96 Camaro Z28 intermittent crank no start issue - CamaroZ28.Com Message Board


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Old 06-13-2018, 07:13 PM   #1  
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96 Camaro Z28 intermittent crank no start issue

So I've been having an intermittent problem with my 96 Camaro z28 with the manual trans. Sometimes (seemingly randomly) when I turn the key to the on position I don't hear the fuel pump prime, and when I try to start the car it'll crank but not start. If it won't start and I let it sit a few hours and come back I'll hear the pump prime and it'll start fine. First thing I did was replace the fuel pump relay because I thought it might've been going bad.

Was fine for a few times and I thought I fixed the problem, obviously not the case because Monday afternoon I got stuck in my school parking lot with it not starting when I was trying to go home. Left the car there and came back a few hours later, still no start. Came back that night and got it to start so drove it home.

While it wasn't starting, I jumped 12v from the battery to the fuel pump test connector to see if the pump was maybe intermittent. I heard the pump whine like it usually does when it primes. Even had a friend hold the 12v to the test connector while I turned over the car, but it still didn't start.

I'm at a loss for what to check next. I feel like I've ruled out fuel. I'm wondering if it's possibly a failing ignition switch, or maybe something with the VATS. I'm under the impression that if it was the ignition switch I wouldn't get any lights on the dash or cranking. I'm wondering if maybe the VATS is acting up. I've been trying to get the car to not start so I can watch for the security light and mess around with the ignition barrel and the resistor contacts on the key to see if that does anything. Of course when I'm trying to mess around with it the car starts every time.

Idk if it's worth saying but the ignition key is slightly bent and I don't have a spare. Just speculation, but maybe the bent key is sometimes preventing proper contact between the resistor and the contacts in the barrel? I tested the resistance on the key with a multimeter and compared it to a chart of the 15 different keys there are for these cars and my measurement is about 3 ohms off from the closest value. I assume that's within the tolerances, just figured I'd mention everything I know.

If anyone has had this problem or has any suggestions for where to look next I'd be happy to hear it.
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Old 06-13-2018, 11:01 PM   #2  
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Re: 96 Camaro Z28 intermittent crank no start issue

The dash warning lights should come on briefly when the key is turned to "run”. The pump should also prime when the key is turned to “run”. It's possible for the contacts in the ignition switch with the key in that position to be OK, but the contacts for the key in “start” position to be intermittent. Seems to be more of this happening with the advanced age of these cars. Heat is melting the switch and contacts. Then there is the issue of the rod that connects the lock cylinder to the switch getting out of adjustment.

Shoebox has a procedure for replacing the ignition switch, and the first paragraph describes the symptoms of switch problems.

4th Gen F-body Ignition Switch Replacement

Here's the starter wiring diagram for your 96:

http://shbox.com/1/starter_charging_96.jpg

At any point have you scanned the PCM for codes? A loss of the low resolution pulse signal from the optical cam position sensor in the Optispark distributor causes the PCM to shut the fuel system down. That sets a code, but this particular code does not turn on the SES light. When the starter is cranking the engine, but the engine is not starting, does the tach needle move upwards to 200-400 RPM? That will help identify a possible Opti problem if the tach doesn’t move.


This will describe the operation and failure modes of PASS-Key (VATS), so you know what to look for:

Courtesy of Shoebox

4th Gen LT1 F-Body Tech-PassKey/VATS

There's a link to a table in there that shows the tolerances on the various key pellet resistor values.
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Old 06-14-2018, 09:21 AM   #3  
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Re: 96 Camaro Z28 intermittent crank no start issue

Thanks for the info! I have not scanned the PCM for codes at all, I don't have a scanner but I can probably borrow one or just invest in one to have. I honestly don't know what the security light and tach do when cranking and not starting because I never took note of them while I was having the problem. I've been trying to recreate the problem but the car has been starting so I'm at a bit of a standstill right now until it doesn't start again. If/When I scan it, would that have to be at a time the car isn't starting to get any info about it, or could I scan it even if the problem isn't occurring at the time?
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Old 06-14-2018, 10:27 AM   #4  
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Re: 96 Camaro Z28 intermittent crank no start issue

Once codes are set in the PCM, they are stored until:

- you remove power from the PCM by disconnecting the battery.

or....

- you pull the “PCM BAT” fuse

or....

- the vehicle is driven multiple drive cycles without the problem recurring.

Look over the article on PASS-Key system, that will tell you what to be looking for with regard to the “SECURITY” when you do have a problem.

From your detailed description, I am assuming that 1) the engine has never just shut off while driving; 2) the starter always engages and cranks the engine.... it just doesn’t fire up. That would tend to minimize possible issues with the ignition switch.
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Old 06-14-2018, 11:20 AM   #5  
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Re: 96 Camaro Z28 intermittent crank no start issue

You're correct in that the engine has never shut off once it's started and the starter always engages and cranks the engine. I feel like if it was a problem with the VATS the starter wouldn't engage, and if it was a problem with the fuel pump I wouldn't have been able to run it from the test connector while it wouldn't start. Also since it didn't even start when I had the pump running off the test connector while cranking I would assume that means it was missing spark. I was told it's possible it's a failing BCM, but I'll be honest even after doing some research I don't entirely understand what the BCM is responsible for. Next time I get the problem I'll be sure to take note of the security light and the tach. And from what I understand 96+ cars are all regular OBDII, so it should be easy enough to find a scanner.
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Old 06-14-2018, 03:22 PM   #6  
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Re: 96 Camaro Z28 intermittent crank no start issue

The PASS-Key system starts at the key. The resistance is seen by the BCM. If it's correct, the BCM sends two separate things - 1) it sends a ground to the TDR (theft deterrent relay = basically the starter relay) that allows the starter to crank; and 2) it sends the 50 Hz signal to the PCM that allows the PCM to activate the injectors. You really need to look over the "Shoebox" description and troubleshooting of the system. It explains it all VERY clearly.

The next best resource is the factory service manual. Free download of the 1996 manual here:

http://www.mediafire.com/?40mfgeoe4ctti

The BCM is covered in Book 1, Part 2 of 2, Section 8D. The theft deterrent system is covered in the same volume, Section 9D.

The description of the "fuel enable signal", and what the PCM does with it is somewhat vague. It says "The PCM reads the fuel enable circuit to determine if fuel injection should be allowed. If the fuel enable signal is not present, the PCM will not allow fuel injection." Notice it does not specifically say it disables the fuel injectors. "Fuel injection" could be achieved by not running the pump, not pulsing the injectors, or both.

Note that the PASS-Key system is standard equipment. There is also an optional alarm system that is controlled by the BCM, and that would show up as RPO code UA6 on the Service Parts label. That system also disables the starter and the fuel system when the alarm is activated (sounding).

The BCM has diagnostic codes that can be pulled with the correct scanner, but they seem to have limited value.

Shoebox has the wiring diagram:

http://shbox.com/1/bcm_1996.jpg

Sounds unlikely that it is your fuel pump. Always a possibility of intermittent contacts at the harness connector in front of the rear axle.

If it doesn't start while cranking, AND you have the fuel pump operating, it is still possible the PCM has deactivated the injectors because of - 1) no fuel enable signalfrom the BCM; 2) no low res pulse signal from the Opti.

Next time it cranks and doesn't start, check for spark at the coil wire, and at a couple cylinders.

P1371 sets for loss of the low res signal. It only interrupts fuel, not spark.


P1626 sets if the PCM is not receiving the fuel enable signal from the BCM.
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Old 06-14-2018, 10:21 PM   #7  
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Re: 96 Camaro Z28 intermittent crank no start issue

Wow thank you that's all really good information. I'll read over that page on Shoebox's site again so I know what to look for in addition to spark at the coil wire and the cylinders next time it happens. Might see about picking up a code reader too.
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