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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27661
Experience:  GM Grand Master Technician 2007. 11 years experience.
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Service light..Actron..PO171 system to lean bank 1, and PO174 system

Resolved Question:

I had a service light on my dash on so I hooked up a Actron pocket scan an 2 codes are coming up. PO171 system to lean bank 1, and PO174 system to lean bank 2.
Submitted: 5 years ago.
Category: Chevy
Expert:  carcareman replied 5 years ago.

Hi Fishbob,

With these 2 codes indicating both banks lean tells you that you have false air entering the engine either in the form of a vacuum leak or a bad air flow sensor or map sensor. But in any case it is un-metered air. Not too many possibilities on this one.Most of the time a vacuum leak.,

carcareman, technician
Category: Chevy
Satisfied Customers: 708
Experience: 25 years experience
carcareman and 10 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
I have reset the engine computer. In the city the message did not come up, as soon as the highway speeds were tested the service engine light came on.
Is there a way to test the vacuum leak near the carborator?
Where is the air flow sensor?
Expert:  carcareman replied 5 years ago.

Hi Fishbob,

This truck is the map sensor type system, as far as testing for vacuum leaks you can run the engine and use carb cleaner and spray around the intake manifold and listen for the rpm`s to increase some and at that point is the area the leak is in. It can be in the form of an intake gasket to a deteriorated vacuum hose. But in any case that is why you are getting lean faults on both banks.

Rich

Customer: replied 5 years ago.
What sensor is in the intake air to the carborator? I changed that a year ago. Where is the map sensor?
Expert:  carcareman replied 5 years ago.

You do not have a carburator, I think the map sensor is what are refering to. Here is a picture of it. Were you not able to find a vacuum leak? Make sure you check all the vacuum hoses good.

Click image to see an enlarged view

Customer: replied 5 years ago.
Rich, I found a 1/2 line loose on the in take air housing downstream of the air filter.

I know this vortex engine is fuel injected but the air intake looks like it connects on a carborator.
Expert:  carcareman replied 5 years ago.

Hi Fishbob,

That is great you found a loose line.The reason I say this is because like I said before in order for you to have lean codes on both banks there has to be a common denominator,(vacuum leak or false air intake). I understand now what you meant about the carburator.If at a later date you end up with this type of fault where both banks are setting lean codes always start with vacuum leaks because 95% of the time that is what it turns out to be. I have a 94 s10 blazer with the 4.3 vortec so I have an owners point of view on this one. I am glad things worked out.

Rich

Customer: replied 5 years ago.
Rich, I already accepted your answer, haven't you been paid.

Bob

Looking at old history
Expert:  carcareman replied 5 years ago.

Hi FishBob,

I have been paid a long time ago I will try to close this question myself. don`t know why it is still open.

 

Rich

Customer: replied 5 years ago.
Rich, with the same vehicle (98 S10, 4.3 Vortex engine)I ran into a catastrophy today. I warmed it up for 20 minutes in 2F temperatures when I entered the car there was no heat and the engine temp was around 260 with a check gauge light on. I thought perhaps the thermostat was stuck shut so I drove 1 mile down hill to see if the thermostat or temp would go down. I pulled over the antifreeze resovoir was full and the fan was running (hist: the water pump was changed 1.5 years ago, the radiator 2 years ago) I drove 3 more miles at 40MPH, lightly accelerating and pulled over again to check the fluids. When I go back into the truck the temp went down to 100F.     I proceeded to drive on the highway at 45, at 3miles I suddenly started loosing power and the engine stopped. I let the engine cool for an hour. The engine oil in normal but the radiator was empty. The resovoir is full (this resovoir was chaned 1.3 years ago. I'm thinking the head gasket is blow, would that empty the radiator? Do you think the engine is ruined, I can't get it to start?
Expert:  carcareman replied 5 years ago.

Hi Fishbob,

You are going to have more than one problem 1 is what caused the overheating and 2 is the engine. If the coolant level is full in the engine then the overheat may have been the thermostat sticking. The bad part of all this is that the engine quit on its own while diving. This is what I would do. Do a compression test and see if there is good compression. Check for spark at the plugs, if both of these check out then check for fuel pressure. If the compression is low then the overheat damaged the engine. You can also do a wet test on the rings by putting a few drops of oil into each cylinder and see if the compression changes allot, if it does then the rings are damaged.

 

Good luck,

Rich

Customer: replied 5 years ago.
<p>Rich, the lovely NH weather this time of year make working outside extremenly dificult. The compression test read out 160 to 165 psi, thw spark plugs seem to be wet with gas. No water is in the oil, but the radiator was empty, (overflow resovior is full). </p><p>The computer reads out P101 - Mass air flow A cucuit, P1176 - engine coolant temp sensor low, P0300 multiple misfire detected, P446 Evaportor emission Sys vent control curcuit.</p><p> </p><p>The spark plugs are wet with gas is there a safety curcuit which will cause the ingnition to be shut down? </p>
Customer: replied 5 years ago.
Rich, I have received an answer please reply. The pressure test are done on the, 3 gallons of antifreeze had to be added to the radiator but it doesn't start could be there a safety curcuit keeping the ignition off?
Customer: replied 5 years ago.
Rich, I have raised the bid from $15 to $21 and have not recieved an answer. Please reply
Expert:  GM Tech (Cam) replied 5 years ago.
Bob, I am GM Tech, I have looked over your question and I think that Rich has sent you on a wild goose chase. The codes P0171 and P0174 are almost always due to a plugged fuel filter or low fuel pressure. IT will also cause the cylinder misfire. It can be caused by air entering, but then you would have an idle issue as well. Lets start by changing the fuel filter if you have not done so. Also test the fuel pressure. It needs to be 60-66 psi for the engine to run. As for the low coolant issue, If I am following that correctly, these engine are bad for the intake gaskets leaking. Low coolant would also cause the P1176. How does all this sound?
Customer: replied 5 years ago.
Let review a couple of items for a 2 month my service light comes on periodically this may relate to P101. The major issue at hand is the engine overheated from just ideling to warm up (no heat). As if the thermostat was sticking. The radiator, thermostat. water pump and plastic resovior have all been changed with in 20,000 miles........ I drove downhill for 1 mile to see if I could loosen up the thermostat, the temp gauge was still on max with the radiator fan running and the resovior full. I drove 3 mile on level ground (7F outside air) pull over and checked the fan and resovior (on and Full). When I jot back in the truck the temp gauge was on 0F. I would have liked to open the radiator cap but I new it was under pressure.

I drove 2 miles the engine engine vibrtated a little lost compression an stalled. Once the engine cooled down after a tow no antifreeze was found in the radiator. 2.5 gallons were added. No smell or signs in the oil. Heat was fine the day before.

1st question is what happened to the antifreeze. Compression is fine in cylinders. The plugs are wet.
2nd question Is there any thing in a safety curcuit that would turn. off the ignition?
I have a Hayes manual but where would I see the intake gasket near the intake air to the engine. Is the a pressure port for the fuel pump test?
Expert:  GM Tech (Cam) replied 5 years ago.

Ok, The antifreeze could have boiled over and blown out past the pressure cap. It is designed to release after 15psi. The intake gaskets could have let some out. They are known for leaking at the front and rear of the intake manifold to head seal.

As for the shutdown, I don't know that these engine have a shut down system in place.

The fuel pump test port is on the steel fuel line at the back left of the intake manifold.

The p0101 is usually a dirty MAF sensor or vacuum leak.

Customer: replied 5 years ago.
<p>yes some fuid leaked out the pressure relief, some steam was coming off the engine but not 2.5 gallons worth. Al thought the second stop when the temp gauge went down maybe some blew off then. Time to pressure test the coolant system.</p><p> </p><p>The intake manafold and the head seal sound like an involed time consuming project with out a garage.</p><p> </p><p>The fuel pump pressure test, can that be test with a set of refrigeration gauges not used any more for refrigeartion (I'm an HVAC Tech) 1/4" sharader valve port?</p>
Expert:  GM Tech (Cam) replied 5 years ago.

My bet is the intake gaskets. Start the engine with the cap off, and fill the system. While it is running, add as needed. This way you can see if there is lots of bubbles and bleed the air out.

It is a 3-4 hour job to replace the intake gaskets.

I think the test port is the same valve as R12, so that may be an option.

If you have not done so, please leave accurate feedback for the question you have accepted of the other expert.

Customer: replied 5 years ago.
Is the intake gasket under the intake filter plastic housing which has a big thumb wing nut you need to loosen to remove the housing.

I did fill up the radiator there was alot of bubles. As I explained earlier I can't run the engine it misfires and shakes/no ignition, the plugs are getting fuel but the engine is not starting. Thats why I was wondering when the antifreeze was low is a safety sensor keeping the ingnition off.

To other expert all the other problem have been solved excellant this one will tyake more time.
Expert:  GM Tech (Cam) replied 5 years ago.
That big plastic part is the upper intake, and it is sealed to the lower intake. That seal between then should be good. It is the gasket between the lower intake manifold to the head that is the issue. Sorry for not making that clear if the first place.
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27661
Experience: GM Grand Master Technician 2007. 11 years experience.
GM Tech (Cam) and 10 other Chevy Specialists are ready to help you
Expert:  GM Tech (Cam) replied 5 years ago.
Thanks for accepting. If you have more questions, please reply to this post. Also, let me know what you find.
Customer: replied 5 years ago.
Is't the fuel pump under engine? Isn't the MAF in the intake air after the filter?
Expert:  GM Tech (Cam) replied 5 years ago.
The fuel pump is in the fuel tank and the MAF is directly after the air filter in the air snorkel.

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