I have a 93 Sierra 1500 with the 5.7L V8 and it runs and idles find in neutral or park and when it is cold. When in gear under any load on the engine and once it gets barely warmed up the engine will start to sputter and backfire intermittently. The RPM's jump up and down by a couple hundred as you accelerate and then sometimes the engine drops out completely and even back fires before immediately regaining power. Sometimes it just seems as if it is starving for fuel.
But as soon as you put it in Nuetral the engine revs just fine!
I have no clue where to start. I can replace parts but diagnostics are not my thing.Please HELP!
93 GMC Sierra 5.7L - Sputter and backfiring under load
Re: 93 GMC Sierra 5.7L - Sputter and backfiring under load
you should scan the engine and see what the fuel is doing and look at your coolant temp sensor too. With a scanner on the truck and watching your data stream you can see if you're running lean or rich. Or if the fuel system looks good and maybe it's an ignition problem.
Browse "SIMILAR TOPICS" At The Bottom Of This Page.
-
- Posts: 2
- Joined: Tue Jun 16, 2015 6:04 am
GMC new fuel pump still wont crank
I have a 1998 GMC Z71 the truck was running good. Got to the lake and killed it and it never cranked again. Fuel pump would not run so I replaced fuel pump brand new. Put it in and the pump came on now I have plenty of fuel to the pressure release valve and still won't crank. I replaced throttle position Sensor the MAP Sensor and it still won't crank. Truck is getting fire and it will run if I pour gas in it at the throttle body and will stay running till it runs dry. Anyone have any idea what is wrong.
Re: Z71 GMC new fuel pump still wont crank
ok, cranks means turns over. cranking, turnover, is when the starter engages the engine and rotates the crankshaft. What you have is: the engine cranks but doesn't start.
if the engine runs with adding fuel manually then you only have to look at fuel pressure and injector pulse. fuel pressure should be 60-66 psi. a new fuel pump should give you that if everything else is good. Now, what about your injector pulse? That's the computer sending the signal for the injector to open and let fuel into the engine. to check the injector pulse is a little tough since your injector are not easy to get at. you will have to check the wiring that goes to the injectors. All the injectors have a battery voltage power wire that is pink. That battery voltage comes from the ECM1 fuse (20A) in the underhood fuse box. If you have battery voltage from the pink wire then that's good. T fire the injectors the computer grounds the circuit.
Injector1 black
Injector2 light green/black
Injector3 pink/black
Injector4 light blue/black
Injector5 black/white
Injector6 yellow/black
Injector7 red/black
Injector8 dark blue/black
you need to know how to check for the computer ground signal. A logic probe or an LED test light, some kind of lighting device that will use less current that the injector, in series with the injector being tested.
No injector pulse but the battery power side stays up at battery voltage, you may have a passlock problem where the antitheft turns off the injectors. What is your security light doing? Would have to scan the passlock for codes and/or look at the resistance/voltage coming back from the key.
No injector pulse but the battery voltage side goes down below battery voltage by a few volts or more, you could have a shorted injector that will rob the power from all the other injectors.
if the engine runs with adding fuel manually then you only have to look at fuel pressure and injector pulse. fuel pressure should be 60-66 psi. a new fuel pump should give you that if everything else is good. Now, what about your injector pulse? That's the computer sending the signal for the injector to open and let fuel into the engine. to check the injector pulse is a little tough since your injector are not easy to get at. you will have to check the wiring that goes to the injectors. All the injectors have a battery voltage power wire that is pink. That battery voltage comes from the ECM1 fuse (20A) in the underhood fuse box. If you have battery voltage from the pink wire then that's good. T fire the injectors the computer grounds the circuit.
Injector1 black
Injector2 light green/black
Injector3 pink/black
Injector4 light blue/black
Injector5 black/white
Injector6 yellow/black
Injector7 red/black
Injector8 dark blue/black
you need to know how to check for the computer ground signal. A logic probe or an LED test light, some kind of lighting device that will use less current that the injector, in series with the injector being tested.
No injector pulse but the battery power side stays up at battery voltage, you may have a passlock problem where the antitheft turns off the injectors. What is your security light doing? Would have to scan the passlock for codes and/or look at the resistance/voltage coming back from the key.
No injector pulse but the battery voltage side goes down below battery voltage by a few volts or more, you could have a shorted injector that will rob the power from all the other injectors.
Browse "SIMILAR TOPICS" At The Bottom Of This Page.
-
- Posts: 2
- Joined: Tue Jun 16, 2015 6:04 am
Re: Z71 GMC new fuel pump still wont crank
Ok will try that. Boy that sounds like a job and the security light goes off after about 3 seconds and truck has no codes at all.
-
- Similar Topics
- Replies
- Views
- Last post
-
- 1 Replies
- 5485 Views
-
Last post by carriedi
Tue Mar 17, 2015 10:26 am
-
- 5 Replies
- 11175 Views
-
Last post by carriedi
Sat Apr 18, 2015 10:56 pm
-
-
New post GMC 2001 Sierra does not always start!
by rkcrump » Wed Oct 19, 2016 8:37 pm » in GMC Trucks - 1 Replies
- 4718 Views
-
Last post by carriedi
Wed Oct 19, 2016 10:54 pm
-
-
- 1 Replies
- 6003 Views
-
Last post by carriedi
Mon Oct 30, 2017 11:26 pm