OK, I've had this 96 z28 for about 6 years and have put on about 70k miles and its always ran perfect until the other day.I have kept up on the maintenance with some upgrades like a k&n air and oil filters,synthetic oil, e3 centerfire plugs and 10.2 mm wires. Its always been reliable and fast as hell. Two days ago I drove it to town and stopped at a store and was inside for under 10 minutes and I came back out and rolled over but wouldn't start. It'd pop once in a while and acted like it was flooded which it never did before. I hauled it home and let it sit and the next day it still did the same thing. I put a scanner on it and the only codes that came up were tp sensor circuit too low, tp sensor circuit too high, manufacturer controlled, and both banks saying cat efficiency below threshold. Hasn't had cats on in years anyway.so I go get a throttle position sensor and still wouldn't start.so I grabbed a map sensor and an ignition control sensor and still nothing. The fuel pump is working and a pressure test showed 50 psi when it runs and holds 40 psi after the pump shuts off. A couple times it almost acted like it wanted to start but nothing. Then it pops and backfires some and that's about it. I had already replaced the cap and rotor a couple years ago and this car doesn't get ran in winter. I have from time to time had the security come on preventing it from rolling over for about 5 minutes but I was told the key may have to be replaced. All the fuses and relays are good so I just don't know where else to go. I cleared the codes and it hasn't generated new ones. Any ideas?

 

Welcome to the site. Have you checked for spark at the coil output, and at a few plugs?

 

What were the exact codes, in particular the one you labeled as "manufacturer controlled"? That would indicate you were working from a generic list, and not the specific code list for your vehicle. The cat codes are set because you don't have cats. They should have been tuned out of the PCM, or you should have installed O2 "sims" to avoid the codes.

https://service.gm.com/gmspo/mode6/p...c57P_FY_yE.pdf

 

The exact codes are p0122 tp sensor circuit low, p1641 manufacturer controlled, p0430 cat efficiency below threshold left, p0420 cat efficiency below threshold right, p0123 tp sensor circuit high. I'm using a cornwell enhanced monitor 4000e diagnostic tester with a otc system smart 25 pin insert and 1996 domestic cartridge.It acts like it wants to fire but that's about it.

 

Oh and there are o2 sensors but like I said no cats.I'm going to be testing each spark plug wire but I'm fairly certain it has fire with it popping off. Someone suggested it possibly jumped time but all of that was replaced not long ago and it literally ran perfect when I shut it off last and it hadn't started at all when I tried restarting it so I'm pretty sure it didn't jump time.I have one more sensor I want to check and that's the crank position sensor even though the only sensor code was for the tps.

 

P1641 is "primary cooling fan relay control circuit malfunction".

You would be better off using the trouble code chart I linked. That is specifically for a 1996 F-Body LT1.

When you replaced the cap and rotor, did you loc-tite the rotor screws? Not unusual for them to fall out, irregular spark or no spark.

 

I did look through the codes you posted and thanks. I just uploaded a video of it on YouTube and here's the link. I did check the cap and its tight and contemplating pulling it off to look but it is a pain in the *** to get to seeing as I have to remove the water pump to do so.Watch "1996 lt1 Camaro not starting" on YouTube
1996 lt1 Camaro not starting:

 

There could be other issues...here are the "crank but will not run" charts out of my 1996 factory manual.

The charts call out P0122 as an issue. Did you check it for proper voltages(with a voltmeter) after you replaced it? I can't remember off the top of my head, but I think 0.8V is closed throttle and 4.5V is wide open. You will need to confirm that(I'll go look it up later today)....I think Injuneer will know off the top of his head. Can your scanner check the throttle position value? Does it read 0% closed and 100% open?

If it checks out, then it might be time to start troubleshooting the Opti. Use the video in the Opti thread at the top of the forum to check the signals.

http://www.ace1252.com/1996_Z28_Fact...ut_no_run1.JPG
http://www.ace1252.com/1996_Z28_Fact...ut_no_run2.JPG
http://www.ace1252.com/1996_Z28_Fact...ut_no_run3.JPG

 

Closed throttle TPS voltage can be anywhere between 0.30 - 0.90V. The PCM reads the voltage at key on and sets that as the 0% throttle position baseline. Anything below 0.20V sets the code (slight variations, year to year - the actual numbers are in the code list I linked)). As you rotate the throttle open, the voltage will increase to about 4V above the closed throttle voltage. Anything over 4.70V sets the code (again, varies year to year, look it up in the 96 code listing). The voltage should increase smoothly with no voltage spikes or dropouts.

 

Well...I think I figured it out. I ran test after test with a volt meter and test light and even a compression test until I got frustrated enough to tear the front of the motor down to get to the cap and rotor. I pealed the cap back and the rotor flopped out and the two little screws were sitting on the bottom of the cap and the plastic pin on the rotor was sheared off. I'm not sure how long its been running on just that pin but it makes sense that it'd still turn to fire but not in time to run and that's why it'd act like it'd pop off one time then pop back the next. Thanks for everyone's help and I'm glad it wasn't anything major. I guess I never thought about the rotor coming loose. Thanks again.

 

Here my friends is the end result after two tiny little screws shut it down.1996 Camaro lt1 finally running:

 

.......

 

Yea....I could've swore I did. I certainly did this time around. That cap and rotor has been on it for almost 60,000 miles so it never crossed my mind that's what it was.however something that hasn't worked since spring of last year is the ABS and traction control. I was thinking the ABS module because I'm getting power to the relay and fuses and to the small connectors on top of the module but the large plug on the side has no power while running. Could that be a pcm problem? The scanner I'm using doesn't have anything for that system.

 

The ABS/Traction Control is not controlled by the PCM. It has it's own computer called the EBTCM (electronic brake and traction control module). You can scan it through the 16-pin data connector, but you need a scanner or software that can scan the EBTCM. Check the Scan9495 software writeup (sticky on the "Computer Diagnostics...." forum). It may be able to scan the later years EBTCM and the air bag system.... can't remember.

 

OK. I did hear that was a stand alone system so ill try that. I was looking at one of those adapters that plugs into the car and runs Bluetooth for apps on a smartphone at advance auto and I believe for the premium app you're supposed to be able to check ABS systems as well. Any thoughts on those seeing as its 70 bucks for the setup? Or should I try to get an actual scanner for it? I've heard it doesn't take much to knock the ABS system out and I've read it could be simply a wheel speed sensor or, and I don't know how far this logic goes, a third brake light bulb. Seems a bit far fetched but doesn't matter anyway because mine all work.thanks again for the help. I'm more of an old school guy and these computer systems are a pain in the rear.