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4.3L engine problems, please help!!!

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Old 08-12-2009, 12:48 PM   #1
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4.3L engine problems, please help!!!

Hello, i am new to this site but am in desperate need of help. I have a 1998 s10 with a 4.3L auto, 2wd and the truck is all prerunnered out, including a fuel cell and think that might be the problem. right now the truck runs terrible, it shakes, stalls and at start up and first 1/4 mile of driving puffs out black smoke. The codes that it reads are P0101, P0300 and P0452. Now i went to autozone and figured out what they are and came up with teh random misfire, mass or volume air flow circuit and evap control system pressure sensor low input.
What i think is the main issue is that the truck has a fuel cell and an aftermarket fuel pump,and i am not able to locate a fuel pressure sensor or regulator. and this is causing a lean misfire which is causing the computer to try and richen the fuel even though it is probably already recieving too much fuel.
All of the codes indicate that a possible problem could be the fuel pressure, and so i was wondering if that seems the logical choice and also how do i check the pressure and what should it be at. also if it is getting too much fuel, am i able to put on a OE pressure regulator with the aftermarket pump, also where would the pressure regulator and the fuel pressure sensor be located???
Any other input on how to resolve my issue and get the truck running so it would pass emissions test would be greatly appreciated and thanks in advanced.
Old 08-12-2009, 01:02 PM   #2
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Re: 4.3L engine problems, please help!!!

there is no fuel pressure "sensor" om these trucks.
the EVAP pressure sensor monitors fuel TANK pressure
for evaporative emissions diagnostics only.

you need to have your PCM re-flashed to remove
all EVAP codes, as well as any other codes you dont
want to see.

the FPR is located on the rear of the injector "module"
inside the upper plenum cover.

the fuel pressure should be around 55-58 psi at idle,
and around 63-66 psi at WOT.
the pressure test port is on the driver side rear of the engine,
just to the right and slightly ahead of the distributor.

Last edited by Crew Cab Sonoma; 08-12-2009 at 01:09 PM.
Old 08-12-2009, 01:15 PM   #3
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Re: 4.3L engine problems, please help!!!

also, the fuel tank EVAP pressure sensor is mounted
on top of the factory tank, on the sender/pump service port.
Old 08-12-2009, 01:32 PM   #4
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Re: 4.3L engine problems, please help!!!

okay thanks, but as far as the fuel tank EVAP pressure sensor i will have to see if it was relocated or something because the truck has a Fuel Safe fuel cell and so there is nothing factory connected to it..

WOuld high fuel pressure causes the truck to misfire along with the possibility that it might not have all the sensors?? because it runs very rich, like the plugs are all carboned and at start up it will billow black smoke. thanks for your help
Old 08-12-2009, 01:43 PM   #5
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Re: 4.3L engine problems, please help!!!

i also had mine throw the p0300 code from an autozone scanner. "random cylinder misfire" so i had it hooked up to a snapon scanner and that one told me i had ZERO misfire on ALL 6 cylinders.

here read up on my thread and post #21 tells you what fixed my problem.
http://www.s10forum.com/forum/f107/p...e-help-411169/
Old 08-12-2009, 02:48 PM   #6
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Re: 4.3L engine problems, please help!!!

Quote: Originally Posted by suzond
okay thanks, but as far as the fuel tank EVAP pressure sensor i will have to see if it was relocated or something because the truck has a Fuel Safe fuel cell and so there is nothing factory connected to it..

WOuld high fuel pressure causes the truck to misfire along with the possibility that it might not have all the sensors?? because it runs very rich, like the plugs are all carboned and at start up it will billow black smoke. thanks for your help
excessive fuel pressure could cause your problems.
if your fuel pump is capable of generating more volume than the FPR
or the rather smallish return tube running through the middle of the
injector module can handle. it would have to be a pretty high volume
pump though, probably greater than 255LPH.

i'm not sure that the EVAP pressure sensor has any real impact on how
the truck runs. i've had mine unplugged in the driveway before, and the
truck idled just fine. like i said, its just there to meet OBD2 requirements
to test the evaporative system for leaks.
Old 08-12-2009, 02:51 PM   #7
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Re: 4.3L engine problems, please help!!!

Quote: Originally Posted by hitnswitches
i also had mine throw the p0300 code from an autozone scanner. "random cylinder misfire" so i had it hooked up to a snapon scanner and that one told me i had ZERO misfire on ALL 6 cylinders.

here read up on my thread and post #21 tells you what fixed my problem.
http://www.s10forum.com/forum/f107/p...e-help-411169/
if his truck is blowing black smoke out the exhaust and sooting the plugs,
its almost a certainty that he actually is having some misfire issues...
Old 08-12-2009, 04:38 PM   #8
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Re: 4.3L engine problems, please help!!!

So i finally was able to get gauge to see what the fuel pressure was, and at idle the truck had from 70-80lbs of pressure, so i am pretty sure that this might be the problem. i now just have to find a fuel regulator that will help me get it down to normal operating pressure. and hopefully if i do that i will be able to fix my misfire
Old 08-12-2009, 04:51 PM   #9
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Re: 4.3L engine problems, please help!!!

thats definetly too much...
what kind of pump are you running?

is it possible you have a blocked or kinked/crushed return line
anywhere?

Last edited by Crew Cab Sonoma; 08-12-2009 at 04:53 PM.
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