I'm leaving this forum and have deleted all my work in this thread.

 

I like atlantic british for new parts too. Good quality, fast shipping, and good prices. You might want to try cleaning the maf sensor first and see if that does the trick.

 

I have been experiencing the same problem with these 2 codes, and it is quite frustrating! My truck also seemingly runs fine with good power after a head gasket job, and replacing upper and lower intake gaskets. From reading on forums, bosch manual, and talking to 2 independent shops, my best understanding is that based on the 02 sensor, MAF, and crankshaft speed sensor readings, the ECU is trying to apply a compensation factor to the fuel injector signal that is out of the acceptable preset range (would be sending excessive fuel through the injector). So -- the possible faults are the front o2 sensors, MAF, crankshaft speed, or an intake or exhaust air leak. If it was an 02 sensor, both would have to go bad in order to get the 2 codes. An independent shop told me that a faulty MAF would also trigger other codes, by the way.

I would suggest starting by checking for intake leaks using a smoke test; if you take it to a shop they use a machine to blow smoke into the intake manifold (while the engine is not running) and look for leaks. If you want to do this yourself, first get some spare vacuum line and a couple of 99 cent swishers. Disconnect the MAF, and block off the intake intake tube using a suitably sized cylindrical object i.e. can. Connect the spare vacuum line to one of the ports on the side of the upper manifold, light up a cigar and blow smoke into the manifold. Use a flashlight to look for smoke leaking out anywhere in the intake system.

Hope this helps, let us know what you find out.

 

Stay away from a MAF till you get other coders that would then indicate a bad MAF, like a 100 to a 105 or a 700 type fault code.
Normally your codes are not caused by an 02 sensor, because those 2 fault codes cover both cylinder banks, not just one like a bad 02 might.
If you want some help with this, PM me your number and lets talk.

 

P1171 is a 'Closed loop malfunction'.

When the O2 sensors heat up and are oscillating up and down in voltage the system is in closed loop.

Meaning - the system holds back fuel and the O2 sensor voltage one way, then adds fuel and the O2 sensors go the other way.

This causes the closed loop - the loop is:

1) ECU Reads O2 sensors and MAF and TPS
2) ECU opens injectors according to (1)
3) Goto step 1

If the loop is broken, the ECU will use a predetermined fuel map which is open loop.

I would put a code scanner on your OBD2 connector and drive the Discovery II and look at the front O2 sensors.
They should go from around .9V to .1V consistently - and rather quickly.
And, the front sensors should have the same rate.

You may have a slow sensor.

Also, you can get some of that CRC sensor cleaner and try to clean the hot wire on the MAF .. WITH ENGINE OFF!!!

Check your brake vacuum line. Make sure the red keeper is holding it into the intake manifold. Make sure on the other side it is ok on the booster.

There are a few other vacuum lines - make sure these are all tidy
for the cruise and for the purge valve.


!!! Looks !!! looks like one guy replaced the MAF and still gets codes..

I am still getting the 1174 and 1171 codes with a brand new bosch MAF and brand new air filter. 0455 went away though. I guess I will start looking for a vaccume leak?? Does anyone know the proper procedure for this or have any tips/suggestions? Thanks!

This guy had some pretty good advice too:

At this point some of the possibilities are as follows:

1 Oxygen sensors, Highly likely the problem. Test them first with ohm meter, and make sure the heater circuit is working.
2 Cats plugging up, check back pressure = gutless question
3 Faulty iacv stuck in a default position. This is why I’m asking the high or low idle question.
4 Miss fires plugs not always lighting the a/f mixture.
5 Coking: this is where the intake is very oily inside, usually due to the crankcase ventilation system……. Pronounced: coke…. ing
6 Ring and or valve guide issues.
7 Although rare, injector or injectors stuck partially open.
8 Faulty coil pack, intermittent problem only.
9 Block or ground issues
10 Faulty processor
11 Fuel soaked Evaporative canister.
12 Fuel pressure too high.
13 Iat sensor out of range ( Intake air temperature )
14 Restrictions in intake

Good luck to you..
J

 

1171 means Oxygen Sensor System is Too Lean for Banks A and B.
Our engine always run in closed loop, as designed, meaning the the engine ECU is reading from all the sensors and adjusting the entire system as necessary where as if in open loop, the engine is in cold start up mode, running full rich to start and warm up faster.

 

Heres an update on my situation, for what its worth --- getting the same codes 1171 and 1174 after replacing the upper and lower intake gaskets. Did another smoke test last evening and found there was still some leakage from under the intake manifold. Checked torque on manifold bolts (I did loctite them) and it was ok. So, now Im guessing that the upper gasket got damaged or displaced during the install. Ordered another one from British Pacific for $9. I guess the moral of the story is that getting the upper intake gasket to fully seal can be tricky..

With that said, Im wondering if the SAI system could also be contributing to the problem. Do others with this issue also have SAI?

Mike, 1171 means too lean on LH bank at low rpm, by the way.

Regards,

BWB

 

Mike is probably spot on.
If that O2 is too lean, it is not responding correctly.
The O2 is not broken - it is reporting voltage - but the O2 sensor
is probably not accurate.

I would replace the O2 sensors.

You can pick them up - new Bosch on Amazon for about $60 each.

I had an O2 related code of my sensor simply quit working here and there.
I replaced the sensor - and no more codes for about 3 weeks now.

Your code is a little more vague.
But, Mike pinned down your code.

If you replace both O2 sensors in the front, you'll probably get 1/2 to 1 MPG better on the highway.
That will pay for them fast.

I did a writeup on how to unplug them from the harness plug.
Only took about 1/2 hour of fiddling to replace the front one on the left side of the truck which is bank #1.

They do it like this:

Bank #1 is close to cylinder #1.
Bank #2 is close to cylinder #2

 

Jfail -- Do you have any insight on why the SAI system might or might not contribute to this issue?

 

SAI is not doing it.
SAI only comes on when the truck is first started.
And, once in a great while when you go from full speed to idle off a highway.
When SAI is on, you know it.
Sounds like a vacuum cleaner.

SAI injects into the heads