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PO171 and PO174 for 1998 GMC Jimmy 4.3L help

Tiny
ROYCAR71
  • MEMBER
  • 1998 GMC JIMMY
  • 6 CYL
  • 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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Tuesday, September 4th, 2012 AT 4:51 PM

24 Replies

Tiny
SATURNTECH9
  • MECHANIC
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Have you actually look for a vacuum leak with some carbs spray?
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Tuesday, September 4th, 2012 AT 5:14 PM
Tiny
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What is correct way to do this?
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Tuesday, September 4th, 2012 AT 5:19 PM
Tiny
SATURNTECH9
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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.
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Tuesday, September 4th, 2012 AT 5:31 PM
Tiny
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This should be done on a warm engine right?
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Tuesday, September 4th, 2012 AT 5:34 PM
Tiny
SATURNTECH9
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The codes set when the engine is warm?If so then when. Warm
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Tuesday, September 4th, 2012 AT 5:36 PM
Tiny
ROYCAR71
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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?
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Friday, September 7th, 2012 AT 10:29 PM
Tiny
SATURNTECH9
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Yes you should do you a plastic manifold on that?
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Friday, September 7th, 2012 AT 10:35 PM
Tiny
ROYCAR71
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  • 354 POSTS
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?
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+1
Friday, September 7th, 2012 AT 10:47 PM
Tiny
SATURNTECH9
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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.
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Friday, September 7th, 2012 AT 11:06 PM
Tiny
ROYCAR71
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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.
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Friday, September 7th, 2012 AT 11:16 PM
Tiny
SATURNTECH9
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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.
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Saturday, September 8th, 2012 AT 12:48 AM
Tiny
ROYCAR71
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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.
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Saturday, September 15th, 2012 AT 12:57 AM
Tiny
SATURNTECH9
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Sounds like you found the problem keep me posted.
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Saturday, September 15th, 2012 AT 4:06 AM
Tiny
ROYCAR71
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  • 354 POSTS
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?
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Friday, September 21st, 2012 AT 10:15 AM
Tiny
ROYCAR71
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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?
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Friday, September 21st, 2012 AT 10:28 AM
Tiny
SATURNTECH9
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Looks like your going to have to do some digging not sure if it is easy to get to or not.
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Friday, September 21st, 2012 AT 8:39 PM
Tiny
ROYCAR71
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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
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Sunday, September 30th, 2012 AT 1:03 AM
Tiny
SATURNTECH9
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The best way to look for leaks is with smoke thats what I would try.
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Sunday, September 30th, 2012 AT 1:55 AM
Tiny
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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.
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Sunday, September 30th, 2012 AT 4:00 AM
Tiny
SATURNTECH9
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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.
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Sunday, September 30th, 2012 AT 4:12 AM

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