump
Plugs - 1 step colder for Nitrous
Wires - Stock
Timing cover gasket, pulled pulley


It also has a K&N CAI, Catback exhaust. I did all the bushings, coilovers, brake upgrade, tires, rims, etc., before the incident so I have quite a bit of time and money invested into this car so I need some help figuring it out PLEASE.


A couple things to note. The coolant temp sensor is unplugged and lying in the engine bay. There is a secondary temp gauge from a port in the water pump. This has been this way since the beginning so not related. I checked for vacuum leaks spraying carb cleaner and did not hear a change in rpm. I'm stumped. Only things I found are there is an EGR solenoid vacuum port that is unhooked? See pic attached. Can't find out where it goes? Also, there is a loose connector lying in the engine bay that I can't find a home for. This has been there all along though too. Perhaps there was a hose for that EGR port that got knocked off when I blew the intake off?


First place to start would be to check for codes (one pops up every once in awhile but it has always done that even when it ran strong). I took it to my buddies Midas and the tech could not get his OBD1 scanner or the paperclip trick to communicate at all! Maybe something is wrong with the wiring from the ECU.


Any ideas on what to look at next considering I cannot get any codes?


EGR solenoid unhooked?
EGR broken
MAP Sensor
Secondary ignition coil
Fuel pump
IAT Sensor
O2 Sensor
Fuel Filter
Fuel injector
TPS
Vacuum Leak
Wires arching


There has to be some relationship to the work I did or NOS backfire event. I'm fairly certain I performed all the work correctly so what on this list could have malfunctioned due to the event or my work? Thinking EGR or the MAP or IAT sensor? How can I test these? Or should I start somewhere else? Thanks in advance!
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Last edited by mschmidt33; 04-21-2017 at 10:39 AM.
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post #2 of 34 (permalink) Old 04-03-2017, 07:59 PM
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First picture looks to me like the temp sensor for the gage in the instrument panel. The sensor in the water pump is connected to the ECU to correct the timing and fuel for engine temperature. The instrument panel sensor does not affect engine running.
EGR is on the back of the engine, so third picture is something different, maybe air injection line for the exhaust manifold?
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post #3 of 34 (permalink) Old 04-03-2017, 09:16 PM Thread Starter
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Thanks for the info. Any suggestions? Can air injection cause any problems? Tonight I unhooked both the MAP and MAF separately and the car ran the same with each unhooked.
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post #4 of 34 (permalink) Old 04-03-2017, 10:03 PM
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You might want to check out this website that has a lot of drawings, how to's and photos of a 95 Z 28. Alot of things also are for other years also. It is from Shbox, who has helped many !

http://shbox.com/page/index.html

95 Z28, Automatic, Stock except for CAI, Throttle Body Bypass, Flowmaster Exhaust. 2:73 Rear, SLP Fan Control, 145k Miles - Runs Great

Last edited by garybo; 04-03-2017 at 10:09 PM.
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post #5 of 34 (permalink) Old 04-04-2017, 12:48 AM Thread Starter
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Thanks. Found out I was looking at the air bleed valve and that no hose goes to it! Back to the drawing board
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post #6 of 34 (permalink) Old 04-05-2017, 01:45 PM Thread Starter
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Bump
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post #7 of 34 (permalink) Old 04-05-2017, 05:04 PM
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Quote:
Originally Posted by mschmidt33 View Post
Thanks. Found out I was looking at the air bleed valve and that no hose goes to it! Back to the drawing board
The AIR non return valve in the exhaust manifold ?
They do fail and will let air into the exhaust screwing with your O2 trims, or melt things if leaking exhaust back into the engine bay.

On a '95 they are a M22 x1.5 bolt thread, easily blanked off.

HTH
Mitch

Terminal Crazy
'95 Z28 M6
Lancashire England
"just the odd mod."
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post #8 of 34 (permalink) Old 04-05-2017, 05:43 PM Thread Starter
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Ok thanks. So you suggest as an easy test I could plug both exhaust manifold bosses. Could this throw a code or mess with the ECU if there is no flow?
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post #9 of 34 (permalink) Old 04-05-2017, 05:44 PM Thread Starter
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I really think I should try using my laptop to do some scans. Maybe the tech at Midas was clueless. What OBD1 to usb cable does everyone recommend for a 94 Z28?
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post #10 of 34 (permalink) Old 04-05-2017, 06:21 PM Thread Starter
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Just ordered a 12 pin obd1 cable from red devil. Reading about software. Hope Midas was wrong. While I'm waiting and figure out datalogging I'm open to suggestions!
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post #11 of 34 (permalink) Old 04-06-2017, 10:32 AM Thread Starter
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UPDATE: Burned through a tank of gas this week and averaged ~10mpg. Thoughts? Spirited driving about 25% of the time. 50% was highway. Other 25% city.
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post #12 of 34 (permalink) Old 04-07-2017, 06:59 AM
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Go to the following link and download "Scan9495" it scans for regular codes, ABS & SIR codes. Does running sensor data scans and will log data to a file for playback. Also tests engine & auto trans actuators. And it's free. www.mediafire.com/?0elo4c935uc5s

Pick the newest version from the v-8 folder. Also you need Microsoft dot net framework version 4.0 or newer to use scan9495. There's a folder at the top you can download it from. Or go to microsoft site.

You might also want to get a pc based oscilloscope. With it you can test your opti low & high resolution pulses to see if they are proper voltage & waveform. Also good for testing the 50 hertz fuel enable sighal used to open fuel injectors. About $70 on Fleabay.

paper clip trick only works on 93 & older cars. Many obd 1 scanners out there only work on some obd1 cars, not all obd 1 cars.

Last edited by cocobolo95; 04-07-2017 at 07:02 AM.
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post #13 of 34 (permalink) Old 04-07-2017, 07:05 AM
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Let me add, I just had a hesitation, stumbling , stalling problem with my 90 speed density car. Turns out that map connector wasn't making good contact even though it looked like a good connection.
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post #14 of 34 (permalink) Old 04-07-2017, 07:25 AM Thread Starter
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Thanks. Thats the exact program I read about and grabbed yesterday. Currently going through the tutorial. Remembers me of the old Hondata days (Sorry I had too). Hopefully this helps me find the issue. I may need to post a log for some additional help. Hopefully I get the cable soon!
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post #15 of 34 (permalink) Old 04-07-2017, 07:27 AM Thread Starter
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Thanks for the idea. Mine appears fine but hopefully the scan will catch something like this? If my MAP doesnt work and it runs up top maybe I should just boost it now lol. Got a few GT35s lying around!
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