03 Envoy cranks but will not start

[fastlane1801]

Hi Y'all,

I have a 4.2 L6 in this truck. It was running fine until one day it would not start anymore. I've checked the fuel pump and pressure is within tolerance (52psi). it does not lose pressure either after sitting for a couple of minutes. When I crank it, it delivers over 60psi on the pump and I also checked the fuel regulator...all good. I got a good spark...but does not even come close to firing up. The only way it will start is with a steady stream of starting fluid through the throttle body. there is no MIL light illuminated. Any thoughts? I'm stumped..

 

[6716]

Hi Y'all,

I have a 4.2 L6 in this truck. It was running fine until one day it would not start anymore. I've checked the fuel pump and pressure is within tolerance (52psi). it does not lose pressure either after sitting for a couple of minutes. When I crank it, it delivers over 60psi on the pump and I also checked the fuel regulator...all good. I got a good spark...but does not even come close to firing up. The only way it will start is with a steady stream of starting fluid through the throttle body. there is no MIL light illuminated. Any thoughts? I'm stumped..

I had a cranking no start a month ago. Throttle body cleaning did the trick.

 

[djthumper]

Is this pressure reading on the fuel rail? You meantioned 60 at the pump but not where you got the 52 at. Did you happen to take the throttle body off before this happened and cleaned it? If not that could be a good starting point along with resetting the PCM by disconnecting the battery while you are cleaning the TB.

Welcome to GMTNation. Please complete your vehicle profile for reference in other threads.

 

[fastlane1801]

I did all the pressure tests at the port by the fuel filter which is underneath the car by the driver door. I'll check pressure at the fuel rail. I'm curious tho...if the throttle body was dirty and I opened up the throttle to let air in while I was cranking it, wouldn't at least try to start?

 

[djthumper]

I did all the pressure tests at the port by the fuel filter which is underneath the car by the driver door. I'll check pressure at the fuel rail. I'm curious tho...if the throttle body was dirty and I opened up the throttle to let air in while I was cranking it, wouldn't at least try to start?

You would think it would, which is why I asked if you had done something prior in the area. Maybe the throttle body is clogged.

 

[fastlane1801]

Nope, done nothing to the throttle. I will clean the throttle and see what happens. But I don't smell any gas going through when I crank it for a long time. It's weird.

 

[gmcman]

Did you perform any work under the hood in the last month? If so please specify.

Did anybody accidently put diesel in the tank? Very easy now since the nozzles are the same size at most stations.

 

[IllogicTC]

1. Dirty throttle body. Cleaning is essentially free if you already have throttle body cleaner laying around so it's worth doing either way.
2. Clogged injectors. Have you confirmed you're getting good spray? I see you have a fuel pressure regulator, which means you're out of range on a TSB regarding excess sediment in the fuel rail but it's still worth looking into, and checking fuel pressure at the rail.

Also keep in mind that a "full-throttle start" doesn't work in these trucks. If it detects you're holding the accelerator to the floor, it disables fuel and cranks the engine to help clear flooding.

 

[Texan]

I did all the pressure tests at the port by the fuel filter which is underneath the car by the driver door. I'll check pressure at the fuel rail. I'm curious tho...if the throttle body was dirty and I opened up the throttle to let air in while I was cranking it, wouldn't at least try to start?

If you have good fuel pressure at the rail, it would make me wonder about a possible blown fuse.

 

[The_Roadie]

I'm curious tho...if the throttle body was dirty and I opened up the throttle to let air in while I was cranking it, wouldn't at least try to start?

If you physically pushed on the throttle body disk (not the accel pedal) while ignition power was on, you could have burned out the stepper motor that moves the disk. All stepper-motor throttles with dive-by-wire systems have this warning in the shop manuals. It's not like the butterfly valves in old carbs.

 

[fastlane1801]

Hi Y'all,

I have a 4.2 L6 in this truck. It was running fine until one day it would not start anymore. I've checked the fuel pump and pressure is within tolerance (52psi). it does not lose pressure either after sitting for a couple of minutes. When I crank it, it delivers over 60psi on the pump and I also checked the fuel regulator...all good. I got a good spark...but does not even come close to firing up. The only way it will start is with a steady stream of starting fluid through the throttle body. there is no MIL light illuminated. Any thoughts? I'm stumped..

Don't know if this has EVER happened to anyone...first time for me. I checked the fuse for the injectors...it was good and I had good power coming off of it. I decided to start cleaning the throttle body and check with a noid light if the injectors were getting a signal. As I removed the intake manifold, there was chunks of dirt on the fuel rail by injector 4 and 5 (didn't think nothing of it). Connecting all the sensors back...I checked a couple of injector harnesses with a noid light and no signal. I decided to check if I had power to one of the injector harnesses and no power either! And that's when I saw it...a rodent had made a home behind the motor and chewed right through the power line for the fuel injector harness. Those chunks of dirt was actually dog food! Took the harness off...fixed the wiring and voilà! started right up! It's funny because all the time I was taking the car apart...I was thinking to myself how it smelled like something died in there...Who woulda thunk it!

Thanks for the help!

 

[IllogicTC]

Don't know if this has EVER happened to anyone...first time for me. I checked the fuse for the injectors...it was good and I had good power coming off of it. I decided to start cleaning the throttle body and check with a noid light if the injectors were getting a signal. As I removed the intake manifold, there was chunks of dirt on the fuel rail by injector 4 and 5 (didn't think nothing of it). Connecting all the sensors back...I checked a couple of injector harnesses with a noid light and no signal. I decided to check if I had power to one of the injector harnesses and no power either! And that's when I saw it...a rodent had made a home behind the motor and chewed right through the power line for the fuel injector harness. Those chunks of dirt was actually dog food! Took the harness off...fixed the wiring and voilà! started right up! It's funny because all the time I was taking the car apart...I was thinking to myself how it smelled like something died in there...Who woulda thunk it!

Thanks for the help!

Thanks for the follow-up. May want to once-over the rest of the engine bay for other possible damage, too. I've seen plenty of photos where air filter boxes either become storehouses for nuts and dog food (why is it always dog food?), or sometimes rats shred up the air filter.