96 Suburban 7.4 Won't Start...help

[ykgoldstar]

The ol' burb (264,00km) refused to start a few days ago - it had been hard to start and rough idle a few days before - occasional backfire.

Checked fuel pressure, was 61psi but did not stay there - drop~10psi in 8 sec. Changed fuel filter (old), no change. Changed fuel pump (2-3 years old - hate that job!), pressure now 59psi, seemed to stay there at first, still won't start.

Checked #1 cylinder, had sparks. Tried to start with quickstart...no go...tried again with quickstart and a bit of gas in the throttle body...still won't start.

Pressure should not drop like that? Could it be the regulator...I assume the only check valve in the system is in the pump....no visible fuel leaks.

Or the fact that it won't start on quickstart mean ignition problem...timing chain? Just guessing here...

 

Any help would be greatly appreciated...6 kids...one vehicle...tough go...

 

Many thanks,

Dave

[GMTRUCKTECH]

The ol' burb (264,00km) refused to start a few days ago - it had been hard to start and rough idle a few days before - occasional backfire.

Checked fuel pressure, was 61psi but did not stay there - drop~10psi in 8 sec. Changed fuel filter (old), no change. Changed fuel pump (2-3 years old - hate that job!), pressure now 59psi, seemed to stay there at first, still won't start.

Checked #1 cylinder, had sparks. Tried to start with quickstart...no go...tried again with quickstart and a bit of gas in the throttle body...still won't start.

Pressure should not drop like that? Could it be the regulator...I assume the only check valve in the system is in the pump....no visible fuel leaks.

Or the fact that it won't start on quickstart mean ignition problem...timing chain? Just guessing here...

 

Any help would be greatly appreciated...6 kids...one vehicle...tough go...

 

Many thanks,

Dave

 

 

We gotta get those kids out the house bro! Well, you say you got fuel pressure close to 60psi so it should start even with the fuel pressure drop and the fact you are spraying it with quick start it should defenity start so it's safe to say it not a fuel feed issue. When you say you got spark is it a nice brite looking spark or looks dull aka weak. Double check that Dave. Lets say the spark is good so there is only a couple things left to check. Your will need a scan tool to check to see if the computer is getting a crank sensor signal which will show up as rpms on the scanner. The computer needs that signal to know what cyn to fire fuel. Pretty common problem on 96 5.7 motors for the crank sensor to go open. If you what to try throwing a crank sensor at it the sensor is located on the bottom front of the engine below the harmonic balancer and in front of the oil pan. Very easy to replace but please use factory parts Dave do yourself that favor.The next step in your diag is to do a compression test with having over 250 thousand miles this could be a issue. Hopefully this take care of it let me know and good luck.

[L29er]

i had a no start problem once with mine, turned out the fuse for the cluster was bad, apparentley doesn`t like to run without it, i guess have a good check with all your fuses too, if you can check em all with a test light, also one i had the connections at the ecm come loose, gave em a wiggle and she ran... just some ideas