Mechanics

PO171 AND PO174 FOR 4.3L HELP

1998 GMC Jimmy • 6 cylinder Automatic • 125,708 miles

I have did the following changes.

-Fuel filter=changed
-Fuel pressure regulator=changed
-Fuel pump=changed
-Mass air flow sensor=changed
-Air filter=changed
-o2 sensor on bank 2 sensor 1=changed
-Took off all six spark plugs inspected and cleaned them with carburetor cleaner
-inspected for lose hoses and wholes and leaks.
-Fuel injection service cleaning at Walmart

I took it too mechanic and they told me I needed now mass air flow sensor and fuel injection cleaning. After doing there recommendations I still get check engine light with PO171 and PO174. I hear a backfiring sound coming from engine compartment area intermittently on start once I step on gas then it takes off fast.
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Roycar71
September 4, 2012.




Have you actually look for a vacuum leak with some carbs spray?


Saturntech9
Sep 4, 2012.
What is correct way to do this?


Tiny
Roycar71
Sep 4, 2012.
Take some carb spray at idle spray around the vaccuum lines intake and all vacuum sources. If the rpms go up down stumbles or dies you found a leak. Do you have a scan tool that will read live engine data?If you do you can use that to find a smaller leak that wont effect engine rpms while spraying carb spray.


Saturntech9
Sep 4, 2012.
This should be done on a warm engine right?


Tiny
Roycar71
Sep 4, 2012.
The codes set when the engine is warm?If so then when. Warm
AD


Saturntech9
Sep 4, 2012.
I tried carb spray did not find change in engine idle. There where 2 bolts prior that would not get tight after change of fuel pressure regulator that is in intake manifold. I did spray in those areas and did not find change in engine idle. Should I take those bolts out and re tap wholes or die bolts?


Tiny
Roycar71
Sep 7, 2012.
Yes you should do you a plastic manifold on that?


Saturntech9
Sep 7, 2012.
The upper part of intake is plastic and bottom part seems to be steel or some type of metal. The bottom is part the bolts get screwed into. Doing this, I may be able to avoid removing whole upper part of manifold. Do you think so?


Tiny
Roycar71
Sep 7, 2012.
When you took it apart did you striaght edge the manifiold to make sure it wasn't warped?Its common for those to warp also did you replace the gaskets what did you torque the manifold too?Also did you make sure the injector nozzles weren't clogged its common for them to clog.


Saturntech9
Sep 7, 2012.
Based on what I saw the everything appeared to right where is needed to be. I tightened bolts as hard as I could. 2 of them only got so tight that they kept on turning. I left them alone thinking that would be good enough. I did change gaskets on throttle body, spider meter unit and upper intake manifold. I did remove spider injector unit but did not check for clogged injector. It runs like a charm other than initial start-up, then take off fast.


Tiny
Roycar71
Sep 7, 2012.

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