Lean fuel situation

KENZIE HAYNIE

MEMBER
1994 GMC SUBURBAN
7.4L
V8
4WD
AUTOMATIC
214,000 MILES

If you step on the gas pedal more than an eighth of the way the engine bogs and will not recover unless you let your foot off the gas back to the about the eighth of a pedal. It does not do it when it is cold when you first start it. But as soon as it warms up for maybe five minutes of driving it does it constantly if you press the gas pedal in to much. I have changed all sensors except for IAC and TPS have a Bluetooth aldl monitor the only thing strange that I see is the O2 sensor jumping from anywhere 200 to 800 constantly everything else seems to be reading fine. When you watch the spray from the two injectors the driver side injector seems to get a smaller spray pattern then the passenger side I am rebuilding the throttle body over the next couple days any help would be greatly appreciated. Thank you.

Sunday, September 18th, 2016 AT 9:11 PM

1 Reply

CARADIODOC

MECHANIC
34,330 POSTS

There is one glaring problem here. If you are watching the injector spray, you must have the fresh air tube removed. Chrysler is the only brand you can do that with. All other manufacturers use a mass air flow sensor as their main fuel metering calculation. You can not have a loose hose clamp, tiny crack, or any other leak including a vacuum leak, and definitely not a removed hose. When any air sneaks into the engine that does not go through the mass air flow sensor, the computer wont know about it and wont command the correct amount of fuel to go with it. Most GM engines wont even start or run with the fresh air tube disconnected.

Once you get the tube reconnected and with no leaks, if the problem is still there, the next common suspect is low fuel pressure. Many engines will run fine with real low fuel pressure, but there are some GM engines that wont even start if the pressure is five pounds low. Most of the time low pressure is caused by a worn fuel pump that is still working. I rarely read of people solving this problem with a new filter.

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Sunday, September 18th, 2016 AT 9:26 PM