cranks, has fuel, spark, compression, timing but won't start
11-28-2012, 03:02 AM
#1
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cranks, has fuel, spark, compression, timing but won't start Some history. My 97 Z28 (all stock) was running OK, but with a bit of a miss. If I drove it everyday it would fire right up, however if I let it stand for more than 24hours it would behave like it was flooded and not start. The only way I could get it started was by removing the fuel injector fuse, then replacing it. This would take several attempts but eventually worked out and after blowing some smoke out the tail pipe, things would clear up and the car would go back to running and starting right up. Finally, one morning after dropping my daughter at school I went to start the car, it cranked, then stumbled and didn't fire up. On subsequent attempts it continued to act like it was flooded, but I was not able to get it started.
Changed out the spark plugs and wires, tried 2 different optisparks, replaced crank sensor and tried a new pcm. Checked connections and grounds. Compression test was OK (between 120 and 140). Timing is OK. Has fuel. Has Spark. Cranks but does not fire up and run. When we attempt to crank the car we had the battery jumped to another vehicle to make sure that it had enough juice. The mechanics that have checked it out say they are stumped. What are we missing??
Here is a list of some specific items that have been checked;
Fuel pressure is correct per spec at 45+ PSI.
fuel bleed down was checked and the pressure held beyond what the spec is..
injectors have been pulled and checked for leaks and are OK.
Spark has been checked with a spark checker, and pulled plugs and have watched them spark while cranking. The fuel injector pulse appears to be in time with the spark.
.
Originally, when the car was still running, the codes on the computer were PO300 (random missfire) and PO441 (Evap emission control incorrect purge flow).
Changed out the spark plugs and wires, tried 2 different optisparks, replaced crank sensor and tried a new pcm. Checked connections and grounds. Compression test was OK (between 120 and 140). Timing is OK. Has fuel. Has Spark. Cranks but does not fire up and run. When we attempt to crank the car we had the battery jumped to another vehicle to make sure that it had enough juice. The mechanics that have checked it out say they are stumped. What are we missing??
Here is a list of some specific items that have been checked;
Fuel pressure is correct per spec at 45+ PSI.
fuel bleed down was checked and the pressure held beyond what the spec is..
injectors have been pulled and checked for leaks and are OK.
Spark has been checked with a spark checker, and pulled plugs and have watched them spark while cranking. The fuel injector pulse appears to be in time with the spark.
.
Originally, when the car was still running, the codes on the computer were PO300 (random missfire) and PO441 (Evap emission control incorrect purge flow).
11-28-2012, 04:00 PM
#2
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Driving it with a misfire most likely melted one of the cats(or both) causing it to clog solid. Have the tech unbolt the exhaust at the manifold and try to start it.
11-28-2012, 04:18 PM
#3
It start a "flooded" LT1 you hold the throttle to the floor, it doesn't inject fuel then and will clear out.
If the "mechanics" that looked at it came up with 120-140 PSI on all cylinders then they are just incompetent and can't even do a compression test right, that or they are incompetent because they proved the motor is junk and failed to realize it.
Most likely they did not hold the throttle open during the test. A proper compression reading on an LT1 is easily 190+psi. Even the iron head LT1s with lower static compression crank 185psi or so well after 150K miles.
The long cranking after it sat for a long time really suggests something fuel related, dripping injector or something.
The fact the "mechanics" came up with 120-140psi and thought that was OK says they are incompetent and I would not trust any other diagnosis they did.
If the "mechanics" that looked at it came up with 120-140 PSI on all cylinders then they are just incompetent and can't even do a compression test right, that or they are incompetent because they proved the motor is junk and failed to realize it.
Most likely they did not hold the throttle open during the test. A proper compression reading on an LT1 is easily 190+psi. Even the iron head LT1s with lower static compression crank 185psi or so well after 150K miles.
The long cranking after it sat for a long time really suggests something fuel related, dripping injector or something.
The fact the "mechanics" came up with 120-140psi and thought that was OK says they are incompetent and I would not trust any other diagnosis they did.
04-01-2016, 08:30 AM
#7
I know this is an old thread but I'm havin the same problems I have changed all sensors and not gettin any codes .. Gettin good fuel pressure and hot spark and it's in time but it will not start any help ???
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04-26-2017, 06:30 AM
#9
I have no real answer, but if it were me and I had to replace the injector fuse to get it started, I would suspect the fuse has an open short and would check the ground, then the hot side.
