Rough Running Chevrolet Truck

magicman_s

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MAKE:Chevrolet
MODEL:Truck
YEAR:1197
MILES:220,000
ENGINE:5.7
DESCRIBE ISSUE....Runs rough at start up even sometimes shutting off, also will bog down when you give it more gas but will slowly gain rpm but the power is not there. It is firing at all cylinders and the timing is at top dead center when checking the number 1 cylinder. Fuel pressure is at 55 psi while idling and will build up to 62 psi when you give it the gas. I'd appreciate some pointers and thanks in advance.
 

kev2

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this is a 1997 - yes?

anyway that fuel pressure seams low I will get exact specs.
Scan for codes yes even if light is off. I expect some lean codes lets see.
 

billr

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Spark timing is TDC? How are you testing that, spark should rarely be TDC; maybe when cranking, and when in decel.
 

kev2

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I have NOT checked the Spec for fuel pressure yet BUT I still think its LOW. Maybe someone has it available.

The code p0101 - do you have a scanner* that shows live data? MAFs report in hertz, and display GM/S.
A good suggestion would be to clean MAF, there is a spray for this, do NOT use an oiled air filter, check for vacuum leaks after MAF.

Those P0420 and P0430 indicate a CAT issue, might want to do an exhaust back pressure test, use a back pressure tester OR attach a vacuum gauge engine @1500rpm observe if vac holds steady OR drops.

* will your scanner show ALL codes? esp those above p0999 -? p1345 maybe?
 
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nickb2

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I am seeing 60-66psi for central SFI and 56-62psi for SFI(8 injectors) with ignition on and should hold.

You may have good pressure, but no flow. Is the fuel filter relatively new?

What does the inside of the dist cap look like? Any corrosion in there. They go through caps like crazy on these trucks.

The only adjustment possible on these engines is cam retard adjustment in case of crossfiring.
 

kev2

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Just got this (60-66 psi) for the CSFI.
And you are below the low end - I see a pump in your weekend plans....
suggest a AC Delco pump aftermarket is not up there in quality.
 

nickb2

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If he is getting 55 to 62 psi. He falls within specs for a SFI. Low of 5 psi if he has central SFI.

System is low efficiency on both banks. Hence the 420 and 430. Always diagnose other codes first before trying to attack the 420 and 430 codes. You have a maf code p0101, probably causing a random misfire p0300. But would be good to check the integrity of the secondary spark system anyway while cleaning that MAF sensor. As I said before, these caps love corrosion. The rotors too.

LOL, now I get to say that. This truck has one. Not a 1.9l saturn. :D
 

kev2

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spider - CSFI with MAF sensor or CPI no MAF sensor
 

nickb2

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I don't see a MAF fault causing a low FP pressure. I would attack the MAF code first, then move on to the 5psi below spec afterwards. Indeed, it does smell of FPump time. But that MAF code is not going away until it is addressed.

The misfires and low efficiency codes can go either way in getting those two low efficiency codes.

Visually inspect for any obstructions or cracks in air inlet duct. Vacuum leak at intake, throttle body if equipped, and at EGR. Check also for proper PCV installation or cracked hose. Are you getting 5v at MAF connector signal circuit to chassis ground, key on? If yes, check MAF ignition feed and MAF connector ground, if less than 4.5v we now have a problem with circuit.
 

magicman_s

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Kev, My scanner is a Actron OBD Pocket Scan Code reader and P0998 is as high as it will read.
 

nickb2

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Most trucks have Central sfi. It will look like this. Injectors will not be visible. SFI, the injectors will be visible.

Here is a picture of CSFI.

s-l1000.jpg
 
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