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.



You should have checked the intake manifold for being warped also the intake gets torqued to spec and has a torque pattern. You also have two bolts that wont tighten so from your codes and what you have told me. You have to check the intake manifold for being warped fix those two holes and torque to spec in the correct torque patteren.


Saturntech9
Sep 8, 2012.
I got upper intake manifold Tightened. Funny thing is I brought a torque wrench and tightened as specified by "alldata" and got bad results with more stumbling. I tightened bolts more than required and trunk runs better. I drove for a few days with no problems until my last day of work than I got that stumble/stalling on initial stepping on gas than it takes off like it got a tuneup. I took it to auto zone and got different code. A PO102, which has something to do with a crack hose or defective mass air flow sensor. I had already replace sensor, so I inspected hoses found one that comes from top of intake manifold parallel with "brake booster" hose and T's off with other hoses and goes down to driver side fender. I searched "2carpos" and found similar issue appears to goto some vacuum switch. I purchased a 7/32 vacuum hose and replaced brittle hose. This made check engine light go off. I the other part of T offed hose seems like 5/32. I will ride around again to no for sure if this was problem. Thanks.


Tiny
Roycar71
Sep 15, 2012.
Sounds like you found the problem keep me posted.


Saturntech9
Sep 15, 2012.
I drove truck around for about week ran fine with occasional hesitation during initial stepping on gas and drives smooths. My wife drove today and check engine light came back on and stayed on until my drive to work and it went off during my drive home tonight. What could be cause of PO102 code?


Tiny
Roycar71
Sep 21, 2012.
There is a T area with hoses going to top on intake manifold that I changed. I am concerned about an area with hose that go into driver side fender near brake booster that is connected to a T check vacuum valve. Do you know if that area is accessible without removing a lot of stuff?


Tiny
Roycar71
Sep 21, 2012.
Looks like your going to have to do some digging not sure if it is easy to get to or not.


Saturntech9
Sep 21, 2012.
Figured out how to get that hose on. I was simply. I just pulled off rotted one and replaced with same 5/32 hose. Strayed down MAF CRC and sprayed hoses around with carb spray. Work good for a week took off with no problems or CEL. Then out of nowhere it started that hesitation when you initially step on gas. Then CEL with PO171 AND po174 pops up again. I read smoking in the hoses can find leaks. Do you recommend this procedure?

P.S. It does not happen like before just that one time I drove it. Thanks


Tiny
Roycar71
Sep 30, 2012.
The best way to look for leaks is with smoke thats what I would try.


Saturntech9
Sep 30, 2012.
Well that is what I want to do. But I do not have a smoke machine. I wanted to see if blow cigarette smoke or cigar is effective. Thanks.


Tiny
Roycar71
Sep 30, 2012.
Cigar smoke yes I have used that method before just make sure you get a decent cigar.I like the flavored primes myself tape throttle body off with a rag. Then blow smoke into the brake booster vacuum hose.


Saturntech9
Sep 30, 2012.
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