Got spark and fuel but won't start
10-19-2018, 06:38 PM
#1
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Got spark and fuel but won't start
I have a 93 z28 lt1 .I replaced the fuel pump. I have plenty of pressure to the rail but it won't start. Starting fluid works but it won't stay running. I have power to the injectors also .The options spark is a brand new MSD and I have good spark. I can't figure out why it won't run.
10-19-2018, 09:41 PM
#2
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Re: Got spark and fuel but won't start
What is the fuel pressure in PSI when the pump primes?
Is the “SECURITY” light on? If there is a problem with the resistor on the key, or other components in the PASS-Key (VATS) system, the fuel pump primes when you turn the key to “run”, but the ECM won't turn it back on until it gets a signal from VATS. The part that sends the signal to the ECM can fail. Since the starter cranks, it would indicate the key circuit is OK. See description of system:
Courtesy of Shoebox:
4th Gen LT1 F-Body Tech-PassKey/VATS
Second possible problem, but wouldn’t have spark.... the fuel pump primes, but the ECM will not fire the injectors unless it sees the cam position signal from the Opti. Expensive as it is, the MSD unit is not very reliable, even when brand new. But you wouldn’t have spark without the cam position signal.
4th Gen LT1 F-body Tech Articles
Is the “SECURITY” light on? If there is a problem with the resistor on the key, or other components in the PASS-Key (VATS) system, the fuel pump primes when you turn the key to “run”, but the ECM won't turn it back on until it gets a signal from VATS. The part that sends the signal to the ECM can fail. Since the starter cranks, it would indicate the key circuit is OK. See description of system:
Courtesy of Shoebox:
4th Gen LT1 F-Body Tech-PassKey/VATS
Second possible problem, but wouldn’t have spark.... the fuel pump primes, but the ECM will not fire the injectors unless it sees the cam position signal from the Opti. Expensive as it is, the MSD unit is not very reliable, even when brand new. But you wouldn’t have spark without the cam position signal.
4th Gen LT1 F-body Tech Articles
10-20-2018, 05:23 AM
#3
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Re: Got spark and fuel but won't start
40 psi at prime and I have good spark and power to the injectors . The engine will start for a second if you spray gas in the throttle body. It basically acts like its not getting fuel to the cylinders. I haven't tried replacing the crank sensor. That's gonna be my next guess but guessing is getting expensive
10-20-2018, 06:46 AM
#4
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Re: Got spark and fuel but won't start
There is no “crank” sensor. The ECM uses only the two cam position pulse signals (high and low resolution) that it gets from an optical module in the Optispark distributor. Crank sensor was added to the LT1 in 1996 for OBD-2 misfire detection. It has nothing to do with whether the engine runs.
The injectors always have power when the ignition is on. The ECM supplies a ground to fire the injectors. Scan the ECM for codes.
http://shbox.com/1/dlc2.jpg
You didn’t answer the question about the “SECURITY” light.
The injectors always have power when the ignition is on. The ECM supplies a ground to fire the injectors. Scan the ECM for codes.
http://shbox.com/1/dlc2.jpg
You didn’t answer the question about the “SECURITY” light.
10-20-2018, 08:58 PM
#5
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Re: Got spark and fuel but won't start
Security light is not on. I'm in the process of getting a code reader for odb1 . When I start it by spraying gas in the intake it runs great for a few seconds. Would it still be the opti msd causing the problem
10-20-2018, 11:07 PM
#6
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Re: Got spark and fuel but won't start
As I mentioned in the first response, if you have confirmed strong spark at all plugs, it's not the Opti.
You can scan a 93 for codes without a “code reader”. You just need a paper clip. Read the link I posted.
You can scan a 93 for codes without a “code reader”. You just need a paper clip. Read the link I posted.
10-21-2018, 02:29 AM
#7
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Re: Got spark and fuel but won't start
The paper clip trick doesn't and won't work on my 93 z28 .I did some research were I found out that for some reason the paperclip don't work .You have to have a reader. I tried the paperclip and my results were the same as many others online. You don't receive codes and cooling fans start running. I'm not sure why but from what I understand the paperclip trick won't work specifically on the 93 z28
10-21-2018, 08:47 AM
#8
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Re: Got spark and fuel but won't start
In the 20 years I have been helping thousands of people on this site, this is the first time I've heard of a 93 not responding to the paper clip. The factory service manual even outlines the procedure. Is your SES light working?
10-22-2018, 09:38 AM
#11
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Re: Got spark and fuel but won't start
SECURITY light should have been on.
DTC 46 can also be due to other components in the VATS system, including loss off the 30 Hz fuel enable signal the Theft Deterrent Module (TDM)sends to the ECM. If the resistor doesn’t solve the problem,read Shoebox's VATS operation and troubleshooting guide, linked in post #2, above.
What code reader did you use - possibly the Actron CP9001?
DTC 46 can also be due to other components in the VATS system, including loss off the 30 Hz fuel enable signal the Theft Deterrent Module (TDM)sends to the ECM. If the resistor doesn’t solve the problem,read Shoebox's VATS operation and troubleshooting guide, linked in post #2, above.
What code reader did you use - possibly the Actron CP9001?
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